Artykuły w czasopismach: „Berezinskii-Kosterlitz-Thouless transition temperature”

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Ashoka, A., Bhagyashree K. S. i S. V. Bhat. "Magnetic Field Induced Berezinskii-Kosterlitz-Thouless Correlations in 3-Dimensional Manganites". MRS Advances 5, nr 44 (2020): 2251–60. http://dx.doi.org/10.1557/adv.2020.320.

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AbstractIdeal two-dimensional (2D) Heisenberg magnets lack long range magnetic order. However, the XY model with spins confined to a plane shows a topological phase transition at a finite temperature corresponding to binding and unbinding of vortices. Experimental evidence for such Berezinskii-Kosterlitz-Thouless (BKT) transitions has been difficult to obtain in condensed matter systems, where, even a weak interlayer coupling that is invariably present leads to long-range order, pre-empting the BKT transition. The BKT signatures are still discernible above the long-range ordering temperature, however, in the characteristic exponential temperature dependence of the coherence length of the fluctuations. In this work we report that an applied magnetic field can induce such BKT correlations not only in quasi 2-dimensional systems but also in nominally 3-dimensional manganites undergoing antiferromagnetic transitions. We arrive at this unexpected conclusion based on our studies of temperature dependence of electron paramagnetic resonance (EPR) linewidth ΔH(T) of Cr3+ doped bismuth strontium manganite Bi0.5Sr0.5Mn1-xCrxO3 (x= 0.04, 0.1) (BSMCO04 and BSMCO10).

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Giedt, Joel, i James Flamino. "Berezinskii-Kosterlitz-Thouless phase transition from lattice sine-Gordon model". EPJ Web of Conferences 175 (2018): 14003. http://dx.doi.org/10.1051/epjconf/201817514003.

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We obtain nonperturbative results on the sine-Gordon model using the lattice field technique. In particular, we employ the Fourier accelerated hybrid Monte Carlo algorithm for our studies. We find the critical temperature of the theory based autocorrelation time, as well as the finite size scaling of the “thickness” observable used in an earlier lattice study by Hasenbusch et al.

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MITROVIĆ, BOŽIDAR, i MICHELLE A. PRZEDBORSKI. "MONTE CARLO STUDY OF THE XY-MODEL ON SIERPIŃSKI CARPET". International Journal of Modern Physics C 25, nr 02 (luty 2014): 1350087. http://dx.doi.org/10.1142/s0129183113500873.

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We have performed a Monte Carlo (MC) study of the classical XY-model on a Sierpiński carpet, which is a planar fractal structure with infinite order of ramification and fractal dimension 1.8928. We employed the Wolff cluster algorithm in our simulations and our results, in particular those for the susceptibility and the helicity modulus, indicate the absence of finite-temperature Berezinskii–Kosterlitz–Thouless (BKT) transition in this system.

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LIU, YING, i JOHN C. PRICE. "IONIZATION OF CHARGE-ANTICHARGE PAIRS IN ULTRATHIN PALLADIUM FILMS". Modern Physics Letters B 09, nr 15 (30.06.1995): 939–46. http://dx.doi.org/10.1142/s0217984995000899.

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The electrical conductance and I–V characteristics of ultrathin Pd films prepared by low temperature deposition have been measured in situ. An Arrhenius behavior was found for the electrical conductance. A crossover between regimes with different activation energies was observed at a temperature TK. Below TK, the I–V characteristics of the film were found to be nonlinear. These observations are explained using a charge Kosterlitz-Thouless-Berezinskii transition picture which involves the ionization of charge-anticharge pairs.

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Xu, Feng, Lei Zhang, Liyun Jiang i Chung-Yu Mou. "Superfluid weight and Berezinskii-Kosterlitz-Thouless transition temperature of strained graphene". Chinese Journal of Physics 70 (kwiecień 2021): 288–96. http://dx.doi.org/10.1016/j.cjph.2021.01.009.

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Kumar, Ankit, Guan-Ming Su, Chau-Shing Chang, Ching-Chen Yeh, Bi-Yi Wu, Dinesh K. Patel, Yen-Ting Fan, Sheng-Di Lin, Lee Chow i Chi-Te Liang. "Topological Transition in a 3 nm Thick Al Film Grown by Molecular Beam Epitaxy". Journal of Nanomaterials 2019 (27.12.2019): 1–6. http://dx.doi.org/10.1155/2019/6376529.

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We have performed detailed transport measurements on a 3 nm thick (as-grown) Al film on GaAs prepared by molecular beam epitaxy (MBE). Such an epitaxial film grown on a GaAs substrate shows the Berezinskii-Kosterlitz-Thouless (BKT) transition, a topological transition in two dimensions. Our experimental data shows that the MBE-grown Al nanofilm is an ideal system for probing interesting physical phenomena such as the BKT transition and superconductivity. The increased superconductor transition temperature (~2.4 K) compared to that of bulk Al (1.2 K), together with the ultrathin film quality, may be advantageous for future superconductor-based quantum devices and quantum information technology.

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Boudjemaa, Abdelaali, Karima Abbas i Nadia Guebli. "Ultradilute Quantum Droplets in the Presence of Higher-Order Quantum Fluctuations". Atoms 10, nr 2 (17.06.2022): 64. http://dx.doi.org/10.3390/atoms10020064.

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We investigate the effects of higher-order quantum fluctuations on the bulk properties of self-bound droplets in three-, two- and one-dimensional binary Bose mixtures using the Hartree–Fock–Bogoliubov theory. We calculate higher-order corrections to the equation of state of the droplet at both zero and finite temperatures. We show that our results for the ground-state energy are in a good agreement with recent quantum Monte Carlo simulations in any dimension. Our study extends to the finite temperature case where it is found that thermal fluctuations may destabilize the droplet state and eventually destroy it. In two dimensions, we reveal that the droplet occurs at temperatures well below the Berezinskii–Kosterlitz–Thouless transition temperature.

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Xiong, Yunuo, i Hongwei Xiong. "Path integral molecular dynamics simulations for Green’s function in a system of identical bosons". Journal of Chemical Physics 156, nr 13 (7.04.2022): 134112. http://dx.doi.org/10.1063/5.0086118.

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Path integral molecular dynamics (PIMD) has been successfully applied to perform simulations of large bosonic systems in a recent study [Hirshberg et al., Proc. Natl. Acad. Sci. U. S. A. 116, 21445 (2019)]. In this work, we extend PIMD techniques to study Green’s function for bosonic systems. We demonstrate that the development of the original PIMD method enables us to calculate Green’s function and extract momentum distribution from our simulations. We also apply our method to systems of identical interacting bosons to study Berezinskii–Kosterlitz–Thouless transition around its critical temperature.

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ARTEMENKO, S. N., i Yu I. LATYSHEV. "TWO-DIMENSIONAL BEHAVIOUR OF LAYERED HIGH-Tc SUPERCONDUCTORS". Modern Physics Letters B 06, nr 07 (20.03.1992): 367–82. http://dx.doi.org/10.1142/s0217984992000454.

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High-T c superconductors (HTSs) have a layered structure, which strongly affects their physics. Bulk crystals exhibit the two-dimensional (2D) behaviour typical for superconducting films of atomic thickness. Fluctuation contribution to conductivity above mean-field critical temperature T c0 is characteristic to 2D superconductors. Finite resistivity in layered HTSs appears above Berezinskii-Kosterlitz-Thouless (BKT) transition T c , which is by several degrees smaller than T c0 . Below T c power-law I-V curves are observed. The transition and its main manifestations are described as a result of thermal creation of 2D-vortices with cores residing inside single superconducting layers. Magnetoresistive effects near the BKT transition are discussed briefly.

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Figueiredo, T. P., i B. V. Costa. "Correlation function behavior in the topological Kosterlitz–Thouless transition using the Replica-Exchange Wang–Landau technique". International Journal of Modern Physics B 33, nr 30 (10.12.2019): 1950361. http://dx.doi.org/10.1142/s0217979219503612.

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In this paper, we use the Replica-Exchange Wang–Landau (REWL) technique to study the behavior of the two-point correlation function of the site diluted classical anisotropic Heisenberg (AH) model in two dimensions. The model has a topological Berezinskii–Kosterlitz–Thouless (BKT) transition for any dilution down to the percolation threshold, [Formula: see text]. Contrary to earlier results that predict the exponent of the correlation function, [Formula: see text], to decay linearly to zero as a function of temperature, we found that it decreases with temperature to a finite value [Formula: see text] at [Formula: see text] for any dilution [Formula: see text].

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Chen, Sheng-Zong, Jing-Wei Yang, Tzu-Yu Peng, Yu-Cheng Chu, Ching-Chen Yeh, I.-Fan Hu, Swapnil Mhatre, Yu-Jung Lu i Chi-Te Liang. "Disorder-induced 2D superconductivity in a NbTiN film grown on Si by ultrahigh-vacuum magneton sputtering". Superconductor Science and Technology 35, nr 6 (21.04.2022): 064003. http://dx.doi.org/10.1088/1361-6668/ac6631.

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Abstract We report on the growth and characterization of a niobium titanium nitride (NbTiN) film on a Si substrate prepared by ultrahigh vacuum sputtering. We show that the superconducting transition temperature is lower than those of high-quality NbTiN films. Interestingly, even though the zero-temperature Ginzburg-Landau coherence length (=9.77 nm) is significantly shorter than the film thickness (=86 nm), we are still able to observe the Berezinskii-Kosterlitz-Thouless-like transition, indicating the two-dimensional (2D) signature of our three-dimensional (3D) sample. We propose that the mechanism of hidden 2D superconducting property is similar to the recently reported results of the disordered induced 3D to 2D superconductor transition. We suggest further theoretical work is required for studying our new experimental results.

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V. Postolova, Svetlana, Alexey Yu. Mironov i Tatyana I. Baturina. "Resistive Width of Superconducting Transition in Titanium Nitride Thin Film". Siberian Journal of Physics 6, nr 2 (1.07.2011): 50–56. http://dx.doi.org/10.54362/1818-7919-2011-6-2-50-56.

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The transition to the superconducting state of the ultrathin (5 nm thick) titanium nitride film was studied. It is found that the nonmonotonic temperature dependence of the resistance, R(T), is a consequence of competition between the contributions to conductivity from quantum corrections stemming from the electron-electron interaction in the diffusion and Cooper channels. It is shown that the appreciable decrease in the resistance at T > Tc (Tc is the superconducting transition temperature) results from the superconducting fluctuations. We present the results of the analysis of low-temperature (T < Tc ) current-voltage characteristics V(I). It is found that they follow the power-law behavior V∝ I α(T) , with α(T) increasing rapidly with the decreasing temperature. The Berezinskii-Kosterlitz-Thouless transition temperature, TBKT, and width of the superconducting transition ∆T = Tc − TБКТ were determined

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Opherden, D., F. Bärtl, M. S. J. Tepaske, C. P. Landee, J. Wosnitza i H. Kühne. "Berezinskii—Kosterlitz—Thouless correlations in copper-based quasi-2D spin systems (Review Article)". Low Temperature Physics 49, nr 7 (1.07.2023): 819–26. http://dx.doi.org/10.1063/10.0019692.

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We present an overview of selected copper-based quasi-2D square-lattice spin-1/2 materials with an easy-plane anisotropy, providing the possibility to study emergent Berezinskii-Kosterlitz-Thouless (BKT) correlations. In particular, in those materials with a comparatively small exchange coupling, the effective XY anisotropy of the low-temperature spin correlations can be controlled by an applied magnetic field, yielding a systematic evolution of the BKT correlations. In cases where the residual interlayer correlations are small enough, dynamical BKT correlations in the critical regime may be observed experimentally, whereas the completion of the genuine BKT transition is preempted by the onset of long-range order.

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KAPLAN, D. B., J. W. LEE, D. T. SON i M. A. STEPHANOV. "CONFORMALITY LOST". International Journal of Modern Physics A 25, nr 02n03 (30.01.2010): 422–32. http://dx.doi.org/10.1142/s0217751x1004872x.

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We consider zero-temperature transitions from conformal to non-conformal phases in quantum theories. We argue that there are three generic mechanisms for the loss of conformality: (i) fixed point goes to zero coupling, (ii) fixed point runs off to infinite coupling, or (iii) an IR fixed point annihilates with a UV fixed point and they both disappear into the complex plane. We give examples of the last case and show that the critical behavior of the mass gap is similar to that of the inverse correlation length in the finite temperature Berezinskii-Kosterlitz-Thouless (BKT) phase transition, ξ ~ exp (c/|T-Tc|1/2). We speculate that the chiral phase transition in QCD at large number of fermion flavors belongs to this universality class, and attempt to identify the UV fixed point that annihilates with the Banks-Zaks fixed point at the lower end of the conformal window.

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Grignani, G., P. Sodano, G. Semenoff i O. Tirkkonen. "Z-Symmetry and Polyakov Loops in Hot Abelian Gauge Theories". International Journal of Modern Physics A 12, nr 06 (10.03.1997): 1205–14. http://dx.doi.org/10.1142/s0217751x97000931.

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We discuss the Z symmetry of finite temperature QED, which is related to the confinement properties of the theory. We show the correlators of Polyakov loop operators with incommensurate charges can be used as order parameters for this symmetry. The screening or confining properties of lower dimensional abelian gauge theories are analyzed. In the Schwinger model, the Z-symmetry is broken and the system is in a screening phase; with a non-vanishing fermion mass the symmetry is recovered and the system confines. In parity invariant 2+1-dimensional QED, there is a phase transition between phases with unbroken and broken realizations of this symmetry. This confinement–deconfinement transition is of the Berezinskii–Kosterlitz–Thouless (BKT) type. When there is a topological mass the model exhibits a screening phase. However, if the topological mass is much smaller than the other dimensional parameters there is a vestige of the BKT transition separating regions with screening and confining behavior.

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Salasnich, Luca, Alberto Cappellaro, Koichiro Furutani, Andrea Tononi i Giacomo Bighin. "First and Second Sound in Two-Dimensional Bosonic and Fermionic Superfluids". Symmetry 14, nr 10 (17.10.2022): 2182. http://dx.doi.org/10.3390/sym14102182.

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We review our theoretical results of the sound propagation in two-dimensional (2D) systems of ultracold fermionic and bosonic atoms. In the superfluid phase, characterized by the spontaneous symmetry breaking of the U(1) symmetry, there is the coexistence of first and second sound. In the case of weakly-interacting repulsive bosons, we model the recent measurements of the sound velocities of 39K atoms in 2D obtained in the weakly-interacting regime and around the Berezinskii–Kosterlitz–Thouless (BKT) superfluid-to-normal transition temperature. In particular, we perform a quite accurate computation of the superfluid density and show that it is reasonably consistent with the experimental results. For superfluid attractive fermions, we calculate the first and second sound velocities across the whole BCS-BEC crossover. In the low-temperature regime, we reproduce the recent measurements of first-sound speed with 6Li atoms. We also predict that there is mixing between sound modes only in the finite-temperature BEC regime.

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Sharma, Meenakshi, Manju Singh, Rajib K. Rakshit, Surinder P. Singh, Matteo Fretto, Natascia De Leo, Andrea Perali i Nicola Pinto. "Complex Phase-Fluctuation Effects Correlated with Granularity in Superconducting NbN Nanofilms". Nanomaterials 12, nr 23 (22.11.2022): 4109. http://dx.doi.org/10.3390/nano12234109.

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Superconducting nanofilms are tunable systems that can host a 3D–2D dimensional crossover leading to the Berezinskii–Kosterlitz–Thouless (BKT) superconducting transition approaching the 2D regime. Reducing the dimensionality further, from 2D to quasi-1D superconducting nanostructures with disorder, can generate quantum and thermal phase slips (PS) of the order parameter. Both BKT and PS are complex phase-fluctuation phenomena of difficult experiments. We characterized superconducting NbN nanofilms thinner than 15 nm, on different substrates, by temperature-dependent resistivity and current–voltage (I-V) characteristics. Our measurements evidence clear features related to the emergence of BKT transition and PS events. The contemporary observation in the same system of BKT transition and PS events, and their tunable evolution in temperature and thickness was explained as due to the nano-conducting paths forming in a granular NbN system. In one of the investigated samples, we were able to trace and characterize the continuous evolution in temperature from quantum to thermal PS. Our analysis established that the detected complex phase phenomena are strongly related to the interplay between the typical size of the nano-conductive paths and the superconducting coherence length.

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José, Jorge V. "Duality, Gauge Symmetries, Renormalization Groups and the BKT Transition". International Journal of Modern Physics B 31, nr 06 (5.03.2017): 1730001. http://dx.doi.org/10.1142/s0217979217300018.

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In this chapter, I will briefly review, from my own perspective, the situation within theoretical physics at the beginning of the 1970s, and the advances that played an important role in providing a solid theoretical and experimental foundation for the Berezinskii–Kosterlitz–Thouless theory (BKT). Over this period, it became clear that the Abelian gauge symmetry of the 2D-XY model had to be preserved to get the right phase structure of the model. In previous analyses, this symmetry was broken when using low order calculational approximations. Duality transformations at that time for two-dimensional models with compact gauge symmetries were introduced by José, Kadanoff, Nelson and Kirkpatrick (JKKN). Their goal was to analyze the phase structure and excitations of XY and related models, including symmetry breaking fields which are experimentally important. In a separate context, Migdal had earlier developed an approximate Renormalization Group (RG) algorithm to implement Wilson’s RG for lattice gauge theories. Although Migdal’s RG approach, later extended by Kadanoff, did not produce a true phase transition for the XY model, it almost did asymptotically in terms of a non-perturbative expansion in the coupling constant with an essential singularity. Using these advances, including work done on instantons (vortices), JKKN analyzed the behavior of the spin–spin correlation functions of the 2D XY-model in terms of an expansion in temperature and vortex-pair fugacity. Their analysis led to a perturbative derivation of RG equations for the XY model which are the same as those first derived by Kosterlitz for the two-dimensional Coulomb gas. JKKN’s results gave a theoretical formulation foundation and justification for BKT’s sound physical assumptions and for the validity of their calculational approximations that were, in principle, strictly valid only at very low temperatures, away from the critical [Formula: see text] temperature. The theoretical predictions were soon tested successfully against experimental results on superfluid helium films. The success of the BKT theory also gave one of the first quantitative proofs of the validity of the RG theory.

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Sukhareva, T. V., i V. A. Finkel. "The Berezinskii-Kosterlitz-Thouless phase transition in the Josephson medium of a two-level granular high-temperature superconductor YBa2Cu3O7-δ". Low Temperature Physics 44, nr 3 (marzec 2018): 194–98. http://dx.doi.org/10.1063/1.5024534.

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Cotón, N., M. V. Ramallo i F. Vidal. "Effects of critical temperature inhomogeneities on the voltage–current characteristics of a planar superconductor near the Berezinskii–Kosterlitz–Thouless transition". Superconductor Science and Technology 24, nr 8 (1.07.2011): 085013. http://dx.doi.org/10.1088/0953-2048/24/8/085013.

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Negrete, Oscar, Patricio Vargas, Francisco Peña, Gonzalo Saravia i Eugenio Vogel. "Entropy and Mutability for the q-State Clock Model in Small Systems". Entropy 20, nr 12 (6.12.2018): 933. http://dx.doi.org/10.3390/e20120933.

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In this paper, we revisit the q-state clock model for small systems. We present results for the thermodynamics of the q-state clock model for values from q = 2 to q = 20 for small square lattices of L × L , with L ranging from L = 3 to L = 64 with free-boundary conditions. Energy, specific heat, entropy, and magnetization were measured. We found that the Berezinskii–Kosterlitz–Thouless (BKT)-like transition appears for q > 5, regardless of lattice size, while this transition at q = 5 is lost for L < 10; for q ≤ 4, the BKT transition is never present. We present the phase diagram in terms of q that shows the transition from the ferromagnetic (FM) to the paramagnetic (PM) phases at the critical temperature T 1 for small systems, and the transition changes such that it is from the FM to the BKT phase for larger systems, while a second phase transition between the BKT and the PM phases occurs at T 2. We also show that the magnetic phases are well characterized by the two-dimensional (2D) distribution of the magnetization values. We made use of this opportunity to carry out an information theory analysis of the time series obtained from Monte Carlo simulations. In particular, we calculated the phenomenological mutability and diversity functions. Diversity characterizes the phase transitions, but the phases are less detectable as q increases. Free boundary conditions were used to better mimic the reality of small systems (far from any thermodynamic limit). The role of size is discussed.

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Orendáčová, Alžbeta, Róbert Tarasenko, Vladimír Tkáč, Erik Čižmár, Martin Orendáč i Alexander Feher. "Interplay of Spin and Spatial Anisotropy in Low-Dimensional Quantum Magnets with Spin 1/2". Crystals 9, nr 1 (21.12.2018): 6. http://dx.doi.org/10.3390/cryst9010006.

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Quantum Heisenberg chain and square lattices are important paradigms of a low-dimensional magnetism. Their ground states are determined by the strength of quantum fluctuations. Correspondingly, the ground state of a rectangular lattice interpolates between the spin liquid and the ordered collinear Néel state with the partially reduced order parameter. The diversity of additional exchange interactions offers variety of quantum models derived from the aforementioned paradigms. Besides the spatial anisotropy of the exchange coupling, controlling the lattice dimensionality and ground-state properties, the spin anisotropy (intrinsic or induced by the magnetic field) represents another important effect disturbing a rotational symmetry of the spin system. The S = 1/2 easy-axis and easy-plane XXZ models on the square lattice even for extremely weak spin anisotropies undergo Heisenberg-Ising and Heisenberg-XY crossovers, respectively, acting as precursors to the onset of the finite-temperature phase transitions within the two-dimensional Ising universality class (for the easy axis anisotropy) and a topological Berezinskii–Kosterlitz–Thouless phase transition (for the easy-plane anisotropy). Experimental realizations of the S = 1/2 two-dimensional XXZ models in bulk quantum magnets appeared only recently. Partial solutions of the problems associated with their experimental identifications are discussed and some possibilities of future investigations in quantum magnets on the square and rectangular lattice are outlined.

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Sukhareva, T. V., i V. A. Finkel. "The Berezinskii–Kosterlitz–Thouless topological phase transition in the Josephson medium of granular high-temperature superconductors under the effect of magnetic and electric fields". Low Temperature Physics 46, nr 5 (maj 2020): 550–53. http://dx.doi.org/10.1063/10.0001060.

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Sukhareva, T. V., i V. A. Finkel. "Visualization of a Berezinskii–Kosterlitz–Thouless Topological Phase Transition in a Josephson Medium: Detection of an Anomalous Temperature Dependence of the Magnetoresistance of YBa2Cu3O7–δ Granular High-Temperature Superconductors". JETP Letters 108, nr 4 (sierpień 2018): 243–46. http://dx.doi.org/10.1134/s0021364018160099.

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Fitta, Magdalena, Robert Pełka, Piotr Konieczny i Maria Bałanda. "Multifunctional Molecular Magnets: Magnetocaloric Effect in Octacyanometallates". Crystals 9, nr 1 (22.12.2018): 9. http://dx.doi.org/10.3390/cryst9010009.

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Octacyanometallate-based compounds displaying a rich pallet of interesting physical and chemical properties, are key materials in the field of molecular magnetism. The [M(CN)8]n− complexes, (M = WV, MoV, NbIV), are universal building blocks as they lead to various spatial structures, depending on the surrounding ligands and the choice of the metal ion. One of the functionalities of the octacyanometallate-based coordination polymers or clusters is the magnetocaloric effect (MCE), consisting in a change of the material temperature upon the application of a magnetic field. In this review, we focus on different approaches to MCE investigation. We present examples of magnetic entropy change ΔSm and adiabatic temperature change ΔTad, determined using calorimetric measurements supplemented with the algebraic extrapolation of the data down to 0 K. At the field change of 5T, the compound built of high spin clusters Ni9[W(CN)8]6 showed a maximum value of −ΔSm equal to 18.38 J·K−1 mol−1 at 4.3 K, while the corresponding maximum ΔTad = 4.6 K was attained at 2.2 K. These values revealed that this molecular material may be treated as a possible candidate for cryogenic magnetic cooling. Values obtained for ferrimagnetic polymers at temperatures close to their magnetic ordering temperatures, Tc, were lower, i.e., −ΔSm = 6.83 J·K−1 mol−1 (ΔTad = 1.42 K) and −ΔSm = 4.9 J·K−1 mol−1 (ΔTad = 2 K) for {[MnII(pyrazole)4]2[NbIV(CN)8]·4H2O}n and{[FeII(pyrazole)4]2[NbIV(CN)8]·4H2O}n, respectively. MCE results have been obtained also for other -[Nb(CN)8]-based manganese polymers, showing significant Tc dependence on pressure or the remarkable magnetic sponge behaviour. Using the data obtained for compounds with different Tc, due to dissimilar ligands or other phase of the material, the ΔSm ~ Tc−2/3 relation stemming from the molecular field theory was confirmed. The characteristic index n in the ΔSm ~ ΔHn dependence, and the critical exponents, related to n, were determined, pointing to the 3D Heisenberg model as the most adequate for the description of these particular compounds. At last, results of the rotating magnetocaloric effect (RMCE), which is a new technique efficient in the case of layered magnetic systems, are presented. Data have been obtained and discussed for single crystals of two 2D molecular magnets: ferrimagnetic {MnII(R-mpm)2]2[NbIV(CN)8]}∙4H2O (mpm = α-methyl-2-pyridinemethanol) and a strongly anisotropic (tetren)Cu4[W(CN)8]4 bilayered magnet showing the topological Berezinskii-Kosterlitz-Thouless transition.

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HUTCHINSON, D. A. W., i P. B. BLAKIE. "PHASE TRANSITIONS IN ULTRA-COLD TWO-DIMENSIONAL BOSE GASES". International Journal of Modern Physics B 20, nr 30n31 (20.12.2006): 5224–28. http://dx.doi.org/10.1142/s0217979206036302.

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We briefly review the theory of Bose-Einstein condensation in the two-dimensional trapped Bose gas and, in particular the relationship to the theory of the homogeneous two-dimensional gas and the Berezinskii-Kosterlitz-Thouless phase. We obtain a phase diagram for the trapped two-dimensional gas, finding a critical temperature above which the free energy of a state with a pair of vortices of opposite circulation is lower than that for a vortex-free Bose-Einstein condensed ground state. We identify three distinct phases which are, in order of increasing temperature, a phase coherent Bose-Einstein condensate, a vortex pair plasma with fluctuating condensate phase and a thermal Bose gas. The thermal activation of vortex-antivortex pair formation is confirmed using finite-temperature classical field simulations.

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Negrete, Oscar A., Patricio Vargas, Francisco J. Peña, Gonzalo Saravia i Eugenio E. Vogel. "Short-Range Berezinskii-Kosterlitz-Thouless Phase Characterization for the q-State Clock Model". Entropy 23, nr 8 (7.08.2021): 1019. http://dx.doi.org/10.3390/e23081019.

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Beyond the usual ferromagnetic and paramagnetic phases present in spin systems, the usual q-state clock model presents an intermediate vortex state when the number of possible orientations q for the system is greater than or equal to 5. Such vortex states give rise to the Berezinskii-Kosterlitz-Thouless (BKT) phase present up to the XY model in the limit q→∞. Based on information theory, we present here an analysis of the classical order parameters plus new short-range parameters defined here. Thus, we show that even using the first nearest neighbors spin-spin correlations only, it is possible to distinguish the two transitions presented by this system for q greater than or equal to 5. Moreover, the appearance at relatively low temperature and disappearance of the BKT phase at a rather fix higher temperature is univocally determined by the short-range interactions recognized by the information content of classical and new parameters.

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28

Halperin, Bertrand I., Gil Refael i Eugene Demler. "RESISTANCE IN SUPERCONDUCTORS". International Journal of Modern Physics B 24, nr 20n21 (30.08.2010): 4039–80. http://dx.doi.org/10.1142/s021797921005644x.

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In this pedagogical review, we discuss how electrical resistance can arise in superconductors. Starting with the idea of the superconducting order parameter as a condensate wave function, we introduce vortices as topological excitations with quantized phase winding, and we show how phase slips occur when vortices cross the sample. Superconductors exhibit non-zero electrical resistance under circumstances where phase slips occur at a finite rate. For one-dimensional superconductors or Josephson junctions, phase slips can occur at isolated points in space-time. Phase slip rates may be controlled by thermal activation over a free-energy barrier, or in some circumstances, at low temperatures, by quantum tunneling through a barrier. We present an overview of several phenomena involving vortices that have direct implications for the electrical resistance of superconductors, including the Berezinskii–Kosterlitz–Thouless transition for vortex-proliferation in thin films, and the effects of vortex pinning in bulk type II superconductors on the nonlinear resistivity of these materials in an applied magnetic field. We discuss how quantum fluctuations can cause phase slips and review the non-trivial role of dissipation on such fluctuations. We present a basic picture of the superconductor-to-insulator quantum phase transitions in films, wires, and Josephson junctions. We point out related problems in superfluid helium films and systems of ultra-cold trapped atoms. While our emphasis is on theoretical concepts, we also briefly describe experimental results, and we underline some of the open questions.

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29

Tsiok, Elena N., Yuri D. Fomin, Eugene A. Gaiduk, Elena E. Tareyeva, Valentin N. Ryzhov, Pavel A. Libet, Nikita A. Dmitryuk, Nikita P. Kryuchkov i Stanislav O. Yurchenko. "The role of attraction in the phase diagrams and melting scenarios of generalized 2D Lennard-Jones systems". Journal of Chemical Physics 156, nr 11 (21.03.2022): 114703. http://dx.doi.org/10.1063/5.0075479.

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Monolayer and two-dimensional (2D) systems exhibit rich phase behavior, compared with 3D systems, in particular, due to the hexatic phase playing a central role in melting scenarios. The attraction range is known to affect critical gas–liquid behavior (liquid–liquid in protein and colloidal systems), but the effect of attraction on melting in 2D systems remains unstudied systematically. Here, we have revealed how the attraction range affects the phase diagrams and melting scenarios in a 2D system. Using molecular dynamics simulations, we have considered the generalized Lennard-Jones system with a fixed repulsion branch and different power indices of attraction from long-range dipolar to short-range sticky-sphere-like. A drop in the attraction range has been found to reduce the temperature of the gas–liquid critical point, bringing it closer to the gas–liquid–solid triple point. At high temperatures, attraction does not affect the melting scenario that proceeds through the cascade of solid–hexatic (Berezinskii–Kosterlitz–Thouless) and hexatic–liquid (first-order) phase transitions. In the case of dipolar attraction, we have observed two triple points inherent in a 2D system: hexatic–liquid–gas and crystal–hexatic–gas, the temperature of the crystal–hexatic–gas triple point is below the hexatic–liquid–gas triple point. This observation may have far-reaching consequences for future studies, since phase diagrams determine possible routes of self-assembly in molecular, protein, and colloidal systems, whereas the attraction range can be adjusted with complex solvents and external electric or magnetic fields. The results obtained may be widely used in condensed matter, chemical physics, materials science, and soft matter.

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30

Julku, A., T. J. Peltonen, L. Liang, T. T. Heikkilä i P. Törmä. "Superfluid weight and Berezinskii-Kosterlitz-Thouless transition temperature of twisted bilayer graphene". Physical Review B 101, nr 6 (24.02.2020). http://dx.doi.org/10.1103/physrevb.101.060505.

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31

Sun, Yun-Zhou, Qin Wu, Xiao-Li Yang, Yan Zhou, Lan-Yan Zhu, Quan Chen i Qing An. "Numerical Studies of Vortices and Helicity Modulus in the Two-Dimensional Generalized XY Model". Frontiers in Physics 10 (4.03.2022). http://dx.doi.org/10.3389/fphy.2022.851322.

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Two-dimensional generalized XY spin model on a triangular lattice is studied by means of Monte-Carlo simulations. The critical temperatures of Berezinskii-Kosterlitz-Thouless (BKT) phase transition are obtained by the method of helicity modulus. It is found that the results are consistent with those obtained by other methods. The vortex density and the vortex-antivortex pair formation energy are also obtained. The result shows that the critical temperature decreases with the increase of the generalization parameter q. While the vortex-antivortex pair formation energy increases with the increase of q when q>1.

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32

Sun, Huimin, Yu Huang, Peng Zhang, Mengyun He, Yu Fu, Kang L. Wang i Qing Lin He. "Topological transitions in the presence of random magnetic domains". Communications Physics 5, nr 1 (27.08.2022). http://dx.doi.org/10.1038/s42005-022-00996-y.

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AbstractThe Berezinskii-Kosterlitz-Thouless (BKT) transition is a topological transition driven by topological defects at a characteristic temperature, below which vortex-antivortex pairs bound and dissociate into free vortices above. Such transitions have been observed in superfluid helium films, superconducting films, quantum Hall systems, planar Josephson junction arrays, graphene, and frustrated magnets. Here we report the BKT-like transition in a quantum anomalous Hall insulator film. This system is a 2D ferromagnet with broken time-reversal symmetry, which results in quantized chiral/antichiral edge states around the boundaries of the magnetic domains/antidomains. The bindings and unbindings of these domain-antidomain pairs can take the roles played by vortex-antivortex pairs while the chirality takes over the vorticity, which drive the system to undergo the BKT-like transition. This multidomain network can be manipulated by coherent/competitive mechanisms like the applied dc current, perpendicular magnetic field, and temperature, the combination of which forms a line of critical points.

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33

Kumar Ojha, Shashank, Prithwijit Mandal, Siddharth Kumar, Jyotirmay Maity i Srimanta Middey. "Flux-flow instability across Berezinskii Kosterlitz Thouless phase transition in KTaO3 (111) based superconductor". Communications Physics 6, nr 1 (5.06.2023). http://dx.doi.org/10.1038/s42005-023-01251-8.

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AbstractThe nature of energy dissipation in 2D superconductors under perpendicular magnetic field at small current excitations has been extensively studied over the past two decades. However, dissipation mechanisms at high current drives remain largely unexplored. Here we report on the distinct behavior of energy dissipation in the AlOx/KTaO3 (111) system hosting 2D superconductivity in the intermediate disorder regime. The results show that below the Berezinskii Kosterlitz Thouless (BKT) phase transition temperature (TBKT), hot-spots and Larkin Ovchinnikov type flux-flow instability (FFI) are the major channels of dissipation, leading to pronounced voltage instability at large currents. Furthermore, such FFI leads to a rare observation of clockwise hysteresis in current-voltage characteristics within the temperature range TBKT < T < TC (TC is superconducting transition temperature). These findings deepen our understanding of how a BKT system ultimately transforms to a normal state under increasing current.

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34

Vasin, M. G. "Theoretical analysis of the Berezinskii–Kosterlitz–Thouless transition critical dynamics near the zero temperature". European Physical Journal Plus 137, nr 9 (15.09.2022). http://dx.doi.org/10.1140/epjp/s13360-022-03256-8.

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35

Zou, Y. Q., B. Bakkali-Hassani, C. Maury, É. Le Cerf, S. Nascimbene, J. Dalibard i J. Beugnon. "Tan’s two-body contact across the superfluid transition of a planar Bose gas". Nature Communications 12, nr 1 (3.02.2021). http://dx.doi.org/10.1038/s41467-020-20647-6.

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AbstractTan’s contact is a quantity that unifies many different properties of a low-temperature gas with short-range interactions, from its momentum distribution to its spatial two-body correlation function. Here, we use a Ramsey interferometric method to realize experimentally the thermodynamic definition of the two-body contact, i.e., the change of the internal energy in a small modification of the scattering length. Our measurements are performed on a uniform two-dimensional Bose gas of 87Rb atoms across the Berezinskii–Kosterlitz–Thouless superfluid transition. They connect well to the theoretical predictions in the limiting cases of a strongly degenerate fluid and of a normal gas. They also provide the variation of this key quantity in the critical region, where further theoretical efforts are needed to account for our findings.

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36

Boudjemâa, Abdelâali. "Many-body and temperature effects in two-dimensional quantum droplets in Bose–Bose mixtures". Scientific Reports 11, nr 1 (5.11.2021). http://dx.doi.org/10.1038/s41598-021-01089-6.

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AbstractWe study the equilibrium properties of self-bound droplets in two-dimensional Bose mixtures employing the time-dependent Hartree–Fock–Bogoliubov theory. This theory allows one to understand both the many-body and temperature effects beyond the Lee–Huang–Yang description. We calculate higher-order corrections to the excitations, the sound velocity, and the energy of the droplet. Our results for the ground-state energy are compared with the diffusion Monte Carlo data and good agreement is found. The behavior of the depletion and anomalous density of the droplet is also discussed. At finite temperature, we show that the droplet emerges at temperatures well below the Berezinskii–Kosterlitz–Thouless transition temperature. The critical temperature strongly depends on the interspecies interactions. Our study is extended to the finite size droplet by numerically solving the generalized finite-temperature Gross-Pitaevskii equation which is obtained self-consistently from our formalism in the framework of the local density approximation.

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37

Jiao, Xiaotong, Wenfeng Dong, Mingxia Shi, Heng Wang, Cui Ding, Zhongxu Wei, Guanming Gong i in. "Significantly enhanced superconductivity in monolayer FeSe films on SrTiO3(001) via metallic δ-doping". National Science Review, 10.08.2023. http://dx.doi.org/10.1093/nsr/nwad213.

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Abstract Superconductivity transition temperature (Tc) marks the inception of a macroscopic quantum phase-coherent paired state in fermionic systems. For two-dimension superconductivity, the paired electrons condense into a coherent superfluid state at Tc, which is usually lower than the pairing temperature, between which intrinsic physics including Berezinskii-Kosterlitz-Thouless transition and pseudogap state are hotly debated. In the case of monolayer FeSe superconducting films on SrTiO3(001), although the pairing temperature (Tp) is revealed to be 65–83 K by spectroscopy characterization, the measured zero-resistance temperature (${T}_{c}^0$) is limited to 20 K. Here, we report significantly enhanced superconductivity in monolayer FeSe films by δ-doping of Eu or Al on SrTiO3(001) surface, in which ${T}_{c}^0$ is enhanced by 12 K with narrowed transition width ΔTc ∼ 8 K, compared with non-doped samples. Using scanning tunneling microscopy/spectroscopy measurements, we demonstrate lowered work function of the δ-doped-SrTiO3(001) surface and enlarged superconducting gaps in the monolayer FeSe with improved morphology/electronic homogeneity. Our work provides a practical route to enhance 2D superconductivity by interface engineering.

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38

Jarjour, Alexander, G. M. Ferguson, Brian T. Schaefer, Menyoung Lee, Yen Lee Loh, Nandini Trivedi i Katja C. Nowack. "Superfluid response of an atomically thin gate-tuned van der Waals superconductor". Nature Communications 14, nr 1 (12.04.2023). http://dx.doi.org/10.1038/s41467-023-37210-8.

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AbstractA growing number of two-dimensional superconductors are being discovered in the family of exfoliated van der Waals materials. Due to small sample volume, the superfluid response of these materials has not been characterized. Here, we use a local magnetic probe to directly measure this key property of the tunable, gate-induced superconducting state in MoS2. We find that the backgate changes the transition temperature non-monotonically whereas the superfluid stiffness at low temperature and the normal state conductivity monotonically increase. In some devices, we find direct signatures in agreement with a Berezinskii-Kosterlitz-Thouless transition, whereas in others we find a broadened onset of the superfluid response. We show that the observed behavior is consistent with disorder playing an important role in determining the properties of superconducting MoS2. Our work demonstrates that magnetic property measurements are within reach for superconducting devices based on exfoliated sheets and reveals that the superfluid response significantly deviates from simple BCS-like behavior.

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39

Shi, Tingting, Wei Zhang i Carlos A. R. Sa de Melo. "Density induced BCS-Bose evolution in gated two-dimensional superconductors: The role of the interaction range in the Berezinskii-Kosterlitz-Thouless transition". Europhysics Letters, 21.06.2022. http://dx.doi.org/10.1209/0295-5075/ac7ace.

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Abstract We discuss the evolution from Bardeen-Cooper-Schrieﬀer (BCS) to Bose superconductivity versus carrier density n in two-dimensional (2D) gated superconductors and address the fundamental role that the interaction range plays in the Berezinskii-Kosterlitz-Thouless transition. We investigate the density dependence of the critical temperature (Tc), superﬂuid density, order parameter modulus, chemical potential and pair size. Our most important ﬁnding is that it is absolutely essential to include classical and quantum phase ﬂuctuations, as well as, ﬁnite-ranged interactions to explain the non-monotonic behavior of Tc versus n and to guarantee that the upper bound on Tcis not exceeded in 2D superconductors, as experimentally observed in LixZrNCl [Science 372, 190 (2021)], a lithium-intercalated layered nitride, and in magic-angle twisted trilayer graphene [Nature 590, 249 (2021)]. Furthermore, we show that we can extract, from measurements of Tc and the order parameter modulus, the eﬀective mass of charge carriers and their interaction strength and range.

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40

Mallik, S., G. C. Ménard, G. Saïz, H. Witt, J. Lesueur, A. Gloter, L. Benfatto, M. Bibes i N. Bergeal. "Superfluid stiffness of a KTaO3-based two-dimensional electron gas". Nature Communications 13, nr 1 (8.08.2022). http://dx.doi.org/10.1038/s41467-022-32242-y.

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AbstractAfter almost twenty years of intense work on the celebrated LaAlO3/SrTiO3system, the recent discovery of a superconducting two-dimensional electron gas (2-DEG) in (111)-oriented KTaO3-based heterostructures injects new momentum to the field of oxides interface. However, while both interfaces share common properties, experiments also suggest important differences between the two systems. Here, we report gate tunable superconductivity in 2-DEGs generated at the surface of a (111)-oriented KTaO3 crystal by the simple sputtering of a thin Al layer. We extract the superfluid stiffness of the 2-DEGs and show that its temperature dependence is consistent with a node-less superconducting order parameter having a gap value larger than expected within a simple BCS weak-coupling limit model. The superconducting transition follows the Berezinskii-Kosterlitz-Thouless scenario, which was not reported on SrTiO3-based interfaces. Our finding offers innovative perspectives for fundamental science but also for device applications in a variety of fields such as spin-orbitronics and topological electronics.

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41

Zhang, Caorong, Junwei Huang, Kun Zhai, Keivan Akhtari, Zhiwei Shen, Lingyi Ao, Zeya Li i in. "Valence-skipping and quasi-two-dimensionality of superconductivity in a van der Waals insulator". Nature Communications 13, nr 1 (14.11.2022). http://dx.doi.org/10.1038/s41467-022-34726-3.

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AbstractValence fluctuation of interacting electrons plays a crucial role in emergent quantum phenomena in correlated electron systems. The theoretical rationale is that this effect can drive a band insulator into a superconductor through charge redistribution around the Fermi level. However, the root cause of such a fluctuating leap in the ionic valency remains elusive. Here, we demonstrate a valence-skipping-driven insulator-to-superconductor transition and realize quasi-two-dimensional superconductivity in a van der Waals insulator GeP under pressure. This is shown to result from valence skipping of the Ge cation, altering its average valency from 3+ to 4+, turning GeP from a layered compound to a three-dimensional covalent system with superconducting critical temperature reaching its maximum of 10 K. Such a valence-skipping-induced superconductivity with a quasi-two-dimensional nature in thin samples, showing a Berezinskii-Kosterlitz-Thouless-like character, is further confirmed by angle-dependent upper-critical-field measurements. These findings provide a model system to examine competing order parameters in valence-skipping systems.

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42

Zhang, Shunhong, Xiaoyin Li, Huisheng Zhang, Ping Cui, Xiaohong Xu i Zhenyu Zhang. "Giant Dzyaloshinskii-Moriya interaction, strong XXZ-type biquadratic coupling, and bimeronic excitations in the two-dimensional CrMnI6 magnet". npj Quantum Materials 8, nr 1 (26.07.2023). http://dx.doi.org/10.1038/s41535-023-00569-4.

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AbstractTwo-dimensional magnets have been discovered recently as a new class of quantum matter exhibiting a broad wealth of exotic phenomena, including notably various topological excitations rooted in emergent exchange couplings between the localized magnetic moments. By analyzing the anisotropies in the single-ion magnetization and two-body exchange couplings obtained from first-principles calculations, we reveal coexistence of both giant Dzyaloshinskii–Moriya interaction and strong anisotropic XXZ-type biquadratic coupling in a recently predicted monolayer CrMnI6 magnet. The former is induced by the spontaneous in-plane inversion symmetry breaking in the bipartite system, the latter is inherently tied to the distinct high-spin state of the Mn sublattice, while the large magnitudes of both stem from the significant spin-orbit coupling. Next, we use atomistic magnetics simulations to demonstrate the vital role of Dzyaloshinskii–Moriya interaction in harboring topological bimeronic excitations, and show that the biquadratic coupling favors a Berezinskii–Kosterlitz–Thouless-like transition as the system reduces its temperature from the paramagnetic phase. These findings substantially enrich our understanding of the microscopic couplings in 2D magnets, with appealing application potentials.

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43

Williamson, Lewis, i Blair Blackie. "Anomalous phase ordering of a quenched ferromagnetic superfluid". SciPost Physics 7, nr 3 (9.09.2019). http://dx.doi.org/10.21468/scipostphys.7.3.029.

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Coarsening dynamics, the canonical theory of phase ordering following a quench across a symmetry breaking phase transition, is thought to be driven by the annihilation of topological defects. Here we show that this understanding is incomplete. We simulate the dynamics of an isolated spin-1 condensate quenched into the easy-plane ferromagnetic phase and find that the mutual annihilation of spin vortices does not take the system to the equilibrium state. A nonequilibrium background of long wavelength spin waves remain at the Berezinskii-Kosterlitz-Thouless temperature, an order of magnitude hotter than the equilibrium temperature. The coarsening continues through a second much slower scale invariant process with a length scale that grows with time as t^{1/3}t1/3. This second regime of coarsening is associated with spin wave energy transport from low to high wavevectors, bringing about the the eventual equilibrium state. The transport displays features of a spin wave energy cascade, providing a potential profitable connection with the emerging field of spin wave turbulence. Strongly coupling the system to a reservoir destroys the second regime of coarsening, allowing the system to thermalise following the annihilation of vortices.

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44

Zimmerman, Michal, Ronen Rapaport i Snir Gazit. "Collective interlayer pairing and pair superfluidity in vertically stacked layers of dipolar excitons". Proceedings of the National Academy of Sciences 119, nr 30 (18.07.2022). http://dx.doi.org/10.1073/pnas.2205845119.

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Layered bosonic dipolar fluids have been suggested to host a condensate of interlayer molecular bound states. However, experimental observation has remained elusive. Motivated by two recent experimental works [C. Hubert et al ., Phys. Rev. X 9, 021026 (2019) and D. J. Choksy et al ., Phys. Rev. B 103, 045126 (2021)], we theoretically study, using numerically exact quantum Monte Carlo calculations, the experimental signatures of collective interlayer pairing in vertically stacked indirect exciton (IX) layers. We find that IX energy shifts associated with each layer evolve nontrivially as a function of density imbalance following a nonmonotonic trend with a jump discontinuity at density balance, identified with the interlayer IX molecule gap. This behavior discriminates between the superfluidity of interlayer bound pairs and independent dipole condensation in distinct layers. Considering finite temperature and finite density imbalance conditions, we find a cascade of Berezinskii–Kosterlitz–Thouless (BKT) transitions, initially into a pair superfluid and only then, at lower temperatures, into complete superfluidity of both layers. Our results may provide a theoretical interpretation of existing experimental observations in GaAs double quantum well (DQW) bilayer structures. Furthermore, to optimize the visibility of pairing dynamics in future studies, we present an analysis suggesting realistic experimental settings in GaAs and transition metal dichalcogenide (TMD) bilayer DQW heterostructures where collective interlayer pairing and pair superfluidity can be clearly observed.

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45

He, Yuan-Yao, Hao Shi i Shiwei Zhang. "Precision Many-Body Study of the Berezinskii-Kosterlitz-Thouless Transition and Temperature-Dependent Properties in the Two-Dimensional Fermi Gas". Physical Review Letters 129, nr 7 (12.08.2022). http://dx.doi.org/10.1103/physrevlett.129.076403.

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46

Hua, Xiangyu, Fanbao Meng, Zongyao Huang, Zhaohang Li, Shuai Wang, Binghui Ge, Ziji Xiang i Xianhui Chen. "Tunable two-dimensional superconductivity and spin-orbit coupling at the EuO/KTaO3(110) interface". npj Quantum Materials 7, nr 1 (23.09.2022). http://dx.doi.org/10.1038/s41535-022-00506-x.

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AbstractUnconventional quantum states, most notably the two-dimensional (2D) superconductivity, have been realized at the interfaces of oxide heterostructures where they can be effectively tuned by the gate voltage (VG). Here we report that the interface between high-quality EuO (111) thin film and KTaO3 (KTO) (110) substrate shows superconductivity with onset transition temperature $$T_{{{\mathrm{c}}}}^{{{{\mathrm{onset}}}}}$$ T c onset = 1.35 K. The 2D nature of superconductivity is verified by the large anisotropy of the upper critical field and the characteristics of a Berezinskii–Kosterlitz-Thouless transition. By applying VG, $$T_{{{\mathrm{c}}}}^{{{{\mathrm{onset}}}}}$$ T c onset can be tuned from ~1 to 1.7 K; such an enhancement can be possibly associated with a boosted spin-orbit energy $$\varepsilon _{{{{\mathrm{so}}}}} = \hbar /\tau _{{{{\mathrm{so}}}}}$$ ε so = ħ / τ so , where τso is the spin-orbit relaxation time. Further analysis of τso based on the upper critical field (Hc2) and magnetoconductance reveals complex nature of spin-orbit coupling (SOC) at the EuO/KTO(110) interface with different mechanisms dominating the influence of SOC effects on the superconductivity and the magnetotransport in the normal state. Our results demonstrate that the SOC should be considered an important factor in determining the 2D superconductivity at oxide interfaces.

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47

Kim, Se Kwon, i Suk Bum Chung. "Transport signature of the magnetic Berezinskii-Kosterlitz-Thouless transition". SciPost Physics 10, nr 3 (12.03.2021). http://dx.doi.org/10.21468/scipostphys.10.3.068.

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Motivated by recent experimental progress in 2D magnetism, we theoretically study spin transport in 2D easy-plane magnets at finite temperatures across the Berezinskii-Kosterlitz-Thouless (BKT) phase transition, by developing a duality mapping to the 2+1D electromagnetism with the full account of spin’s finite lifetime. In particular, we find that the non-conservation of spin gives rise to a distinct signature across the BKT transition, with the spin current decaying with distance power-law (exponentially) below (above) the transition; this is detectable in the proposed experiment with NiPS_33 and CrCl_33.

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48

van Engelenburg, Diederik, i Marcin Lis. "An Elementary Proof of Phase Transition in the Planar XY Model". Communications in Mathematical Physics, 15.11.2022. http://dx.doi.org/10.1007/s00220-022-04550-3.

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AbstractUsing elementary methods we obtain a power-law lower bound on the two-point function of the planar XY spin model at low temperatures. This was famously first rigorously obtained by Fröhlich and Spencer (Commun Math Phys 81(4):527–602, 1981) and establishes a Berezinskii–Kosterlitz–Thouless phase transition in the model. Our argument relies on a new loop representation of spin correlations, a recent result of Lammers (Probab Relat Fields, 2021) on delocalisation of general integer-valued height functions, and classical correlation inequalities.

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49

Huang, Chun-Jiong, Xiaoqun Wang, Ziqiang Wang i Gang Chen. "Emergent Halperin–Saslow mode, gauge glass and quenched disorders in quantum Ising magnet TmMgGaO₄". International Journal of Modern Physics B, 4.03.2023. http://dx.doi.org/10.1142/s0217979224500401.

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Quenched disorders could bring novel quantum excitations and models to certain quantum magnets. Motivated by recent experiments on the quantum Ising magnet TmMgGaO4, we explore the effects of the quenched disorder and the interlayer coupling in this triangular lattice Ising antiferromagnet. It is pointed out that the weak quenched (nonmagnetic) disorder would convert the emergent 2D Berezinskii–Kosterlitz–Thouless (BKT) phase and the critical region into a U(1) gauge glass. There will be an emergent Halperin–Saslow mode associated with this gauge glass. Using the Imry-Ma’s renormalization group result, we explain the fate of the finite-field [Formula: see text] symmetry breaking transition at the low temperatures. The ferromagnetic interlayer coupling would suppress the BKT phase and generate a tiny ferromagnetism. With quenched disorders, this interlayer coupling changes the 2D gauge glass into a 3D gauge glass, and the Halperin–Saslow mode persists. This work merely focuses on addressing a phase regime in terms of emergent U(1) gauge glass behaviors and hope to inspire future works and thoughts in weakly disordered frustrated magnets in general.

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50

Devreese, Jeroen P. A., Jacques Tempere i Carlos A. R. Sá de Melo. "Quantum phase transitions and Berezinskii-Kosterlitz-Thouless temperature in a two-dimensional spin-orbit-coupled Fermi gas". Physical Review A 92, nr 4 (20.10.2015). http://dx.doi.org/10.1103/physreva.92.043618.

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