Journal articles: 'Optically generated spin currents'

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LIU, XIONG-JUN, L. C. KWEK, and C. H. Oh. "QUANTUM SPIN CURRENT INDUCED THROUGH OPTICAL DIPOLE TRANSITION PROCESS IN SEMICONDUCTORS." International Journal of Modern Physics B 22, no. 01n02 (January 20, 2008): 44–56. http://dx.doi.org/10.1142/s0217979208046037.

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We propose a scheme to generate quantum spin current via linear optical process. By interacting a three-level system based on the spin states of charged particles (electrons or holes in semiconductor, etc) with the angular momentum states of an optical field, we show that the dynamics of charged particles equipped with different spin polarizations are governed by different (opposite) additional effective magnetic fields. In this way, a pure dissipationless quantum spin current can be generated. No spin-orbit interaction (e.g., Rashba or Dresselhaus term) is needed in this scheme. We also calculate the effect of nonmagnetic impurities on the created spin currents and show that the vertex correction of the spin hall conductivity in the ladder approximation is exactly zero. Paper presented at NTU Spintronics Workshop, Singapore, May 2006.

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Miah, M. Idrish, I. V. Kityk, and E. MacA Gray. "Detection and study of photo-generated spin currents in nonmagnetic semiconductor materials." Acta Materialia 55, no. 18 (October 2007): 6392–400. http://dx.doi.org/10.1016/j.actamat.2007.07.050.

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Zucchetti, C., F. Scali, P. Grassi, M. Bollani, L. Anzi, G. Isella, M. Finazzi, F. Ciccacci, and F. Bottegoni. "Non-local architecture for spin current manipulation in silicon platforms." APL Materials 11, no. 2 (February 1, 2023): 021102. http://dx.doi.org/10.1063/5.0130759.

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We have developed a non-local architecture for spin current injection, manipulation, and detection in n-doped bulk Si at room temperature. Spins are locally generated at the indirect gap of bulk Si by means of circularly polarized light and then detected by exploiting the inverse spin-Hall effect (ISHE) occurring inside a thin Pt pad deposited at the top of the Si substrate. We demonstrate that it is possible to modulate the transport properties of the optically injected spin current by applying a bias voltage along the direction of motion of the particles. In this case, we are able to explore both the spin diffusion regime, characterized by a spin diffusion length Ls ≈ 12 μm, and the spin drift regime with applied electric fields up to E = 35 V/cm. We demonstrate that the spin transport length of the electrons can be increased (or decreased) by more than 100% for electric fields antiparallel (or parallel) to the diffusion direction. As a consequence, the ISHE signal can be electrically controlled to have high or low output voltages from the non-local device.

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Dotsenko, Victor S., Pascal Viot, Alberto Imparato, and Gleb Oshanin. "Cooperative dynamics in two-component out-of-equilibrium systems: molecular ‘spinning tops’." Journal of Statistical Mechanics: Theory and Experiment 2022, no. 12 (December 1, 2022): 123211. http://dx.doi.org/10.1088/1742-5468/aca900.

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Abstract We study the two-dimensional Langevin dynamics of a mixture of two types of particles that live respectively at two different temperatures. Dynamics is constrained by an optical trap and the dissimilar species interact via a quadratic potential. We realize that the system evolves toward a peculiar non-equilibrium steady-state with a non-zero probability current possessing a non-zero curl. This implies that if the particles were to have a finite-size and therefore a rotational degree of freedom, they would experience a torque generated by the non-zero local curl and spin around their geometric centers, like ‘spinning top’ toys. Our analysis shows that the spinning motion is correlated and also reveals an emerging cooperative behavior of the spatial components of the probability currents of dissimilar species.

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Bhat, R. D. R., and J. E. Sipe. "Optically Injected Spin Currents in Semiconductors." Physical Review Letters 85, no. 25 (December 18, 2000): 5432–35. http://dx.doi.org/10.1103/physrevlett.85.5432.

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Thouless, David. "ANDERSON LOCALIZATION IN THE SEVENTIES AND BEYOND." International Journal of Modern Physics B 24, no. 12n13 (May 20, 2010): 1507–25. http://dx.doi.org/10.1142/s0217979210064496.

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Little attention was paid to Anderson's challenging paper on localization for the first ten years, but from 1968 onwards it generated a lot of interest. Around that time a number of important questions were raised by the community, on matters such as the existence of a sharp distinction between localized and extended states, or between conductors and insulators. For some of these questions the answers are unambiguous. There certainly are energy ranges in which states are exponentially localized, in the presence of a static disordered potential. In a weakly disordered one-dimensional potential, all states are localized. There is clear evidence, in three dimensions, for energy ranges in which states are extended, and ranges in which they are diffusive. Magnetic and spin-dependent interactions play an important part in reducing localization effects. For massive particles like electrons and atoms the lowest energy states are localized, but for massless particles like photons and acoustic phonons the lowest energy states are extended. Uncertainties remain. Scaling theory suggests that in two-dimensional systems all states are weakly localized, and that there is no minimum metallic conductivity. The interplay between disorder and mutual interactions is still an area of uncertainty, which is very important for electronic systems. Optical and dilute atomic systems provide experimental tests which allow interaction to be much less important. The quantum Hall effect provided a system where states on the Fermi surface are localized, but non-dissipative currents flow in response to an electric field.

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Madjar, A., P. R. Herczfeld, and A. Paolella. "Analytical model for optically generated currents in GaAs MESFETs." IEEE Transactions on Microwave Theory and Techniques 40, no. 8 (1992): 1681–91. http://dx.doi.org/10.1109/22.149548.

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Miah, M. Idrish. "Electric-field effects in optically generated spin transport." Physics Letters A 373, no. 23-24 (May 2009): 2097–100. http://dx.doi.org/10.1016/j.physleta.2009.04.021.

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Takeuchi, Akihito, and Gen Tatara. "Charge and Spin Currents Generated by Dynamical Spins." Journal of the Physical Society of Japan 77, no. 7 (July 15, 2008): 074701. http://dx.doi.org/10.1143/jpsj.77.074701.

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Lin, Zheng-Zhe, and Xi Chen. "Spin-polarized currents generated by magnetic Fe atomic chains." Nanotechnology 25, no. 23 (May 21, 2014): 235202. http://dx.doi.org/10.1088/0957-4484/25/23/235202.

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Davidson, Angie, Vivek P. Amin, Wafa S. Aljuaid, Paul M. Haney, and Xin Fan. "Perspectives of electrically generated spin currents in ferromagnetic materials." Physics Letters A 384, no. 11 (April 2020): 126228. http://dx.doi.org/10.1016/j.physleta.2019.126228.

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Dale, Matthew W., Daniel J. Cheney, Claudio Vallotto, and Christopher J. Wedge. "Viscosity effects on optically generated electron and nuclear spin hyperpolarization." Physical Chemistry Chemical Physics 22, no. 48 (2020): 28173–82. http://dx.doi.org/10.1039/d0cp04012f.

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NAKATA, KOUKI. "TEMPERATURE DEPENDENCE OF SPIN CURRENTS CARRIED BY JORDAN–WIGNER FERMIONS AND MAGNONS IN INSULATORS." International Journal of Modern Physics B 26, no. 01 (January 10, 2012): 1250011. http://dx.doi.org/10.1142/s0217979211102071.

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The temperature dependence of spin currents in insulators at the finite temperature near zero Kelvin is theoretically studied. The spin currents are carried by Jordan–Wigner fermions and magnons in one- and three-dimensional insulators. These spin currents are generated by the external magnetic field gradient along the quantization axis and also by the two-particle interaction gradient. In one-dimensional insulators, quantum fluctuations are strong and the spin current carried by Jordan–Wigner fermions shows the stronger dependence on temperatures than the one by magnons.

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Ikeda, Tatsuhiko N. "Generation of DC, AC, and Second-Harmonic Spin Currents by Electromagnetic Fields in an Inversion-Asymmetric Antiferromagnet." Condensed Matter 4, no. 4 (December 11, 2019): 92. http://dx.doi.org/10.3390/condmat4040092.

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Manipulating spin currents in magnetic insulators is a key technology in spintronics. We theoretically study a simple inversion-asymmetric model of quantum antiferromagnets, where both the exchange interaction and the magnetic field are staggered. We calculate spin currents generated by external electric and magnetic fields by using a quantum master equation. We show that an ac electric field with amplitude E 0 leads, through exchange-interaction modulation, to the dc and second-order harmonic spin currents proportional to E 0 2 . We also show that dc and ac staggered magnetic fields B 0 generate the dc and ac spin currents proportional to B 0 , respectively. We elucidate the mechanism by an exactly solvable model, and thereby propose the ways of spin current manipulation by electromagnetic fields.

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Panda, S. N., S. Mondal, J. Sinha, S. Choudhury, and A. Barman. "All-optical detection of interfacial spin transparency from spin pumping in β-Ta/CoFeB thin films." Science Advances 5, no. 4 (April 2019): eaav7200. http://dx.doi.org/10.1126/sciadv.aav7200.

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Generation and utilization of pure spin current have revolutionized energy-efficient spintronic devices. Spin pumping effect generates pure spin current, and for its increased efficiency, spin-mixing conductance and interfacial spin transparency are imperative. The plethora of reports available on generation of spin current with giant magnitude overlook the interfacial spin transparency. Here, we investigate spin pumping in β-Ta/CoFeB thin films by an all-optical time-resolved magneto-optical Kerr effect technique. From variation of Gilbert damping with Ta and CoFeB thicknesses, we extract the spin diffusion length of β-Ta and spin-mixing conductances. Consequently, interfacial spin transparency is derived as 0.50 ± 0.03 from the spin Hall magnetoresistance model for the β-Ta/CoFeB interface. Furthermore, invariance of Gilbert damping with Cu spacer layer thickness inserted between β-Ta and CoFeB layers confirms the absence of other interface effects including spin memory loss. This demonstrates a reliable and noninvasive way to determine interfacial spin transparency and signifies its role in generation of pure spin current by spin pumping effect.

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Volkov, Oleksii M., Volodymyr P. Kravchuk, Denis D. Sheka, Franz G. Mertens, and Yuri Gaididei. "Periodic magnetic structures generated by spin–polarized currents in nanostripes." Applied Physics Letters 103, no. 22 (November 25, 2013): 222401. http://dx.doi.org/10.1063/1.4831748.

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Göbbels, Stefan, Gernot Güntherodt, and Bernd Beschoten. "Time-resolved lateral spin-caloric transport of optically generated spin packets in n-GaAs." Journal of Physics D: Applied Physics 51, no. 21 (May 2, 2018): 214003. http://dx.doi.org/10.1088/1361-6463/aabd99.

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Ahn, Changhyun. "Higher spin currents with manifest SO(4) symmetry in the large 𝒩 = 4 holography." International Journal of Modern Physics A 33, no. 35 (December 20, 2018): 1850208. http://dx.doi.org/10.1142/s0217751x18502081.

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The large [Formula: see text] nonlinear superconformal algebra is generated by six spin-[Formula: see text] currents, four spin-[Formula: see text] currents and one spin-[Formula: see text] current. The simplest extension of these [Formula: see text] currents is described by the [Formula: see text] higher spin currents of spins [Formula: see text]. In this paper, by using the defining operator product expansions (OPEs) between the [Formula: see text] currents and [Formula: see text] higher spin currents, we determine the [Formula: see text] higher spin currents (the higher spin-[Formula: see text] currents were found previously) in terms of affine Kac–Moody spin-[Formula: see text], one currents in the Wolf space coset model completely. An antisymmetric second rank tensor, three antisymmetric almost complex structures or the structure constant are contracted with the multiple product of spin-[Formula: see text] currents. The eigenvalues are computed for coset representations containing at most four boxes, at finite [Formula: see text] and [Formula: see text]. After calculating the eigenvalues of the zeromode of the higher spin-[Formula: see text] current acting on the higher representations up to three (or four) boxes of Young tableaux in [Formula: see text] in the Wolf space coset, we obtain the corresponding three-point functions with two scalar operators at finite [Formula: see text]. Furthermore, under the large [Formula: see text] ’t Hooft-like limit, the eigenvalues associated with any boxes of Young tableaux are obtained and the corresponding three-point functions are written in terms of the ’t Hooft coupling constant in simple form in addition to the two-point functions of scalars and the number of boxes.

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Zhang, J. J., F. Liang, and J. Wang. "Charge Hall effect generated by spin-polarized current injected into Rashba spin orbit coupling media." European Physical Journal B 72, no. 1 (September 11, 2009): 105–12. http://dx.doi.org/10.1140/epjb/e2009-00305-2.

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Pushp, Aakash, Timothy Phung, Charles Rettner, Brian P. Hughes, See-Hun Yang, and Stuart S. P. Parkin. "Giant thermal spin-torque–assisted magnetic tunnel junction switching." Proceedings of the National Academy of Sciences 112, no. 21 (May 13, 2015): 6585–90. http://dx.doi.org/10.1073/pnas.1507084112.

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Spin-polarized charge currents induce magnetic tunnel junction (MTJ) switching by virtue of spin-transfer torque (STT). Recently, by taking advantage of the spin-dependent thermoelectric properties of magnetic materials, novel means of generating spin currents from temperature gradients, and their associated thermal-spin torques (TSTs), have been proposed, but so far these TSTs have not been large enough to influence MTJ switching. Here we demonstrate significant TSTs in MTJs by generating large temperature gradients across ultrathin MgO tunnel barriers that considerably affect the switching fields of the MTJ. We attribute the origin of the TST to an asymmetry of the tunneling conductance across the zero-bias voltage of the MTJ. Remarkably, we estimate through magneto-Seebeck voltage measurements that the charge currents that would be generated due to the temperature gradient would give rise to STT that is a thousand times too small to account for the changes in switching fields that we observe.

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Parkin, Stuart. "Spin-Polarized Current in Spin Valves and Magnetic Tunnel Junctions." MRS Bulletin 31, no. 5 (May 2006): 389–94. http://dx.doi.org/10.1557/mrs2006.99.

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AbstractSpin-polarized currents can be generated by spin-dependent diffusive scattering in magnetic thin-film structures or by spin-dependent tunneling across ultrathin dielectrics sandwiched between magnetic electrodes.By manipulating the magnetic moments of the magnetic components of these spintronic materials, their resistance can be significantly changed, allowing the development of highly sensitive magnetic-field detectors or advanced magnetic memory storage elements.Whereas the magneto-resistance of useful devices based on spin-dependent diffusive scattering has hardly changed since its discovery nearly two decades ago, in the past five years there has been a remarkably rapid development in both the basic understanding of spin-dependent tunneling and the magnitude of useful tunnel magnetoresistance values.In particular, it is now evident that the magnitude of the spin polarization of tunneling currents in magnetic tunnel junctions not only is related to the spin-dependent electronic structure of the ferromagnetic electrodes but also is considerably influenced by the properties of the tunnel barrier and its interfaces with the magnetic electrodes.Whereas the maximum tunnel magnetoresistance of devices using amorphous alumina tunnel barriers and 3d transition-metal alloy ferromagnetic electrodes is about 70% at room temperature, using crystalline MgO tunnel barriers in otherwise the same structures gives tunnel magnetoresistance values of more than 350% at room temperature.

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Ahmed Al-Shareefi, Nael, Jaafar A. Aldhaibaini, Sura Adil Abbas, and Hadeel S. Obaid. "Towards 5G millimeter-wave wireless networks: a comparative study on electro-optical upconversion techniques." Indonesian Journal of Electrical Engineering and Computer Science 20, no. 3 (December 1, 2020): 1471. http://dx.doi.org/10.11591/ijeecs.v20.i3.pp1471-1478.

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<span>Fifth−generation (5G) wireless networks that use the MM−W hold a great promise to revolutionize wireless industry. However, the difficulty in generating and transmitting these high‐frequency signals in the electrical−domain due to bandwidth limitation of electronic components, and high absorption loss limits current applications. Consequently, optical generation and transmission of MM−W signals are a viable option. In this paper, a comparative study is carried out on three electro−optical upconversion (EOU) techniques to generate 60−GHz MM−W signal, namely 4−tupling, 6−tupling and 8−tupling. The paper briefly describes the three techniques and analyses the optical harmonic distortion suppression ratio (OHDSR) and electrical spurious suppression ratio (ESSR) generated by each one of the techniques. OHDSR and ESSR have been compared to show the trade-off between the techniques. In addition, the paper compares the implementation of non−ideal phase shifting on OHDSR for the three EOU techniques Finally, the performance of the three EOU techniques after transmission over optical fiber is evaluated by quality factor (Q−factor) and eye pattern test. The results of the simulation illustrate well the benefits of the performed study and confirm that the 4−tupling constitutes a cost−effective technique to generate MM−W signals.</span>

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Ralph, D. C., Y. T. Cui, L. Q. Liu, T. Moriyama, C. Wang, and R. A. Buhrman. "Spin-transfer torque in nanoscale magnetic devices." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369, no. 1951 (September 28, 2011): 3617–30. http://dx.doi.org/10.1098/rsta.2011.0169.

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We discuss recent highlights from research at Cornell University, Ithaca, New York, regarding the use of spin-transfer torques to control magnetic moments in nanoscale ferromagnetic devices. We highlight progress on reducing the critical currents necessary to produce spin-torque-driven magnetic switching, quantitative measurements of the magnitude and direction of the spin torque in magnetic tunnel junctions, and single-shot measurements of the magnetic dynamics generated during thermally assisted spin-torque switching.

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Anderson, Dylan, A. Spicer Bak, Katherine L. Brodie, Nicholas Cohn, Rob A. Holman, and John Stanley. "Quantifying Optically Derived Two-Dimensional Wave-Averaged Currents in the Surf Zone." Remote Sensing 13, no. 4 (February 13, 2021): 690. http://dx.doi.org/10.3390/rs13040690.

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Complex two-dimensional nearshore current patterns are generated by feedbacks between sub-aqueous morphology and momentum imparted on the water column by breaking waves, winds, and tides. These non-stationary features, such as rip currents and circulation cells, respond to changing environmental conditions and underlying morphology. However, using fixed instruments to observe nearshore currents is limiting due to the high costs and logistics necessary to achieve adequate spatial sampling resolution. A new technique for processing surf-zone imagery, WAMFlow, quantifies fluid velocities to reveal complex, multi-scale (10 s–1000 s meters) nearshore surface circulation patterns. We apply the concept of a wave-averaged movie (WAM) to measure surf-zone circulation patterns on spatial scales of kilometers in the alongshore and 100 s of meters in the cross-shore. The approach uses a rolling average of 2 Hz optical imagery, removing the dominant optical clutter of incident waves, to leave the residual foam or water turbidity features carried by the flow. These residual features are tracked as quasi-passive tracers in space and time using optical flow, which solves for u and v as a function of image intensity gradients in x, y, and t. Surf zone drifters were deployed over multiple days with varying nearshore circulations to validate the optically derived flow patterns. Root mean square error are reduced to 0.1 m per second after filtering based on image attributes. The optically derived patterns captured longshore currents, rip currents, and gyres within the surf zone. Quantifying nearshore circulation patterns using low-cost image platforms and open-source computer vision algorithms presents the potential to further our understanding of fundamental surf zone dynamics.

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Bierhance, Genaro, Anastasios Markou, Oliver Gueckstock, Reza Rouzegar, Yannic Behovits, Alexander L. Chekhov, Martin Wolf, Tom S. Seifert, Claudia Felser, and Tobias Kampfrath. "Spin-voltage-driven efficient terahertz spin currents from the magnetic Weyl semimetals Co₂MnGa and Co₂MnAl." Applied Physics Letters 120, no. 8 (February 21, 2022): 082401. http://dx.doi.org/10.1063/5.0080308.

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Magnetic Weyl semimetals are an emerging material class that combines magnetic order and a topologically non-trivial band structure. Here, we study ultrafast optically driven spin injection from thin films of the magnetic Weyl semimetals Co2MnGa and Co2MnAl into an adjacent Pt layer by means of terahertz emission spectroscopy. We find that (i) Co2MnGa and Co2MnAl are efficient terahertz spin-current generators reaching efficiencies of typical 3d-transition-metal ferromagnets such as Fe. (ii) The relaxation of the spin current provides an estimate of the electron-spin relaxation time of Co2MnGa (170 fs) and Co2MnAl (100 fs), which is comparable to Fe (90 fs). Both observations are consistent with a simple analytical model and highlight the large potential of magnetic Weyl semimetals as spin-current sources in terahertz spintronic devices. Finally, our results provide a strategy to identify magnetic materials that offer maximum spin-current amplitudes for a given deposited optical energy density.

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Savitsky, Anton, Jingfu Zhang, and Dieter Suter. "Variable bandwidth, high efficiency microwave resonator for control of spin-qubits in nitrogen-vacancy centers." Review of Scientific Instruments 94, no. 2 (February 1, 2023): 023101. http://dx.doi.org/10.1063/5.0125628.

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Nitrogen-Vacancy (NV) centers in diamond are attractive tools for sensing and quantum information. Realization of this potential requires effective tools for controlling the spin degree of freedom by microwave (mw) magnetic fields. In this work, we present a planar microwave resonator optimized for microwave-optical double resonance experiments on single NV centers in diamond. It consists of a piece of wide microstrip line, which is symmetrically connected to two 50 Ω microstrip feed lines. In the center of the resonator, an Ω-shaped loop focuses the current and the mw magnetic field. It generates a relatively homogeneous magnetic field over a volume of 0.07 × 0.1 mm3. It can be operated at 2.9 GHz in both transmission and reflection modes with bandwidths of 1000 and 400 MHz, respectively. The high power-to-magnetic field conversion efficiency allows us to produce π-pulses with a duration of 50 ns with only about 200 and 50 mW microwave power in transmission and reflection, respectively. The transmission mode also offers capability for efficient radio frequency excitation. The resonance frequency can be tuned between 1.3 and 6 GHz by adjusting the length of the resonator. This will be useful for experiments on NV-centers at higher external magnetic fields and on different types of optically active spin centers.

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Kuroda, S., K. Marumoto, H. Ito, N. C. Greenham, R. H. Friend, Y. Shimoi, and S. Abe. "Spin distributions and excitation spectra of optically generated polarons in poly(p-phenylenevinylene) derivatives." Chemical Physics Letters 325, no. 1-3 (July 2000): 183–88. http://dx.doi.org/10.1016/s0009-2614(00)00684-9.

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Bottegoni, F., A. Ferrari, F. Rortais, C. Vergnaud, A. Marty, G. Isella, M. Finazzi, M. Jamet, and F. Ciccacci. "Spin diffusion in Pt as probed by optically generated spin currents." Physical Review B 92, no. 21 (December 2, 2015). http://dx.doi.org/10.1103/physrevb.92.214403.

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Zhao, Yunxiu, Anabil Gayen, Lin Huang, Xiao You, Nguyen Le Thi, Qoimatul Mustaghfiroh, Fathiya Rahmani, et al. "Quantifying Spin‐Charge Conversion Mechanisms for THz Emission in Magnetic Multilayers." Advanced Optical Materials, April 9, 2024. http://dx.doi.org/10.1002/adom.202302571.

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AbstractUltrafast control of both electric and spin currents triggered by femtosecond laser pulse has attracted much attention due to future applications for broadband THz emitter as well as high‐speed spintronic devices. Optically generated spin current is converted to charge current via multiple spin‐charge conversion mechanisms, generating THz wave emission in magnetic multilayers. However, to date, quantitative and comparative investigation of THz emission originating from spin‐charge conversion mechanisms has not yet been fully explored. Here, direct and straightforward nondestructive probing to measure THz emission is provided at original Co/Pt and Co/Ta interfaces embedded in Pt/Co/Ta multilayers with polarization analysis of both optical pump and THz emission. These results allow a fundamental understanding of various spin‐charge conversion phenomena, which is a key basis for future spintronic THz source development.

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Wang, Chuangtang, Yihao Xu, and Yongmin Liu. "Photon Energy‐Dependent Optical Spin‐Orbit Torque in Heavy Metal–Ferromagnet Bilayers." Advanced Functional Materials, October 18, 2023. http://dx.doi.org/10.1002/adfm.202307753.

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AbstractThe manipulation of magnetization through optically generated ultrafast spin currents is a fascinating area that needs a thorough understanding for its potential future applications. In this work, a comprehensive investigation of helicity‐driven optical spin‐orbit torque in heavy metal/ferromagnetic metal heterostructures is presented, specifically cobalt capped with gold or platinum, subject to laser pumping at different wavelengths. The results demonstrate up to tenfold enhancement in optical spin‐orbit torque quantum efficiency for gold compared to platinum of the same thickness when pumped with a visible laser. Additionally, the study provides the first experimental analysis of the photon energy dependence of optical spin‐orbit torque and derives the optical spin orientation spectra for both gold/cobalt and platinum/cobalt heterostructures. A key insight gained from the study is the impact of photon energy‐dependent spin transport in the system, which suggests the use of a high photon energy pump for efficient spin transport. These findings highlight the potential of spin current generation and manipulation in gold/ferromagnet heterostructures for a wide range of applications such as all‐optical magnetization switching, spin‐wave generation and control, and spintronic terahertz emission.

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Michiardi, M., F. Boschini, H. H. Kung, M. X. Na, S. K. Y. Dufresne, A. Currie, G. Levy, et al. "Optical manipulation of Rashba-split 2-dimensional electron gas." Nature Communications 13, no. 1 (June 2, 2022). http://dx.doi.org/10.1038/s41467-022-30742-5.

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AbstractIn spintronics, the two main approaches to actively control the electrons’ spin involve static magnetic or electric fields. An alternative avenue relies on the use of optical fields to generate spin currents, which can bolster spin-device performance, allowing for faster and more efficient logic. To date, research has mainly focused on the optical injection of spin currents through the photogalvanic effect, and little is known about the direct optical control of the intrinsic spin-splitting. To explore the optical manipulation of a material’s spin properties, we consider the Rashba effect. Using time- and angle-resolved photoemission spectroscopy (TR-ARPES), we demonstrate that an optical excitation can tune the Rashba-induced spin splitting of a two-dimensional electron gas at the surface of Bi2Se3. We establish that light-induced photovoltage and charge carrier redistribution - which in concert modulate the Rashba spin-orbit coupling strength on a sub-picosecond timescale - can offer an unprecedented platform for achieving optically-driven spin logic devices.

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He, Jiexuan, and Shufeng Zhang. "Magnetic dynamic phase generated by spin currents." Physical Review B 78, no. 1 (July 24, 2008). http://dx.doi.org/10.1103/physrevb.78.012414.

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Hintermayr, Julian, Paul M. P. van Kuppevelt, and Bert Koopmans. "Coherent control of terahertz-scale spin resonances using optical spin–orbit torques." APL Materials 12, no. 6 (June 1, 2024). http://dx.doi.org/10.1063/5.0205962.

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Using optically generated spin–orbit torques induced by the heavy metal Pt, we demonstrate coherent control of GHz ferromagnetic resonances in Pt/Co/Pt multilayers as well as sub-THz exchange resonances in [Gd/Co]2 multilayers. Employing a double-pump setup, we show that depending on the helicities of the pump pulses, spin resonances can either be coherently amplified or suppressed if the time delay between the arrival of the pump beams is chosen appropriately. Furthermore, by investigating the phase and amplitude of the exchange-driven modes, we identify features that challenge the current understanding of optically generated spin–orbit torques and discuss possible explanations.

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Wang, Xiaoche, Yuxuan Xiao, Chuanpu Liu, Eric Lee-Wong, Nathan J. McLaughlin, Hanfeng Wang, Mingzhong Wu, Hailong Wang, Eric E. Fullerton, and Chunhui Rita Du. "Electrical control of coherent spin rotation of a single-spin qubit." npj Quantum Information 6, no. 1 (September 8, 2020). http://dx.doi.org/10.1038/s41534-020-00308-8.

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Abstract Nitrogen vacancy (NV) centers, optically active atomic defects in diamond, have attracted tremendous interest for quantum sensing, network, and computing applications due to their excellent quantum coherence and remarkable versatility in a real, ambient environment. One of the critical challenges to develop NV-based quantum operation platforms results from the difficulty in locally addressing the quantum spin states of individual NV spins in a scalable, energy-efficient manner. Here, we report electrical control of the coherent spin rotation rate of a single-spin qubit in NV-magnet based hybrid quantum systems. By utilizing electrically generated spin currents, we are able to achieve efficient tuning of magnetic damping and the amplitude of the dipole fields generated by a micrometer-sized resonant magnet, enabling electrical control of the Rabi oscillation frequency of NV spins. Our results highlight the potential of NV centers in designing functional hybrid solid-state systems for next-generation quantum-information technologies. The demonstrated coupling between the NV centers and the propagating spin waves harbored by a magnetic insulator further points to the possibility to establish macroscale entanglement between distant spin qubits.

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Ren, Ruizhi, and Yan Liu. "Nucleation and manipulation of skyrmions by spin currents mediated by an antiferromagnetic layer." Journal of Physics D: Applied Physics, June 19, 2023. http://dx.doi.org/10.1088/1361-6463/acdf6c.

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Abstract Magnetic skyrmions can be used as information carriers in advanced memories, logic gates and computing devices in the future. How to generate skyrmions rapidly in zero field becomes an urgent problem. The application of spin currents will play a major role in promoting the applications of skyrmions in spintronic devices. In this paper, we propose a new mechanism to generate skyrmions by spin currents. A multilayer structure (Pt/Cr2O3/Co/Pt) is designed, where an antiferromagnetic layer (Cr2O3) is inserted into the traditional trilayer structure (Pt/Co/Pt). A spin current generated on the heavy metal layer makes the magnetizations of antiferromagnetic layer oscillate, and then the magnetizations in ferromagnetic layer is driven to oscillate through the interlayer exchange interaction, magnetic skyrmions can be nucleated in Co layer finally. Through this unique combination of spin currents and antiferromagnetic layer, we effectively reduce current density and increase operability, and this application provides more possibilities for future information transmission.

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Tian, Yuan, M. Shoufie Ukhtary, and Riichiro Saito. "Switching performance of optically generated spin current at the graphene edge." Physical Review B 106, no. 4 (July 22, 2022). http://dx.doi.org/10.1103/physrevb.106.045420.

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Mou, Ye, Xingyu Yang, Bruno Gallas, and Mathieu Mivelle. "A Reversed Inverse Faraday Effect." Advanced Materials Technologies, August 16, 2023. http://dx.doi.org/10.1002/admt.202300770.

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AbstractThe inverse Faraday effect is a magneto‐optical process allowing the magnetization of matter by an optical excitation carrying a non‐zero spin. In particular, a right circular polarization generates a magnetization in the direction of light propagation and a left circular polarization in the opposite direction to this propagation. Herein, it demonstrates that by manipulating the spin density of light, i.e., its polarization, in a plasmonic nanostructure, a reversed inverse Faraday effect is generated. A right circular polarization will generate a magnetization in the opposite direction of the light propagation, a left circular polarization in the direction of propagation. Also, it demonstrates that this new physical phenomenon is chiral, generating a strong magnetic field only for one helicity of the light, the opposite helicity producing this effect only for the mirror structure. This new optical concept opens the way to the generation of magnetic fields with unpolarized light, finding application in the ultrafast manipulation of magnetic domains and processes, such as spin precession, spin currents, and waves, magnetic skyrmion or magnetic circular dichroism, with direct applications in data storage and processing technologies.

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Wang, Jian, Yukiko K. Takahashi, and Ken-ichi Uchida. "Magneto-optical painting of heat current." Nature Communications 11, no. 1 (January 7, 2020). http://dx.doi.org/10.1038/s41467-019-13799-7.

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AbstractActive control of heat flow is crucial for the thermal management of increasingly complex electronic and spintronic devices. In addition to conventional heat transport engineering, spin caloritronics has received extensive attention as a heat control principle owing to its high controllability and unique thermal energy conversion symmetry. Here we demonstrate that the direction of heat currents generated by spin-caloritronic phenomena can be changed simply by illuminating magnetic materials with visible light. The optical control of heat currents is realized through a combination of the spin-driven thermoelectric conversion called an anomalous Ettingshausen effect and all-optical helicity-dependent switching of magnetization. This approach enables not only pinpoint manipulation and flexible design of the heat current distribution by patterning the illuminating light but also on/off control of the resulting temperature modulation by tuning the light polarization. These versatile heat control functionalities will open up a pathway for nanoscale thermal energy engineering.

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Agarwal, Piyush, Yingshu Yang, Rohit Medwal, Hironori Asada, Yasuhiro Fukuma, Marco Battiato, and Ranjan Singh. "Secondary Spin Current Driven Efficient THz Spintronic Emitters." Advanced Optical Materials, August 24, 2023. http://dx.doi.org/10.1002/adom.202301027.

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AbstractFemtosecond laser‐induced photoexcitation of ferromagnet (FM)/heavy metal (HM) heterostructures has attracted attention by emitting broadband terahertz frequencies. The phenomenon relies on the formation of an ultrafast spin current, which is primarily attributed to the direct photoexcitation of the FM layer. However, during the process, the FM layer also experiences a secondary excitation led by the hot electrons from the HM layer that travel across the FM/HM interface and transfer additional energy in the FM. Thus, the generated secondary spins enhance the total spin current formation and lead to amplified spintronic terahertz emission. These results emphasize the significance of the secondary spin current, which even exceeds the primary spin currents when FM/HM heterostructures with thicker HM are used. An analytical model is developed to provide deeper insights into the microscopic processes within the individual layers, underlining the generalized ultrafast superdiffusive spin‐transport mechanism.

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Yang, Xingyu, Ye Mou, Romeo Zapata, Benoît Reynier, Bruno Gallas, and Mathieu Mivelle. "An inverse Faraday effect generated by linearly polarized light through a plasmonic nano-antenna." Nanophotonics, January 27, 2023. http://dx.doi.org/10.1515/nanoph-2022-0488.

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Abstract The inverse Faraday effect (IFE) generates magnetic fields by optical excitation only. Since its discovery in the 60 s, it was believed that only circular polarizations could magnetize matter by this magneto-optical phenomenon. Here, we demonstrate the generation of an IFE via a linear polarization of light. This new physical concept results from the local manipulation of light by a plasmonic nano-antenna. We demonstrate that a gold nanorod excited by a linear polarization generates non-zero magnetic fields by IFE when the incident polarization of the light is not parallel to the long axis of the rod. We show that this dissymmetry generates hot spots of local non-vanishing spin densities (local elliptical polarization state), introducing the concept of super circular light, allowing this magnetization. Moreover, by varying the angle of the incident linear polarization with respect to the nano-antenna, we demonstrate the on-demand flipping of the magnetic field orientation. Finally, this linear IFE generates a magnetic field 25 times stronger than a gold nanoparticle via a classical IFE. Because of its all-optical character, this light–matter interaction opens the way to ultrafast nanomanipulation of magnetic processes such as domain reversal, skyrmions, circular dichroism, control of the spin, its currents, and waves, among others.

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Zhao, Lijuan, Yuzhi Li, Yongzuo Wang, Peng Chen, Bing Lv, and Cunxu Gao. "Anomalous Hall effect in naturally oxidized normal-metal Al/Cu double films." Journal of Physics D: Applied Physics, October 25, 2023. http://dx.doi.org/10.1088/1361-6463/ad06ed.

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Abstract An unexpectedly larger current-induced spin-orbit torque in oxidized Cu (CuOx)/Ferromagnet (FM) than heavy-metal/FM has recently attracted intense attention in spintronic studies. Although the two mechanisms, interfacial Rashba Edelstein effect and spin-vorticity coupling, have been put forward based on the two different conductive features of CuOx, i.e., electrical insulator and gradient of electrical mobility, the detailed investigation of transport of CuOx is still lacking. Here we experimentally report the positive and negative anomalous Hall effect in naturally oxidized normal-metal Al/Cu double films. We found that the onset temperature of anomalous Hall effect corresponds to magnetic transition temperature of CuOx. Furthermore, by comparing Hall resistance of the crystalline and amorphous Cu/Al double films, we identify that the positive anomalous Hall resistance attributes to magnetic moment of CuOx itself, while the negative anomalous Hall resistance can originate from the spin or orbital currents generated at the CuOx/AlOx interface interact with magnetization of CuOx and its inverse process.

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Zhang, Chen, Takuya Ishida, Seung Hyuk Lee, and Tetsu Tatsuma. "Magneto-optical properties of superparamagnetic CoPt alloy nanoparticles in the UV–visible range." Applied Physics Letters 124, no. 26 (June 24, 2024). http://dx.doi.org/10.1063/5.0211367.

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Superparamagnetic CoPt alloy nanoparticles were synthesized via a wet chemical method and exhibited intense magnetic circular dichroism (MCD) in the UV–visible range. The dissymmetry factor of MCD, gMCD, for the CoPt nanoparticles was 0.034 at room temperature in a magnetic field of ±1.6 T. The MCD responses may be due to plasmonic circular currents generated in the metallic CoPt nanoparticles by circularly polarized light. The responses were higher than those of the Co nanoparticles, likely due to the chemical stability and spin–orbit coupling.

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Kholid, Farhan Nur, Dominik Hamara, Ahmad Faisal Bin Hamdan, Guillermo Nava Antonio, Richard Bowen, Dorothée Petit, Russell Cowburn, et al. "The importance of the interface for picosecond spin pumping in antiferromagnet-heavy metal heterostructures." Nature Communications 14, no. 1 (February 1, 2023). http://dx.doi.org/10.1038/s41467-023-36166-z.

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AbstractInterfaces in heavy metal (HM) - antiferromagnetic insulator (AFI) heterostructures have recently become highly investigated and debated systems in the effort to create spintronic devices that function at terahertz frequencies. Such heterostructures have great technological potential because AFIs can generate sub-picosecond spin currents which the HMs can convert into charge signals. In this work we demonstrate an optically induced picosecond spin transfer at the interface between AFIs and Pt using time-domain THz emission spectroscopy. We select two antiferromagnets in the same family of fluoride cubic perovskites, KCoF3 and KNiF3, whose magnon frequencies at the centre of the Brillouin zone differ by an order of magnitude. By studying their behaviour with temperature, we correlate changes in the spin transfer efficiency across the interface to the opening of a gap in the magnon density of states below the Néel temperature. Our observations are reproduced in a model based on the spin exchange between the localized electrons in the antiferromagnet and the free electrons in Pt. Through this comparative study of selected materials, we are able to shine light on the microscopy of spin transfer at picosecond timescales between antiferromagnets and heavy metals and identify a key figure of merit for its efficiency: the magnon gap. Our results are important for progressing in the fundamental understanding of the highly discussed physics of the HM/AFI interfaces, which is the necessary cornerstone for the designing of femtosecond antiferromagnetic spintronics devices with optimized characteristics.

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Huang, Xinhao, Yaru Zhao, Xinran Wang, Fei Wang, Liang Liu, Hyunsoo Yang, Weisheng Zhao, and Shuyuan Shi. "Implementing Versatile Programmable Logic Functions Using Two Magnetization Switching Types in a Single Device." Advanced Functional Materials, October 15, 2023. http://dx.doi.org/10.1002/adfm.202308219.

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AbstractThe efficient manipulation of magnetization using spin‐orbit torques (SOTs) generated by heavy metals and topological insulators has attracted significant attention. However, the symmetry of these conventional materials makes it challenging to achieve deterministic switching of perpendicular magnetization by currents, which prevents the practical application of SOT‐based spintronic devices such as magnetic memories and logics. Here, a composition gradient in a TaxTi1‐x alloy is introduced and the field‐free magnetization switching in TaxTi1‐x/CoFeB heterostructures with controllable SOT efficiencies is realized. Additionally, by engineering the gradient with a tilting angle relative to the current injection arm of the device, highly asymmetric switching loops are achieved, which are attributed to tilted spin polarization. Based on these two switching types, namely field‐free switching and field‐assisted asymmetric switching, five programmable Boolean logic functions are successfully demonstrated using a single device. This work paves the way for high‐density computing‐in‐memory applications with industry compatible artificially‐designed asymmetric SOT materials.

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Cheng, Hao, Yangkai Wang, Zheng Liu, Xiangyu Jia, Qiuping Huang, and Yalin Lu. "Terahertz spin-to-charge conversion in ferromagnetic Ni nanofilms." Nanophotonics, May 11, 2023. http://dx.doi.org/10.1515/nanoph-2023-0089.

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Abstract Spintronic terahertz (THz) emission via spin-to-charge conversion (SCC) has been widely studied in ferromagnets (FM)/nonmagnets (NM) structures, in which various mechanisms of SCC have been confirmed in different NM materials. However, it is rare to find a material having multiple SCC mechanisms at the same time. Here, we report a ferromagnetic metal Ni film with diverse functions in the SCC process, by performing THz emission experiments in single Ni layer, FM/Ni, Ni/NM bilayers and FM/Ni/NM trilayers. It is demonstrated that in Ni monolayer, THz emission is radiated by the anomalous Hall effect and ultrafast demagnetization of Ni film. In FM/Ni, the Ni film acts as an SCC implementer and THz emission is mainly generated by the inverse spin Hall effect (ISHE) of Ni. In Ni/NM, the Ni film acts as a spin injector and provides spin currents to be converted to charge current via ISHE of heavy metal NM, inducing THz emission. In FM/Ni/NM, THz emission mainly comes from ISHE of FM/Ni, Ni/NM, and FM/NM, and their domination is relative to Ni thickness. Our findings show a ferromagnetic film not only acts as a spin injector but also as an SCC implementer, providing a new concept to design spintronic THz emitters.

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Hong, Xiaochen, Matthias Gillig, Weiliang Yao, Lukas Janssen, Vilmos Kocsis, Sebastian Gass, Yuan Li, Anja U. B. Wolter, Bernd Büchner, and Christian Hess. "Phonon thermal transport shaped by strong spin-phonon scattering in a Kitaev material Na2Co2TeO6." npj Quantum Materials 9, no. 1 (February 10, 2024). http://dx.doi.org/10.1038/s41535-024-00628-4.

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AbstractThe report of a half-quantized thermal Hall effect and oscillatory structures in the magnetothermal conductivity in the Kitaev material α-RuCl3 have sparked a strong debate on whether it is generated by Majorana fermion edge currents, spinon Fermi surface, or whether other more conventional mechanisms are at its origin. Here, we report low temperature thermal conductivity (κ) of another candidate Kitaev material, Na2Co2TeO6. The application of a magnetic field (B) along different principal axes of the crystal reveals a strong directional-dependent B impact on κ, while no evidence for mobile quasiparticles except phonons can be concluded at any field. Instead, severely scattered phonon transport prevails across the B−T phase diagram, revealing cascades of phase transitions for all B directions. Our results thus cast doubt on recent proposals for significant itinerant magnetic excitations in Na2Co2TeO6, and emphasize the importance of discriminating true spin liquid transport properties from scattered phonons in candidate materials.

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Ludovico, María Florencia, and Massimo Capone. "Charge and energy transfer in ac-driven Coulomb-coupled double quantum dots." European Physical Journal B 95, no. 6 (June 2022). http://dx.doi.org/10.1140/epjb/s10051-022-00365-2.

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Abstract We study the dynamics of charge and energy currents in a Coulomb-coupled double quantum dot system, when only one of the two dots is adiabatically driven by a time-periodic gate that modulates its energy level. Although the Coulomb coupling does not allow for electron transfer between the dots, it enables an exchange of energy between them which induces a time variation of charge in the undriven dot. We describe the effect of electron interactions at low temperature using a time-dependent slave-spin 1 formulation within mean field that efficiently captures the main effects of the strong correlations as well as the dynamical nature of the driving. We find that the currents induced in the undriven dot due to the mutual friction between inter-dot electrons are of the same order as those generated in the adiabatically driven dot. Interestingly, up to 43% of the energy injected by the ac sources can be transferred from the driven dot to the undriven one. We complete our analysis by studying the impact of the Coulomb interaction on the resistance of the quantum dot that is driven by the gate. Graphic abstract

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Amin, V. P., J. Zemen, and M. D. Stiles. "Interface-Generated Spin Currents." Physical Review Letters 121, no. 13 (September 26, 2018). http://dx.doi.org/10.1103/physrevlett.121.136805.

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Oue, Daigo, and Mamoru Matsuo. "Optically induced electron spin currents in the Kretschmann configuration." Physical Review B 102, no. 12 (September 24, 2020). http://dx.doi.org/10.1103/physrevb.102.125431.

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Korenev, V. L. "Bulk electron spin polarization generated by the spin Hall current." Physical Review B 74, no. 4 (July 24, 2006). http://dx.doi.org/10.1103/physrevb.74.041308.

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Journal articles on the topic 'Optically generated spin currents'

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