Journal articles: 'Excitonic ferromagnetism'

1

Balents, Leon, and Chandra M. Varma. "Ferromagnetism in Doped Excitonic Insulators." Physical Review Letters 84, no. 6 (February 7, 2000): 1264–67. http://dx.doi.org/10.1103/physrevlett.84.1264.

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Ghose, Srabantika, N. Gogurla, R. Ranganathan, and D. Jana. "The simultaneous emergence of free exciton emission and d0 ferromagnetism for undoped ZnO nanoparticles." RSC Advances 6, no. 87 (2016): 83909–15. http://dx.doi.org/10.1039/c6ra17151f.

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3

Balents, Leon. "Excitonic order at strong coupling: Pseudospin, doping, and ferromagnetism." Physical Review B 62, no. 4 (July 15, 2000): 2346–57. http://dx.doi.org/10.1103/physrevb.62.2346.

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4

Kasuya, Tadao. "Excitonic Wigner crystal and high Tc ferromagnetism in RB6." Journal of Magnetism and Magnetic Materials 222, no. 1-2 (December 2000): 233–43. http://dx.doi.org/10.1016/s0304-8853(00)00570-9.

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Kumar, S., J. K. Sharma, S. K. Sharma, A. Dhupar, V. Sharma, and A. Gaur. "Structural, electrical and magnetic properties of glucose-capped CdS nanoparticles." International Journal of Materials Research 111, no. 10 (October 1, 2020): 799–806. http://dx.doi.org/10.1515/ijmr-2020-1111003.

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Abstract CdS nanoparticles are synthesized by a simple chemical coprecipitation technique using glucose as a capping/complexing agent and their structural, morphological, electrical and magnetic properties are studied. X-ray diffraction results reveal the pure phase formation of CdS nanoparticles along with a wurtzite structure. The interaction of the glucose with CdS nanoparticles is evident from the distinct absorption bands and peaks in the Fourier transform infrared spectra. Field effect scanning electron microscope and high resolution transmission electron microscope images depict weakly aggregated spherical nanoparticles of size ~2- 20 nm. The selective area electron diffraction pattern exhibits well-resolved diffraction rings representing the polycrystalline nature of the nanoparticles. The optical band gap has been calculated using Tauc’s plot and found to be 2.58 eV, which is higher than the band gap of the bulk phase wurtzite CdS. The existence of the excitonic peak and the blue-shift in the absorption threshold confirm the quantum confinement in the synthesized nanoparticles. The temperature dependence of d. c. conductivity is studied and observed a linear response through current-voltage characteristics. Weak ferromagnetism is also observed in the synthesized CdS nanoparticles irrespective of the diamagnetic nature of CdS in bulk form. The observation of weak ferromagnetism in the synthesized nanoparticles proposes them as a potential candidate for diluted magnetic semiconductors.

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Родина, А. В., А. А. Головатенко, Е. В. Шорникова, and Д. Р. Яковлев. "Спиновая физика экситонов в коллоидных нанокристаллах." Физика твердого тела 60, no. 8 (2018): 1525. http://dx.doi.org/10.21883/ftt.2018.08.46337.07gr.

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AbstractWe present a review of spin-dependent properties of excitons in semiconductor colloidal nanocrystals. The photoluminescences (PL) properties of neutral and charged excitons (trions) are compared. The mechanisms and the polarization of radiative recombination of a “dark” (spin-forbidden) exciton that determines the low-temperature PL of colloidal nanocrystals are discussed in detail. The radiative recombination of a dark exciton becomes possible as a result of simultaneous flips of the surface spin and electron spin in a dark exciton that leads to admixture of bright exciton states. This recombination mechanism is effective in the case of a disordered state of the spin system and is suppressed if the polaron ferromagnetic state forms. The conditions and various mechanisms of formation of the spin polaron state and possibilities of its experimental detection are discussed. The experimental and theoretical studies of magnetic field-induced circular polarization of PL in ensembles of colloidal nanocrystals are reviewed.

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Kamran, Muhammad Arshad, Bingsuo Zou, Kang Zhang, Xiongtao Yang, Fujian Ge, Lijie Shi, and Thamer Alharbi. "Dual-Color Lasing Lines from EMPs in Diluted Magnetic Semiconductor CdS:NiI Structure." Research 2019 (October 29, 2019): 1–15. http://dx.doi.org/10.34133/2019/6956937.

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Have one ever seen a semiconductor that can issue two-color lasing lines? The diluted magnetic semiconductor (DMS) can do this. Here, we have observed dual lasing lines of 530 nm and 789 nm from a DMS structure of CdS:NiI, in which the excitonic magnetic polaron (EMP) and localized excitonic magnetic polaron (LEMP) are excitations out of ferromagnetic (NiS)x nanocluster and NiI2 nanoclusters within CdS lattice; both of them could lead to the collective EMP state at high excitation and therein produce coherent emission lines simultaneously. This occurrence is due to the superposition of EMP near CdS bandedge and the combination of the charge-transfer band of (NiI)n cluster with the LEMP within CdS lattice by overcoming the strong electron correlation of NiI cluster in a DMS structure, evidenced also by ab initio calculation. This finding opens a way to understand the collective behaviour of spin-coupled excitons in DMS and to find novel applications in the spin-related quantum technology.

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CAO, WEI, VLADIMIR PANKRATOV, MARKO HUTTULA, LIANA SHIRMANE, YU RAN NIU, and FENG WANG. "X-RAY PHOTOEMISSION ELECTRON MICROSCOPE DETERMINATION OF ORIGINS OF ROOM TEMPERATURE FERROMAGNETISM AND PHOTOLUMINESCENCE IN HIGH Co-CONTENT CoxZn1-xO FILMS." Surface Review and Letters 21, no. 04 (August 2014): 1450058. http://dx.doi.org/10.1142/s0218625x14500589.

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In this paper, we reported on the X-ray photoemission electron microscope (XPEEM) determination of magnetic and luminescence origins for two Co x Zn 1-x O films. The cobalt fraction x of radio frequency co-sputtered samples were 0.86(2) and 0.92(2), respectively. Films were ferromagnetic and semiconductive. Unique narrow green color lines beside the ZnO intrinsic emissions were found with a decay time in microsecond range at room temperature. Origins of magnetic and luminescence properties were determined with XPEEM. The X-ray absorption near edge structure at the Co L3-edge denoted that Co was partially oxidized, and phase-contrast images together with chemical composition identification further proved that Co and CoO co-existed in the samples. The ferromagnetism was attributed to ferromagnetism of Co clusters partially canceled by the antiferromagnetism of its oxide, and the photoluminescence to bound exciton in ZnO nanoclusters and defect related centers of ZnO nanoclusters in a Co -rich matrix. Present results show possibilities for adjusting magnetic and luminescence properties of Co – ZnO compounds by changing the cobalt concentration.

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9

Fernández-Rossier, J., and C. Tejedor. "Ferromagnetism in 2D Exciton Condensates." physica status solidi (a) 164, no. 1 (November 1997): 343–46. http://dx.doi.org/10.1002/1521-396x(199711)164:1<343::aid-pssa343>3.0.co;2-0.

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10

Li, Bao-Xing. "The Condensation and Ferromagnetism of Triplet Frenkel Excitons." physica status solidi (b) 168, no. 2 (December 1, 1991): 479–87. http://dx.doi.org/10.1002/pssb.2221680210.

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11

Kucherenko, M. G. "SPIN-SELECTIVE INTERACTION OF TRIPLET-EXCITED MOLECULES ON THE SURFACE OF A FERROMAGNETIC NANOPARTICLE." Eurasian Physical Technical Journal 19, no. 4 (December 26, 2022): 5–16. http://dx.doi.org/10.31489/2022no4/5-16.

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Influence of a magnetic field generated by a ferromagnetic nanoparticle on the annihilation of triplet-excited organic molecules or triplet excitons in a near-surface particle layer is studied. A detailed mathematical model is presented that accounts for electron excitation diffusive mobility and geometry of the system. The kinetic operator is given in the complete 9x9 basis of triplet- triplet pair spin states. Time dependencies of the singlet spin state population of the triplet-triplet pair and the dependence of the triplet-triplet annihilation magnetic response profile (magnetic reaction effect) from the magnetic field induction are obtained. It is found that the influence of a magnetic field gradient on the reaction yield dominates over the other known mechanisms of spin-dynamics in triplet- triplet pairs.

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12

Golovnev, Yu F., and Ya V. Vlasova. "Exciton Polaritons in Ferromagnetic Semiconductor EuO." Bulletin of the Russian Academy of Sciences: Physics 83, no. 7 (July 2019): 825–27. http://dx.doi.org/10.3103/s1062873819070189.

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13

Chatterjee, R., and P. Amerl. "Exciton Solitons in One-Dimensional Ferromagnetic Chains." physica status solidi (b) 180, no. 1 (November 1, 1993): K15—K18. http://dx.doi.org/10.1002/pssb.2221800130.

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14

Zolfaghari, Mahmoud, and Mahshid Chireh. "Effect of Mn Dopant on Lattice Parameters and Band Gap Energy of Semiconductor ZnO Nanoparticles." Advanced Materials Research 829 (November 2013): 784–89. http://dx.doi.org/10.4028/www.scientific.net/amr.829.784.

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ZnO belongs to the II-VI semiconductor group with a direct band-gap of 3.2-3.37 eV in 300K and a high exciton binding energy of 60 meV. It has good transparency, high electron mobility, wide, and strong room-temperature luminescence. These properties have many applications in a wide area of emerging applications. Doping ZnO with the transition metals gives it magnetic property at room temperature hence making it multifunctional material, i.e. coexistence of magnetic, semiconducting and optical properties. The samples can be synthesized in the bulk, thin film, and nanoforms which show a wide range of ferromagnetism properties. Ferromagnetic semiconductors are important materials for spintronic and nonvolatile memory storage applications. Doping of transition metal elements into ZnO offers a feasible means of tailoring the band gap to use it as light emitters and UV detector. As there are controversial on the energy gap value due to change of lattice parameters we have synthesized Mn-doped ZnO nanoparticles by co-precipitation method with different concentrations to study the effect of lattice parameters changes on gap energy. The doped samples were studied by XRD, SEM, FT-IR., and UV-Vis. The XRD patterns confirm doping of Mn into ZnO structure. As Mn concentrations increases the peak due to of Mn impurity in FT-IR spectra becomes more pronounces hence confirming concentrations variation. We find from UV-Vis spectra that the gap energy due to doping concentration increases due to the Goldschmidt-Pauling rule this increase depends on dopant concentrations and increases as impurity amount increases.

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15

Golovnev, Yu F., and D. A. Nurguleev. "Spin Filter Based on EuO Monoxide." Journal of the Russian Universities. Radioelectronics, no. 2 (June 5, 2018): 55–59. http://dx.doi.org/10.32603/1993-8985-2018-21-2-55-59.

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The basis of spin filter operation is the possibility to obtain different population of states with spins up and down for free electrons. However, in a magnetic macroscopic field, scattering by heavy atoms reduces their population density by 106 times. To obtain the maximum possible degree of spin polarization it is proposed to use ferromagnetic EuO in semiconductor superlattices, e. g. EuO–SrO. The article substantiates the creation of a spin filter based on a superlattice composed of SrO and EuO nanolayers. The scheme of ferromagnetic semiconductor EuO energy levels is demonstrated as well as splitting of 5d EuO levels by crystal field. The position of 4f 7-multiplet and the energy of formation of triplet exciton are determined.

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16

WYSMOLEK, A., M. KAMIŃSKA, A. TWARDOWSKI, M. POTEMSKI, M. BOĆKOWSKI, and I. GRZEGORY. "MAGNETO-LUMINESCENCE OF GADOLINIUM DOPED GALLIUM NITRIDE." International Journal of Modern Physics B 23, no. 12n13 (May 20, 2009): 2994–98. http://dx.doi.org/10.1142/s0217979209062694.

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The results of luminescence measurements in magnetic fields up to 23T of strain free GaN bulk crystals doped with gadolinium are presented. The magnetic field splitting pattern observed for the Gd -related transitions in the "red" spectral range is consistent with its identification as due to intracenter transitions between Gd 3+ ion levels. The Gd -related emission structures observed close to the GaN bandgap show magnetic field behavior which could be understood in terms bound exciton or donor-acceptor pair recombination involving Gd ions. Disappointingly, no giant Zeeman splitting, which otherwise could confirm ferromagnetism in this material, was observed.

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17

Verma, K. C., Navdeep Goyal, and R. K. Kotnala. "Lattice defect-formulated ferromagnetism and UV photo-response in pure and Nd, Sm substituted ZnO thin films." Physical Chemistry Chemical Physics 21, no. 23 (2019): 12540–54. http://dx.doi.org/10.1039/c9cp02285f.

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The induction of charge and spin in diluted magnetic semiconductor ZnO is explored for spintronic devices and its wide direct band gap (3.37 eV) and large exciton binding energy (60 meV) exhibit potential in UV photodetectors.

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18

Yoon, Im Taek, Yoon Shon, Younghae Kwon, Young S. Park, Chang Soo Park, and Tae Won Kang. "Magnetic Characteristics of Mn-Implanted GaN Nanorods Followed by Thermal Annealing." Journal of Nanomaterials 2012 (2012): 1–6. http://dx.doi.org/10.1155/2012/653650.

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We have investigated the magnetic and optical properties of dislocation-free vertical GaN nanorods with diameters of 150 nm grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy followed by Mn ion implantation and annealing. The GaN nanorods are fully relaxed and have a very good crystal quality characterized by extremely strong and narrow photoluminescence excitonic lines near 3.47 eV. For GaMnN nanorods, it can be concluded that the ferromagnetic property of GaMnN nanorod with a Curie temperature over 300 K is associated with the formation of Mn4Si7magnetic phase which results from the effects of magnetic and structural disorder introduced by a random incorporation and inhomogeneous distribution of Mn atoms in the porous layer between the nanorods that form precipitates in the Si substrate before or during the annealing step amongst the GaN nanorods.

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19

Freire, J. A. K., A. Matulis, F. M. Peeters, V. N. Freire, and G. A. Farias. "Exciton trapping in a hybrid ferromagnetic/semiconductor magnetic antidot." Journal of Magnetism and Magnetic Materials 226-230 (May 2001): 2038–39. http://dx.doi.org/10.1016/s0304-8853(00)01081-7.

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20

Golovnev, Yu F., and A. B. Lakovtsev. "Collective properties of triplet excitons in heterostructures based on ferromagnetic semiconductors." Bulletin of the Russian Academy of Sciences: Physics 75, no. 2 (February 2011): 178–80. http://dx.doi.org/10.3103/s1062873811020109.

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21

Li, Jian-Min, Xian-Lin Zeng, Guo-Qian Wu, and Zhu-An Xu. "Exciton quenching and ferromagnetism-to-ferrimagnetism crossover in diluted magnetic semiconducting Zn1−xCoxO nanogranular nanofibers." CrystEngComm 14, no. 2 (2012): 525–32. http://dx.doi.org/10.1039/c1ce06033c.

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22

Halm, S., F. Seifert, T. Kümmell, G. Bacher, E. Schuster, W. Keune, J. Puls, and F. Henneberger. "Manipulation of exciton spin states in a dilute magnetic semiconductor by nanostructured ferromagnets." physica status solidi (c) 3, no. 4 (March 2006): 1122–25. http://dx.doi.org/10.1002/pssc.200564740.

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23

Golik, L. L., and Z. E. Kunkova. "Non-Linearities in the Faraday Rotation and Absorption Due to Excitons in the Ferromagnetic Semiconductor CdCr2Se4." physica status solidi (b) 219, no. 2 (June 2000): 411–20. http://dx.doi.org/10.1002/1521-3951(200006)219:2<411::aid-pssb411>3.0.co;2-a.

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24

Lee, Juwon, Yoon Shon, Younghae Kwon, Ji-Hoon Kyhm, Deuk Young Kim, Joon Hyun Kang, Chang-Soo Park, Kyoung Su Lee, and Eun Kyu Kim. "Effects of Thermal Annealing on Optical and Microscopic Ferromagnetic Properties in InZnP:Ag Nano-Rods." Nanomaterials 12, no. 23 (November 25, 2022): 4200. http://dx.doi.org/10.3390/nano12234200.

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InZnP:Ag nano-rods fabricated by the ion milling method were thermally annealed in the 250~350 °C temperature range and investigated the optimum thermal annealing conditions to further understand the mutual correlation between the optical properties and the microscopic magnetic properties. The formation of InZnP:Ag nano-rods was determined from transmission electron microscopy (TEM), total reflectivity and Raman scattering analyses. The downward shifts of peak position for LO and TO modes in the Raman spectrum are indicative of the production of Ag ion-induced strain during the annealing process of the InZnP:Ag nano-rod samples. The appearance of two emission peaks of both (A0 X) and (e, Ag) in the PL spectrum indicated that acceptor states by Ag diffusion are visible due to the effective incorporation of Ag-creating acceptor states. The binding energy between the acceptor and the exciton measured as a function of temperature was found to be 21.2 meV for the sample annealed at 300 °C. The noticeable MFM image contrast and the clear change in the MFM phase with the scanning distance indicate the formation of the ferromagnetic spin coupling interaction on the surface of InZnP:Ag nano-rods by Ag diffusion. This study suggests that the InZnP:Ag nano-rods should be a potential candidate for the application of spintronic devices.

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25

Hu, Bin, Yue Wu, Zongtao Zhang, Sheng Dai, and Jian Shen. "Effects of ferromagnetic nanowires on singlet and triplet exciton fractions in fluorescent and phosphorescent organic semiconductors." Applied Physics Letters 88, no. 2 (January 9, 2006): 022114. http://dx.doi.org/10.1063/1.2162801.

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26

Nguyen, Lan-Anh T., Krishna P. Dhakal, Yuhan Lee, Wooseon Choi, Tuan Dung Nguyen, Chengyun Hong, Dinh Hoa Luong, et al. "Spin-Selective Hole–Exciton Coupling in a V-Doped WSe₂ Ferromagnetic Semiconductor at Room Temperature." ACS Nano 15, no. 12 (November 22, 2021): 20267–77. http://dx.doi.org/10.1021/acsnano.1c08375.

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27

Jeon, H. C., T. W. Kang, T. W. Kim, and Y. H. Cho. "Band-edge exciton transitions in (Ga1−xMnx)N diluted magnetic semiconductor films with above room temperature ferromagnetic transition." Solid State Communications 138, no. 9 (June 2006): 444–47. http://dx.doi.org/10.1016/j.ssc.2006.04.010.

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28

FUKUOKA, DAISUKE, KOUSHIRO ARAHARA, TAKAAKI KOYAMA, NAOKI TANAKA, KENICHI OTO, KIYOFUMI MURO, SHOJIRO TAKEYAMA, GREGOSZ KARCZEWSKI, THOMASZ WOJTOWICZ, and JACEK KOSSUT. "COMPREHENSIVE STUDY OF SPIN-FLIP EXCITATIONS IN CdZnTe/CdZnMnTe QUANTUM WELLS." International Journal of Modern Physics B 21, no. 08n09 (April 10, 2007): 1610–14. http://dx.doi.org/10.1142/s0217979207043294.

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Spin-flip excitations in non-doped Cd 0.93 Zn 0.07 Te/Cd 0.48 Zn 0.04 Mn 0.48 Te quantum wells have been comprehensively studied by spin-flip Raman scattering (SFRS) spectroscopy and time-resolved Kerr rotation (TRKR) spectroscopy. In 4 nm quantum well, two spin-flip Raman peaks were observed in addition to the multiple Mn 2+ spin-flip scatterings. The spin-flip energies are isotropic against the magnetic field direction and well described by modified Brillouin functions. Based on the circumstantial analysis, they are assigned to the spin-flip of residual electrons and the electron spin-flip in the localized exciton, respectively, even though the large energy difference between the two electron spin-flip processes is a puzzle. While, in 9 nm quantum well a strange spin-flip excitation was observed together with a very weak Mn 2+ spin-flip scattering. The spin-flip energy changed strangely up to the magnetic field 4T, and then linearly increased with field (| g *|=1.15). A high-resolution TRKR spectroscopy revealed an unusual temperature dependence, which resembled "softening mode" of spin resonance observed in p-doped ferromagnetic CdMnTe quantum wells. However, these behaviors are well understood by an "inverted spin configuration", which results from a negative g*-factor and a very weak s-d interaction between the electrons and the manganese ions in the barrier.

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29

Mohanapriya, P., and N. Victor Jaya. "Near Band Edge Emission by Free Exciton Decay and Intrinsic Ferromagnetic Ordering of Cu-Doped SnO₂ Hollow Nanofibers." Journal of Nanoscience and Nanotechnology 15, no. 3 (March 1, 2015): 2226–33. http://dx.doi.org/10.1166/jnn.2015.8702.

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30

Giuliani, G. F., and J. J. Quinn. "Triplet exciton and ferromagnetic instability of a two-dimensional electron gas in a large magnetic field with filling factor v=2." Solid State Communications 54, no. 11 (June 1985): 1013–16. http://dx.doi.org/10.1016/0038-1098(85)90176-0.

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31

Pálmai, Marcell, Kyle Tomczak, and Preston Snee. "Enhanced Property Tunability of Doubly Doped Semiconductor Nanomaterials Using the Cluster Seed Method." ECS Meeting Abstracts MA2022-02, no. 20 (October 9, 2022): 902. http://dx.doi.org/10.1149/ma2022-0220902mtgabs.

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Semiconductor Quantum Dots (QDs) have great potential in applications for renewable energy generation due to their size-tunable redox potentials. They may be prepared with different morphologies and coated to create complex heterostructures. Doping of semiconductor nanomaterials is another mechanism to realize property tunability, and doped QDs are playing an increasing role in green energy generation applications. In 2013 our group reported a method to create a batch of doped quantum dots where each particle was embedded with the same number of guest ions, thus circumventing Poisson statistics. This was accomplished by nucleating the QD around an organometallic seed cluster that contains guest ions. As a result, each QD has the same number of dopants, which eliminates problems due to inhomogeneity of the guest ion stoichiometry. These materials were studied using time-resolved X-ray absorption spectroscopy, which allows us to characterize the electronic and coordination structure in both the ground and excited states. Current research reveals the potential to doubly dope semiconductors using cluster seeding, and that the originating organometallic structure may be represented in the final material product. To this end, ZnCdSe nanowires were prepared in the presence of (MnTe)4 cluster seeds. The results reveal that Mn(2+) has been successfully incorporated into the host matrix, while temperature dependent optical measurements suggest significantly enhanced semiconductor exciton-magnetic dopant interactions in materials prepared by cluster seeding compared to doped control samples. This could be due to ferromagnetic Mn-Mn interactions in the host resulting from enhanced exchange coupling mediated by highly spin-orbit coupled tellurium bridging. Consequently, cluster seeding may be used to "dope the dopants", affording a heretofore unrealized method for developing designer materials with enhanced electronic and optical properties. Figure 1

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32

Kazemi, Masoumeh, Vanik Shahnazaryan, Yaroslav Zhumagulov, Pavel F. Bessarab, and Ivan Shelykh. "Interaction of excitons with magnetic topological defects in 2D magnetic monolayers: localization and anomalous Hall effect." 2D Materials, October 4, 2022. http://dx.doi.org/10.1088/2053-1583/ac973d.

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Abstract Novel 2D material CrI3 reveals unique combination of 2D ferromagnetism and robust excitonic response. We demonstrate that the possibility of the formation of magnetic topological defects, such as Neel skyrmions, together with large excitonic Zeeman splitting, leads to giant scattering asymmetry, which is the necessary prerequisite for the excitonic anomalous Hall effect. In addition, the diamagnetic effect breaks the inversion symmetry, and in certain cases can result in exciton localization on the skyrmion. This enables the formation of magnetoexcitonic quantum dots with tunable parameters.

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33

Veillette, M. Y., and L. Balents. "Weak ferromagnetism and excitonic condensates." Physical Review B 65, no. 1 (December 11, 2001). http://dx.doi.org/10.1103/physrevb.65.014428.

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34

Bascones, E., A. A. Burkov, and A. H. MacDonald. "Theory of Ferromagnetism in Doped Excitonic Condensates." Physical Review Letters 89, no. 8 (August 2, 2002). http://dx.doi.org/10.1103/physrevlett.89.086401.

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35

Ichinomiya, Takashi. "Impurity-induced ferromagnetism in a doped triplet excitonic insulator." Physical Review B 63, no. 4 (January 2001). http://dx.doi.org/10.1103/physrevb.63.045113.

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36

Lan, Shoufeng, Xiaoze Liu, Siqi Wang, Hanyu Zhu, Yawen Liu, Cheng Gong, Sui Yang, Jing Shi, Yuan Wang, and Xiang Zhang. "Observation of strong excitonic magneto-chiral anisotropy in twisted bilayer van der Waals crystals." Nature Communications 12, no. 1 (April 7, 2021). http://dx.doi.org/10.1038/s41467-021-22412-9.

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AbstractThe interplay between chirality and magnetism generates a distinct physical process, the magneto-chiral effect, which enables one to develop functionalities that cannot be achieved solely by any of the two. Such a process is universal with the breaking of parity-inversion and time-reversal symmetry simultaneously. However, the magneto-chiral effect observed so far is weak when the matter responds to photons, electrons, or phonons. Here we report the first observation of strong magneto-chiral response to excitons in a twisted bilayer tungsten disulfide with the amplitude of excitonic magneto-chiral (ExMCh) anisotropy reaches a value of ~4%. We further found the ExMCh anisotropy features with a spectral splitting of ~7 nm, precisely the full-width at half maximum of the excitonic chirality spectrum. Without an externally applied strong magnetic field, the observed ExMCh effect with a spontaneous magnetic moment from the ferromagnetic substrate of thulium iron garnet at room temperature is favorable for device applications. The unique ExMCh processes provide a new pathway to actively control magneto-chiral applications in photochemical reactions, asymmetric synthesis, and drug delivery.

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37

Jin, Wencan, Hyun Ho Kim, Zhipeng Ye, Gaihua Ye, Laura Rojas, Xiangpeng Luo, Bowen Yang, et al. "Observation of the polaronic character of excitons in a two-dimensional semiconducting magnet CrI3." Nature Communications 11, no. 1 (September 22, 2020). http://dx.doi.org/10.1038/s41467-020-18627-x.

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Abstract Exciton dynamics can be strongly affected by lattice vibrations through electron-phonon coupling. This is rarely explored in two-dimensional magnetic semiconductors. Focusing on bilayer CrI3, we first show the presence of strong electron-phonon coupling through temperature-dependent photoluminescence and absorption spectroscopy. We then report the observation of periodic broad modes up to the 8th order in Raman spectra, attributed to the polaronic character of excitons. We establish that this polaronic character is dominated by the coupling between the charge-transfer exciton at 1.96 eV and a longitudinal optical phonon at 120.6 cm−1. We further show that the emergence of long-range magnetic order enhances the electron-phonon coupling strength by ~50% and that the transition from layered antiferromagnetic to ferromagnetic order tunes the spectral intensity of the periodic broad modes, suggesting a strong coupling among the lattice, charge and spin in two-dimensional CrI3. Our study opens opportunities for tailoring light-matter interactions in two-dimensional magnetic semiconductors.

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38

Taraphder, A., M. S. Laad, L. Craco, and A. N. Yaresko. "GdI2: A New Ferromagnetic Excitonic Solid?" Physical Review Letters 101, no. 13 (September 26, 2008). http://dx.doi.org/10.1103/physrevlett.101.136410.

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39

Wang, Dan, and Xiaolong Zou. "Tunable valley band and exciton splitting by interlayer orbital hybridization." npj Computational Materials 8, no. 1 (November 15, 2022). http://dx.doi.org/10.1038/s41524-022-00932-2.

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AbstractMagnetic proximity effect has been demonstrated to be an effective routine to introduce valley splitting in two-dimensional van der Waals heterostructures. However, the control of its strength and the induced valley splitting remains challenging. In this work, taking heterobilayers combining monolayer MSe2 (M = Mo or W) with room-temperature ferromagnetic VSe2 as examples, we demonstrate that the valley splitting for both band edges and excitons can be modulated by the tuning of the interlayer orbital hybridization, achieved by inclusion of different amounts of exact Hartree exchange potential via hybrid functionals. Besides, we show such tuning of orbital hybridization could be experimentally realized by external strain and electric field. The calculations suggest that large valley band splitting about 30 meV and valley exciton splitting over 150 meV can be induced in monolayer MSe2. Our work reveals a way to control proximity effects and provides some guidance for the design of optoelectronic and valleytronic devices.

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Shim, Y. P., and A. H. MacDonald. "Spin-orbit interactions in bilayer exciton-condensate ferromagnets." Physical Review B 79, no. 23 (June 25, 2009). http://dx.doi.org/10.1103/physrevb.79.235329.

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Hao, Kai, Robert Shreiner, Andrew Kindseth, and Alexander A. High. "Optically controllable magnetism in atomically thin semiconductors." Science Advances 8, no. 39 (September 30, 2022). http://dx.doi.org/10.1126/sciadv.abq7650.

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We report evidence that ferromagnetic order in electrostatically doped, monolayer transition metal dichalcogenide (TMD) semiconductors can be stabilized and controlled at zero magnetic field by local optical pumping. We use circular dichroism (CD) in reflectivity from excitonic states as a spatially resolved probe of charge-carrier spin polarization. At electron densities n e ~ 10 12 cm −2 , a diffraction-limited, circularly polarized optical pump breaks symmetry between oppositely polarized magnetic states and stabilizes long-range magnetic order, with carrier polarization exceeding 80% over an 8 μm by 5 μm extent. In time-resolved measurements with pulsed optical excitation, we observe that magnetic interactions amplify the initial pump-induced spin polarization by more than an order of magnitude. The optical control of magnetism with local optical pumps will unlock advancements in spin and optical technologies and provides a versatile tool in the study of correlated phases in two-dimensional electron gases.

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Russ, Andreas, Mesut Yasar, Athos Petrou, George Kioseoglou, Connie Li, Aubrey Hanbicki, Berend Jonker, Marek Korkusinski, and Pawel Hawrylak. "Injection of spin polarized electrons in InAs quantum dots." MRS Proceedings 1208 (2009). http://dx.doi.org/10.1557/proc-1208-o02-02.

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AbstractWe present the results of an electrical injection study of spin polarized electrons from ferromagnetic Fe contacts into electronic shells of self-assembled InAs quantum dots (QDs) incorporated in GaAs/AlGaAs spin LED structures. The circular polarization of the emitted light was measured as function of current and magnetic field. The polarization of the EL spectra exhibits strong maxima at energies that do not coincide with the electroluminescence (EL) intensity peaks. The magnetic field dependence of the polarization maxima is consistent with spin injection from the ferromagnetic Fe contacts. The experimental results are compared with calculated emission spectra from multi-exciton complexes (N = 2 and N = 6) as function of electron spin polarization. The energies of the EL features as well as their polarization characteristics are understood in terms of energy shifts due to exchange interactions between spin-down electrons occupying adjacent shells.

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Wu, Meng, Zhenglu Li, Ting Cao, and Steven G. Louie. "Physical origin of giant excitonic and magneto-optical responses in two-dimensional ferromagnetic insulators." Nature Communications 10, no. 1 (May 30, 2019). http://dx.doi.org/10.1038/s41467-019-10325-7.

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Norden, Tenzin, Chuan Zhao, Peiyao Zhang, Renat Sabirianov, Athos Petrou, and Hao Zeng. "Giant valley splitting in monolayer WS2 by magnetic proximity effect." Nature Communications 10, no. 1 (September 13, 2019). http://dx.doi.org/10.1038/s41467-019-11966-4.

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Abstract Lifting the valley degeneracy of monolayer transition metal dichalcogenides (TMDs) would allow versatile control of the valley degree of freedom. We report a giant valley exciton splitting of 16 meV/T for monolayer WS2, using the proximity effect from an EuS substrate, which is enhanced by nearly two orders of magnitude from that obtained by an external magnetic field. More interestingly, a sign reversal of the valley splitting is observed as compared to that of WSe2 on EuS. Using first principles calculations, we investigate the complex behavior of exchange interactions between TMDs and EuS. The sign reversal is attributed to competing ferromagnetic (FM) and antiferromagnetic (AFM) exchange interactions for Eu- and S- terminated EuS surface sites. They act differently on the conduction and valence bands of WS2 compared to WSe2. Tuning the sign and magnitude of the valley exciton splitting offers opportunities for control of valley pseudospin for quantum information processing.

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Tagliente, Maria Antonella, Marcello Massaro, Giovanni Mattei, Paolo Mazzoldi, Giovanni Pellegrini, Valentina Bello, and Daniela Carbone. "On the Structural and Optical Properties of ZnO Nanoparticles Formed in Silica by Ion Implantation." MRS Proceedings 942 (2006). http://dx.doi.org/10.1557/proc-0942-w08-36.

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ABSTRACTZinc Oxide (ZnO) is a II-VI semiconductor material with a wide direct band-gap of 3.37 eV at room temperature (RT). In the past decades, the material has been used for a variety of applications such as gas sensors, surface acoustic wave devices, or transparent contacts. Recently, ZnO has gained a new substantial interest primarily because to its potentialities for optoelectronic and spintronic applications. The renewed interest has been fueled by the availability of high-quality bulk substrates, reports of p-type conduction and theoretical predictions of its ferromagnetic behavior at room temperature when doped with transition metals. In the domain of optoelectronics, its main applications include devices emitting in the blue and UV regions by exploiting its wide band-gap such as light-emitting and laser diodes. With respect to several wide band-gap semiconductor materials, ZnO has the advantage of a larger exciton binding energy (about 60 meV) which paves the way for an intense near-band-edge excitonic emission at room and higher temperatures. On the other hand, a band gap engineering can be also achieved by the incorporation of Cadmium and Magnesium atoms into the ZnO lattice.Many techniques have been used to prepare ZnO in various forms, such as single crystals, powders and films. In the past few years, the great attention toward materials with nanometric size have motivated a number of studies on the synthesis of ZnO nanocrystals. Ion implantation is one of the most effective and versatile technique to obtain nanoparticles. ZnO particles embedded in silica matrix have been successfully prepared by ion implantation followed by thermal oxidation.In this work, we report on a detailed structural and optical characterization of the ZnO-silica nanocomposites by using several complementary techniques; in particular, Glancing Incidence X-ray Diffraction (GIXRD), Rutherford Backscattering Spectrometry (RBS), linear Optical Absorption (OA) in the UV-near IR spectrum and Photo-Luminescence (PL). The ZnO nanoparticles embedded in SiO2 matrix were prepared by implanting the substrates with 130 keV Zn+ ions at doses of 1, 1.5 and 2´1017 ions/cm2. Subsequently, the implanted samples were annealed for 1h in a furnace at a temperature between 500 and 800°C under flowing O2 gas. X-ray diffraction results indicate the formation of Zn and ZnO nanoparticles in the as-implanted and annealed samples, respectively. Moreover, the ZnO nanocrystals embedded in the SiO2 matrix have a (002) preferred orientation. After the oxidation, the optical absorption spectra show an absorption edge at about 374 nm by confirming the presence of the ZnO particles. A relatively strong exciton photoluminescence peak was observed at room temperature under pulsed N2 laser excitation at l=337nm. The results obtained, peculiarly related to the implantation doses and annealing temperature, are discussed.

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Sajjan, Manas, Hadiseh Alaeian, and Sabre Kais. "Magnetic Phases of Spatially-Modulated Spin-1 Chains in Rydberg Excitons: Classical andQuantum Simulations." Journal of Chemical Physics, November 30, 2022. http://dx.doi.org/10.1063/5.0128283.

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In this work, we study the magnetic phases of a spatially-modulated chain of spin-1 Rydberg excitons. Using the Density Matrix Renormalization Group (DMRG) technique we study various magnetic and topologically nontrivial phases using both single-particle properties like local magnetization and quantum entropy as well as many-body ones like pair-wise Néel and long-range string correlations. In particular, we investigate the emergence and robustness of Haldane phase, a topological phase of anti-ferromagnetic spin-1 chains. Further, we devise a hybrid quantum algorithm employing Restricted Boltzmann Machine to simulate the ground state of such a system which shows very good agreement with the results of exact diagonalization (ED) and DMRG.

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"Spin dynamics and absorption-band profiles for the planar two-dimensional easy-plane ionic ferromagnet Rb 2 CrCl 4." Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences 415, no. 1849 (February 9, 1988): 277–302. http://dx.doi.org/10.1098/rspa.1988.0014.

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Eigenvalues and eigenfunctions of the spin waves in Rb 2 CrCl 4 , in the absence or presence of a magnetic field oriented along (or slightly off) one of the major crystallographic axes, are given in detail for the first time. We present a simple model to simulate the profiles of exchange induced exciton-magnon combination bands in canted ferromagnets, under various experimental conditions of temperature and magnetic field. This model is used to analyse new high-resolution magneto-optical data at low and very low (0.35 K) temperatures and to derive precise anisotropy parameters. It can be applied with only slight modifications to metamagnets showing axial or planar anisotropy.

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Ohadi, H., A. Dreismann, Y. G. Rubo, F. Pinsker, Y. del Valle-Inclan Redondo, S. I. Tsintzos, Z. Hatzopoulos, P. G. Savvidis, and J. J. Baumberg. "Spontaneous Spin Bifurcations and Ferromagnetic Phase Transitions in a Spinor Exciton-Polariton Condensate." Physical Review X 5, no. 3 (July 8, 2015). http://dx.doi.org/10.1103/physrevx.5.031002.

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Galvez, Marco A., Oscar Perales-Perez, and Surinder P. Singh. "Effect Co- and Sc- Doping on the Functional Properties of Nanocrystalline Powders and Thin Films of ZnO." MRS Proceedings 1256 (2010). http://dx.doi.org/10.1557/proc-1256-n11-23.

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AbstractA modified sol-gel approach to synthesize well-crystallized pure and doped ZnO nanocrystalline powders and thin films has been developed. The attachment of ZnO films onto quartz substrates was optimized by selecting suitable organic agents to control the viscosity of precursor solutions. Thermo-gravimetric analyses on pure and doped precursor solids suggested the need for annealing temperatures above 400 °C to assure the effective crystallization of the oxide phase. The average crystallite size in powders and thin films varied from 25.9 nm to 33.7 nm when pure ZnO films were annealed for 1 hour in the 450 °C - 600 °C range. The average crystallite size ranged between 30 nm and 33 nm in the presence of cobalt (5 at%) and decreased from 33.7 nm to 21.1 nm when scandium ions was used in the 0.0 at% - 10 at% range under similar annealing conditions. UV-vis measurements showed a sharp exciton peak centered at 370 nm whereas photoluminescence analyses detected the characteristic ZnO emission band in the UV region. No photoluminescence band in the visible region, usually attributed to defect states in ZnO, was observed in our measurements. Magnetization measurements revealed a weak ferromagnetism in Co-doped ZnO whereas a clear diamagnetism was evident in the Sc-doped sample.

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Shen, Jie, Wen Qi Dong, Xuewei Shi, Jing Wang, Yang Wang, and Han Min Liu. "The model for non-Abelian field topology for the multilayer fractional quantum anomalous Hall device." Frontiers in Physics 10 (December 9, 2022). http://dx.doi.org/10.3389/fphy.2022.978220.

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From the recent empirical discovery of the quantum anomalous Hall effect (QAHE), the interaction of the particle with spin–orbit coupling (SOC) plays an essential role in the cause of the QAHE, which includes three terms: external, internal, and chiral symmetric terms. Then, the non-Abelian quantum field theory was adopted to analyze and prove the conjecture on the causes that can lead to the fractional quantum Hall effect (FQHE). The spontaneously topological chiral symmetry breaking is the main contribution to the FQHE, which also includes two terms: the hopping of sublattice and Coulomb energy by the interaction of many-body particles. More generally, this exciton possesses an intermediate characteristic between the Wannier regimes and displays a peculiar two-dimensional wavefunction in the three-dimensional FQHE states. Finally, a bilayer three-dimensional model is proposed to implement the FQHE on the lattice by incorporating ferromagnetic dopants into three-dimensional topological insulative thin films. This study theoretically predicts the FQHE on the basis of other reports that have experimentally verified the rationality of the proposed model in magnetic topological insulators.

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Journal articles on the topic 'Excitonic ferromagnetism'

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