JPS Conference Proceedings (Internet), 38, p.011161_1 - 011161_6, 2023/05
In recent years, phenomena originating from spin-orbit coupling (SOC), such as topological phenomena, have been intensively studied. To realize these phenomena, materials containing heavy elements have been investigated because of large SOC. On the other hand, to enhance the effect of the SOC, it may be possible to use enhancement of the effective SOC by the Coulomb interaction between electrons. In this study, to investigate such enhancement of the SOC, we consider a two-orbital model, which is a minimal model to include SOC. By using the variational Monte Carlo method, we find that the effective SOC can become several times larger than the bare value by the Coulomb interaction. This study will expand the target materials for the SOC-originated phenomena to strongly correlated metals without heavy elements.
大西 弘明; 宮下 精二*
JPS Conference Proceedings (Internet), 38, p.011157_1 - 011157_6, 2023/05
We have proposed a Hubbard model which exhibits itinerant ferromagnetism by extending the model of Nagaoka ferromagnetism. In the present work, we confirm that the idea of the realization of itinerant ferromagnetism works in two- and three-dimensional lattices as well as a one-dimensional lattice which we studied previously. We also investigate the temperature dependence of the magnetic ordering and present a magnetic phase diagram in the space of the temperature and the chemical potential. In the obtained phase diagram, we find a V-shape structure for the magnetic ordering near a quantum phase transition. Besides, we find an additional peak exhibiting a dome structure. Temperature dependences of related spin correlation functions are studied in detail.
高濱 隆成*; 有薗 実駿*; 犬童 代梧*; 吉永 汰正*; 寺倉 千恵子*; 竹下 直*; 白崎 巧*; 野田 正亮*; 桑原 英樹*; 梶本 亮一; et al.
JPS Conference Proceedings (Internet), 38, p.011114_1 - 011114_6, 2023/05
We investigated the transport and magnetic properties of single crystals of the pseudobrookite AlTiO for grown using a floating zone. We found a correlation of spin-singlet Ti-Ti dimers even in the conductive and phases which develops with increasing . The development of the dimer correlation suppresses the magnetic susceptibility at the low temperature and enhances the electric conductivity perhaps due to the suppression of the magnetic scattering at the isolated Ti ions. The compound shows the best conductivity in the phase near the phase boundary between the and phases where the dimer correlation is much developed. Some exotic conductive state may be realized under the background of fluctuation of the spin-singlet dimer in the phase near the phase boudary.
Chen, Y.*; 浅野 駿*; Wang, T.*; Xie, P.*; 北山 慎之介*; 石井 賢司*; 松村 大樹; 辻 卓也; 谷口 貴紀*; 藤田 全基*
JPS Conference Proceedings (Internet), 38, p.011050_1 - 011050_6, 2023/05
To investigate the variation of the electronic state of -type cuprate due to annealing, we performed Cu -edge X-ray absorption fine structure measurements on PrCuO (PCO) and PrLaCuO (PLCO). The induced electrons due to annealing () in PCO and PLCO were approximately 2, consistent with a model of electron doping to Mott insulator. Here, and represent the amount of excess oxygen from the stoichiometric composition in the as-sintered compound and that of oxygen loss due to annealing, respectively. Furthermore, the energy of the Einstein oscillator () for the Cu-O bond was evaluated by extended X-ray absorption fine structure analysis. (O denotes the in-plane oxygen.) We found a small annealing effect on for both PCO and PLCO.
下田 愛海*; 岩佐 和晃*; 桑原 慶太郎*; 佐賀山 基*; 中尾 裕則*; 石角 元志*; 大原 高志; 中尾 朗子*; 星川 晃範*; 石垣 徹*
JPS Conference Proceedings (Internet), 38, p.011091_1 - 011091_6, 2023/05
Synchrotron X-ray diffraction study revealed that NdSn ( = Rh and Ir) undergo structural phase transitions characterized by the wave vector =(1/2,1/2,0). Neutron diffraction study revealed antiferromagnetic ordering below = 1.65 and 1.42 K for NdRhSn and NdIrSn, respectively, which is similar to that previously reported for NdCoSn. These compounds show a magnetic susceptibility saturation behavior below approximately 3 K. The results indicate emergence of anomalous electronic correlation in NdSn ( = Co, Rh, and Ir) above .
no journal, ,
田端 千紘; 今 布咲子*; 村田 怜也*; 網塚 浩*; 中尾 裕則*; 松本 裕司*; 金子 耕士; 芳賀 芳範
no journal, ,
UPtGa is a recently discovered compound in a material search in the U-T-X (T: transition metal, X: Al, Ga) ternary system. It crystallizes in a hexagonal structure (space group P6/mmc), where U-Ga layers stacked along the c-axis with c/2 spacing, and between them, Pt and Ga form nested triangular lattice layers. A detailed single-crystal structural analysis shows, however, that the hexagonal structure is an average structure, and that the actual one has a kind of crystallographic disorder: 1/3 of U sites on the triangular lattice are not occupied, resulting in a honeycomb layer formed by the rest occupied U sites, with a larger orthorhombic unit cell. From a microscopic viewpoint, occupied U sites do not have inversion center, which makes this material of interest as a new candidate material for the emergence of unconventional cross-correlation phenomena. From measurements of bulk physical properties such as magnetization and specific heat, it was revealed that UPtGa undergoes an antiferromagnetic phase transition at a transition temperature of 26 K. To clarify a microscopic picture of this magnetic ordering, we have performed resonant X-ray scattering (RXS) experiments to observe resonant magnetic reflections. Using 3.72 keV synchrotron X-rays, we observed diffractions of resonant scatterings at the M4 absorption edge of U at BL-11B Photon Factory of KEK. The reflections with the q = (1/6, 1/6, 0) propagation vector were observed below TN at the resonant energy of the M4 absorption edge. The polarization dependence of the RXS signal strongly suggests that the ordered magnetic moments of U are parallel to the hexagonal caxis, which is consistent with the strong magnetic anisotropy observed in magnetization measurements.
金子 耕士; 田端 千紘*; 竹内 徹也*; Frontzek, M. D.*; 松田 雅昌*; 大石 一城*; 伊藤 孝; 宗像 孝司*; 鬼柳 亮嗣; 垣花 将司*; et al.
no journal, ,
Magnetic skyrmion, particle-like topologically non-trivial spin textures, attracts surge of interests from both fundamental and application points of view. Since the first discovery in MnSi crystallizing in the cubic space group , intensive research on magnetic skyrmions has conducted for materials particularly in this space group. This leads to findings of new class of materials, whereas magnetic ions were mostly limited to d electron systems. Recently, it turned out that f-electron compounds can host magnetic skyrmion lattice as well. The magnetic skyrmions in f-electron compounds possess contrasting characteristics, such as short periodicity and strong anisotropy. Among recent discoveries, cubic chiral compound EuPtSi provides ideal opportunities to compare with d-electron systems as it crystallizes in the same space group as MnSi, namely . We will present our neutron and X-ray scattering studies to characterize magnetic skyrmion lattice in this compound.
角田 一樹; 鹿子木 将明*; 桜庭 裕弥*; 増田 啓介*; 河野 嵩*; 後藤 一希*; 宮本 幸治*; 三浦 良雄*; 宝野 和博*; 奥田 太一*; et al.
no journal, ,
Heusler alloy CoMnSi is theoretically predicted to be a half-metal ferromagnet exhibiting 100 spin-polarization. In fact, a huge output has been reported for tunnel magnetoresistance (TMR) devices using CoMnSi films. However, such a giant TMR ratio is observed only at low temperatures, and the output drastically decreases at room temperature. Several theoretical models have been proposed for the spin-depolarization at room temperature, but the mechanism remains unclear. In this study, we have fabricated CoMnSi films and performed temperature-dependent spin- and angle-resolved photoelectron spectroscopy. We confirmed a steep hole-band at point and electron-band at X point. Those experimentally observed bands are well reproduced by the calculations. More importantly, the temperature-dependent spin-polarization can be nicely fitted by Bloch law. This implies that the spin-depolarization can be explained by the thermally excited magnon model.
芳賀 芳範; Opletal, P.; 酒井 宏典; 山本 悦嗣; 神戸 振作; 徳永 陽; 常盤 欣文
no journal, ,
A detailed investigation of magnetization behavior of an unconventional superconductor UTe under a wide temperature-field range is shown. Magnetic characteristics are discussed based on field-dependent magnetic entropy obtained using thermodynamic relations.
神戸 振作; 酒井 宏典; 芳賀 芳範; 徳永 陽; 金城 克樹*; 北川 俊作*; 石田 憲二*; 播磨 尚朝*
no journal, ,
藤森 伸一; 川崎 郁斗; 竹田 幸治; 山上 浩志; 仲村 愛*; 本間 佳哉*; 青木 大*
no journal, ,
The electronic structure of UTe was studied by resonant photoelectron spectroscopy (RPES) and angle-resolved photoelectron spectroscopy (ARPES) with soft X-ray synchrotron radiation. The partial U 5f density of states of UTe were imaged by the U~- RPES and it was found that the U~ state has an itinerant character, but there exists an incoherent peak due to the strong electron correlation effects. The band structure of UTe was obtained by ARPES and its overall band structure was mostly explained by band structure calculations, except for the incoherent band at eV. These results suggest that the U~ states of UTe have itinerant but strongly-correlated nature with enhanced hybridization with the Te~ states. In addition, the valence state of UTe was studied by core-level photoelectron spectroscopy. The main peak position of the U~ core-level spectrum of UTe coincides with that of UB, which is an itinerant compound with a nearly configuration. However, the main peak of UTe is broader than that of UB, and satellite structures are observed in the higher binding energy side of the main peak, which are characteristics of mixed-valence uranium compounds. These results suggest that the U~ state in UTe is in a mixed valence state with a dominant contribution from the itinerant 5 configuration.
荒木 康史; 山ノ内 路彦*; 酒井 貴樹*; 植村 哲也*; 家田 淳一
no journal, ,
We present our theoretical and experimental findings of the electric manipulation of magnetic textures enhanced by the electron topology. We first show the theory of the non-dissipative torques acting on magnetic textures, by classifying the electrically-induced spin torques phenomenologically. We propose the "topological Hall torque (THT)", which emerges from the combination of the anomalous velocity from the Berry curvature and the spin-momentum locking structure from the strong spin-orbit coupling (SOC). In contrast to the conventional spin-transfer torque (STT), which is driven by the transport current and suffers from energy dissipation by the Joule heating, the THT is capable of manipulating magnetic textures in a non-dissipative manner. The THT is present even in centrosymmetric crystals, such as the bulk WSMs. The emergence of the THT was verified experimentally, by measuring the current-induced magnetization switching in a ferromagnetic oxide SrRuO (SRO). SRO becomes ferromagnetic below the transition temperature 147K. After preparing a domain wall (DW) in a film of SRO, we measured the effective magnetic field exerted on the DW by a current in a wide temperature range. As a result, the measured revealed a nonmonotonic temperature dependence at low temperature, and a large magnitude compared with that arising from the conventional STT and the spin-orbit torque. Those unconventional behaviors of are successfully described by the THT, in connection with the large Berry curvature of the Weyl fermions present in SRO. The idea of the THT discussed here may help design the spintronics device highly efficient, from the viewpoint of band topology.
徳永 陽; 酒井 宏典; 神戸 振作; 芳賀 芳範; 常盤 欣文; Opletal, P.; 藤林 裕己*; 金城 克樹*; 北川 俊作*; 石田 憲二*; et al.
no journal, ,
UTe is a novel uranium-based superconductor with a rather high transition temperature of K. The compound attracted particular attention, because of the strong possibility of the spin-triplet Cooper pairing, which is a natural candidate for topological superconductivity in a bulk material. In this study, we performed Te-NMR experiments on a Te enriched single crystal of UTe. The field and temperature dependences of the spin-spin relaxation rate of in field applied along the -axis revealed slow electronic dynamics developing in the paramagnetic state. The observed slow fluctuations are concerned with a successive growth of long-range electronic correlations below 3040 K. We suggest that UTe would be located on the paramagnetic side near an electronic phase boundary, where either the magnetic or Fermi-surface instability would be the origin of the characteristic fluctuations.
Opletal, P.; 酒井 宏典; 芳賀 芳範; 常盤 欣文; 山本 悦嗣; 神戸 振作; 徳永 陽
no journal, ,
Magnetic semimetals are currently focus of research due to possible electronic topological features. Topological features originate from nontrivial band characters. One of the most interesting state is Weyl fermion which originate from band splitting driven by spin-orbit interaction due to the inversion symmetry breaking or time-reversal symmetry breaking. The materials with these properties are called Weyl semimetals. Wey fermions are expected to be robust and have high mobility, which is important for practical application of topological matter. Uranium materials are candidates for Weyl semimetals due to their strong spin-orbit interaction causing band inversion and/or strong electronic correlations, often observed as 5f magnetism. One of the possible candidates are UOX (X = S, Se, Te) compounds. UOX (X = S, Se, Te) crystallizes in tetragonal PbFCl-type structure (P4/nmm space group). Only polycrystalline samples are reported in literature. UOS, UOSe and UOTe were reported to be antiferromagnets with T = 55, 100 and 160 K, respectively. Magnetic structure of UOS and UOSe were reported to have moment along the c-axis with Q = (0,0,1/2). UOS and UOSe were both reported to exhibit semiconducting behavior on polycrystalline samples. UOTe was theoretically predicted to have nontrivial topology. Recently we have prepared first single crystals of UOX (X = S, Se, Te) and shown they exhibit semimetallic conductivity in contrast to published literature. We will present the method of preparation of single crystals, results of magnetic, transport and thermal measurements and discuss these results in connection to Weyl semimetals and results published in literature.