DOI： 10.1103/PhysRevB.111.L180403

The quest for non-Abelian anyons is attracting tremendous attention. A Majorana quasiparticle has attracted great interest since the non-Abelian anyon is a key particle for topological quantum computation. Much effort has been made toward the quest of the Majorana state in solids, and some candidate material platforms have been reported. Among various materials that can host the Majorana state, a chiral 𝑝-wave superconductor is one of the suitable materials, and the iron-based layered superconductor FeTeSe is one of the promising material platforms because its surface can host an effective 𝑝-wave superconducting state that is analogous to the chiral 𝑝-wave superconducting state thanks to its topological surface state. Given that a chiral 𝑝-wave superconductor possesses spin polarization, detecting the spin polarization can be evidence for the chiral 𝑝-wave trait, which results in the existence of Majorana excitation. Here, we show successful detection of the spin polarization at the surface of FeTe₀.₆⁢Se₀.₄ in its superconducting state, where the spin polarization is detected via a potentiometric method. Amplitudes of the spin signal exhibit characteristic dependence for temperature and bias current, suggesting detection of spin polarization of the Bogoliubov quasiparticles. Our achievement opens an avenue to exploration of topological superconductivity for fault-tolerant quantum computation.

CiNii Research

掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.111.L140406

<p>Nonlinear phenomena have been a focus of research for many years. Known for their complex responses to external stimuli, these phenomena provide both a platform for fundamental investigations and a wealth of practical applications in various scientific disciplines. The emergence of two-dimensional and topological materials, as well as advances in fabrication techniques for quantum wells and metamaterials, have brought these materials to the forefront of recent research in this field. These developments have opened new avenues for exploring nonlinear phenomena in systems with broken inversion symmetry. This talk will cover two topics related to nonlinear phenomena in inversion-asymmetric materials.</p><p></p><p>The first is the nonlinear Hall effect observed in topological crystalline insulators with broken inversion symmetry^[1]. We show the discovery of controllable and non-volatile topological functionality at room temperature in a topological crystalline insulator (TCI), Pb_1-xSn_xTe. This functionality stems from the interplay between the ferroelectric and topological nature (specifically, the Berry curvature dipole, BCD) of Pb_1-xSn_xTe, where the BCD is invoked by its topological character and stabilized by its ferroelectricity. The discovery of this topological effect -termed the ferroic BCD- at room temperature opens a new frontier in topological material science. The ferroic BCD provides a new type of non-volatility in a single material, where the stored information can be read out as a voltage and/or charge current along the Hall direction with a second-order harmonic response.</p><p></p><p>The second topic is the magneto-photogalvanic effect found in conventional metals, which also arises from nonlinear photocurrent generation in inversion-asymmetric materials. One type of nonlinear phenomenon, photocurrent generation, is shown to extend even to nonmagnetic single-element metals—a category that has been largely overlooked in this field. The photocurrent generation is attributed to spin accumulation due to the spin Hall effect at the edges of the metals, locally breaking time-reversal and space-inversion symmetries. This study challenges the conventional focus on exotic materials and demonstrates that even seemingly simple single-element metals can exhibit complex nonlinear phenomena. The observed photocurrent belongs to a recently highlighted class of nonlinear effects that occur under PT-symmetric conditions, where time-reversal and space-inversion symmetries are individually broken but preserved in combination. The discovery of such phenomena in single-element metals has the potential to reshape our approach to materials science and unlock new opportunities for exploiting these effects in a wide range of scientific fields.</p><p></p><p>[1] T. Nishijima, T. Watanabe, H. Sekiguchi, Y. Ando, E. Shigematsu, R. Ohshima, S. Kuroda and M. Shiraishi, Nano Letters <b>23</b>, 2247 (2023).</p><p>[2] T. Nishijima, R. Ohshima, Y. Yanase, R. Ishii, M. Shiraishi, Y. Ando, Physical Review B <b>111</b>, L140406 (2025).</p>

DOI： 10.14886/jvss.2025.0_3b02

CiNii Research

掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/physrevb.110.l220407

その他URL： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.110.L220407/fulltext

掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/physrevb.110.094419

その他URL： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.110.094419/fulltext

We investigate unidirectional spin Hall magnetoresistance (USMR) in Ta/Co bilayer systems with various Co thicknesses. A negative USMR is observed when the thickness of Co is thin due to the negative spin Hall angle of Ta, as expected from the conventional framework. However, as the Co thickness increases, the amplitude of USMR becomes strongly suppressed, and the sign of USMR becomes positive, which cannot be explained by theoretical calculation considering only the spin Hall effect (SHE) in the Ta layer. We successfully explain the anomalous thickness dependence of USMR by considering USMR induced by SHE in the Co layer. This work verifies the significant influence of SHE in ferromagnets on the measurement of USMR and will contribute to a better understanding of USMR.

CiNii Research

DOI： 10.3379/msjmag.2403r003

CiNii Research

掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/physrevb.109.l020406

その他URL： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.109.L020406/fulltext

The ability to control the Gilbert damping which determines the lifetime of spin information is crucial for designing spintronic and magnonic devices. Thus, controlling the Gilbert damping parameter α has been a significant research target for several decades. Although numerous approaches have been explored to control α, few reports of large changes of this parameter have been presented. Herein, we demonstrate significant change of α in 2-nm-thick Co₂₅⁢Fe₇₅ films originating from uniaxial surface magnetic anisotropy, which affects the two-magnon scattering. We report a change in α by approximately 0.02, or 300%. The value for α and its change are comparable to those observed in a previous study using a film that is one order of magnitude thicker. Our results achieved with Co₂₅⁢⁢Fe₇₅ can be directly transferred to other ultrathin ferromagnetic materials, which are a promising platform for spin information processing, and thus represents a versatile approach to modulate the Gilbert damping.

CiNii Research

掲載種別：研究論文（学術雑誌）  

<jats:p>A spin-splitting state due to a Rashba-type spin–orbit interaction is investigated using two-dimensional electron gas (2DEG) at the surface of SrTiO3. The circular photogalvanic effect is utilized to detect the spin-splitting state. Both the polarization and incident light angle dependence of the measured photocurrent generated in the 2DEG unequivocally show the presence of surface spin splitting in the 2DEG, and variation of the carrier densities of the 2DEG provides further supporting evidence. This finding could pave the way for investigating spin textures and spin physics in two-dimensional carrier gas systems.</jats:p>

DOI： 10.1063/5.0190118

CiNii Research

<p>水素終端ダイヤモンド表面に誘起される2次元ホールガス（2DHG）は、ラシュバ効果によるバンドのスピン分裂を有し、ゲート電圧の印加により最大24.5 meVになることが報告されている。このようなスピン分裂したバンド構造を持つ系では、面内の垂直磁場に対して電気伝導特性が非相反性を示す。本研究では、この非相反性を測定することで水素終端ダイヤモンド表面の2DHGにおけるラシュバ効果の大きさを評価した。</p>

DOI： 10.11316/jpsgaiyo.79.2.0_1417

CiNii Research

<p>水素終端ダイヤモンド表面に誘起される2次元ホールガス（2DHG）は、構成元素が炭素と水素のみであるが、強いラシュバ型スピン軌道相互作用の存在が示唆されている。本研究では、水素終端ダイヤモンドと強磁性金属の2層構造に対し2次高調波ホール測定を行うことでスピン軌道トルクを測定した。強磁性金属の膜厚依存性などから2DHG由来のスピン軌道トルクが存在することを確認し、その大きさを評価した。</p>

DOI： 10.11316/jpsgaiyo.79.1.0_905

CiNii Research

<p>超伝導ダイオード効果はエネルギー無散逸かつ方向制御可能な電荷輸送技術への応用が期待されており，その材料系の開拓と，詳細な背景物理解明が望まれている．報告されている本効果のほとんどは外部磁場によって変調されるが，本研究では層状超伝導体FeTe_0.6_Se_0.4_において，外部磁場に非依存な超伝導ダイオード効果を観測した．そして対照実験により，その起源が素子の非対称なジオメトリに起因する熱勾配であることを突き止めた．</p>

DOI： 10.11316/jpsgaiyo.79.2.0_1488

CiNii Research

<p>SrTiO_3_表面をミリングすると酸素欠損による電子ドーピングによって表面に二次元電子層が発現し，また表面における対称性の破れがラシュバ型スピン分裂を生じることが知られている． 偏光依存性を持った光電流，またこの偏光依存電流の入射光角度依存性を観測することで，SrTiO_3_表面におけるスピン分裂状態を検出した．加えて二次元電子層のキャリア密度に応じた光電流の振る舞いも評価した．</p>

DOI： 10.11316/jpsgaiyo.79.1.0_896

CiNii Research

<p>本研究では，ワイル強磁性体であるCo_2_MnGaにおいて，強磁性体の電流-スピン流変換で生じたスピン流が自身の磁化に作用して生じる自己誘起スピン軌道トルクの観測を報告する．上下がMgOに接合された外部スピン流源無しの構造においても，重金属/強磁性体構造に匹敵する巨大な自己誘起スピン軌道トルクが観測された．加えてトルクの符号及び大きさが，結晶軸に対する印加電流の方向で大きく依存することを見出した．対照実験と第一原理計算を用い，波数空間におけるワイル点由来のベリー曲率の分布が異方性を説明する可能性があることを示した．</p>

DOI： 10.11316/jpsgaiyo.79.1.0_904

CiNii Research

<p>PbSnTeはトポロジカル結晶絶縁体である同時に強誘電性を有する物質として知られている。本研究では電界印加による強誘電性の発現と原子変位が生み出すBerry曲率双極子を、原子変位による系の反転対称性の破れが誘起する非線形ホール効果をプローブとして観測した。Berry曲率双極子の分極は室温に至るまでの広範な温度領域で測定でき、その分極の大きさも十分大きいことを明らかにした[1]。 [1] T. Nishijima, Y. Ando, et al., Nano Lett. 23, 2247 (2023).</p>

DOI： 10.11316/jpsgaiyo.79.1.0_1055

CiNii Research

<p>CuにBiを微小ドープしたCuBi合金のトルク効率について評価した。CuBi合金は高いトルク効率と高い伝導率が両立する材料であると期待される。CuBi合金が長いスピン拡散長をもつことに留意し、スピンシンク層を導入した3層構造の系においてトルク効率のBiドープ率依存性を評価した。解析においては、Cuの比較的大きな軌道ホール効果についても考慮した。手法としてはスピントルク強磁性共鳴法及び2次高調波ホール測定を用いた。</p>

DOI： 10.11316/jpsgaiyo.79.1.0_902

CiNii Research

会議種別：口頭発表（一般）  

開催地：愛媛、日本