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

Publishing type：Research paper (scientific journal)  

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

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/physrevb.110.l220407

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

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/physrevb.110.094419

Other 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

<p>  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.</p>

DOI： 10.3379/msjmag.2403r003

CiNii Research

Publishing type：Research paper (scientific journal)  

DOI： 10.1103/physrevb.109.l020406

Other 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

Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0190118

CiNii Research

DOI： 10.11316/jpsgaiyo.79.2.0_1417

CiNii Research

DOI： 10.11316/jpsgaiyo.79.1.0_905

CiNii Research

DOI： 10.11316/jpsgaiyo.79.2.0_1488

CiNii Research

DOI： 10.11316/jpsgaiyo.79.1.0_896

CiNii Research

DOI： 10.11316/jpsgaiyo.79.1.0_904

CiNii Research

DOI： 10.11316/jpsgaiyo.79.1.0_1055

CiNii Research

DOI： 10.11316/jpsgaiyo.79.1.0_902

CiNii Research

Presentation type：Oral presentation (general)  

Venue：愛媛、日本