IOP Publishing Acta Medica Okayama 1882-0778 18 9 2025 Fundamentals and advances in transverse thermoelectrics 090101 EN Hiroto Adachi Research Institute for Interdisciplinary Science, Okayama University Fuyuki Ando Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science Takamasa Hirai Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science Rajkumar Modak Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science Matthew A. Grayson Department of Electrical and Computer Engineering, Northwestern University Ken-ichi Uchida Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science Transverse thermoelectric effects interconvert charge and heat currents in orthogonal directions due to the breaking of either time-reversal symmetry or structural symmetry, enabling simple and versatile thermal energy harvesting and solid-state cooling/heating within single materials. In comparison to the complex module structures required for the conventional Seebeck and Peltier effects, the transverse thermoelectric effects provide the complete device structures, potentially resolving the fundamental issue of multi-module degradation of thermoelectric conversion performance. This review article provides an overview of all currently known transverse thermoelectric conversion phenomena and principles, as well as their characteristics, and reclassifies them in a unified manner. The performance of the transverse thermoelectric generator, refrigerator, and active cooler is formulated, showing that thermal boundary conditions play an essential role in discussion on their behaviors. Examples of recent application research and material development in transverse thermoelectrics are also introduced, followed by a discussion of future prospects. No potential conflict of interest relevant to this article was reported.

Informa UK Limited Acta Medica Okayama 1468-6996 26 1 2025 Quantitative measurements of transverse thermoelectric generation and cooling performances in SmCo5/Bi0.2Sb1.8Te3-based artificially tilted multilayer module 2535955 EN Masayuki Murata Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Technology Fuyuki Ando Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science Takamasa Hirai Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science Hiroto Adachi Research Institute for Interdisciplinary Science, Okayama University Ken-ichi Uchida Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science The transverse thermoelectric generation and cooling performances in a thermopile module composed of recently developed SmCo5/Bi0.2Sb1.8Te3 artificially tilted multilayers are evaluated quantitatively. When a large temperature difference of 405°C is applied to the SmCo5/Bi0.2Sb1.8Te3-based module, the open-circuit voltage and output power reach 0.51 V and 0.80 W, respectively. The corresponding maximum power density is 0.16 W/cm2, even if the power is normalized by the device area including areas that do not contribute to the power generation, such as epoxy resin, electrodes, and insulating layers. The maximum energy conversion efficiency for our module in this condition is experimentally determined to be 0.92%. Under the cooling operation, the same module exhibits the maximum temperature difference of 9.0°C and heat flow at the cold side of 1.6 W. Although these values are lower than the ideal thermoelectric performance expected from the material parameters due to the imperfections associated with modularization, the systematic investigations reported here clarify a potential of the SmCo5/Bi0.2Sb1.8Te3 artificially tilted multilayers as thermoelectric generators and cooling devices. No potential conflict of interest relevant to this article was reported.

American Physical Society (APS) Acta Medica Okayama 2469-9950 109 17 2024 Time-dependent Ginzburg-Landau theory of the vortex spin Hall effect 174503 EN Hiroto Adachi Research Institute for Interdisciplinary Science, Okayama University Yusuke Kato Department of Basic Science, University of Tokyo Jun-ichiro Ohe Department of Physics, Toho University Masanori Ichioka Research Institute for Interdisciplinary Science, Okayama University We develop a time-dependent Ginzburg-Landau theory of the vortex spin Hall effect, i.e., a spin Hall effect that is driven by the motion of superconducting vortices. For the direct vortex spin Hall effect in which an input charge current drives the transverse spin current accompanying the vortex motion, we start from the well-known Schmid-Caroli-Maki solution for the time-dependent Ginzburg-Landau equation under the applied electric field, and find out the expression of the induced spin current. For the inverse vortex spin Hall effect in which an input spin current drives the longitudinal vortex motion and produces the transverse charge current, we microscopically construct the time-dependent Ginzburg-Landau equation under the applied spin accumulation gradient, and calculate the induced transverse charge current as well as the open circuit voltage. The time-dependent Ginzburg-Landau equation and its analytical solution developed here can be a basis for more quantitative numerical simulations of the vortex spin Hall effect. No potential conflict of interest relevant to this article was reported.

American Physical Society (APS) Acta Medica Okayama 2469-9950 107 15 2023 Ginzburg-Landau action and polarization current in an excitonic insulator model of electronic ferroelectricity 155142 EN Hiroto Adachi Research Institute for Interdisciplinary Science, Okayama University Naoshi Ikeda Department of Physics, Okayama University Eiji Saitoh Department of Applied Physics, The University of Tokyo In comparison to transport of spin polarization in ferromagnets, transport of electric polarization in ferroelectrics remains less explored. Taking an excitonic insulator model of electronic ferroelectricity as a prototypical example, we theoretically investigate the low-energy dynamics and transport of electric polarization by microscopically constructing the Ginzburg-Landau action. We show that, because of the scalar nature of the excitonic order parameter, only the longitudinal fluctuations are relevant to the transport of electric polarization. We also formulate the electric-polarization diffusion equation, in which the electric-polarization current is defined purely electronically without recourse to the lattice degrees of freedom. No potential conflict of interest relevant to this article was reported.

American Physical Society (APS) Acta Medica Okayama 2469-9950 105 10 2022 Antiferromagnetic spin Seebeck effect across the spin-flop transition: A stochastic Ginzburg-Landau simulation 104417-1 104417-14 EN Yutaka Yamamoto Department of Physics, Okayama University Masanori Ichioka Research Institute for Interdisciplinary Science, Okayama University Hiroto Adachi Research Institute for Interdisciplinary Science, Okayama University We investigate the antiferromagnetic spin Seebeck effect across the spin-flop transition in a numerical simulation based on the time-dependent Ginzburg-Landau equation for a bilayer of a uniaxial insulating antiferromagnet and an adjacent metal. By directly simulating the rate of change of the conduction-electron spin density s in the adjacent metal layer, we demonstrate that a sign reversal of the antiferromagnetic spin Seebeck effect across the spin-flop transition occurs when the interfacial coupling of s to the staggered magnetization n of the antiferromagnet dominates, whereas no sign reversal appears when the interfacial coupling of s to the magnetization m dominates. Moreover, we show that the sign reversal is influenced by the degree of spin dephasing in the metal layer. Our result indicates that the sign reversal is not a generic property of a simple uniaxial antiferromagnet, but controlled by microscopic details of the exchange coupling at the interface and the spin dephasing in the metal layer. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 2073-8994 12 1 2020 Relation of Superconducting Pairing Symmetry and Non-Magnetic Impurity Effects in Vortex States 175 EN Yasuaki Sera Department of Physics, Okayama University Takahiro Ueda Department of Physics, Okayama University Hiroto Adachi Department of Physics, Okayama University Masanori Ichioka Department of Physics, Okayama University Non-magnetic impurity scattering effects on the vortex core states are theoretically studied to clarify the contributions from the sign-change of the pairing function in anisotropic superconductors. The vortex states are calculated by the Eilenberger theory in superconductors with px-wave pairing symmetry, as well as the corresponding anisotropic s-wave symmetry. From the spatial structure of the pair potential and the local electronic states around a vortex, we examine the differences between anisotropic superconductors with and without sign-change of the pairing function, and estimate how twofold symmetric vortex core images change with increasing the impurity scattering rate both in the Born and the unitary limits. We found that twofold symmetric vortex core image of zero-energy local density of states changes the orientation of the twofold symmetry with increasing the scattering rate when the sign change occurs in the pairing function. Without the sign change, the vortex core shape reduces to circular one with approaching dirty cases. These results of the impurity effects are valuable for identifying the pairing symmetry by observation of the vortex core image by the STM observation. No potential conflict of interest relevant to this article was reported.