東京大学 · 物理学・天文学
長岡直人教授の研究室は、電子相関とトポロジーが関与する量子物性を核に、反強磁性や非中心対称格子に由来する新しい量子状態の解明を進めています。特に、スピン-軌道相互作用に起因する異常ホール効果や、非時間反転対称系におけるトポロジカルな電気的性質の理論的・実験的解明が中心です。近年では、酸化物超伝導体の異常な常時性状や、2次元材料における磁気的・電気的特異性の関係にも注目しています。
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The anomalous Hall effect (AHE) occurs in solids with broken time-reversal symmetry, typically in a ferromagnetic phase, as a consequence of spin-orbit coupling. Experimental and theoretical studies of the AHE are reviewed, focusing on recent developments that have provided a more complete framework for understanding this subtle phenomenon and have, in many instances, replaced controversy by clarity. Synergy between experimental and theoretical works, both playing a crucial role, has been at the
We study a version of the uniform resonating-valence-band state in which fermions and spinless bosons are coupled by a gauge field. We show that above the Bose-Einstein temperature, the boson inverse lifetime due to scattering by the gauge field is of order kT, which suppresses the condensation temperature and leads to a linear T resistivity. The Hall number is proportional to the hole density and temperature dependent. The single-particle spectral weight exhibits a continuum plus a broadened pe
Lack of spatial inversion symmetry in crystals offers a rich variety of physical phenomena, such as ferroelectricity and nonlinear optical effects (for example, second harmonic generation). One such phenomenon is magnetochiral anisotropy, where the electrical resistance depends on the current direction under the external magnetic field. We demonstrate both experimentally and theoretically that this magnetochiral anisotropy is markedly enhanced by orders of magnitude once the materials enter into
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