第4回物理工学科教室談話会[Prof. Ashvin Vishwanath・7/15(火)15:00～16:00]

講　師：Prof. Ashvin Vishwanath
所　属：Harvard University（ハーバード大学）
題　目：Superconductors are topological phases protected by generalized symmetries
日　時：2025 年 7 月 15 日(火)15:00～16:00
Date and Time: July 15, 2025 (Tuesday) 15:00-16:00
場　所：工 6 号館 2 階 64 号講義室
Place: Lecture Room 64, 2nd floor, Engineering Bldg. 6

Abstract:
Recently, major strides have been taken towards a complete classification of gapped quantum states of matter. Yet a commonly observed gapped state—ordinary superconductors—sits awkwardly within this classification. Here we will answer the question of classification by proposing that the minimal description of a superconductor is in terms of symmetry protected topological (SPT) phases. A key role is played by the magnetic symmetry, a 1-form symmetry in three spatial dimensions, which encodes the absence of magnetic monopoles. The known properties of superconductors can be reproduced from the SPT characterization. Besides providing a minimalist derivation that is complementary to the Landau-Ginzburg approach, the non-perturbative nature of this viewpoint may be useful in situations when fluctuations are significant.

Furthermore, this approach reveals an unexpected relation between persistent currents at the surface of a superconductor and the Josephson effect on the one hand and Thouless pumps and the quantum spin Hall effect on the other.

紹介教員：渡辺悠樹准教授（物理工学専攻）、求幸年教授（物理工学専攻）