12/11：講演会のお知らせ　田仲由喜夫 氏　(名古屋大学 准教授)

題目 ： 「Theory of edge states and charge transport in unconventional superconductors」
講師 ： 田仲 由喜夫 氏（名古屋大学 教授）
日時 ： 12月11日(木) 15:30～17:20（7-8限）
会場 ： 理学部本館 第31講義室　

【講演要旨】
Theory of the tunneling effect of superconducting junctions was established in the 1960s for conventional metallic superconductors but did not exist for unconventional superconductors like spin singlet d-wave or spin-triplet p-wave superconductors. In the 1990s, stimulated the debates of the pairing symmetry of high Tc cuprate, we derived a theory of tunneling effect and Josephson effect in d-wave superconductor and contributed the determination of the pairing symmetry of cuprate. It was clarified that the surface Andreev bound states (SABS) called edge states have a crucial role in the quasiparticle tunneling and Josephson current [1]. The physical origin of these edge states is clarified by the topological invariant defined in bulk Hamiltonian [2]. Furthermore, it is recognized that all nodal superconductors can be regarded as topological superconductors with edge states [2-4].
We have also clarified that in spin-triplet p-wave superconductor junctions, the edge states can penetrate from the superconductor into the diffusive normal metal, as the anomalous proximity effect, which is a novel proximity effect in which the quasiparticle density of states in the diffusive normal metal peaks at zero energy [5]. It has been theoretically elucidated that this originates from odd-frequency electron pairs[3,6], which are unique electron pairs that do not form pairs at the same time called odd-frequency spin-triplet pairing [3,6,8].
Recently, we clarified the realization and control of subgap states by tailored altermagnetic fields on
unconventional superconductors. Distinct types of subgap states are realized, including curved and flat bands, that can be detected by tunneling spectroscopy [9]. We have also found that exotic surface Andreev bound states can arise in three-dimensional (3d) altermagnets coupled to 3d chiral d-wave superconductors [10].

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[3] Y. Tanaka, M. Sato, N. Nagaosa, J. Phys. Soc. Jpn. 81, 011013, 2012.
[4] 超伝導接合の物理 田仲由喜夫 (名古屋大学出版会) 2021年
[5] Y. Tanaka and S. Kashiwaya, Phys. Rev. B, 70, 012507, 2004.
[6] Y. Tanaka and A. Golubov, Phys. Rev. Lett. 98, 037003, 2007.
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[9] Bo Lu, P. Mercebach, P. Burset, K. Yada, J. Cayao, Y. Tanaka, Y. Fukaya, arXiv:2508.03364.
[10]Y. Fukaya, Bo Lu, K. Yada, Y. Tanaka, J. Cayao, arXiv:2510.14724.