Dr. Shingo Kobayashi (Nagoya University)
"Flat-band Andreev bound states in nodal crystalline superconductors"
Over the last few years, the study on node structures in
superconductors (SCs) has received renewed interest due to the fact
that they are a kind of topological objects [1]. In this context, the
node structures are related to topology of quasi-particles in the
superconducting states and ensure the existence of surface-zero-energy
Andreev bound states (ABSs). Above all, a line node in time-reversal
(TR) invariant SCs is protected by a one-dimensional topological
number and induces a flat-band ABS on a surface. The flat-band ABSs
exhibit a zero-bias conductance peak through the tunneling measurement
for TR invariant SCs such as high-/T/c//cuprate//SCs and
non-centrosymmetric SCs, which gives a conclusive evidence for the
bulk topological line nodes.
In this talk, we study topology of symmetry-protected line nodes in
unconventional SCs, where line nodes are protected by the
mirror-reflection symmetry. Establishing a one-to-one correspondence
between group theoretical and topological classifications, we classify
the symmetry-protected line nodes based on topological numbers and
clarify that line-nodal SCs are classified into three classes by
flat-band ABSs: (i) odd-parity SCs with either TR symmetry or a
magnetic translation, (ii) even-parity SCs with TR symmetry, and (iii)
even-parity SCs with a magnetic translation [2]. These classes of SCs
are distinguishable through surface sensitive experiments.
[1] SK, K. Shiozaki, Y. Tanaka, and M. Sato, Phys. Rev. B 90, 024516
(2014)
[2] SK, S. Sumita, Y. Yanase, and M. Sato, arXiv:1711.06421