Possible topological phases in quantum anomalous Hall insulator/unconventional superconductor hybrid systems
Ryoi Ohashi, Shingo Kobayashi, Yukio Tanaka
DOI 10.1103/PhysRevB.104.134518 · Physical Review B
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Abstract
Quantum anomalous Hall insulator (QAH)/s-wave superconductor (SC) hybrid systems are known to be an ideal platform for realizing two-dimensional topological superconductors with chiral Majorana edge modes. In this paper we study QAH/unconventional SC hybrid systems whose pairing symmetry is p wave, d wave, chiral p wave, or chiral d wave. The hybrid systems are a generalization of the QAH/s-wave SC hybrid system. In view of the symmetries of the QAH and pairings, we introduce three topological numbers to classify the topological phases of the hybrid systems. One is the Chern number, which characterizes chiral Majorana edge modes, and the others are topological numbers associated with crystalline symmetries. We numerically calculate the topological numbers and associated surface states for three characteristic regimes that feature the influence of unconventional SCs on QAHs. Our calculation shows a rich variety of topological phases and unveils the following topological phases that are not counterparts of the s-wave case: crystalline symmetry-protected helical Majorana edge modes, a line node phase (a crystalline-symmetry-protected Bogoliubov Fermi surface), and multiple chiral Majorana edge modes. The phenomena result from a nontrivial topological interplay between the QAH and unconventional SCs. Finally, we discuss tunnel conductance in a junction between a normal metal and the hybrid systems and show that the chiral and helical Majorana edge modes are distinguishable in terms of the presence or absence of a zero-bias conductance peak.
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