Quantum oscillations and Dirac-Landau levels in Weyl superconductors

Abstract

When magnetic field is applied to metals and semimetals quantum oscillations appear as individual Landau levels cross the Fermi level. Quantum oscillations generally do not occur in superconductors (SC) because magnetic field is either expelled from the sample interior or, if strong enough, drives the material into the normal state. In addition, elementary excitations of a superconductor -- Bogoliubov quasiparticles -- do not carry a well defined electric charge and therefore do not couple in a simple way to the applied magnetic field. We predict here that in Weyl superconductors certain types of elastic strain have the ability to induce chiral pseudo-magnetic field which can reorganize the electronic states into Dirac-Landau levels with linear band crossings at low energy. The resulting quantum oscillations in the quasiparticle density of states and thermal conductivity can be experimentally observed under a bending deformation of a thin film Weyl SC and provide new insights into this fascinating family of materials.Comment: Version accepted by PRB, minor changes, references adde

Weyl superconductor phases in a Weyl-semimetal/superconductor multilayer

“…The Berry curvature can have a monopole structure even in superconductors and superfluids, the resulting phases of which are referred to as Weyl-superconductor/superfluid phases [34][35][36][37][38][39] . The Weyl-superfluid phase has been studied in the context of the ABM phase of superfluid 3 He 40 . The pair potential has pairs of nodal points at the position of monopoles in the momentum space where the superconducting energy gap closes.…”

“…Topologically nontrivial superconducting phases have been tuned and engineered in strong spin-orbit-coupled materials by making contact with conventional superconductors. When the surface of a topological insulator is attached with a conventional superconductor, the gapless surface mode turns into a fully-gapped two-dimensional topological superconductor due to the superconducting proximity effect 45,46 . Even a normal metal can become a topological superconductor when Rashba spin-orbit coupling and the proximity effect are present [47][48][49] .…”

“…When the surface of a topological insulator is attached with a conventional superconductor, the gapless surface mode turns into a fully-gapped two-dimensional topological superconductor due to the superconducting proximity effect 45,46 . Even a normal metal can become a topological superconductor when Rashba spin-orbit coupling and the proximity effect are present [47][48][49] . The surface of an inversion-symmetry-broken Weyl semimetal hosts a flat band of the Majorana fermions by attaching superconductors with π-phase difference making a Josephson junction 50 .…”

“…The surface of an inversion-symmetry-broken Weyl semimetal hosts a flat band of the Majorana fermions by attaching superconductors with π-phase difference making a Josephson junction 50 . In the case of two dimensions, a quantum-anomalous-Hall insulator in proximity to a conventional superconductor realizes a topological-superconductor phase 51 .…”

“…In this paper, we investigate the superconducting proximity effect in the bulk electronic states of a time-reversalsymmetry-broken Weyl semimetal by considering a multilayer structure of the alternation of Weyl-semimetal and superconductor layers (WSM-SC). Thus, our model is a hybrid of the WSM-NI model 52 and the TI-SC model 36 , and inherits physical properties from both models, that is, our model realizes both Weyl-superconductor phases and topologicalsuperconductor phases with arbitrary Chern numbers. In addition, our model has controlable transparency of the interface by inserting potential barriers between layers, and does not require π-phase difference of superconductor layers like in the TI-SC model 36 .…”