Abstract
Bound states at interfaces between superconductors and other materials are a powerful tool to characterize the nature of the involved systems, and to engineer elusive quantum excitations. In-gap excitations of conventional s-wave superconductors occur, for instance, at magnetic impurities with net magnetic moment breaking time-reversal symmetry. Here we show that interfaces between a superconductor and a quantum antiferromagnet can host robust in-gap excitations, without breaking time-reversal symmetry. We illustrate this phenomenon in a one-dimensional model system with an interface between a conventional s-wave superconductor and a one-dimensional Mott insulator described by a standard Hubbard model. This genuine many-body problem is solved exactly by employing a combination of kernel polynomial and tensor network techniques. We unveil the nature of such zero modes by showing that they can be adiabatically connected to solitonic solutions between a superconductor and a classical antiferromagnet. Our results put forward a new class of in-gap excitations between superconductors and a disordered quantum spin phase can be relevant for a wider range of heterostructures.
Highlights
Topological modes emerging in condensed matter systems are among the most intriguing features in physics
We show that interfaces between a superconductor and a quantum antiferromagnet can host robust in-gap excitations, without breaking time-reversal symmetry
We model our system by the following Hamiltonian of a one-dimensional chain, that allows us incorporate an interface between a conventional superconductor and a quantum antiferromagnet in the simplest way: H = Hkin + HU + HSC, where Hkin is the kinetic energy term in a tight-binding form
Summary
Topological modes emerging in condensed matter systems are among the most intriguing features in physics. Increasing complexity, for instance, through heterostructures connecting a superconductor to materials of various properties offers an attractive platform to create new emergent phases [18,19,20] This is the basis for a plethora of proposals to engineer Majorana bound states [21], to explore unusual Andreev physics [22,22,23,24,25] and even to design higher-dimensional topological superconductors [26,27]. We show that time-reversal symmetry needs not to be broken and that these modes can be adiabatically connected with solitonic zero modes of the antiferromagnetically ordered phase violating time-reversal symmetry In this way, we extend the set of situations where the composition of different materials can generate a nontrivial phase at interfaces.
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