# Topological properties of multi-terminal superconducting nanostructures: effect of a continuous spectrum

## TL;DR

This paper explores how the continuous spectrum in multi-terminal superconducting nanostructures influences their topological properties, revealing non-quantized contributions to transconductance and conditions under which these effects vanish.

## Contribution

It introduces a redefined Berry curvature accounting for the continuous spectrum and derives explicit expressions for weak energy dependence and Weyl singularities.

## Key findings

- Continuous spectrum adds non-quantized parts to transconductance.
- Time-reversible scattering matrices eliminate non-topological contributions.
- Derived compact formulas for Berry curvature near Weyl points.

## Abstract

Recently, it has been shown that multi-terminal superconducting nanostructures may possess topological properties that involve Berry curvatures in the parametric space of the superconducting phases of the terminals, and associated Chern numbers that are manifested in quantized transconductances of the nanostructure. In this Article, we investigate how the continuous spectrum that is intrinsically present in superconductors, affects these properties. We model the nanostructure within scattering formalism deriving the action and the response function that permits a re-definition of Berry curvature for continuous spectrum. We have found that the re-defined Berry curvature may have a non-topological phase-independent contribution that adds a non-quantized part to the transconductances. This contribution vanishes for a time-reversible scattering matrix. We have found compact expressions for the redefined Berry curvature for the cases of weak energy dependence of the scattering matrix and investigated the vicinity of Weyl singularities in the spectrum.