Probing the topological band structure of diffusive multiterminal Josephson junction devices with conductance measurements

TL;DR

This paper demonstrates that conductance measurements can directly probe the topological band structure of diffusive multiterminal Josephson junctions, revealing the evolution of their quasiparticle spectra with phase differences.

Contribution

It introduces a method to experimentally access the topological band structure of multiterminal Josephson junctions through conductance measurements.

Findings

Conductance measurements reveal the density of states at the Fermi energy.

The method allows rapid characterization of the energy spectrum.

The approach can identify topological features in the band structure.

Abstract

The energy of an Andreev bound state in a clean normal metal in contact with two superconductors disperses with the difference $\Delta \phi$ in the superconducting phase between the superconductors in much the same way as the energies of electrons in a one-dimensional crystal disperse with the crystal momentum $k$ of the electrons. A normal metal with $n$ superconductors maps on to a $n-1$ dimensional crystal, each dimension corresponding to the phase difference $\phi_i$ between a specific pair of superconductors. The resulting band structure as a function of the phase differences $\{\Delta \phi_i\}$ has been proposed to have a topological nature, with gapped regions characterized by different Chern numbers separated by regions where the gap in the quasiparticle spectrum closes. A similar complex evolution of the quasiparticle spectrum with $\{\Delta \phi_i\}$ has also been predicted for diffusive normal metals in contact with multiple superconductors. Here we show that the variation of the density of states at the Fermi energy of such a system can be directly probed by relatively simple conductance measurements, allowing rapid characterization of the energy spectrum.