Possible observation of Leggett-like modes in a coherent two-phase medium

Abstract

Spontaneous symmetry breaking is a ubiquitous phenomenon in physics responsible for various collective modes. Collective excitations predicted by Leggett in 1966 are specific for multiband superfluids and reflect oscillations of the relative phase of different band components. In this work, we argue that such modes should exist also in a multiphase medium with a coherent Josephson-like coupling between the different superconducting components. Point-contact experiments on superconducting ceramics formed by grains of two bismuth-based superconducting oxides with transition temperatures of about 70 and 100 K made it possible to reveal multiple periodic conductance peaks, which we have attributed to elastic scatterings by a Leggett-like mode inherent in the studied two-phase samples. We believe there should be a large group of superconducting materials where such modes could exist and assert that point-contact spectroscopy is one of the best ways to identify and characterize them.