Absence of cyclotron resonance in the anomalous metallic phase in InO$_x$

TL;DR

This study reveals that the anomalous metallic phase in weakly disordered InO$_x$ films lacks cyclotron resonance, indicating non-Drude behavior and strong phase fluctuations, challenging conventional Fermi liquid theories.

Contribution

It demonstrates the absence of cyclotron resonance in the anomalous metallic phase of InO$_x$, highlighting non-Fermi liquid properties and the role of short-range superconducting correlations.

Findings

No cyclotron resonance observed in the anomalous metal phase.

Microwave conductivity shows signatures of superconducting correlations.

Emergent particle-hole symmetry indicates non-Fermi liquid behavior.

Abstract

It is observed that many thin superconducting films with not too high disorder level (generally R$_N/\Box \leq 2000 \Omega$) placed in magnetic field show an anomalous metallic phase where the resistance is low but still finite as temperature goes to zero. Here we report in weakly disordered amorphous InO$_x$ thin films, that this "Bose metal" metal phase possesses no cyclotron resonance and hence non-Drude electrodynamics. Its microwave dynamical conductivity shows signatures of remaining short-range superconducting correlations and strong phase fluctuations through the whole anomalous regime. The absence of a finite frequency resonant mode can be associated with a vanishing downstream component of the vortex current parallel to the supercurrent and an emergent particle-hole symmetry of this anomalous metal, which establishes its non-Fermi liquid character.