Field induced density wave in a kagome superconductor

TL;DR

This study reveals a novel field-induced phase transition in the kagome superconductor KV3Sb5, involving a coexistence of charge density wave states and broken symmetry, driven by magnetic field effects.

Contribution

It introduces a minimal theoretical model explaining the emergence of an incommensurate CDW state under high magnetic fields in kagome superconductors.

Findings

Discovery of a hysteretic anomaly in resistivity below 6 K.

Observation of a change in electronic symmetry with magnetic field.

Evidence of a coexisting or nearly degenerate broken symmetry state.

Abstract

On the kagome lattice, electrons benefit from the simultaneous presence of band topology, flat electronic bands, and van Hove singularities, forming competing or cooperating orders. Understanding the interrelation between these distinct order parameters remains a significant challenge, leaving much of the associated physics unexplored. In the kagome superconductor KV3Sb5, which exhibits a charge density wave (CDW) state below T = 78 K, we uncover an unpredicted field-induced phase transition below 6 K. The observed transition is marked by a hysteretic anomaly in the resistivity, nonlinear electrical transport, and a change in the symmetry of the electronic response as probed via the angular dependence of the magnetoresistivity. These observations surprisingly suggest the emergence of an unanticipated broken symmetry state coexisting with the original CDW. To understand this experimental observation, we developed a theoretical minimal model for the normal state inside the high-temperature parent CDW phase where an incommensurate CDW order emerges as an instability sub-leading to superconductivity. The incommensurate CDW emerges when superconducting fluctuations become fully suppressed by large magnetic fields. Our results suggest that, in kagome superconductors, quantum states can either coexist or are nearly degenerate in energy, indicating that these are rich platforms to expose new correlated phenomena.