Recent high-magnetic-field studies of unusual groundstates in quasi-two-dimensional crystalline organic metals and superconductors

TL;DR

This paper explores exotic high-magnetic-field phases in quasi-two-dimensional organic metals and superconductors, revealing a modulated charge-density-wave state and persistent current phenomena indicative of a new quantum state of matter.

Contribution

It reports the discovery of a modulated CDW phase and persistent current effects in organic conductors under high magnetic fields, advancing understanding of their groundstates.

Findings

Evidence of a fully gapped CDW state above the Pauli limit

Observation of persistent currents similar to superconductors

Detection of flux quantization and edge confinement of Hall potential

Abstract

After a brief introduction to crystalline organic superconductors and metals, we shall describe two recently-observed exotic phases that occur only in high magnetic fields. The first involves measurements of the non-linear electrical resistance of single crystals of the charge-density-wave (CDW) system (Per)$_2$Au(mnt)$_2$ in static magnetic fields of up to 45 T and temperatures as low as 25 mK. The presence of a fully gapped CDW state with typical CDW electrodynamics at fields higher that the Pauli paramagnetic limit of 34 T suggests the existence of a modulated CDW phase analogous to the Fulde-Ferrell-Larkin-Ovchinnikov state. Secondly, measurements of the Hall potential of single crystals of $\alpha$-(BEDT-TTF)$_2$KHg(SCN)$_4$, made using a variant of the Corbino geometry in quasistatic magnetic fields, show persistent current effects that are similar to those observed in conventional superconductors. The longevity of the currents, large Hall angle, flux quantization and confinement of the reactive component of the Hall potential to the edge of the sample are all consistent with the realization of a new state of matter in CDW systems with significant orbital quantization effects in strong magnetic fields.