The Elusive Bose Metal

TL;DR

This paper discusses the unexpected metallic phase observed in low-dimensional systems, challenging traditional theories by analyzing experiments and theories suggesting a bosonic, possibly glassy, nature of this phase.

Contribution

It provides a comprehensive analysis of experimental evidence and theoretical proposals for the bosonic Bose metal phase in low-dimensional systems.

Findings

Experimental evidence supports a bosonic metallic phase between superconductor and insulator.

Theoretical models include glassy states as a possible explanation for the Bose metal.

Implications for vortex glass states in high-temperature superconductors are explored.

Abstract

The conventional theory of metals is in crisis. In the last 15 years, there has been an unexpected sprouting of metallic states in low dimensional systems directly contradicting conventional wisdom. For example, bosons are thought to exist in one of two ground states: condensed in a superconductor or localized in an insulator. However, several experiments on thin metal alloy films have observed that a metallic phase disrupts the direct transition between the superconductor and the insulator. We analyze the experiments on the insulator-superconductor transition and argue that the intervening metallic phase is bosonic. All relevant theoretical proposals for the Bose metal are discussed, particularly the recent idea that the metallic phase is glassy. The implications for the putative vortex glass state in the copper-oxide superconductors are examined.