Metal-insulator transition via control of spin liquidity in a doped Mott insulator

TL;DR

This study demonstrates how controlling spin liquidity and lattice geometry in a doped Mott insulator induces a transition from insulating to metallic states, highlighting the role of spin frustration in charge delocalization.

Contribution

It introduces a new method combining uniaxial and hydrostatic pressures to explore spin-charge entanglement effects in doped Mott insulators.

Findings

Electronic state changes from insulator to Fermi liquid with frustration variation.

Spin liquidity enhances charge delocalization.

Frustration in spin degrees impacts charge transport.

Abstract

Quantum spin liquid states, in which spins are quantum-mechanically delocalized in direction, have been so far studied for charge-localized Mott insulators arising from strong repulsive interaction. Recently, however, it was found that the doped Mott insulator with a triangular lattice, $\kappa$-(ET)$_4$Hg$_{2.89}$Br$_8$, exhibits both spin-liquid-like magnetism and metallic electrical conduction. Thus, it is now possible to experimentally explore how the spin liquidity affects the electrical conduction, an issue that has received a great deal of theoretical attention. Here, with a newly developed method to combine uniaxial and hydrostatic pressures, we investigate the electrical conduction in the doped Mott insulator with controlling the triangular lattice geometry and the repulsion strength which determines the spin-liquidity and Mottness, respectively. We found that, in a strongly interacting regime, the electronic state drastically changes from an insulator to a Fermi liquid via a non-Fermi liquid with varying geometrical frustration, which suggests that spin liquidity promotes delocalization of charges. This result indicates that frustration in spin degrees of freedom has a decisive impact on the transport of charges through the entanglement of spin and charge in a doped Mott insulator.