Mott transition and superconductivity in the strongly correlated organic superconductor $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}]$Br

TL;DR

This study investigates how magnetic fields influence the phase diagram of a strongly correlated organic superconductor, revealing the behavior of the Mott transition and superconductivity under varying conditions.

Contribution

It experimentally determines the lower critical point of the Mott transition and its relation to the superconducting phase diagram in the organic superconductor.

Findings

Lower critical point of Mott transition identified in magnetic fields.

The Mott transition curve reaches zero temperature at high magnetic fields.

The lower critical end point shifts to lower temperatures with suppressed superconductivity.

Abstract

The magnetic field effect on the phase diagram of the organic Mott system $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br in which the bandwidth was tuned by the substitution of deuterated molecules was studied by means of the resistivity measurements performed in magnetic fields. The lower critical point of the first-order Mott transition, which ended on the upper critical field $H_{\rm c2}$-temperature plane of the superconductivity, was determined experimentally in addition to the previously observed upper critical end point. The lower critical end point moved to a lower temperature with the suppression of $T_{\rm c}$ in magnetic fields and the Mott transition recognized so far as the $S$-shaped curve reached $T =$ 0 when $H > H_{\rm c2}$ in the end.