Failed superconductivity in a Mott spin liquid material

TL;DR

This study investigates why global superconductivity does not develop in a Mott spin liquid material, revealing inhomogeneous superconducting domains and quantum fluctuations that shed light on the phenomenon of failed superconductivity.

Contribution

It provides new insights into failed superconductivity by demonstrating the presence of superconducting domains and quantum phase fluctuations in a Mott spin liquid system.

Findings

Superconducting fluctuations appear in the phase coexistence region.

Global superconductivity fails to establish at low temperatures.

Universal conductance fluctuations are observed at high magnetic fields.

Abstract

A central challenge for understanding unconventional superconductivity in most strongly correlated electronic materials is their complicated band structure and presence of competing orders. In contrast, quasi-two-dimensional organic spin liquids are single-band systems with superconductivity arising near the bandwidth-tuned Mott metal-insulator transition in the absence of other orders. Here, we study chemically substituted $\kappa$-organics in which superconducting fluctuations emerge in the phase coexistence region between the Mott insulator and the Fermi liquid. Using magnetotransport and ac susceptibility measurements, we find that global superconductivity fails to set in as temperature $T\rightarrow 0$. Our results indicate instead the presence of superconducting domains embedded in the metallic percolating cluster that undergo a magnetic field-tuned quantum superconductor-to-metal phase transition. Surprisingly, albeit consistent with the percolation picture, universal conductance fluctuations are seen at high fields in macroscopic samples. The observed interplay of the intrinsic inhomogeneity and quantum phase fluctuations provides a new insight into failed superconductivity, a phenomenon seen in various conventional and unconventional superconductors, including cuprates.