Non-Fermi liquid transport and strong mass enhancement near the nematic quantum critical point in FeSe$_x$Te$_{1-x}$ thin films

TL;DR

This study reveals that nematic fluctuations near a quantum critical point in FeSe$_x$Te$_{1-x}$ thin films cause non-Fermi liquid transport behavior and strong mass enhancement, impacting both normal and superconducting states.

Contribution

It provides direct experimental evidence linking nematic quantum criticality to non-Fermi liquid behavior and mass enhancement in FeSe$_x$Te$_{1-x}$ thin films.

Findings

Observation of linear resistivity and divergent thermoelectricity near the QCP.

Sharp thermoelectric peak at the nematic quantum critical point.

Crossover of pair-breaking mechanisms indicating mass enhancement.

Abstract

Unconventional superconductivity is often accompanied by non-Fermi liquid (NFL) behavior, which emerges near a quantum critical point (QCP) - a point where an electronic ordered phase is terminated at absolute zero under non-thermal parameters. While nematic orders, characterized by broken rotational symmetry, are sometimes found in unconventional superconductors, the role of nematic fluctuations in driving NFL transport behavior remains unclear. Here, we investigated electrical and thermoelectric transport properties in FeSe$_x$Te$_{1-x}$ thin films and observed hallmark NFL behavior: temperature-linear resistivity and logarithmic divergence of thermoelectricity at low temperatures. Notably, the thermoelectricity peaks sharply at the nematic QCP ($x$ = 0.45), highlighting the dominant role of nematic fluctuations in the NFL transport. Furthermore, we found that the pair-breaking mechanisms in the superconducting phase crosses over from orbital- to Pauli-limited effects, indicating the mass enhancement near the nematic critical regime. These findings reveal the profound impact of nematic fluctuations on both normal-state transport and superconducting properties.