Pure Nematic Quantum Criticality in FeSe_1-xTe_x superconductor

The role of a quantum critical point (QCP) in unconventional superconductors has been a subject of extensive debate for decades. In particular, the quantum criticality of the electronic nematic phase, a correlated state that spontaneously breaks rotational symmetry while preserving translation symmetry, has yet to be conclusively demonstrated experimentally, as electronic nematicity in most real materials is often intertwined with other charge or spin density wave orders. In this work, we will discuss the quantum criticality of a pure electronic nematic phase in the iron-based superconductor FeSe_1-xTe_x, which is decoupled from both charge and spin degree of freedom. Elastoresistivity measurements provide considerable evidence for a pure nematic QCP accompanied by a superconducting dome [1]. Notably, even under the high magnetic field, the superconducting dome remains straddling this nematic QCP. Further analysis of the upper critical field reveals that the Pauli-limiting field is enhanced toward the QCP, indicating that the pairing interaction is strengthened by nematic critical fluctuations [2]. Moreover, low temperature form of the normal-state resistivity, unmasked under the high magnetic field, exhibits strange metal behavior over an extended range of the phase diagram, with a scattering rate that approximately scales with the superconducting transition temperature [3].

[1] K. Ishida et al., PNAS 119, e2110501119 (2022). [2] K. Mukasa*, K. Ishida* et al., Phys. Rev. X 13, 011032 (2023). [3] K. Ishida*, K. Mukasa* et al., preprint