Coupling of structure to magnetic and superconducting orders in quasi-one-dimensional $\text{K}_2\text{Cr}_3\text{As}_3$

TL;DR

This study reveals that the quasi-one-dimensional superconductor K2Cr3As3 exhibits short-range magnetic fluctuations and lattice coupling near its superconducting transition, indicating proximity to magnetic instability and competition with superconductivity.

Contribution

First neutron scattering evidence of magnetic fluctuations and lattice response in K2Cr3As3, linking magnetic order to superconductivity in this novel family.

Findings

Neutron diffraction shows lattice response at T_c.

Inelastic scattering reveals magnetic fluctuations at q=(00½).

Magnetic fluctuations diminish below T_c, indicating competition with superconductivity.

Abstract

Quasi-one-dimensional $A_2\text{Cr}_3\text{As}_3$ (with $A = \text{K, Cs, Rb}$) is an intriguing new family of superconductors which exhibit many similar features to the cuprate and iron-based unconventional superconductor families. Yet in contrast to these systems, no charge or magnetic ordering has been observed which could provide the electronic correlations presumed necessary for an unconventional superconducting pairing mechanism - an absence which defies predictions of first principles models. We report the results of neutron scattering experiments on polycrystalline $\text{K}_2\text{Cr}_3\text{As}_3$ $(T_c \sim 7\text{K})$ which probed the low temperature dynamics near $T_c$ . Neutron diffraction data evidence a strong response of the nuclear lattice to the onset of superconductivity while inelastic scattering reveals a highly dispersive column of intensity at the commensurate wavevector $q = (00\frac{1}{2})$ which loses intensity beneath $T_c$ - indicative of short-range magnetic fluctuations. Using linear spin-wave theory we model the observed scattering and suggest a possible structure to the short-range magnetic order. These observations suggest that $\text{K}_2\text{Cr}_3\text{As}_3$ is in close proximity to a magnetic instability and that the incipient magnetic order both couples strongly to the lattice and competes with superconductivity - in direct analogy with the iron-based superconductors.