STRANGE METAL TRANSPORT IN THE ELECTRONIC NEMATIC FeSe_1-xS_x

Matija Čulo, Salvatore Licciardello, and Nigel Hussey, HFML.

Researchers from HFML, UK, USA, and Japan have carried out a detailed magnetotransport study of the electronic nematic superconductor FeSe_1-xS_x that reveals key signatures of the so-called ‘strange metal’ behavior in vicinity of its nematic quantum critical point (QCP) x_с ≈ 0.17. More importantly, the work points towards the co-existence of two distinct charge sectors in the normal (i.e., nonsuperconducting) state, a conventional (Fermi-liquid) component and a strange metal component. The change in the electrical resistivity with temperature and magnetic field provides crucial information on the nature of charge transport within a material. In ordinary metals, resistivity scales as the square of both temperature and field. In strange metals, however, the resistivity shows a peculiar linear dependence in both quantities. The origin of this linear dependence is still not understood, though it appears to arise in metals close to a zero-temperature phase transition between ordered and disordered phases, i.e., a QCP. Until now, these two forms of magnetotransport behavior, standard quadratic and ‘strange metallic’ linear, have only been observed in isolation, never together, suggesting that they are associated with different limits, i.e., near or far from the QCP. Here, the team measured both the high-field magnetoresistance and Hall response of iron chalcogenide FeSe_1-xS_x which uniquely, as a function of sulfur doping, passes through a QCP of a pure electronic nematic origin (i.e., without accompanying magnetism). Their magnetoresistance study revealed the coexistence of both the quadratic and linear forms of the magnetoresistance; the latter evolving in a manner determined by the proximity to the nematic QCP (blue squares in figure). The Hall response was also found to comprise both the conventional and the strange component, the latter exhibiting a peculiar exponential decay at high fields and a 1/T divergence upon approach to the QCP (red circles in central panel of figure). This 1/T divergence of the Hall response provides a possible explanation for the phenomenon of (transport and Hall) lifetime separation observed in other strange metal candidates. The combined study presents a new paradigm in the transport behavior of correlated electron systems by revealing, in contrast to common preconceptions, the possibility of the coexistence of conventional and strange charge sectors in such systems. The key step now is to understand how such dual character emerges.

Figure: Magnetotransport properties of the strange metal (SM)component in FeSe_1-xS_x. Red circles show the T dependence of the maximum in the Hall resistivity ρ^SM_yx (H) normalized to its value at 30 K (left axis) and the blue squares β_SM, the slope of the field-linear magnetoresistance, similarly normalized (right axis). The greyscale schematically represents the exponent a in the T dependence of the resistivity ρ(T) ∝ Ta. Here, dark grey represents a = 1, i.e., the ‘strange metallic’ linear T dependence, and white represents a = 2, i.e., standard Fermi-liquid quadratic T dependence. Note, how both quantities peak upon approach to the nematic QCP where T-linear resistivity persists down to the lowest accessible temperatures.

Putative Hall response of the strange metal component in FeSe_1-xS_x, M. Čulo, M. Berben, Y.-T. Hsu, J. Ayres, R. D. H. Hinlopen, S. Kasahara, Y. Matsuda, T. Shibauchi, and N. E. Hussey, Phys. Rev. Research 3, 023069 (2021).

https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.3.023069

Contact: nigel.hussey@ru.nl