engleski

Strange metal transport in FeSe1-xSx

The “normal” metallic state of many unconventional superconductors is in fact highly unconventional with many physical properties showing marked deviations from standard Fermi liquid (FL) theory. This so-called strange metallic behavior is believed to be governed by proximity to a quantum critical point (QCP) where critical fluctuations of the associated order parameter give rise to additional scattering of quasiparticles pushing the system towards the Planckian dissipation limit – maximum dissipation allowed by quantum mechanics. Interestingly, instead of reaching the QCP, many systems go superconducting (SC) with the maximum SC transition temperature occurring precisely at the point where the QCP would occur in the absence of superconductivity. It is therefore believed that unconventional superconductivity, strange metallic behavior and quantum criticality are intimately related phenomena. Here, we present our recent magnetotransport study of FeSe1-xSx, which is unique among unconventional superconductors in that the strange metallic behavior is likely to be governed by a purely nematic phase that is postulated to vanish at a QCP at xc ~ 0.17. Classic signatures of quantum criticality around xc were revealed upon suppressing superconductivity with a high magnetic field, including: a) a T-linear resistivity extending down to the lowest accessible temperatures at the QCP, b) standard quadratic T-dependence away from the QCP with c) a coefficient that is enhanced upon approach to the QCP. Our subsequent high-field transverse magnetoresistance (MR) study revealed the presence of two distinct components in the MR, one conventional, the other quantum critical. A complementary high-field Hall effect study, performed on the same series of single crystals, revealed a Hall response similarly delineated into two components with distinct field dependences. Finally, analysis of the magnetotransport in terms of a hot-spot model sheds new light on the strange metallic behaviour in FeSe1-xSx, in particular the origin of lifetime separation seen in the low-field Hall response.

unconventional superconductivity ; Fermi liquid ; strange metal ; quantum critical point ; Planckian dissipation ; FeSe1-xSx ; nematicity ; T-linear resistivity ; magnetoresistance ; Hall effect ; hot spot model ; lifetime separation

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