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Abstract
The existence of a nematic phase transition in iron-chalcogenide superconductors poses an intriguing question about its impact on superconductivity. To understand the nature of this unique quantum phase transition, it is essential to study how the electronic structure changes across this transition at low temperatures. Here, we investigate the evolution of the Fermi surfaces and electronic interactions across the nematic phase transition of FeSe1−xSx using Shubnikov-de Haas oscillations in high magnetic fields up to 45 T in the low temperature regime down to 0.4 K. Most of the Fermi surfaces of FeSe1−xSx monotonically increase in size except for a prominent low frequency oscillation associated with a small, but highly mobile band, which disappears at the nematic phase boundary near x ~ 0.17, indicative of a topological Lifshitz transition. The quasiparticle masses are larger inside the nematic phase, indicative of a strongly correlated state, but they become suppressed outside it. The experimentally observed changes in the Fermi surface topology, together with the varying degree of electronic correlations, will change the balance of electronic interactions in the multi-band system FeSe1−xSx and promote different kz-dependent superconducting pairing channels inside and outside the nematic phase.
Highlights
Nematic electronic order is believed to play an important role in the phenomenology of superconductivity in iron-based and copper oxide superconductors.[1,2] FeSe is an ideal system to study nematicity, in the absence of long-range magnetism, which manifests itself in substantial distortions of the Fermi surfaces,[3,4] as well as a strong twofold anisotropy, detected in quasiparticle interference spectra.[5]
A clean route to investigate the interplay between nematicity, magnetism and superconductivity in FeSe is using chemical pressure-induced by isoelectronic substitution of selenium with sulphur in FeSe1−xSx, which suppresses both the nematic phase transition temperature and its related electronic anisotropies.[9,10]
Chemical pressure could mimic the effect of applied hydrostatic pressure by bringing the FeSe layers closer together, increasing the bandwidth and suppressing the electronic correlations towards FeS, as found recently by angle resolved photoemission spectroscopy (ARPES).[11]
Summary
Nematic electronic order is believed to play an important role in the phenomenology of superconductivity in iron-based and copper oxide superconductors.[1,2] FeSe is an ideal system to study nematicity, in the absence of long-range magnetism, which manifests itself in substantial distortions of the Fermi surfaces,[3,4] as well as a strong twofold anisotropy, detected in quasiparticle interference spectra.[5].
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