Quasiparticle excitations in the ultra-nodal pairing state of tetragonal FeSe<sub>1-x</sub>S
ORAL
Abstract
The isovalently substituted superconductor FeSe1-xSx has attracted significant attention owing to its rich interplay among nematicity, magnetism, and unconventional superconductivity [1]. Of particular interest is the abrupt change in the superconducting gap function that occurs at the nematic critical point at xc ~ 0.17 [2-6]. In tetragonal FeSe1-xSx, a large residual density of states has been observed by various experimental probes, including specific heat, thermal conductivity, and scanning tunneling spectroscopy, indicating the presence of numerous quasiparticles even deep in the superconducting state. Although various theoretical models have been proposed --- including the formation of an “ultra-nodal” pairing state with a Bogoliubov Fermi surface [7], the effect of soft nematic fluctuations [8], and competition with magnetism [9] --- the nature of this anomalous pairing state in tetragonal FeSe1-xSx remains largely elusive. Here, using high-quality single crystals of FeSe1-xSx we report detailed field dependences of the longitudinal and transverse thermal conductivities. The thermal Hall effect reveals dominant quasiparticle excitations arising from the Femi pockets. Together with the results of high-resolution heat-capacity measurements. we discuss the nature of quasiparticle excitations in the ultra-nodal pairing state of tetragonal FeSe1-xSx.
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[1] T. Shibauchi, T. Hanaguri, Y. Matsuda, J. Phys. Soc. Jpn. 89, 102002 (2020).
[2] S. Hosoi et al., Proc. Natl. Acad. Sci. U.S.A. 113, 8139 (2016).
[3] Y. Sato et al., Proc. Natl. Acad. Sci. U.S.A. 115, 1227 (2018).
[4] T. Hanaguri et al., Sci. Adv. 4, eaar6419 (2018).
[5] T. Matsuura et al., Proc. Natl. Acad. Sci. U.S.A. 120, e2208276120 (2023).
[6] T. Nagashima et al., https://doi.org/10.21203/rs.3.rs-2224728/v1
[7] C. Setty et al., Nat. Commun. 11, 523 (2020); Phys. Rev. B 102, 064504 (2020).
[9] K. R. Islam and A. Chubukov, npj Quantum Mater. 9, 28 (2024).
[10] H. Wu et al., Phys. Rev. B 109, L220501 (2024)
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Presenters
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Shigeru Kasahara
- Okayama Univ