Two superconducting states with broken time-reversal symmetry in FeSe1-xSx

Kohei Matsuura; Masaki Roppongi; Mingwei Qiu; Qi Sheng; Yipeng Cai; Kohtaro Yamakawa; Zurab Guguchia; Ryan P. Day; Kenji M. Kojima; Andrea Damascelli; Yuichi Sugimura; Mikihiko Saito; Takaaki Takenaka; Kota Ishihara; Yuta Mizukami; Kenichiro Hashimoto; Yilun Gu; Shengli Guo; Licheng Fu; Zheneng Zhang; Fanlong Ning; Guoqiang Zhao; Guangyang Dai; Changqing Jin; James W. Beare; Graeme M. Luke; Yasutomo J. Uemura; Takasada Shibauchi

doi:10.1073/pnas.2208276120

Two superconducting states with broken time-reversal symmetry in FeSe_1-xS_x

Kohei Matsuura, Masaki Roppongi, Mingwei Qiu, Qi Sheng, Yipeng Cai, Kohtaro Yamakawa, Zurab Guguchia, Ryan P. Day, Kenji M. Kojima, Andrea Damascelli, Yuichi Sugimura, Mikihiko Saito, Takaaki Takenaka, Kota Ishihara, Yuta Mizukami, Kenichiro Hashimoto, Yilun Gu, Shengli Guo, Licheng Fu, Zheneng ZhangFanlong Ning, Guoqiang Zhao, Guangyang Dai, Changqing Jin, James W. Beare, Graeme M. Luke, Yasutomo J. Uemura, Takasada Shibauchi

Research output: Contribution to journal › Article › peer-review

9 Scopus citations

Abstract

Iron-chalcogenide superconductors FeSe1-xSx possess unique electronic properties such as nonmagnetic nematic order and its quantum critical point. The nature of superconductivity with such nematicity is important for understanding the mechanism of unconventional superconductivity. A recent theory suggested the possible emergence of a fundamentally new class of superconductivity with the so-called Bogoliubov Fermi surfaces (BFSs) in this system. However, such an ultranodal pair state requires broken time-reversal symmetry (TRS) in the superconducting state, which has not been observed experimentally. Here, we report muon spin relaxation (μSR) measurements in FeSe1-xSx superconductors for 0 ≤ x ≤ 0:22 covering both orthorhombic (nematic) and tetragonal phases. We find that the zero-field muon relaxation rate is enhanced below the superconducting transition temperature Tc for all compositions, indicating that the superconducting state breaks TRS both in the nematic and tetragonal phases. Moreover, the transverse-field μSR measurements reveal that the superfluid density shows an unexpected and substantial reduction in the tetragonal phase (x > 0:17). This implies that a significant fraction of electrons remain unpaired in the zero-temperature limit, which cannot be explained by the known unconventional superconducting states with point or line nodes. The TRS breaking and the suppressed superfluid density in the tetragonal phase, together with the reported enhanced zeroenergy excitations, are consistent with the ultranodal pair state with BFSs. The present results reveal two different superconducting states with broken TRS separated by the nematic critical point in FeSe1-xSx, which calls for the theory of microscopic origins that account for the relation between nematicity and superconductivity.

Original language	English
Article number	e2208276120
Journal	Proceedings of the National Academy of Sciences of the United States of America
Volume	120
Issue number	21
DOIs	https://doi.org/10.1073/pnas.2208276120
State	Published - 2023
Externally published	Yes

Funding

ACKNOWLEDGMENTS. We thank D. F. Agterberg, P. M. R. Brydon, R. M. Fernandes, T. Hanaguri, P. J. Hirschfeld, K. Kuboki, Y. Matsuda, E.-G. Moon, C. Setty, and M. Sigrist for fruitful discussions. This work was supported by Grants-in-Aid for Scientific Research (Nos. JP22H00105, JP21H01793, JP19H00649, JP18H05227, and JP18KK0375), Grant-in-Aid for Scientific Research on innovative areas “Quantum Liquid Crystals” (No. JP19H05824) and Grant-in-Aid for Scientific Research for Transformative Research Areas (A) “Condensed Conjugation” (No. JP20H05869) from Japan Society for the Promotion of Science, and CREST (No. JPMJCR19T5) from Japan Science and Technology. The work at Columbia and TRIUMF has been supported by the US NSF Grant Nos. DMR-2104661, DMR-1610633, and the DMREF Project No. DMR-1436095, the Reimei Project from the Japan Atomic Energy Agency, andasupportfromtheFriendsofTokyoUniversityInc.G.Q.Z.hasbeensupported in part by CAS Project for Young Scientists in Basic Research (2022YSBR-048). ThisresearchwasundertakenthanksinparttofundingfromtheMaxPlanck-UBC- We thank D. F. Agterberg, P. M. R. Brydon, R. M. Fernandes, T. Hanaguri, P. J. Hirschfeld, K. Kuboki, Y. Matsuda, E.-G. Moon, C. Setty, and M. Sigrist for fruitful discussions. This work was supported by Grants-in-Aid for Scientific Research (Nos. JP22H00105, JP21H01793, JP19H00649, JP18H05227, and JP18KK0375), Grant-in-Aid for Scientific Research on innovative areas "Quantum Liquid Crystals" (No. JP19H05824) and Grant-in-Aid for Scientific Research for Transformative Research Areas (A) "Condensed Conjugation" (No. JP20H05869) from Japan Society for the Promotion of Science, and CREST (No. JPMJCR19T5) from Japan Science and Technology. The work at Columbia and TRIUMF has been supported by the USNSF Grant Nos. DMR-2104661, DMR-1610633, and the DMREF Project No. DMR-1436095, the Reimei Project from the Japan Atomic Energy Agency, anda support from the Friends of Tokyo University Inc. G.Q.Z. has been supported in part by CAS Project for Young Scientists in Basic Research (2022YSBR-048). This research was under taken thanks in part to funding from the Max Planck-UBC-UTokyo Centre for Quantum Materials and the Canada First Research Excellence Fund, Quantum Materials and Future Technologies Program.

Keywords

Bogoliubov Fermi surface
iron-based superconductors
muon spin relaxation
superconducting gap
unconventional superconductivity

Access to Document

10.1073/pnas.2208276120

Cite this

Matsuura, K., Roppongi, M., Qiu, M., Sheng, Q., Cai, Y., Yamakawa, K., Guguchia, Z., Day, R. P., Kojima, K. M., Damascelli, A., Sugimura, Y., Saito, M., Takenaka, T., Ishihara, K., Mizukami, Y., Hashimoto, K., Gu, Y., Guo, S., Fu, L., ... Shibauchi, T. (2023). Two superconducting states with broken time-reversal symmetry in FeSe_1-xS_x. Proceedings of the National Academy of Sciences of the United States of America, 120(21), Article e2208276120. https://doi.org/10.1073/pnas.2208276120

@article{094b491cd4474166ae27903d80b71bbf,

title = "Two superconducting states with broken time-reversal symmetry in FeSe1-xSx",

abstract = "Iron-chalcogenide superconductors FeSe1-xSx possess unique electronic properties such as nonmagnetic nematic order and its quantum critical point. The nature of superconductivity with such nematicity is important for understanding the mechanism of unconventional superconductivity. A recent theory suggested the possible emergence of a fundamentally new class of superconductivity with the so-called Bogoliubov Fermi surfaces (BFSs) in this system. However, such an ultranodal pair state requires broken time-reversal symmetry (TRS) in the superconducting state, which has not been observed experimentally. Here, we report muon spin relaxation (μSR) measurements in FeSe1-xSx superconductors for 0 ≤ x ≤ 0:22 covering both orthorhombic (nematic) and tetragonal phases. We find that the zero-field muon relaxation rate is enhanced below the superconducting transition temperature Tc for all compositions, indicating that the superconducting state breaks TRS both in the nematic and tetragonal phases. Moreover, the transverse-field μSR measurements reveal that the superfluid density shows an unexpected and substantial reduction in the tetragonal phase (x > 0:17). This implies that a significant fraction of electrons remain unpaired in the zero-temperature limit, which cannot be explained by the known unconventional superconducting states with point or line nodes. The TRS breaking and the suppressed superfluid density in the tetragonal phase, together with the reported enhanced zeroenergy excitations, are consistent with the ultranodal pair state with BFSs. The present results reveal two different superconducting states with broken TRS separated by the nematic critical point in FeSe1-xSx, which calls for the theory of microscopic origins that account for the relation between nematicity and superconductivity.",

keywords = "Bogoliubov Fermi surface, iron-based superconductors, muon spin relaxation, superconducting gap, unconventional superconductivity",

author = "Kohei Matsuura and Masaki Roppongi and Mingwei Qiu and Qi Sheng and Yipeng Cai and Kohtaro Yamakawa and Zurab Guguchia and Day, {Ryan P.} and Kojima, {Kenji M.} and Andrea Damascelli and Yuichi Sugimura and Mikihiko Saito and Takaaki Takenaka and Kota Ishihara and Yuta Mizukami and Kenichiro Hashimoto and Yilun Gu and Shengli Guo and Licheng Fu and Zheneng Zhang and Fanlong Ning and Guoqiang Zhao and Guangyang Dai and Changqing Jin and Beare, {James W.} and Luke, {Graeme M.} and Uemura, {Yasutomo J.} and Takasada Shibauchi",

note = "Publisher Copyright: Copyright {\textcopyright} 2023 the Author(s).",

year = "2023",

doi = "10.1073/pnas.2208276120",

language = "English",

volume = "120",

journal = "Proceedings of the National Academy of Sciences of the United States of America",

issn = "0027-8424",

publisher = "National Academy of Sciences",

number = "21",

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Matsuura, K, Roppongi, M, Qiu, M, Sheng, Q, Cai, Y, Yamakawa, K, Guguchia, Z, Day, RP, Kojima, KM, Damascelli, A, Sugimura, Y, Saito, M, Takenaka, T, Ishihara, K, Mizukami, Y, Hashimoto, K, Gu, Y, Guo, S, Fu, L, Zhang, Z, Ning, F, Zhao, G, Dai, G, Jin, C, Beare, JW, Luke, GM, Uemura, YJ & Shibauchi, T 2023, 'Two superconducting states with broken time-reversal symmetry in FeSe_1-xS_x', Proceedings of the National Academy of Sciences of the United States of America, vol. 120, no. 21, e2208276120. https://doi.org/10.1073/pnas.2208276120

TY - JOUR

T1 - Two superconducting states with broken time-reversal symmetry in FeSe1-xSx

AU - Matsuura, Kohei

AU - Roppongi, Masaki

AU - Qiu, Mingwei

AU - Sheng, Qi

AU - Cai, Yipeng

AU - Yamakawa, Kohtaro

AU - Guguchia, Zurab

AU - Day, Ryan P.

AU - Kojima, Kenji M.

AU - Damascelli, Andrea

AU - Sugimura, Yuichi

AU - Saito, Mikihiko

AU - Takenaka, Takaaki

AU - Ishihara, Kota

AU - Mizukami, Yuta

AU - Hashimoto, Kenichiro

AU - Gu, Yilun

AU - Guo, Shengli

AU - Fu, Licheng

AU - Zhang, Zheneng

AU - Ning, Fanlong

AU - Zhao, Guoqiang

AU - Dai, Guangyang

AU - Jin, Changqing

AU - Beare, James W.

AU - Luke, Graeme M.

AU - Uemura, Yasutomo J.

AU - Shibauchi, Takasada

PY - 2023

Y1 - 2023

N2 - Iron-chalcogenide superconductors FeSe1-xSx possess unique electronic properties such as nonmagnetic nematic order and its quantum critical point. The nature of superconductivity with such nematicity is important for understanding the mechanism of unconventional superconductivity. A recent theory suggested the possible emergence of a fundamentally new class of superconductivity with the so-called Bogoliubov Fermi surfaces (BFSs) in this system. However, such an ultranodal pair state requires broken time-reversal symmetry (TRS) in the superconducting state, which has not been observed experimentally. Here, we report muon spin relaxation (μSR) measurements in FeSe1-xSx superconductors for 0 ≤ x ≤ 0:22 covering both orthorhombic (nematic) and tetragonal phases. We find that the zero-field muon relaxation rate is enhanced below the superconducting transition temperature Tc for all compositions, indicating that the superconducting state breaks TRS both in the nematic and tetragonal phases. Moreover, the transverse-field μSR measurements reveal that the superfluid density shows an unexpected and substantial reduction in the tetragonal phase (x > 0:17). This implies that a significant fraction of electrons remain unpaired in the zero-temperature limit, which cannot be explained by the known unconventional superconducting states with point or line nodes. The TRS breaking and the suppressed superfluid density in the tetragonal phase, together with the reported enhanced zeroenergy excitations, are consistent with the ultranodal pair state with BFSs. The present results reveal two different superconducting states with broken TRS separated by the nematic critical point in FeSe1-xSx, which calls for the theory of microscopic origins that account for the relation between nematicity and superconductivity.

AB - Iron-chalcogenide superconductors FeSe1-xSx possess unique electronic properties such as nonmagnetic nematic order and its quantum critical point. The nature of superconductivity with such nematicity is important for understanding the mechanism of unconventional superconductivity. A recent theory suggested the possible emergence of a fundamentally new class of superconductivity with the so-called Bogoliubov Fermi surfaces (BFSs) in this system. However, such an ultranodal pair state requires broken time-reversal symmetry (TRS) in the superconducting state, which has not been observed experimentally. Here, we report muon spin relaxation (μSR) measurements in FeSe1-xSx superconductors for 0 ≤ x ≤ 0:22 covering both orthorhombic (nematic) and tetragonal phases. We find that the zero-field muon relaxation rate is enhanced below the superconducting transition temperature Tc for all compositions, indicating that the superconducting state breaks TRS both in the nematic and tetragonal phases. Moreover, the transverse-field μSR measurements reveal that the superfluid density shows an unexpected and substantial reduction in the tetragonal phase (x > 0:17). This implies that a significant fraction of electrons remain unpaired in the zero-temperature limit, which cannot be explained by the known unconventional superconducting states with point or line nodes. The TRS breaking and the suppressed superfluid density in the tetragonal phase, together with the reported enhanced zeroenergy excitations, are consistent with the ultranodal pair state with BFSs. The present results reveal two different superconducting states with broken TRS separated by the nematic critical point in FeSe1-xSx, which calls for the theory of microscopic origins that account for the relation between nematicity and superconductivity.

KW - Bogoliubov Fermi surface

KW - iron-based superconductors

KW - muon spin relaxation

KW - superconducting gap

KW - unconventional superconductivity

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U2 - 10.1073/pnas.2208276120

DO - 10.1073/pnas.2208276120

M3 - Article

C2 - 37186859

AN - SCOPUS:85159464538

SN - 0027-8424

VL - 120

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

IS - 21

M1 - e2208276120

ER -