Signatures of nodal superconductivity in stoichiometric FeTe

Abstract

Superconductivity in stoichiometric FeTe opens access to the FeTe endpoint of the Fe(Se,Te) phase diagram, yet the nature of its superconducting pairing state remains unresolved. In this work, we combine scanning superconducting quantum interference device (SQUID) microscopy, electrical transport, scanning tunneling microscopy and spectroscopy (STM/S), and mean-field calculations to investigate the local superfluid response and pairing state of FeTe thin films with tunable stoichiometry. Even in stoichiometric FeTe, we observe micrometer-scale spatial variations in both superfluid stiffness and superconducting transition temperature T_c, while the London penetration depth remains non-saturating down to 0.02T_c and follows a power-law temperature dependence with an exponent of approximately 1-1.5. Together with a V-shaped low-energy density of states and two-gap modeling, these results indicate a superconducting state with gap nodes or deep minima, consistent with either a d-wave or nodal s-wave superconducting state. Our findings establish stoichiometric FeTe as a distinct superconducting regime that departs from the trend toward more isotropic gaps at intermediate Se/Te compositions, providing a new benchmark for modern microscopic theories of iron-chalcogenide superconductivity. Our work also reveals a crossover from weak to rapid suppression of T_c as superfluid stiffness decreases, connecting FeTe to the broader phenomenology observed in unconventional superconductors.

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Cite

BibTeX RIS

BibTeX

@misc{li2026signatures,
  title = {{Signatures of nodal superconductivity in stoichiometric FeTe}},
  author = {Cequn Li and Zi-Jie Yan and Yang Ge and Zihao Wang and Bing Xia and Stephen Paolini and Pu Xiao and Lok-Kan Lai and Jiatao Song and Austin R. Kaczmarek and Lujin Min and Kenji Yasuda and Peter J. Hirschfeld and Jiabin Yu and Cui-Zu Chang and Katja C. Nowack},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.08116},
  eprint = {2609.08116},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.08116},
  note = {CC BY 4.0},
}

RIS

TY  - UNPB
TI  - Signatures of nodal superconductivity in stoichiometric FeTe
AU  - Cequn Li
AU  - Zi-Jie Yan
AU  - Yang Ge
AU  - Zihao Wang
AU  - Bing Xia
AU  - Stephen Paolini
AU  - Pu Xiao
AU  - Lok-Kan Lai
AU  - Jiatao Song
AU  - Austin R. Kaczmarek
AU  - Lujin Min
AU  - Kenji Yasuda
AU  - Peter J. Hirschfeld
AU  - Jiabin Yu
AU  - Cui-Zu Chang
AU  - Katja C. Nowack
PY  - 2026
DA  - 2026/09/08
PB  - arXiv
DO  - 10.48550/arxiv.2609.08116
UR  - https://arxiv.org/abs/2609.08116
AB  - Superconductivity in stoichiometric FeTe opens access to the FeTe endpoint of the Fe(Se,Te) phase diagram, yet the nature of its superconducting pairing state remains unresolved. In this work, we combine scanning superconducting quantum interference device (SQUID) microscopy, electrical transport, scanning tunneling microscopy and spectroscopy (STM/S), and mean-field calculations to investigate the local superfluid response and pairing state of FeTe thin films with tunable stoichiometry. Even in stoichiometric FeTe, we observe micrometer-scale spatial variations in both superfluid stiffness and superconducting transition temperature T_c, while the London penetration depth remains non-saturating down to 0.02T_c and follows a power-law temperature dependence with an exponent of approximately 1-1.5. Together with a V-shaped low-energy density of states and two-gap modeling, these results indicate a superconducting state with gap nodes or deep minima, consistent with either a d-wave or nodal s-wave superconducting state. Our findings establish stoichiometric FeTe as a distinct superconducting regime that departs from the trend toward more isotropic gaps at intermediate Se/Te compositions, providing a new benchmark for modern microscopic theories of iron-chalcogenide superconductivity. Our work also reveals a crossover from weak to rapid suppression of T_c as superfluid stiffness decreases, connecting FeTe to the broader phenomenology observed in unconventional superconductors.
ER  -

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