State with spontaneously broken time-reversal symmetry above the superconducting phase transition

Grinenko V, Weston D, Caglieris F, Wuttke C, Hess C, Gottschall T, Maccari I, Gorbunov D, Zherlitsyn S, Wosnitza J, Rydh A, Kihou K, Lee CH, Sarkar R, Dengre S, Garaud J, Charnukha A, Huehne R, Nielsch K, Buechner B, Klauss HH, Babaev E (2021)

Publication Type: Journal article

Publication year: 2021

Journal

Nature Physics Nature Research

Book Volume: 17

Pages Range: 1254-1259

Journal Issue: 11

DOI: 10.1038/s41567-021-01350-9

Abstract

The most well-known example of an ordered quantum state—superconductivity—is caused by the formation and condensation of pairs of electrons. Fundamentally, what distinguishes a superconducting state from a normal state is a spontaneously broken symmetry corresponding to the long-range coherence of pairs of electrons, leading to zero resistivity and diamagnetism. Here we report a set of experimental observations in hole-doped Ba1−xKxFe2As2. Our specific-heat measurements indicate the formation of fermionic bound states when the temperature is lowered from the normal state. However, when the doping level is x ≈ 0.8, instead of the characteristic onset of diamagnetic screening and zero resistance expected below the superconducting phase transition, we observe the opposite effect: the generation of self-induced magnetic fields in the resistive state, measured by spontaneous Nernst effect and muon spin rotation experiments. This combined evidence indicates the existence of a bosonic metal state in which Cooper pairs of electrons lack coherence, but the system spontaneously breaks time-reversal symmetry. The observations are consistent with the theory of a state with fermionic quadrupling, in which long-range order exists not between Cooper pairs but only between pairs of pairs.

Involved external institutions

Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden e.V. (IFW) / Leibniz Institute for Solid State and Materials Research Dresden DE Germany (DE) Helmholtz-Zentrum Dresden-Rossendorf (HZDR) DE Germany (DE) Technische Universität Dresden DE Germany (DE) Stockholm University / Stockholms universitet SE Sweden (SE) National Institute of Advanced Industrial Science and Technology / 産業技術総合研究所 (AIST) JP Japan (JP) Royal Institute of Technology / Kungliga Tekniska Högskolan (KTH) SE Sweden (SE) François Rabelais University Tours FR France (FR)

How to cite

APA:

Grinenko, V., Weston, D., Caglieris, F., Wuttke, C., Hess, C., Gottschall, T.,... Babaev, E. (2021). State with spontaneously broken time-reversal symmetry above the superconducting phase transition. Nature Physics, 17(11), 1254-1259. https://doi.org/10.1038/s41567-021-01350-9

MLA:

Grinenko, Vadim, et al. "State with spontaneously broken time-reversal symmetry above the superconducting phase transition." Nature Physics 17.11 (2021): 1254-1259.

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