Tunable unconventional kagome superconductivity in charge ordered RbV3Sb5 and KV3Sb5

Z Guguchia; C Mielke 3rd; D Das; R Gupta; J-X Yin; H Liu; Q Yin; M H Christensen; Z Tu; C Gong; N Shumiya; Md Shafayat Hossain; Ts Gamsakhurdashvili; M Elender; Pengcheng Dai; A Amato; Y Shi; H C Lei; R M Fernandes; M Z Hasan; H Luetkens; R Khasanov

doi:10.1038/s41467-022-35718-z

Tunable unconventional kagome superconductivity in charge ordered RbV₃Sb₅ and KV₃Sb₅

Nat Commun. 2023 Jan 11;14(1):153. doi: 10.1038/s41467-022-35718-z.

Authors

Z Guguchia¹, C Mielke 3rd², D Das², R Gupta², J-X Yin³, H Liu^{4

5}, Q Yin⁶, M H Christensen⁷, Z Tu⁶, C Gong⁶, N Shumiya⁸, Md Shafayat Hossain⁸, Ts Gamsakhurdashvili², M Elender², Pengcheng Dai⁹, A Amato², Y Shi^{4

5}, H C Lei⁶, R M Fernandes¹⁰, M Z Hasan^{8

11

12

13}, H Luetkens¹⁴, R Khasanov¹⁵

Affiliations

¹ Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232, Villigen PSI, Switzerland. zurab.guguchia@psi.ch.
² Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232, Villigen PSI, Switzerland.
³ Department of Physics, Southern University of Science and Technology, Shenzhen, Guangdong, 518055, China.
⁴ Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, 100190, Beijing, China.
⁵ University of Chinese Academy of Sciences, 100049, Beijing, China.
⁶ Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices, Renmin University of China, 100872, Beijing, China.
⁷ Niels Bohr Institute, University of Copenhagen, Copenhagen, 2100, Denmark.
⁸ Laboratory for Topological Quantum Matter and Advanced Spectroscopy (B7), Department of Physics, Princeton University, Princeton, NJ, 08544, USA.
⁹ Department of Physics and Astronomy, Rice University, Houston, TX, 77005, USA.
¹⁰ School of Physics and Astronomy, University of Minnesota, Minneapolis, MN, 55455, USA.
¹¹ Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, NJ, 08540, USA.
¹² Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
¹³ Quantum Science Center, Oak Ridge, TN, 37831, USA.
¹⁴ Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232, Villigen PSI, Switzerland. hubertus.luetkens@psi.ch.
¹⁵ Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232, Villigen PSI, Switzerland. rustem.khasanov@psi.ch.

Abstract

Unconventional superconductors often feature competing orders, small superfluid density, and nodal electronic pairing. While unusual superconductivity has been proposed in the kagome metals AV₃Sb₅, key spectroscopic evidence has remained elusive. Here we utilize pressure-tuned and ultra-low temperature muon spin spectroscopy to uncover the unconventional nature of superconductivity in RbV₃Sb₅ and KV₃Sb₅. At ambient pressure, we observed time-reversal symmetry breaking charge order below [Formula: see text] 110 K in RbV₃Sb₅ with an additional transition at [Formula: see text] 50 K. Remarkably, the superconducting state displays a nodal energy gap and a reduced superfluid density, which can be attributed to the competition with the charge order. Upon applying pressure, the charge-order transitions are suppressed, the superfluid density increases, and the superconducting state progressively evolves from nodal to nodeless. Once optimal superconductivity is achieved, we find a superconducting pairing state that is not only fully gapped, but also spontaneously breaks time-reversal symmetry. Our results point to unprecedented tunable nodal kagome superconductivity competing with time-reversal symmetry-breaking charge order and offer unique insights into the nature of the pairing state.