Tunable unconventional kagome superconductivity in charge ordered RbV3Sb5 and KV3Sb5

Z. Guguchia, C. Mielke, 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. HasanH. Luetkens, R. Khasanov

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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 T1*≃ 110 K in RbV3Sb5 with an additional transition at T2*≃ 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.

Original languageEnglish (US)
Article number153
JournalNature communications
Issue number1
StatePublished - Dec 2023

Bibliographical note

Funding Information:
The μSR experiments were carried out at the Swiss Muon Source (SμS) Paul Scherrer Institute, Villigen, Switzerland. M.H.C. was supported by the Carlsberg foundation. M.Z.H. acknowledges visiting scientist support from IQIM at the California Institute of Technology. Experimental work at Princeton University was supported by the Gordon and Betty Moore Foundation (GBMF4547 and GBMF9461; M.Z.H.) and the material characterization is supported by the US Department of Energy under the Basic Energy Sciences program (grant no. DOE/BES DE-FG-02-05ER46200). Y.S. acknowledges the National Natural Science Foundation of China (U2032204) and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (No. XDB33000000). H.C.L. was supported by Ministry of Science and Technology of China (Grant No. 2018YFE0202600), Beijing Natural Science Foundation (Grant No. Z200005). The work of R.G. was supported by the Swiss National Science Foundation (SNF-Grant No. 200021-175935). R.M.F (phenomenological modeling) was supported by the Air Force Office of Scientific Research under award number FA9550-21-1-0423. P.D. at Rice is supported by U.S. DOE BES DE-SC0012311. Z.G. acknowledges useful discussions with Dr. Robert Johann Scheuermann.

Publisher Copyright:
© 2023, The Author(s).

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