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

    Nature communications, 01/2023, Volume: 14, Issue: 1
    Journal Article

    Abstract Unconventional superconductors often feature competing orders, small superfluid density, and nodal electronic pairing. While unusual superconductivity has been proposed in the kagome metals A V 3 Sb 5 , 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 RbV 3 Sb 5 and KV 3 Sb 5 . At ambient pressure, we observed time-reversal symmetry breaking charge order below $${T}_{{{\rm{1}}}^{*}\simeq$$ T 1 * ≃ 110 K in RbV 3 Sb 5 with an additional transition at $${T}_{{{\rm{2}}}^{*}\simeq$$ T 2 * ≃ 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.