• Fernandes, Rafael
• Gong, C.
• Khasanov, Rustem
• Luetkens, Hubertus
• Mielke Iii, Charles
• Elender, M.
• Das, Debarchan
• Amato, Alex
• Tu, Z.
• Christensen, M. H.
• Shumiya, N.
• Yin, J.-X.
• Hossain, Md Shafayat
• Gamsakhurdashvili, Ts.
• Dai, Pengcheng
• Yin, Q.
• Liu, H.
• Shi, Y.

Abstract

<jats:title>Abstract</jats:title><jats:p>Unconventional superconductors often feature competing orders, small superfluid density, and nodal electronic pairing. While unusual superconductivity has been proposed in the kagome metals <jats:italic>A</jats:italic>V<jats:sub>3</jats:sub>Sb<jats:sub>5</jats:sub>, 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<jats:sub>3</jats:sub>Sb<jats:sub>5</jats:sub> and KV<jats:sub>3</jats:sub>Sb<jats:sub>5</jats:sub>. At ambient pressure, we observed time-reversal symmetry breaking charge order below <jats:inline-formula><jats:alternatives><jats:tex-math>{T}_{{{{{{{{{1}}}}}}}}}^{*}</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mi>1</mml:mi></mml:mrow><mml:mrow><mml:mo>*</mml:mo></mml:mrow></mml:msubsup><mml:mo>≃</mml:mo></mml:math></jats:alternatives></jats:inline-formula> 110 K in RbV<jats:sub>3</jats:sub>Sb<jats:sub>5</jats:sub> with an additional transition at <jats:inline-formula><jats:alternatives><jats:tex-math>{T}_{{{{{{{{{2}}}}}}}}}^{*}</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>T</mml:mi></mml:mrow><mml:mrow><mml:mi>2</mml:mi></mml:mrow><mml:mrow><mml:mo>*</mml:mo></mml:mrow></mml:msubsup><mml:mo>≃</mml:mo></mml:math></jats:alternatives></jats:inline-formula> 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.</jats:p>

Topics

• density
• impedance spectroscopy
• superconductivity
• superconductivity