Nodeless electron pairing in CsV3Sb5-derived kagome superconductors

Abstract

Nodeless electron pairing in CsV3Sb5-derived kagome superconductorsThe newly discovered kagome superconductors represent a promising platform for investigating the quantum interplay between band topology, electronic order, and lattice geometry 1-8 . Despite extensive research efforts on this system, the nature of the superconducting ground state remains elusive 9-15 . In particular, consensus on the electron pairing symmetry has not been achieved so far [16][17][18] , in part owing to the lack of a momentum-resolved measurement of the superconducting gap structure. Here we report the direct observation of a nodeless, nearly isotropic and orbital-independent superconducting gap in the momentum space of two exemplary CsV3Sb5-derived kagome superconductors -Cs(V0.93Nb0.07)3Sb5 and Cs(V0.86Ta0.14)3Sb5, using ultrahigh resolution and low temperature angle-resolved photoemission spectroscopy (ARPES). Remarkably, we find that such a gap structure is robust to the appearance or absence of charge order in the normal state, tuned by isovalent Nb/Ta substitutions of V. Moreover, the scaling ratio of gap versus superconducting transition temperature is close to the Bardeen-Cooper-Schrieffer (BCS) value, indicating a pairing in the weak-coupling regime. Our direct observation of the superconducting gap structure points to a persistent s-wave pairing in such kagome superconductors.Superconductivity often emerges in the vicinity of other ordered electronic states with a broken symmetry, such as antiferromagnetic order and charge density wave. Their interdependence has been widely studied in cuprate and iron-based superconductors 19,20 , while persists as a key issue for understanding the high temperature superconductivity. In certain cases, the ordered state and superconductivity can even coexist 21,22 , which may indicate an unconventional pairing and have a dramatic impact on the superconducting mechanism.Because of the unique lattice geometry and unusual electronic features in a kagome lattice [1][2][3]23 , the recently discovered kagome superconductors stand out as a new platform for inspecting the superconductivity emerging from a complex landscape of electronic orders 4,5,24,25 . Of particular interest is the nonmagnetic family of AV3Sb5 (A = K, Rb, Cs) 4,6 , in which a variety of intriguing phenomena have been uncovered, including a tantalizing time-reversal symmetry broken charge density wave (CDW) order 7,8,26,27 , a pair density wave 9 , electronic nematicity 8,28-30 ,

Ultrafast Condensed Matter Physics at Attoseconds

“…[123,124] (iii) For exciton dynamics, on the other hand, the high temporal resolution of ATAS/ATRS can well separate the time scale of exciton formation/melting (∼ fs) and lattice dynamics (∼ ps), [125] which would contribute to determine the competition mechanism between excitonic insulator and CDW in 1T-TiSe2 and Ta2NiSe5, [126][127][128][129] and even to estimate the time scale of exciton condensation. [130] More interestingly, the recently discovered Kagome materials 𝐴V3Sb5 (𝐴 = K, Rb, or Cs), [131][132][133] where the flat band, Dirac cone and van Hove singularity coexist, have displayed the rich phase diagrams including the novel charge phases (CDW, pair density wave and electronic nematicity [134][135][136] ), the topology and anomalous Hall effects, [137,138] the double-peak domain of superconductivity, [139,140] and antiferromagnet. [141] The sensitivity of attosecond dynamics to various microscopic degrees of freedom, as displayed previously, would help to uncover abundant dynamic mechanism behind these competitive and coexisting phases.…”

Effects of carrier density and interactions on pairing symmetry in a t2g model

“…In recent years, there has been a growing interest in the study of unconventional superconductivity (SC) in multi-orbital systems, including Fe-based superconductors, [1][2][3][4][5][6][7] Sr 2 RuO 4 , [8][9][10][11][12][13][14] vanadium-based kagome superconductors, [15][16][17][18][19][20][21][22][23][24] and Ni-based superconducting materials. [25][26][27][28][29][30][31] In these superconductors, the low-energy physical properties are mainly determined by the d-orbital electrons of the transition metal atoms.…”

Resonant x-ray diffraction measurements in charge ordered kagome superconductors KV3Sb5 and RbV3Sb5

“…They exhibit a charge density wave (CDW) order which sets in at 80-110 K. In addition to CDW, superconductivity is observed below the transition temperature T c , which varies between ≃0.9 and ≃3.0 K for different alkali metals [1][2][3]. T c is further changed, reaching in some cases values as high as ≃7-8 K, either by doping [16] or application of pressure [17][18][19].…”