Doping evolution of superconductivity, charge order and band topology in hole-doped topological kagome superconductors Cs(V$_{1-x}$Ti$_x$)$_3$Sb$_5$

Abstract

The newly discovered Kagome superconductors AV3Sb5 (A = K, Rb, Cs) exhibit superconductivity, charge order, and band topology simultaneously. To explore the intricate interplay between the superconducting and charge orders, we investigate the doping evolution of superconductivity, charge-density-wave (CDW) order and band topology in doped topological kagome superconductors Cs(V1−xTix)3Sb5 where the Ti-dopant introduces hole-like charge carriers. Despite the absence of the CDW phase transition in doped compounds even for the lowest doping level of x = 0.047, the superconductivity survives in all doped samples with enhanced critical temperatures. The high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements reveal that the Ti-dopant in the kagome plane lowers the chemical potential, pushing the van Hove singularity (VHS) at M point above the Fermi level. First-principle simulations corroborate the doping evolution of the band structure observed in ARPES, and affirm that the CDW instability does not occur once the VHS is pushed above the Fermi level, explaining the absence of the CDW ordering in our doped samples Cs(V1−xTix)3Sb5. Our results demonstrate a competition between the CDW and superconducting orders in the kagome-metal superconductor CsV3Sb5, although the superconductivity is likely inconsequential of the CDW order.

Charge density wave order and fluctuations above T$_{CDW}$ and below superconducting T$_c$ in the kagome metal CsV$_{3}$Sb$_{5}$

“…Previous high-pressure measurements on this kagome metal system AV 3 Sb 5 show that superconductivity coexists with CDW order under ambient pressure, however superconducting T c increases while T CDW decreases with increasing pressure, suggesting a competition between CDW order and superconductivity [9,25,34,35]. Evidence for such competition is also provided by holedoping studies [34,36,37], systematic studies of finite crystal thickness [34,38], and measurements under uniaxial strain [39]. In contrast, our x-ray results on the ambient pressure CDW state in CsV 3 Sb 5 show it to be robust and to co-exist well with its superconducting instability below T c = 2.9 K, at least as low as T = 2 K.…”

Charge density wave order in kagome metal AV$_3$Sb$_5$ (A= Cs, Rb, K)

“…These results establish a solid foundation to study the interplay between the primary and secondary CDW order parameters in kagome metal system. They guide to identify the primary and secondary order parameters as well as their interplay, when these CDW order parameters are tuned by carrier doping [26][27][28], external pressure [24,25], or strain [66]. We choose êi and ês to be X, Y , R, and L, where X = (1 0 0), Y = (0 1 0), R = 1/ √ 2 (1 i 0), and L = 1/ √ 2 (1 − i 0).…”

“…in AV 3 Sb 5 , as T c increases when the CDW order is suppressed by hydrostatic pressure [24,25], or by the hole doping [26][27][28], or by thickness reduction [28,29]. Furthermore, the CDW state shows a large extrinsic anomalous Hall effect [30,31] in the absence of magnetic ordering [32].…”

Chiral excitonic order from twofold van Hove singularities in kagome metals

“…First principles calculations could relate our phase diagram to these experiments by determining δ, µ and couplings as a function of pressure. Variation of doping and pressure indicates the presence of two distinct superconducting phases [46][47][48]; it is possible that the TvHS dominates the physics in one doping regime, while other interaction physics could be important elsewhere in the phase diagram [82][83][84][85][86][87]-e.g. it has been shown that sublattice interference near the K-points can result in higher-order topological multigap s-or p-wave states [11,86,87].…”