Fermi Surface Mapping and the Nature of Charge-Density-Wave Order in the Kagome Superconductor CsV3Sb5

Role of Sb in the superconducting kagome metal CsV$_3$Sb$_5$ revealed by its anisotropic compression

“…This approach gives more reliable and unambiguous results compared to the fully ab initio procedure where structural parameters are relaxed, and inaccuracies in the description of anisotropic chemical bonding by DFT functionals are included in the calculated band structure implicitly. Indeed, previous DFT studies at ambient pressure revealed significant discrepancies in the energies of the saddle points at M [5,6,9], likely because of the different input crystal structures used in the calculations. For example, full structural relaxation results in the unit cell volume V = 237.7 Å 3 and c/a = 1.675 with the PBE functional or V = 240.8 Å 3 and c/a = 1.715 with the D3 correction [36], to be compared with the experimental structural parameters V = 243.4 Å 3 and c/a = 1.694 at ambient pressure [5].…”

“…We now turn to the CDW state and calculate its stabilization energy as a function of pressure (Fig. 3c) using tri-hexagonal (inverse star-of-David) type of distortion as the most plausible model of the CDW [8,9,[42][43][44]. Note that similar arguments apply to any other type of distortion that involves the modulation of V-V bonds.…”

“…Here, the presence of linear bands, Dirac points, and band saddle points (van Hove singularities) in the electronic structure of a nearest-neighbor kagome metal causes multiple electronic instabilities that have been studied theoretically [1][2][3][4] but did not find their way into the lab until the recent discovery of the AV 3 Sb 5 compound family with A = K, Rb, Cs [5]. Both charge-density wave (CDW) order [6][7][8][9][10][11] and superconductivity [12][13][14][15][16][17] observed experimentally in these compounds closely resemble theoretical findings for a simple kagome metal with the Fermi energy lying near the van Hove singularity at the filling level of 5 12 [18,19]. In AV 3 Sb 5 , the corresponding saddle points are clearly visible in the vanadium bands around the M point slightly below the Fermi level (Fig.…”

Observation of anomalous amplitude modes in the kagome metal CsV$_3$Sb$_5$

“…X-ray diffraction [12] and scanning tunneling microscopy (STM) found a 2×2 modulation of the crystal lattice [19,[31][32][33]. The CDW was shown to be three-dimensional, featuring a c-axis modulation that either doubles [33] or quadruples the original periodicity [34]. STM also found a 1 × 4 unidirectional modulation emerging only below 50 K [19,31,32], which was suggested to be of surface origin [32,35].…”

Chiral excitonic order from twofold van Hove singularities in kagome metals

“…The materials consist of a stack of two dimensional layers-a kagome lattice of vanadium and antimony alternating with a hexagonal lattice of antimony and triangular lattice of the alkali metal K/Rb/Cs-with electrical transport predominantly in-plane, as demonstrated by the large ratio between the out-of-and in-plane resistivity R c /R ab ≈ 600. The Fermi surface of these materials consists of several distinct contours, including nearly circular contours centered at the Γ and K points as well as two * Electronic address: h.scammell@unsw.edu.au approximately hexagonal contours [49]. Systems with hexagonal Fermi surfaces, corresponding to saddle points in the electronic dispersion, have been predicted to give rise to chiral superconductivity and competing density wave order, due to the effects of Fermi surface nesting [57].…”