Charge order and superconductivity in kagome materials

Abstract

Lattice geometry, topological electron behaviour and the competition between different possible ground states all play a role in determining the properties of materials with a kagome lattice structure. In particular, the compounds KV3Sb5, CsV3Sb5 and RbV3Sb5 all feature a kagome net of vanadium atoms. These materials have recently been shown to exhibit superconductivity at low temperature and an unusual charge order at high temperature, revealing a connection to the underlying topological nature of the band structure. We highlight these discoveries, place them in the context of wider research efforts in topological physics and superconductivity, and discuss the open problems for this field.

Optical study of RbV$_3$Sb$_5$: Multiple density-wave gaps and phonon anomalies

“…Recent quantum oscillation [46] and ARPES [11,12] studies suggested that vanadium bands around the M point become gapped, in line with theoretical proposals of band saddle points at M as the main origin of the density-wave instability [15,48]. The presence of multiple d-bands in AV 3 Sb 5 [7] implies that this instability can have more than one energy scale revealed by several gap features that were indeed detected spectroscopically, but only with surface-sensitive techniques, so far [11,12,20].…”

“…This results in an overall quasi-2D structure with well-isolated kagome planes. All key features of a nearest-neighbor kagome metal -linear bands, saddle points, and flat bands -can be indeed distinguished in electronic structures of AV 3 Sb 5 [7].…”

Tunable nodal kagome superconductivity in charge ordered RbV3Sb5

“…Due to their inherent geometric frustration and unique band structure, kagome materials [1] represent an excellent platform for discovering, classifying and under-standing correlated electronic phases of quantum matter [2][3][4][5][6]. The novel family of kagome metals AV 3 Sb 5 (A = K, Rb, Cs) [7][8][9][10][11] exhibit an array of interesting effects such as giant anomalous Hall conductivity [12,13], charge order [11,[14][15][16][17][18][19][20][21][22], orbital order [23], and possible unconventional superconductivity [7,8,10]. An important feature of the charge order, which onsets at temperatures T co ∼ 100 K at ambient pressure, is the breaking of time-reversal symmetry, as reported by scanning tunneling microscopy (STM) measurements [11,14,15,17] in (K,Rb,Cs)V 3 Sb 5 , by muon spin relaxation (µSR) in KV 3 Sb 5 [24] and CsV 3 Sb 5 [25], and by Kerr effect measurements in CsV 3 Sb 5 [26].…”

Crucial role of out-of-plane Sb-$p$ orbitals in Van Hove singularity formation and electronic correlation for superconducting Kagome metal CsV$_3$Sb$_5$

“…Several different CDW orders have been observed and/or suggested, including the one with broken time-reversal symmetry 2-13, [26][27][28][29][30][31][32][33] . Whereas some important experimental features remain controversial [9][10][11][21][22][23][24][34][35][36] , theoretical studies have been actively conducted in order to provide a plausible understanding of their microscopic origins and the interrelationships between different orders, stimulating further explorations [11][12][13][15][16][17][18][19][20][21][22][23][24][25] .…”