Ultralow-temperature heat transport evidence for residual density of states in the superconducting state of CsV3Sb5

TL;DR

This study provides evidence of residual electronic states in the superconducting phase of CsV3Sb5 through ultralow-temperature heat transport and STM measurements, highlighting the role of charge density wave order.

Contribution

It demonstrates the presence of residual density of states in CsV3Sb5's superconducting state and links it to charge density wave order, offering new insights into its unconventional superconductivity.

Findings

Residual density of states observed in CsV3Sb5

No residual DOS in Ta-doped CsV3Sb5 without CDW

Charge density wave order influences superconducting gap structure

Abstract

The V-based kagome superconductors $A$V$_3$Sb$_5$ ($A$ = K, Rb, and Cs) host charge density wave (CDW) and a topological nontrivial band structure, thereby provide a great platform to study the interplay of superconductivity (SC), CDW, frustration, and topology. Here, we report ultralow-temperature thermal conductivity measurements on CsV$_3$Sb$_5$ and Ta-doped Cs(V$_{0.86}$Ta$_{0.14}$)$_3$Sb$_5$ and scanning tunneling microscopy (STM) measurements on CsV$_3$Sb$_5$. The finite residual linear term of thermal conductivity at zero magnetic field suggests the existence of a residual density of states (DOS) in the superconducting state of CsV$_3$Sb$_5$. This is supported by the observation of non-zero conductance at zero bias in STM spectrum at an electronic temperature of 90 mK. However, in Cs(V$_{0.86}$Ta$_{0.14}$)$_3$Sb$_5$, which does not have CDW order, there is no evidence for residual DOS. These results show the importance of CDW order for the residual DOS, and a nodal $s$-wave gap or residual Fermi arc may be the origin of the residual DOS in such an unusual multiband kagome superconductor, CsV$_3$Sb$_5$.