Possible star-of-David pattern charge density wave with additional modulation in the kagome superconductor CsV$_3$Sb$_5$

TL;DR

This study uses NMR and NQR techniques to reveal that the charge density wave in CsV$_3$Sb$_5$ has a star-of-David pattern with additional modulation, providing new insights into its unconventional CDW order.

Contribution

It is the first to identify the star-of-David pattern with extra modulation in the CDW order of CsV$_3$Sb$_5$ using nuclear magnetic resonance techniques.

Findings

CDW transition is first order at ~98 K.

Charge modulation is of star-of-David pattern.

Additional charge modulation appears below ~40 K.

Abstract

$A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) is a novel kagome superconductor coexisting with the charge density wave (CDW) order. Identifying the structure of the CDW order is crucial for understanding the exotic normal state and superconductivity in this system. Here, we report $^{51}$V nuclear magnetic resonance (NMR) and $^{121/123}$Sb nuclear quadrupole resonance (NQR) studies on kagome-metal CsV$_3$Sb$_5$. Below the CDW transition temperature $T_\textrm{CDW} \sim$ 98 K, an abrupt change of spectra was observed, indicating that the transition is of the first order. By further analysing the spectra, we find that the CDW order is commensurate. And most remarkably, the obtained experimental results suggest that the charge modulation of the CDW order is of star-of-David pattern and accompanied by an additional charge modulation in bulk below $T^* \sim$ 40 K. Our results revealing the unconventional CDW order provide new insights into $A$V$_3$Sb$_5$.