Observation of Room-temperature Charge Density Wave Correlations via Coherent Phonon Spectroscopy in Sn-doped Kagome Superconductor CsV$_3$Sb$_5$

Abstract

In this work, we perform ultrafast time-resolved reflectivity measurements to track the evolution of charge density wave (CDW) correlations in Sn-doped Kagome superconductor CsV$_3$Sb$_{5-x}$Sn$_x$. By extracting the coherent phonon spectrum, we evidence robust signatures of CDW correlations at temperature and doping ranges far beyond the phase boundary of long-range CDW order. Remarkably, we unveil short-range CDW correlations survive up to room temperature in $x = 0.32$ Sn-doped CsV$_3$Sb$_5$, supported by synchrotron X-ray diffraction measurements. We point out the introduction of quenched disorder by Sn doping can pin the CDW and form static short-range CDW, which can explain the observed persistent CDW signatures. Our results thus corroborate the ubiquity and robustness of CDW correlations in Sn-doped CsV$_3$Sb$_5$ and provide new insights on the role of disorders on the CDW correlations in AV$_3$Sb$_5$ family.

Figures (5)

• Figure 1: (a) Crystal structure of CsV$_3$Sb$_{5-x}$Sn$_x$. (b) Temperature-doping phase diagram for CsV$_3$Sb$_{5-x}$Sn$_x$. (c) $\Delta$R/R vs. temperature in undoped CsV$_3$Sb$_5$deng2025coherent. (d) Temperature dependence of coherent phonon spectra in undoped CsV$_3$Sb$_5$deng2025coherent.
• Figure 2: Evolution of the coherent phonon spectrum in CsV$_3$Sb$_{5-x}$Sn$_x$ with $x = 0.32$ with temperature. (a) TR-reflectivity curves $\Delta$R/R in the temperature range of 3 K – 296 K. (b) Temperature dependence of Coherent phonon spectra. The curves are offset for clarity.
• Figure 3: Room temperature short-range charge orders in CsV$_3$Sb$_{5-x}$Sn$_x$ with $x = 0.32$. (a) Zoom-in of $\Delta$R/R at $T$ = 296 K. (b) Coherent phonon spectrum at $T$ = 296 K. The red arrow marks the 1.3 THz mode. (c) X-ray $(H, K)$-map at $L = -5.5$ for CsV$_3$Sb$_{5-x}$Sn$_x$, $x = 0.32$ at 200 K. (d) Representative linecuts perpendicular to the stripe direction (along [-1, 2, 0]) on the peak (-3, 1.6, -5.5) at 200 K and 300 K with correlation lengths $\xi$. Fits were performed using Lorentzian functions with a linear background.
• Figure 4: Coherent phonon spectra among different doping levels of CsV$_3$Sb$_{5-x}$Sn$_x$ with (a) $x = 0.03-0.04$ (b) $x = 0.09$ (c) $x = 0.2$ and (d) $x = 0.68$ vs. temperature. The curves are offset for clarity.
• Figure 5: The main lattice mode frequency as a function of the doping level $x$ in CsV$_3$Sb$_{5-x}$Sn$_x$.