Superconductivity in kagome metal YRu3Si2 with strong electron correlations

TL;DR

YRu$_{3}$Si$_{2}$ is a kagome-lattice metal that hosts bulk superconductivity at $T_c\approx$ $3.0$ K. Through structural, transport, magnetization, and specific-heat measurements, the study shows a type-II superconducting state with $H_{c1}(0)\approx28$ mT and $H_{c2}(0)\approx0.655$ T, and GL parameters $\xi_{GL}\approx22.4$ nm, $\lambda_{GL}\approx24.8$ nm, yielding $\kappa_{GL}\approx1.11$. The normal-state behavior and thermodynamics indicate weak-to-moderate electron-phonon coupling with a Debye temperature $\Theta_D\approx460$ K and $\gamma\approx27.5$ mJ mol$^{-1}$ K$^{-2}$, while the sizeable Kadawaki–Woods ratio $A/\gamma^2\approx3.15$ μΩ cm mol$^{2}$ K$^{2}$ J$^{-2}$ and Wilson ratio $R_W\approx1.49$ reveal strong electron correlations, potentially tied to the kagome flat band. Together, these results position YRu$_{3}$Si$_{2}$ as a compelling platform to study the interaction between correlated electron physics and kagome topology in superconductors, extending insights beyond LaRu$_{3}$Si$_{2}$ and into flat-band kagome systems.

Abstract

We report the detailed physical properties of YRu3Si2 with the Ru kagome lattice at normal and superconducting states. The results of resistivity and magnetization show that YRu3Si2 is a type-II bulk superconductor with Tc ~ 3.0 K. The specific heat measurement further suggests that this superconductivity could originate from the weak or moderate electron-phonon coupling. On the other hand, both large Kadawaki-Woods ratio and Wilson ratio indicate that there is a strong electron correlation effect in this system, which may have a connection with the featured flat band of kagome lattice.

Figures (5)

• Figure 1: (a) Crystal structure of YRu$_{3}$Si$_{2}$. The blue, red and yellow balls represent Y, Ru and Si atoms, respectively. (b) Top view of the 2D distorted kagome lattice of Ru atoms. Two different bond distances are labelled with green and orange lines. (c) Powder XRD pattern and Rietveld refinement of YRu$_{3}$Si$_{2}$ polycrystal.
• Figure 2: (a) Temperature dependence of magnetic susceptibility $4\pi\chi(T)$ at 1 mT with ZFC and FC models. (b) Magnetization hysteresis loop for YRu$_{3}$Si$_{2}$ at 1.8 K. (c) Low-field dependence of magnetization $4\pi M(\mu_{0}H)$ at various temperatures below $T_{c}$. (d) $\mu_{0}H_{c1}$ as a function of $T/T_{c}$. The red line represents the fit using G-L equation.
• Figure 3: (a) Temperature dependence of electrical resistivity $\rho(T)$ for YRu$_{3}$Si$_{2}$ polycrystal at zero field. The red solid line represents the fit using the formula $\rho(T)=\rho_{0}+AT^2+BT^{5}$. Inset: enlarged view of $\rho(T)$ curve near superconducting transition. (b) Temperature dependence of $\mu_{0}H_{c2}(T)$. The blue circles and orange triangles represent the $\mu_{0}H_{c2}(T)$ determined from resistivity and specific heat measurements, respectively. The error bars for the former are determined from the 10% and 90% of normal state resistivity just above superconducting transition. The error bars for the later are determined from the starting points and peak positions of jumps on the $C_{p}(T)$ curves. The green and purple lines represent the fits using the G - L and WHH formulas. Inset: $\rho(T)$ as a function of $T$ at various magnetic fields.
• Figure 4: (a) Temperature dependence of zero-field $C_{p}(T)$ from 300 K to 2 K. (b) $C_{p}$ vs $T$ at various magnetic fields. (c) Temperature dependence of $C_{p}(T)$ at $\mu_{0}H$ = 0.5 T. The red solid line represents the fit using the formula $C_{p}=\gamma T+\beta T^3+\eta T^5$. Inset: ${C_{p}}/{T}$ vs $T^{2}$ at $\mu_{0}H$ = 0.5 T. (d) ${C_{\rm ele}}/{T}$ as a function of $T$ at zero field.
• Figure 5: Temperature dependence of $\chi(T)$ measured at $\mu_{0}H$ = 0.5 T with ZFC mode. The red solid line presents the fit using the formula $\chi(T)$ = $\chi(0)[1-(T/T_{\rm E})^{2}]+C/(T+T_{0})$.