Bulk superconductivity in the kagome metal YRu3B2

TL;DR

This work demonstrates bulk superconductivity in the kagome metal YRu$_{3}$B$_{2}$ with a transition near $T_c ≈ 0.71 K$, extending the family of kagome superconductors that includes LaRu$_{3}$Si$_{2}$ with $T_c ≈ 6.8 K$. The authors synthesize high-purity crystals by arc melting and confirm phase integrity via structural characterization, then establish superconductivity through resistivity, magnetization, and heat capacity showing a thermodynamic anomaly consistent with BCS-like behavior, with $Δc_P/(γ T_c) ≈ 1.30$. The work highlights the role of lattice structure and electronic topology in kagome metals and suggests that chemical composition and lattice tuning can modulate $T_c$ or reveal competing orders such as charge-density waves. This study provides a benchmark for kagome superconductivity and motivates further investigation into electron-phonon coupling and lattice effects in these systems.

Abstract

Materials with a kagome sublattice have been heavily studied recently for their exotic electronic band structure, structural frustration, high-temperature charge order transitions, and unconventional electron-phonon coupling. In LaRu3Si2, it was proposed that electronic flat bands conspire with the characteristic phonon spectrum of the kagome lattice to drive enhanced superconductivity at Tc = 7 K. Here, we report bulk superconductivity in the structural analogue YRu3B2, which hosts a structurally pristine kagome lattice. We observe a superconducting transition at Tc = 0.7 K through magnetization, resistivity, and heat-capacity measurements in this novel kagome metal.

Figures (4)

• Figure 1: (color online). Superconducting transition in the kagome metal YRu$_3$B$_2$. (a) Resistivity $\rho_{xx}$ versus temperature $T$ measured on a bar-shaped sample in zero magnetic field, $H_\mathrm{ext} = 0$. Right axis: derivative $d\rho_{xx}/dT$ with respect to temperature. The transition width is $40\,$mK. (b) Magnetic susceptibility $\chi$ as a function of $T$ in $\mu_0H_\mathrm{ext} = 0.3\,$mT applied magnetic field, in zero-field cooled (ZFC) condition. Right axis: derivative $d\chi/dT$ with respect to temperature. The transition width is $70\,$mK. A demagnetization correction was applied to the $\chi(T)$ data.
• Figure 2: (color online). Perfect diamagnetism in YRu$_3$B$_2$ detected by DC magnetometry. The magnetization isotherm $M(H)$ at base temperature, $T=0.4\,$K, shows a butterfly shape typical for type-II superconductors Tinkham2004. The critical field is $\mu_0H_{\mathrm{c2}}=30\,$mT. The curve is recorded in the sequence red (initial, zero-field cooled), blue ($\partial H /\partial t<0$), black ($\partial H / \partial t >0$).
• Figure 3: (color online). Thermodynamic evidence for superconductivity in YRu$_3$B$_2$. (a) Molar heat capacity at constant pressure, $c_\mathrm{P}$, at $B=0\,$T, $1\,$T for a polycrystalline sample of YRu$_3$B$_2$. The blue line indicates a polynomial fit to the high field data comprising electronic and phononic terms. (b) Superconducting part of $c_\mathrm{P}$ at $B=0\,$T. A fit to the BCS expression, with equal area construction for the anomaly in $c_\mathrm{P}$, is shown by the black line (see text for discussion).
• Figure 4: (color online). Rietveld refinement of the crystal structure of YRu$_3$B$_2$, based on a crushed polycrystalline sample. The powder X-ray data was obtained on a commercial Rigaku SmartLab diffractometer with Cu-$K_\alpha$ radiation (wavelength $\lambda = 1.5406 \, \AA$).