Uniaxial stress enhanced anisotropic magnetoresistance and superconductivity in the kagome superconductor LaRu$_{3}$Si$_{2}$

Abstract

Elucidating the role of the kagome electronic structure in determining the various quantum ground states is of fundamental importance. In this work, we employ in-plane uniaxial stress as a tuning parameter to probe the electronic structure and its impact on the superconducting and normal-state properties of the kagome superconductor LaRu$_{3}$Si$_{2}$, combining magnetotransport measurements with first-principles calculations. We identify a pronounced anisotropy in both the upper critical field and the normal-state magnetoresistance, indicating strong electronic anisotropy despite the three-dimensional crystal structure. Furthermore, we find that the superconducting transition temperature $T_{\rm c}$ increases under in-plane stress applied within the kagome plane, although the enhancement is modest, reaching approximately 0.3 K at 0.6 GPa. Furthermore, the absolute magnetoresistance exhibits a pronounced increase from about 22${\%}$ at zero stress to 35${\%}$ at 0.6 GPa, indicating a substantial modification of the normal state above $T_{\rm c}$. Previous studies have reported time-reversal-symmetry (TRS) breaking below a temperature scale that coincides with the onset of magnetoresistance. The simultaneous enhancement of both $T_{\rm c}$ and magnetoresistance under stress therefore suggests a positive correlation between superconductivity and normal-state electronic and magnetic properties in LaRu$_{3}$Si$_{2}$. Detailed calculations demonstrate that stress-induced changes in $T_{\rm c}$ arise from the joint evolution of the total density of states and the flat band, whereas the large magnetoresistance enhancement is dominated by the stress-driven downward shift of the Ru $dz^{2}$ kagome flat band.

Figures (4)

• Figure 1: (a-c) Schematic representations of the experimental configurations with varying orientations of the electrical current and magnetic field relative to the crystallographic $c$-axis. Panels below display the corresponding measurements for each configuration. (d-f) Electrical resistivity across the superconducting transition measured under the application of various magnetic fields. (g-i) Magnetoresistance curves measured at selected temperatures for each of the three measurement configurations.
• Figure 2: (a) The temperature dependence of electrical resistivity, normalized to its value at 10 K, for LaRu$_{3}$Si$_{2}$, measured under various in-plane uniaxial stress values. (b) The field dependence of magnetoresistance, measured under various in-plane uniaxial stress values. These measurements were performed with the following configuration $i \perp \mu_{0}H \perp c$.
• Figure 3: (a) A simplified schematic illustration of the uniaxial stress setup, with the directions of the applied stress, transport current, and magnetic field indicated. (b) Uniaxial stress dependence of the superconducting transition temperature (left axis) and the magnetoresistance (right axis) in LaRu$_{3}$Si$_{2}$. The chemical doping (LaRu$_{3}$(Si$_{1-x}$Ge$_{x}$)$_{2}$) effect on $T_{\rm c}$ is shown for comparison, as wellmisawa2025chemical.
• Figure 4: (a) Crystal structure and Brillouin zone ($k_z=0$ plane) of the CO-II phase, with the folded Brillouin zone induced by structural distortion indicated. (b, c) Band structures and projected density of states (PDOS) at 0 GPa (b) and under 0.61 GPa uniaxial stress along the $a$-axis (c). The size of the red circles scales with the spectral weight of the Ru $d_{z^2}$ orbitals. Dashed lines and arrows are intended to guide the reader in identifying stress-induced changes. The dashed lines indicate the Fermi level, while the arrows highlight regions showing a continuous shift of the bands away from the Fermi level. (d) Evolution of the total density of states (TDOS) near the Fermi level under uniaxial stress along the $a$-axis. (e) Evolution of the Ru $d_{z^2}$ PDOS as a function of uniaxial stress. (f) (left axis) Calculated TDOS at the Fermi level as a function of uniaxial stress applied along the $a$ and $b$ axes. (right axis) Energy position of the Ru $d_{z^2}$-dominated flat-band peak center as a function of uniaxial stress along the $a$ and $b$ axes. (g) Calculated magnetoresistance as a function of magnetic field $H$ for different $a$-axis uniaxial stress values.