Giant critical current peak induced by pressure in kagome superconductor RbV$_{3}$Sb$_{5}$

Abstract

Superconductivity can coexist or compete with other orders such as magnetism or density waves. Optimizing superconductivity requires identifying competing orders that may disrupt Cooper pair coherence. Here, we use the self-field critical current ($I_{\rm c,sf}$) to probe pressure-tuned superconductivity in the kagome superconductor RbV$_3$Sb$_5$. As pressure destabilizes the charge-density wave (CDW) state, $I_{\rm c,sf}$ drastically enhances, peaking near the critical pressure where the CDW state is completely suppressed at zero temperature. Surprisingly, a weaker $I_{\rm c,sf}$ peak emerges within the CDW phase. Near the pressure of the weaker peak, the superconducting phase transition temperature shifts from an increasing trend with pressure to a near plateau. Our analysis suggests the possibility of a sudden change in the CDW pattern or a Lifshitz transition, highlighting the need for microscopic examinations of the CDW state for understanding the pressure evolution of superconductivity in RbV$_3$Sb$_5$.

Figures (5)

• Figure 1: a) Temperature dependence of the electrical resistance $R$ at various pressures in RbV$_{3}$Sb$_{5}$ (S1). The black arrows indicate the charge density wave transition temperature $T_{\rm CDW}$. The traces are vertically offset for clarity. b) Corresponding temperature derivatives $dR/dT$. The CDW transition (sharp peak feature) becomes indistinguishable above 18.9 kbar. c) Normalized superconducting transitions shown in $0–8$ K range. The dashed lines extrapolate to zero resistance, and $T_c$ is defined as the temperature where the resistance reaches zero and is used for the calculation of 2$\Delta_{0}/k_{\rm B}T_{\rm c}$ in Figure \ref{['fig4']}.
• Figure 2: a) $V$-$I$ characteristics for sample S1 at 1 bar, b) 15.5 kbar and c) 23.4 kbar. The calculated first derivative of $V(I)$, $dV/dI$ for each pressure are shown in d, e) and f), respectively. g) $dV/dI$ curves at 100 mK for five selected pressures, plotted with a logarithmic scale on the $x$-axis. Numerical labels adjacent to curves indicate multiplicative scaling factors applied to the ordinate ($y$-axis) values for clarity. Short arrows in (d-g) denote the onset current ($I_c$), defined as the deviation point from $dV/dI = 0$. $V$-$I$ characteristics and the associated first derivatives for all other pressures are presented in Supporting Information.
• Figure 3: Temperature Dependence of $I_{\rm c,sf}$ under Various Pressures. Experimentally obtained $I_{\rm c,sf}(T)$ at eight representative pressures. Sample classification: S1 (a,d,e,g,h), S2 (b,f), S3 (c). The solid curves are the single $s$-wave gap fits. The extracted superconducting gap $\Delta_0$ are 0.25 meV at 1 bar, 0.42 meV at 8.5 kbar, 1.10 meV at 15 kbar, 1.00 meV at 15.5 kbar, 1.13 meV at 18.9 kbar, 1.46 meV at 21.4 kbar, 1.18 meV at 23.4 kbar and 1.00 meV at 26.8 kbar, respectively. See Supporting Information for $I_{\rm c,sf}(T)$ at all other pressures.
• Figure 4: a) Ratio of superconducting gap to critical temperature ($2\Delta_0/k_BT_c$) at various pressure in three samples. The black dash line indicates the BCS weak-coupling limit. b) Temperature-pressure phase diagram. $T_{\rm CDW}$ and $T_{\rm c}$ correspond to orange and pink hollow markers, respectively. Blue cross symbols denote the critical current ratio $I_{\rm N}$ = $I_{\rm c,sf}$(0)$_p$ / $I_{\rm c,sf}$(0)$_{p = 1 \rm bar}$. For clarity, $T_{\rm c}$ values are scaled by a factor of three. The gray dashed lines demarcate $p'$ and $p_c$.
• Figure 5: a) The band dispersion and b) Fermi surface at $\Delta_{\rm{CDW}} =0.135$ eV. c, d) The corresponding band dispersion and Fermi surface at a higher pressure with a smaller $\Delta_{\rm{CDW}}$ of $0.045$ eV. The horizontal lines in (a,b) indicate, from top to bottom, the Fermi energy of CsV$_{3}$Sb$_{5}$, the Fermi energy of RbV$_{3}$Sb$_{5}$, and the energy of the (degenerate) van Hove singularities.