Pressure-induced double superconducting domes and charge instability in the kagome metal ${\mathrm{KV}}_3{\mathrm{Sb}}_5$

The kagome metal ${\mathrm{KV}}_3{\mathrm{Sb}}_5$ hosts charge order, topologically nontrivial Dirac band crossings, and a superconducting ground state with unconventional characteristics, providing an ideal platform to investigate the interplay between different electronic states on the kagome lattice. Here we study the evolution of charge order and superconductivity in ${\mathrm{KV}}_3{\mathrm{Sb}}_5$ under hydrostatic pressure using electrical resistivity measurements. With the application of pressure, the superconducting transition temperature $T_{\mathrm{c}}=0.9$ K under ambient pressure quickly increases to 3.1 K at $p=0.4$ GPa, as charge order progressively weakens. Upon further increasing pressure, signatures of charge order disappear at $p_{\mathrm{c}1}\approx 0.5$ GPa and $T_{\mathrm{c}}$ is gradually suppressed, forming a superconducting dome that terminates at $p\approx 10$ GPa. Beyond $p\approx 10$ GPa, a second superconducting dome emerges with maximum $T_{\mathrm{c}}\approx 1.0$ K at $p_{\mathrm{c}2}\approx 22$ GPa, which becomes fully suppressed at $p\approx 28$ GPa. The suppression of superconductivity for the second superconducting dome is associated with the appearance of a unique high-pressure phase, possibly a distinct charge order.

Figure 1

Schematic phase diagrams of the interplay between charge order and superconductivity, (a) where the two orders compete and (b) when quantum fluctuations associated with charge order are dominant, leading to a fan of non-Fermi-liquid behavior. The orange shaded region corresponds to charge order (CO), and the purple shaded region corresponds to superconductivity (SC). In the normal state without charge order, the system may exhibit Fermi-liquid (FL) or non-Fermi-liquid (NFL) behavior.

Figure 2

In-plane resistivity $\rho \left(T\right)$ of ${\mathrm{KV}}_3{\mathrm{Sb}}_5$ under pressures from (a) 0.1–2.3 GPa, (b) 4.9–21.5 GPa, and (c) 23.6–27.9 GPa. The corresponding $d\rho \left(T\right)$/$dT$ are respectively shown in (d), (e), and (f). Data in (a) are measured in a piston-cylinder cell, and data in (b) and (c) are measured in a diamond anvil cell. Aside from the one $\rho \left(T\right)$ curve at 27.9 GPa which is measured upon warming, all data are taken upon cooling. The inset in (c) zooms into the temperature region with hysteretic resistivity at 27.9 GPa.

Figure 3

In-plane resistivity $\rho \left(T\right)$ of ${\mathrm{KV}}_3{\mathrm{Sb}}_5$ under pressures from (a) 0.1–9.2 GPa, (b) 10.3–19 GPa, and (c) 21.5–27.9 GPa, zoomed in for $T\le 4$ K. Low-temperature resistivity $\rho \left(T\right)$ under various $c$-axis magnetic fields for (d) 4.9 GPa and (e) 21.5 GPa. (f) The upper critical field of ${\mathrm{KV}}_3{\mathrm{Sb}}_5$ as a function of temperature under 4.9 and 21.5 GPa. Fits to the WHH model are shown as dashed lines.

Figure 4

(a) The temperature-pressure phase diagram of ${\mathrm{KV}}_3{\mathrm{Sb}}_5$. Two superconducting regions (SC1 and SC2), the low-pressure charge order (LPCO), and the high-pressure phase (HPP) can be identified in the figure. The inset zooms into the low-pressure region, highlighting the interplay between superconductivity and the LPCO. (b) Pressure dependence of the electrical resistivity change $\delta \rho =\rho \left(300\mathrm{K}\right)-{\rho }_0$. The solid line is a guide to the eye. Full symbols correspond to points obtained using a PCC, and empty symbols correspond to points obtained using a DAC. For measurements using a DAC, two samples were studied [33] and are presented using different symbols.