Pressure-induced superconductivity in the kagome single-crystal ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$

The kagome lattice offers unique opportunities for the exploration of unusual quantum states of correlated electrons. Here, we report on the observation of superconductivity in a kagome single-crystal ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$ when a semiconducting-to-metallic transition is driven by pressure. High-pressure resistance measurements show that the metallization and superconductivity are simultaneously observed at about 11 GPa. With increasing pressure, the superconducting critical temperature $T_c$ is monotonously enhanced from 2.6 K to a maximum 7.7 K at $\sim 52\mathrm{GPa}$. Interestingly, superconductivity is retained when the pressure is fully released. Synchrotron x-ray diffraction and Raman experiments consistently evidence that the emergence of superconductivity is accompanied with an amorphization, and the retainability of superconductivity upon decompression can be attributed to the irreversibility of the amorphization.

Figure 1

(a) Temperature-dependent resistance curves $R\left(T\right)$ for the ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$ single crystal measured at different pressures. The inset displays the curves for low pressures of 7.5 GPa and 8.6 GPa. (b) A zoomed-in view of the $R\left(T\right)$ curves near the superconducting critical temperatures. (c) The $R\left(T\right)$ curves upon decompression from 37.8 GPa to 1.7 GPa.

Figure 2

(a) Magnetic-field evolution of superconducting resistive transition measured at pressure 52.2 GPa. (b) The upper critical field ${\mu }_0{H}_{c2}\left(T\right)$ as a function of superconducting critical temperature $T_c^{90\%}$.

Figure 3

(a) High-pressure powder XRD patterns measured on grounded ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$ crystals for pressures up to 39.9 GPa, and then down to 3.0 GPa (“d” means decompression). For $P=0.5\mathrm{GPa}$, a red solid line presents a representative fitting. (b) Crystal structure of ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$ from a top view and side view, where the kagome lattice of Pd atoms is clearly shown. (c) Pressure dependences of the fitted lattice parameters $a$ and $c$. (d) Pressure dependence of the unit-cell volume $V$. The red solid line represents a fitting to the data using the third-order Birch–Murnaghan equation of states.

Figure 4

(a) Optical micrographs of the ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$ single crystal collected at different pressures. The last one, 0.5 GPa (D), is for a state after decompression. (b) Raman spectra of the ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$ single crystal for different pressures, which are collected at room temperature with a laser wavelength of $\lambda =532\mathrm{nm}$. (c) Pressure-dependent frequencies of the detected Raman modes.

Figure 5

The phase diagram of ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$ as a function of pressure. The left axis stands for the Raman intensity of a representative mode $E_g^3$. The right axis corresponds to the superconducting critical temperatures $T_c^{\mathrm{onset}}$ and $T_c^{\mathrm{zero}}$. The colored areas are guides to the eyes, indicating the distinct conducting phases of semiconductor, metal, and superconductor.