Pressure-induced superconductivity in quasi-one-dimensional semimetal ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$

Here we report the discovery of pressure-induced superconductivity in quasi-one-dimensional ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$, through a combination of electrical transport, synchrotron x-ray diffraction, and theoretical calculations. Our transport measurements show that the superconductivity appears at a critical pressure $P_{\mathrm{c}}\sim 18.3\mathrm{GPa}$ and is robust upon further compression up to 62.6 GPa. The estimated upper critical field ${\mu }_0{H}_{\mathrm{c}2}\left(0\right)$ in the pressurized ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$ is much lower than the Pauli limiting field, in contrast to the case in its isostructural analogs $M_2{\mathrm{Pd}}_{\mathrm{x}}{X}_5$ $(M=\mathrm{Nb}, \mathrm{Ta}; X=\mathrm{S}, \mathrm{Se})$. Concomitant with the occurrence of superconductivity, anomalies in pressure-dependent transport properties are observed, including sign reversal of Hall coefficient, abnormally enhanced resistance, and dramatically suppressed magnetoresistance. Meanwhile, room-temperature synchrotron x-ray diffraction experiments reveal the stability of the pristine monoclinic structure (space group $C2$/$m$) upon compression. Combined with the density functional theory calculations, we argue that a pressure-induced Lifshitz transition could be the electronic origin of the emergent superconductivity in ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$.

Figure 1

(a) Schematic crystal structure of ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$ (monoclinic, space group $C2$/$m$). The blue, green, and orange spheres represent Ta, Pd, and Se, respectively. (b) XRD pattern of ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$ single crystal at room temperature $\left(\lambda =1.5406\AA \right)$. The inset shows a picture of as-grown single crystals. (c) Energy-dispersive x-ray spectroscopy of a piece of single crystal with area-scanning mode. (d) Temperature dependence of resistance of a piece of single crystal with a residual resistance ratio $\mathrm{RRR}=1136$ at ambient pressure. Inset: Schematic configuration of the four-probe electrical transport measurement.

Figure 2

Pressure evolution of resistance-temperature curves in ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$. The arrow in (a) indicates the onset of resistance drop around 1.9 K. Inset of (b): Enlarged view of the low-temperature region in run 1.

Figure 3

(a) Pressure evolution of representative magnetoresistance curves in ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$ at 10 K. Inset: Enlarged view of the pressure above 15.3 GPa in run 1. (b) Pressure evolution of representative Hall resistivity curves ${\rho }_{\mathrm{xy}}\left(H\right)$ in ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$ at 10 K. Inset: Schematic configuration of the electrical transport measurement with five probes.

Figure 4

Pressure evolution of resistance-temperature curves in run 3. (a) Enlarged view of the low-temperature region. Temperature-dependent resistance curves in ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$ under various magnetic fields at (b) 20.1 GPa and (d) 39.7 GPa in run 3. (c), (e) Temperature dependence of the upper critical field ${\mu }_0{H}_{\mathrm{c}2}$. The solid lines represent the WWH fitting.

Figure 5

(a) Pressure dependence of XRD patterns of ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$ at room temperature $\left(\lambda =0.6199\AA \right)$. (b) Lattice parameters $a$, $b$, and $c$ as a function of pressure. (c) Volume-pressure phase diagram. The solid red line is fits based on the third-order Birch-Murnaghan equation of states.

Figure 6

Pressure-temperature phase diagram of ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$ and pressure-dependent Hall coefficient. (a) The red, green, and brown solid dots represent $T_{\mathrm{c}}^{\mathrm{zero}}$ for run 1, run 2, and run 3, respectively. (b) Hall coefficient ($R_{\mathrm{H}}$) as a function of pressure measured at 10 K and 5 T. Inset: Pressure-dependent resistance of ${\mathrm{Ta}}_2{\mathrm{PdSe}}_6$ at 10 K for three runs.

Figure 7

(a)–(e) Calculated GGA + MBJ + SOC band structure at different pressure points (0, 10, 20, 30, and 40 GPa). Pressure-dependent evolution of hole band pocket around Γ point [marked by black arrow in (c)–(e)]. (f) High symmetry points of the Brillouin zone.