Superconductivity in multiple phases of compressed $\mathrm{GeS}{\mathrm{b}}_2\mathrm{T}{\mathrm{e}}_4$

Here we report the discovery of superconductivity in multiple phases of the compressed $\mathrm{GeS}{\mathrm{b}}_2\mathrm{T}{\mathrm{e}}_4$ (GST) phase change memory alloy, which has attracted considerable attention for the last decade due to its unusual physical properties with many potential applications. Superconductivity is observed through electrical transport measurements, both for the amorphous $(a$-GST) and for the crystalline $(c$-GST) phases. The superconducting critical temperature $T_c$ continuously increases with applied pressure, reaching a maximum $T_c=6\mathrm{K}$ at $P=20\mathrm{GPa}$ for $a$-GST, whereas the critical temperature of the cubic phase reaches a maximum $T_c=8\mathrm{K}$ at 30 GPa. This material system, exhibiting a superconductor-insulator quantum phase transition, has an advantage over disordered metals since it has a continuous control of the crystal structure and the electronic properties using pressure as an external stimulus.

Figure 1

Room temperature resistance under pressure. (a) Six platinum triangles under pressure in one of the measurement setups. (b) Resistance as a function of pressure of $a$-GST. (c) Pressure dependence of resistance of $c$-GST. Shaded regions in different colors [(in both (b) and (c)] are according to previously published XRD data [16, 17] and our resistance measurements.

Figure 2

Temperature dependence of $a$-GST samples demonstrating the superconductor-insulator transition (SIT). The Mott variable range hopping is clearly observed at pressures between 3.0 and 7.5 GPa, as seen from the inset.

Figure 3

Superconducting transitions of $a$-GST. (a) Temperature dependence of resistance at different pressures using four-probe geometry (sample 1) and (b) using quasi-four-probe geometry (sample 2). Two distinct superconducting transitions are observed.

Figure 4

Pressure dependence of the critical field of $a$-GST (sample 1). (a) Resistance as a function of magnetic field at different pressures. (b) Zoomed portion of the transitions from (a) for 34.3, 40.6, and 45.2 GPa showing two transitions in the last two pressures. (c) Variation of the critical field as a function of pressure.

Figure 5

Superconducting transitions of $c$-GST. (a) Temperature dependence of resistance at different pressures. (b) Same measurements using two wires after subtracting residual resistance values (1.329 and 1.564 Ω for 14.2 and 30.7 GPa, respectively).

Figure 6

Superconducting phase diagram of (a) $a$-GST and (b) $c$-GST. Shaded regions in different colors are according to our superconductivity measurements. Since the superconducting transition is not completed at 12.3 GPa, which is the first point in (b), only the onset temperature is given. The points inside rectangles in (b) are measured during the recompression cycle.