Pressure-induced metallization and superconductivity in the layered van der Waals semiconductor GaTe

We present a systematic high-pressure study of layered van der Waals semiconductor GaTe through electrical transport, photoluminescence, and Raman spectroscopy measurements. We report observation of pressure-induced metallization and superconductivity (SC) in GaTe simultaneously occurring at ∼3 GPa, with an onset superconducting critical temperature of $T_{\mathrm{C}}^{\mathrm{onset}}\sim 5.0\mathrm{K}$. Analysis shows that a quasi–two-dimensional to three-dimensional structural crossover plays a crucial role in driving the observed metallization and SC. Upon further compression, $T_{\mathrm{C}}^{\mathrm{onset}}$ first decreases gradually and then begins to increase above ∼10 GPa, displaying a V-shaped feature (SC-I→SC-II) due to a structural transition ($C2/m\to Fm\text{−}3m$). After reaching a local maximum of 4.5 K at ∼18 GPa, $T_{\mathrm{C}}^{\mathrm{onset}}$ remains almost unchanged up to a highest pressure of 48.1 GPa. A comparison of the upper critical fields at different pressures spanning the SC-I and SC-II phases reveals that their pairing mechanisms may be different from each other. These results demonstrate that the band gap of layered semiconductor GaTe is highly tunable, which may stimulate further investigations by strain engineering, intercalation, and electrostatic doping.

Figure 1

(a) Schematic of the GaTe lattice structure. The Ga and Te atoms are represented by golden and blue spheres, respectively. (b) Single-crystal XRD pattern of GaTe. The inset shows a photo of a piece of as-grown GaTe single crystal. (c) Energy-dispersive x-ray spectroscopy of GaTe. (d) Powder XRD pattern. Red solid line is standard Rietveld refinement to the data (black circle).

Figure 2

(a)–(c) Temperature-dependent in-plane resistance in the temperature range of 1.8–300 K. Resistance of the low-temperature region in pressure range of 3.3 to 7.8 GPa (d), 10.3 to 28.2 GPa (e), and 33.4 to 48.1 GPa (f).

Figure 3

(a)–(c) Temperature dependence of resistance under different magnetic fields perpendicular to the layer plane at 3.3,18, and 33.4 GPa, respectively. (d)–(f) Upper critical field ${\mu }_0{H}_{C2}$ vs $Tc$ at various pressures. Dashed lines represent the fits to the empirical Ginzburg-Landau (GL) formula.

Figure 4

(a) PL spectrum of GaTe at ambient pressure. (b) PL spectra at high pressures from 0.4 to 4.7 GPa. (c) Pressure dependence of the PL peak energy. The dashed line is a least-square fit to the experimental points.

Figure 5

(a) Raman spectrum of GaTe at ambient pressure. (b) Pressure dependence of Raman spectra at various pressures. (c) Intensity evolution of several separate modes as a function of pressure (left column). Corresponding atomic vibrational motions for each separate mode from Ref. [2]. (d) Normalized cell parameters ratio $a/b$ for the monoclinic GaTe at various pressures to 7.8 GPa calculated based on XRD data in Ref. [15].

Figure 6

Temperature-pressure phase diagram of GaTe. SC-I and SC-II stand for the two superconducting phases of GaTe under pressure due to a structural transition.