Superconductivity in Pristine $2H_a\text{−}{\mathrm{MoS}}_2$ at Ultrahigh Pressure

As a follow-up of our previous work on pressure-induced metallization of the $2H_c\text{−}{\mathrm{MoS}}_2$ [Chi et al., Phys. Rev. Lett. 113, 036802 (2014)], here we extend pressure beyond the megabar range to seek after superconductivity via electrical transport measurements. We found that superconductivity emerges in the $2H_a\text{−}{\mathrm{MoS}}_2$ with an onset critical temperature $T_c$ of ca. 3 K at ca. 90 GPa. Upon further increasing the pressure, $T_c$ is rapidly enhanced beyond 10 K and stabilized at ca. 12 K over a wide pressure range up to 220 GPa. Synchrotron x-ray diffraction measurements evidenced no further structural phase transition, decomposition, and amorphization up to 155 GPa, implying an intrinsic superconductivity in the $2H_a\text{−}{\mathrm{MoS}}_2$. DFT calculations suggest that the emergence of pressure-induced superconductivity is intimately linked to the emergence of a new flat Fermi pocket in the electronic structure. Our finding represents an alternative strategy for achieving superconductivity in $2H\text{−}{\mathrm{MoS}}_2$ in addition to chemical intercalation and electrostatic gating.

Figure 1

Temperature-dependent resistance of $2H_a\text{−}{\mathrm{MoS}}_2$ at elevated pressures. (a) $R\text{−}T$ curves at pressures between 30 and 70 GPa in run 1. (b) $R\text{−}T$ curves at pressures between 100 and 145 GPa in run 2. (c) $R\text{−}T$ curves at pressures between 145 and 220 GPa in run 3. The inset in (b) and (c) is the close-up of the low-temperature region, highlighting the superconducting transition.

Figure 2

The determination of zero-temperature upper critical magnetic field ${\mu }_0{H}_{c2}(0)$ of $2H_a\text{−}{\mathrm{MoS}}_2$ at 220 GPa. (a) $R\text{−}T$ curves under external magnetic fields of up to 6.5 T at steps of 0.5 T. (b) ${\mu }_0{H}_{c2}\text{−}T$ phase diagram. The solid line in red and blue represents fitting by the WHH formula and GL equation, respectively.

Figure 3

Pressure-temperature ($P\text{−}T$) phase diagram of $2H\text{−}{\mathrm{MoS}}_2$. The vertical dashed line demarcates the boundary between the semiconducting and metallic states. The inset displays the $T^3$ linear dependence of $R$ following the equation of $R(T)=R_0+A{T}^n$ with $n=3(\pm 0.2)$ over the temperature range from $T_c$ up to 50 K at 220 GPa, where $R_0$ is the residual resistance and $A$ is the thermal coefficient. The error bar on $T_c$ indicates the uncertainty due to pressure gradient. The error bar on pressure indicates 95% confidence interval.

Figure 4

High-pressure synchrotron x-ray diffraction analysis of $2H\text{−}{\mathrm{MoS}}_2$. (a) XRD patterns from ambient pressure up to 155 GPa at room temperature (run 1, $\lambda =0.3999\AA$). (b) Rietveld refinements on XRD patterns of the $2H_c$ phase at 0 GPa and the $2H_a$ phase at 52 GPa (run 2, $\lambda =0.3091\AA$). (c)–(f) Pressure dependence of experimental and calculated lattice constant $c$, lattice constant $a$, axial ratio $c/a$ and unit-cell volume. The solid line represents the fitting of experimental $P\text{−}V$ data by the Birch-Murnaghan equation of state.