High-temperature superconductivity in sulfur hydride evidenced by alternating-current magnetic susceptibility

Abstract

The search for high-temperature superconductivity is one of the research frontiers in physics. In the sulfur hydride system, an extremely high T _c (∼200 K) has been recently developed at pressure. However, the Meissner effect measurement above megabar pressures is still a great challenge. Here, we report the superconductivity identification of sulfur hydride at pressure, employing an in situ alternating-current magnetic susceptibility technique. We determine the superconducting phase diagram, finding that superconductivity suddenly appears at 117 GPa and T _c reaches 183 K at 149 GPa before decreasing monotonically with increasing pressure. By means of theoretical calculations, we elucidate the variation of T _c in the low-pressure region in terms of the changing stoichiometry of sulfur hydride and the further decrease in T _c owing to a drop in the electron-phonon interaction parameter λ. This work provides a new insight into clarifying superconducting phenomena and anchoring the superconducting phase diagram in the hydrides.

Keywords: Meissner effect; high pressure; hydrides; superconductivity.

Figure 1.

Schematic image of the experimental set-up for alternating-current magnetic susceptibility measurement. (a) Simplified flow chart for the magnetic susceptibility measurement set-up for the diamond anvil cell (DAC). LIA and AC denote lock-in amplifier and alternating-current source, respectively. (b) The sample in the gasket hole at 2 GPa and 200 K (left), and at 155 GPa and 300 K (right), respectively. (c) A pickup coil wound around a diamond anvil and a compensating coil connected in opposition.

Figure 2.

Magnetic susceptibility signals of sulfur hydride at various pressures. Curves show typical amplitude records from the coil system during each temperature scan at (a) 117 GPa, (b) 130 GPa, (c) 149 GPa and (d) 155 GPa. To obtain the strong amplitude signal, we kept the sample and compensating coil signals in phase. The critical temperature T_c is estimated from the onset of the superconducting transition.

Figure 3.

The measured T_c and calculated superconducting parameters at different pressures. (a) Pressure dependence of T_c in sulfur hydride. Filled circles show data from this experiment while filled squares and triangles indicate our reported theoretical work [10]. The open circles, squares and triangles show experimental results reported by Drozdov et al. [14,15] and Einaga et al. [22], respectively. The blue pentagram is obtained from the magnetic experiment by Drozdov et al. [15]. Lower panels show (b) the calculated parameter λ, (c) the logarithmic average phonon frequency ω_log, (d) the average squared phonon frequencies 〈ω²〉 and (e) the electronic DOS at the Fermi level N(ϵ_F) at different pressures of the Im-3 m structure.

Figure 4.

Snapshot of the molecular dynamics trajectory and polymeric networks of the S–H coordinated configuration. The structure views of molecular dynamics are at (a) 140 GPa and 100 K, and (b) 140 GPa and 300 K, respectively.