Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system

Abstract

A superconductor is a material that can conduct electricity without resistance below a superconducting transition temperature, Tc. The highest Tc that has been achieved to date is in the copper oxide system1: 133 kelvin at ambient pressure2 and 164 kelvin at high pressures3. As the nature of superconductivity in these materials is still not fully understood (they are not conventional superconductors), the prospects for achieving still higher transition temperatures by this route are not clear. In contrast, the Bardeen–Cooper–Schrieffer theory of conventional superconductivity gives a guide for achieving high Tc with no theoretical upper bound—all that is needed is a favourable combination of high-frequency phonons, strong electron–phonon coupling, and a high density of states4. These conditions can in principle be fulfilled for metallic hydrogen and covalent compounds dominated by hydrogen5,6, as hydrogen atoms provide the necessary high-frequency phonon modes as well as the strong electron–phonon coupling. Numerous calculations support this idea and have predicted transition temperatures in the range 50–235 kelvin for many hydrides7, but only a moderate Tc of 17 kelvin has been observed experimentally8. Here we investigate sulfur hydride9, where a Tc of 80 kelvin has been predicted10. We find that this system transforms to a metal at a pressure of approximately 90 gigapascals. On cooling, we see signatures of superconductivity: a sharp drop of the resistivity to zero and a decrease of the transition temperature with magnetic field, with magnetic susceptibility measurements confirming a Tc of 203 kelvin. Moreover, a pronounced isotope shift of Tc in sulfur deuteride is suggestive of an electron–phonon mechanism of superconductivity that is consistent with the Bardeen–Cooper–Schrieffer scenario. We argue that the phase responsible for high-Tc superconductivity in this system is likely to be H3S, formed from H2S by decomposition under pressure. These findings raise hope for the prospects for achieving room-temperature superconductivity in other hydrogen-based materials.

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Figure 1: Temperature dependence of the resistance of sulfur hydride measured at different pressures, and the pressure dependence of Tc.
Figure 2: Pressure and temperature effects on Tc of sulfur hydride and sulfur deuteride.
Figure 3: Temperature dependence of the resistance of sulfur hydride in different magnetic fields.
Figure 4: Magnetization measurements.

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Acknowledgements

Support provided by the European Research Council under the 2010 Advanced Grant 267777 is acknowledged. We appreciate help provided in MPI Chemie by U. Pöschl. We thank P. Alireza and G. Lonzarich for help with samples of CuTi; J. Kamarad, S. Toser and C. Q. Jin for sharing their experience on SQUID measurements; K. Shimizu and his group for cooperation; P. Chu and his group for many discussions and collaboration, and L. Pietronero, M. Calandra and T. Timusk for discussions. V.K. and S.I.S. acknowledge the DFG (Priority Program No. 1458) for support. M.I.E. thanks H. Musshof and R. Wittkowski for precision machining of the DACs.

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Contributions

A.P.D. performed the most of the experiments and contributed to the data interpretation and writing the manuscript. M.I.E. designed the study, wrote the major part of the manuscript, developed the DAC for SQUID measurements, and participated in the experiments. I.A.T. participated in experiments. V.K. and S.I.S. performed the magnetic susceptibility measurements and contributed to writing the manuscript. M.I.E. and A.P.D. contributed equally to this paper.

Corresponding author

Correspondence to M. I. Eremets.

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The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Raman spectra of sulfur hydride at different pressures.

a, Spectra of sulfur hydride at increasing pressure at 230 K. The spectra are shifted relative to each other. At 51 GPa there is a phase transformation, as follows from disappearance of the characteristic vibron peaks in the 2,100–2,500 cm−1 range. The corresponding spectrum is highlighted as a bold curve. Bold curves at higher pressure (and the temperature of the measurement) are shown to follow qualitatively the changes of the spectra. The pressure corresponding to the unassigned plots can be determined from the Raman spectra of the stressed diamond anvil32. b, Raman spectra of sulfur deuteride measured at T ≈ 170 K and over the pressure range 1–70 GPa.

Extended Data Figure 2 Temperature dependence of the resistance of sulfur hydride at 143 GPa.

In this run the sample was clamped in the DAC at T ≈ 200 K, and the pressure then increased to 103 GPa at this temperature; the further increase of pressure to 143 GPa was at 100 K. a, After next cooling to 15 K and subsequent warming, a superconducting transition with Tc ≈ 60 K was observed, then the resistance strongly decreased with increasing temperature. After successive cooling and warming (b; only the warming curve is shown) a kink at 185 K appeared, indicating the onset of superconductivity. The superconducting transition is very broad: resistance dropped to zero only at 22 K. There are apparent ‘oscillations’ on the slope. Their origin is not clear, though they probably reflect inhomogeneity of the sample in the transient state before complete annealing. Similar ‘oscillations’ have also been observed for other samples (see, for example, figure 3 in the Supplementary Information of ref. 9).

Extended Data Figure 3 Electrical measurements.

a, Schematic drawing of diamond anvils with electrical leads separated from the metallic gasket by an insulating layer (shown orange). b, Ti electrodes sputtered on a diamond anvil shown in transmitted light. c, Scheme of the van der Pauw measurements: current leads are indicated by I, and voltage leads as U. d, Typical superconducting step measured in four channels (for different combinations of current and voltage leads shown in c). A sum resistance obtained from the van der Pauw formula is shown by the green line. Note here that the superconducting transition was measured with the un-annealed sample9. After warming to room temperature and successive cooling, Tc should increase. e, Residual resistance measured below the superconducting transition (d). Rmin and ρmin are averaged over four channels shown by different colours.

Extended Data Figure 4 Loading of H2S.

Gaseous H2S is passed through the capillary into a rim around the diamond anvils (upper panel). When the sample liquefies, in the temperature range 191 K < T < 213 K, it is clamped. The process of loading is shown on a video (https://vimeo.com/131914556) and a still is shown here (lower panel). On the video, the camera is looking through a hole in the transparent gasket (CaSO4), and shows a view through the diamond anvil. At T ≈ 200 K, the line to the H2S gas cylinder was opened and the gas condensed. At this moment, the picture changes due to the different refractive index of H2S. The second anvil with the sputtered electrodes was then pushed forward, and the hole was clamped. The sample changed colour during the next application of pressure. The red point is from the focused HeNe laser beam.

Extended Data Figure 5 View of D2S sample with electrical leads and transparent gasket (CaSO4) at different pressures.

The D2S is in the centre of these photographs, which were taken in a cryostat at 220 K with mixed illumination, both transmitted and reflected. Under this illumination, the insulating transparent gasket shows blue, and the electrodes yellow. The red spot is the focused HeNe laser beam. The sample, which is initially transparent, becomes opaque and then reflective as pressure is increased.

Extended Data Figure 6 Magnetic susceptibility measurements with a SQUID.

A typical sample (Fig. 4) has a disk shape (diameter 50–100 μm and thickness of few micrometres). In the superconductive state the magnetic moment for this disk is estimated as M(disk) ≈ 0.2r3H (ref. 33). For a disk of radius r = 40 μm (a sample size typical for DACs in the megabar range) and H = 2 mT the expected diamagnetic signal, M(disk) is estimated as 2.6 × 10−7 emu. This value is well above the sensitivity of the SQUID which is 10−8 emu and, therefore, the signal can be detected. A high-pressure DAC made of Cu:Ti alloy has its own magnetic background signal (a) which increases sharply at low temperatures due to residual paramagnetic impurities. Signal from a large superconducting sample (for example, a Bi-2223 superconductor) could still be detected without magnetic background subtraction. However, the sulfur hydride sample is not seen (b) unless background has been subtracted (c, d). The background signal acquired in the normal state immediately above Tonset has been used for subtraction over all the temperature range taking into account that the magnetic moment of the DAC is fairly temperature independent above 100 K. c, Magnetic measurements for the sample of sulfur hydride at different magnetic fields (labels on curves). The data on sulfur deuteride (d) are compared with the superconducting transition in resistivity measurements (blue curve) which has been scaled to fit the susceptibility data (black points).

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Drozdov, A., Eremets, M., Troyan, I. et al. Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system. Nature 525, 73–76 (2015). https://doi.org/10.1038/nature14964

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