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

Journal name:
Nature
Volume:
525,
Pages:
73–76
Date published:
DOI:
doi:10.1038/nature14964
Received
Accepted
Published online

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.

At a glance

Figures

  1. Temperature dependence of the resistance of sulfur hydride measured at different pressures, and the pressure dependence of Tc.
    Figure 1: Temperature dependence of the resistance of sulfur hydride measured at different pressures, and the pressure dependence of Tc.

    a, Main panel, temperature dependence of the resistance (R) of sulfur hydride at different pressures. The pressure values are indicated near the corresponding plots. At first, the sample was loaded at T 200 K and the pressure was increased to ~100 GPa; the sample was then cooled down to 4 K. After warming to ~100 K, pressure was further increased. Plots at pressures <135 GPa have been scaled (reduced) as follows—105 GPa, by 10 times; 115 GPa and 122 GPa, by 5 times; and 129 GPa by 2 times—for easier comparison with the higher pressure steps. The resistance was measured with a current of 10 μA. Bottom panel, the resistance plots near zero. The resistance was measured with four electrodes deposited on a diamond anvil that touched the sample (top panel inset). The diameters of the samples were ~25 μm and the thickness was ~1 μm. b, Blue round points represent values of Tc determined from a. Other blue points (triangles and half circles) were obtained in similar runs. Measurements at P >~160 GPa revealed a sharp increase of Tc. In this pressure range the R(T) measurements were performed over a larger temperature range up to 260 K, the corresponding experimental points for two samples are indicated by adding a pink colour to half circles and a centred dot to filled circles. These points probably reflect a transient state for these particular P/T conditions. Further annealing of the sample at room temperature would require stabilizing the sample (Fig. 2a). Black stars are calculations from ref. 10. Dark yellow points are Tc values of pure sulfur obtained with the same four-probe electrical measurement method. They are consistent with literature data30 (susceptibility measurements) but have higher values at P > 200 GPa.

  2. Pressure and temperature effects on Tc of sulfur hydride and sulfur deuteride.
    Figure 2: Pressure and temperature effects on Tc of sulfur hydride and sulfur deuteride.

    a, Changes of resistance and Tc of sulfur hydride with temperature at constant pressure—the annealing process. The sample was pressurized to 145 GPa at 220 K and then cooled to 100 K. It was then slowly warmed at ~1 K min−1; Tc = 170 K was determined. At temperatures above ~250 K the resistance dropped sharply, and during the next temperature run Tc increased to ~195 K. This Tc remained nearly the same for the next two runs. (We note that the only point for sulfur deuteride presented in ref. 9 was determined without sample annealing, and Tc would increase after annealing at room temperature.) b, Typical superconductive steps for sulfur hydride (blue trace) and sulfur deuteride (red trace). The data were acquired during slow warming over a time of several hours. Tc is defined here as the sharp kink in the transition to normal metallic behaviour. These curves were obtained after annealing at room temperature as shown in a. c, Dependence of Tc on pressure; data on annealed samples are presented. Open coloured points refer to sulfur deuteride, and filled points to sulfur hydride. Data shown as the magenta point were obtained in magnetic susceptibility measurements (Fig. 4a). The lines indicate that the plots are parallel at pressures above ~170 GPa (the isotope shift is constant) but strongly deviate at lower pressures.

  3. Temperature dependence of the resistance of sulfur hydride in different magnetic fields.
    Figure 3: Temperature dependence of the resistance of sulfur hydride in different magnetic fields.

    a, The shift of the ~60 K superconducting transition in magnetic fields of 0–7 T (colour coded). The upper and lower parts of the transition are shown enlarged in the insets (axes as in main panel). The temperature dependence of the resistance without an applied magnetic field was measured three times: before applying the field, after applying 1, 3, 5, 7 T and finally after applying 2, 4, 6 T (black, grey and dark grey colours). b, The same measurements but for the 185 K superconducting transition. c, The temperature dependence of the critical magnetic field strengths of sulfur hydride. Tc (black points deduced from a, b) are plotted for the corresponding magnetic fields. To estimate the critical magnetic field Hc, the plots were extrapolated to high magnetic fields using the formula Hc(T) = Hc0(1 − (T/Tc)2). The extrapolation has been done with 95% confidence (band shown as grey lines).

  4. Magnetization measurements.
    Figure 4: Magnetization measurements.

    a, Temperature dependence of the magnetization of sulfur hydride at a pressure of 155 GPa in zero-field cooled (ZFC) and 20 Oe field cooled (FC) modes (black circles). The onset temperature is Tonset = 203(1) K. For comparison, the superconducting step obtained for sulfur hydride from electrical measurements at 145 GPa is shown by red circles. Resistivity data (Tonset = 195 K) were scaled and moved vertically to compare with the magnetization data. Inset, optical micrograph of a sulfur hydride sample at 155 GPa in a CaSO4 gasket (scale bar 100 μm). The high Tonset = 203 K measured from the susceptibility can be explained by a significant input to the signal from the periphery of the sample which expanded beyond the culet where pressure is smaller than in the culet centre (Tc increases with decreasing pressure (Fig. 2b)). b, Non-magnetic diamond anvil cell (DAC) of diameter 8.8 mm. c, Magnetization measurements M(H) of sulfur hydride at a pressure of 155 GPa at different temperatures (given as curve labels). The magnetization curves show hysteresis, indicating a type II superconductor. The magnetization curves are however distorted by obvious paramagnetic input (which is also observed in other superconductors31). In our case, the paramagnetic signal is probably from the DAC, but further study of the origin of this input is required. The paramagnetic background increases when temperature is decreased. The minima of the magnetization curves (~35 mT) are the result of the diamagnetic input from superconductivity and the paramagnetic background. The first critical field Hc1 30 mT can be roughly estimated as the point where magnetization deviates from linear behaviour. At higher fields, magnetization increases due to the penetration of magnetic vortexes. As the sign of the field change reverses, the magnetic flux in the Shubnikov phase remains trapped and therefore the back run (that is, with decreasing field) is irreversible—the returning branch of the magnetic cycle (shown by filled points) runs above the direct one. Hysteretic behaviour of the magnetization becomes more clearly visible as the temperature decreases. d, At high temperatures T > 200 K, the magnetization decreases sharply. e, Extrapolation of the pronounced minima at the magnetization curves to higher temperatures gives the onset of superconductivity at T = 203.5 K.

  5. Raman spectra of sulfur hydride at different pressures.
    Extended Data Fig. 1: Raman spectra of sulfur hydride at different pressures.

    a, Spectra of sulfur hydride at increasing pressure at ~230K. The spectra are shifted relative to each other. At 51GPa there is a phase transformation, as follows from disappearance of the characteristic vibron peaks in the 2,100–2,500cm−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 T170K and over the pressure range 1–70GPa.

  6. Temperature dependence of the resistance of sulfur hydride at 143 GPa.
    Extended Data Fig. 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).

  7. Electrical measurements.
    Extended Data Fig. 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.

  8. Loading of H2S.
    Extended Data Fig. 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.

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

  10. Magnetic susceptibility measurements with a SQUID.
    Extended Data Fig. 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).

References

  1. Bednorz, J. G. & Mueller, K. A. Possible high TC superconductivity in the Ba-La-Cu-O system. Z. Phys. B 64, 189193 (1986)
  2. Schilling, A., Cantoni, M. & Guo, J. D. &. Ott, H. R. Superconductivity above 130 K in the Hg-Ba-Ca-Cu-O system. Nature 363, 5658 (1993)
  3. Gao, L. et al. Superconductivity up to 164 K in HgBa2Cam−lCumO2m+2+δ (m = l, 2, and 3) under quasihydrostatic pressures. Phys. Rev. B 50, 42604263 (1994)
  4. Ginzburg, V. L. Once again about high-temperature superconductivity. Contemp. Phys. 33, 1523 (1992)
  5. Ashcroft, N. W. Metallic hydrogen: A high-temperature superconductor? Phys. Rev. Lett. 21, 17481750 (1968)
  6. Ashcroft, N. W. Hydrogen dominant metallic alloys: high temperature superconductors? Phys. Rev. Lett. 92, 187002 (2004)
  7. Wang, Y. & Ma, Y. Perspective: Crystal structure prediction at high pressures. J. Chem. Phys. 140, 040901 (2014)
  8. Eremets, M. I., Trojan, I. A., Medvedev, S. A., Tse, J. S. & Yao, Y. Superconductivity in hydrogen dominant materials: silane. Science 319, 15061509 (2008)
  9. Drozdov, A. P., Eremets, M. I. & Troyan, I. A. Conventional superconductivity at 190 K at high pressures. Preprint at http://arXiv.org/abs/1412.0460 (2014)
  10. Li, Y., Hao, J., Li, Y. & Ma, Y. The metallization and superconductivity of dense hydrogen sulfide. J. Chem. Phys. 140, 174712 (2014)
  11. Nagamatsu, J., Nakagawa, N., Muranaka, T., Zenitani, Y. & Akimitsu, J. Superconductivity at 39 K in magnesium diboride. Nature 410, 6364 (2001)
  12. McMahon, J. M., Morales, M. A., Pierleoni, C. & Ceperley, D. M. The properties of hydrogen and helium under extreme conditions. Rev. Mod. Phys. 84, 16071653 (2012)
  13. Eremets, M. I. & Troyan, I. A. Conductive dense hydrogen. Nature Mater. 10, 927931 (2011)
  14. Fujihisa, H. et al. Molecular dissociation and two low-temperature high-pressure phases of H2S. Phys. Rev. B 69, 214102 (2004)
  15. Sakashita, M. et al. Pressure-induced molecular dissociation and metallization in hydrogen-bonded H2S solid. Phys. Rev. Lett. 79, 10821085 (1997)
  16. Kometani, S., Eremets, M., Shimizu, K., Kobayashi, M. & Amaya, K. Observation of pressure-induced superconductivity of sulfur. J. Phys. Soc. Jpn. 66, 25642565 (1997)
  17. Shimizu, H. et al. Pressure-temperature phase diagram of solid hydrogen sulfide determined by Raman spectroscopy. Phys. Rev. B 51, 93919394 (1995)
  18. Shimizu, H., Murashima, H. & Sasaki, S. High-pressure Raman study of solid deuterium sulfide up to 17 GPa. J. Chem. Phys. 97, 71377139 (1992)
  19. Matula, R. A. Electrical resistivity of copper, gold, palladium, and silver. J. Phys. Chem. Ref. 8, 11471298 (1979)
  20. Duan, D. et al. Pressure-induced metallization of dense (H2S)2H2 with high-Tc superconductivity. Sci. Rep. 4, 6968 (2014)
  21. Strobel, T. A., Ganesh, P., Somayazulu, M., Kent, P. R. C. & Hemley, R. J. Novel cooperative interactions and structural ordering in H2S–H2. Phys. Rev. Lett. 107, 255503 (2011)
  22. Duan, D. et al. Pressure-induced decomposition of solid hydrogen sulfide. Phys. Rev. B 91, 180502(R) (2015)
  23. Bernstein, N., Hellberg, C. S., Johannes, M. D., Mazin, I. I. & Mehl, M. J. What superconducts in sulfur hydrides under pressure, and why. Phys. Rev. B 91, 060511(R) (2015)
  24. Errea, I. et al. Hydrogen sulfide at high pressure: a strongly-anharmonic phonon-mediated superconductor. Phys. Rev. Lett. 114, 157004 (2015)
  25. Flores-Livas, J. A., Sanna, A. & Gross, E. K. U. High temperature superconductivity in sulfur and selenium hydrides at high pressure. Preprint at http://arXiv.org/abs/1501.06336v1 (2015)
  26. Papaconstantopoulos, D. A., Klein, B. M., Mehl, M. J. & Pickett, W. E. Cubic H3S around 200 GPa: an atomic hydrogen superconductor stabilized by sulfur. Phys. Rev. B. 91, 184511 (2015)
  27. Akashi, R., Kawamura, M., Tsuneyuki, S., Nomura, Y. & Arita, R. Fully non-empirical study on superconductivity in compressed sulfur hydrides. Preprint at http://arXiv.org/abs/1502.00936v1 (2015)
  28. Cohen, M. L. in BCS: 50 years (eds Cooper, L. N. & Feldman, D.) 375389 (World Scientific, 2011)
  29. An, J. M. & Pickett, W. E. Superconductivity of MgB2: covalent bonds driven metallic. Phys. Rev. Lett. 86, 43664369 (2001)
  30. Gregoryanz, E. et al. Superconductivity in the chalcogens up to multimegabar pressures. Phys. Rev. B 65, 064504 (2002)
  31. Senoussi, S., Sastry, P., Yakhmi, J. V. & Campbell, I. Magnetic hysteresis of superconducting GdBa2Cu3O7 down to 1.8 K. J. Phys. 49, 21632164 (1988)
  32. Eremets, M. I. Megabar high-pressure cells for Raman measurements. J. Raman Spectrosc. 34, 515518 (2003)
  33. Landau, L. D. & Lifshitz, E. M. Electrodynamics of Continuous Media Vol. 8, 1st edn, 173 (Pergamon, 1960)

Download references

Author information

  1. These authors contributed equally to this work.

    • A. P. Drozdov &
    • M. I. Eremets

Affiliations

  1. Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, 55128 Mainz, Germany

    • A. P. Drozdov,
    • M. I. Eremets &
    • I. A. Troyan
  2. Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität Mainz, Staudingerweg 9, 55099 Mainz, Germany

    • V. Ksenofontov &
    • S. I. Shylin

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.

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to:

Author details

Extended data figures and tables

Extended Data Figures

  1. Extended Data Figure 1: Raman spectra of sulfur hydride at different pressures. (494 KB)

    a, Spectra of sulfur hydride at increasing pressure at ~230K. The spectra are shifted relative to each other. At 51GPa there is a phase transformation, as follows from disappearance of the characteristic vibron peaks in the 2,100–2,500cm−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 T170K and over the pressure range 1–70GPa.

  2. Extended Data Figure 2: Temperature dependence of the resistance of sulfur hydride at 143 GPa. (90 KB)

    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).

  3. Extended Data Figure 3: Electrical measurements. (247 KB)

    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.

  4. Extended Data Figure 4: Loading of H2S. (587 KB)

    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.

  5. Extended Data Figure 5: View of D2S sample with electrical leads and transparent gasket (CaSO4) at different pressures. (359 KB)

    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.

  6. Extended Data Figure 6: Magnetic susceptibility measurements with a SQUID. (240 KB)

    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).

Additional data