Periodic Reporting for period 4 - HPSuper (High-Pressure High-Temperature Superconductivity)
Período documentado: 2021-08-01 hasta 2023-01-31
Superconductors allow to transmit electrical currents without losses. This is used for applications including very strong magnets for imagining in medicine and for power transmission. First prototypes of superconducting motors in cargo ships are operational and airplanes are being developed. All these applications, however, are limited by the need to cool superconductors below a transition temperature. Most applications use niobium-based superconductors which require cooling to below -250 °C.
New superconductors with a higher transition temperature are thus very desirable for applications. Hydrogen compounds have recently achieved high transition temperatures close to 0°C. This includes hydrogen sulphide H3S with a transition temperature of -70°C found in 2015 while transition temperatures of -15°C and -45°C were found for lanthanum hydride LaH10 and yttrium hydride YH6. All these compounds are superconductors at very high pressures of 1-2 million bar only. Such high pressures are achieved with diamond anvil pressure cells where only micrometre-sized samples are produced. Whilst such high pressures are not suitable for applications, these materials provide the opportunity to study high-transition-temperature superconductors. This insight will help to design superconductors for use at room temperature and ambient pressure. This research project aims to reveal the microscopic mechanism of superconductivity in hydrogen compounds at high pressures.
Understanding the mechanism of high-temperature superconductivity is achieved through detailed studies of the properties of hydrogen-based superconductors such as H3S, LaH10 and related compounds at high pressures. We focus on several key parameters of the superconducting and normal metal states including the charge carrier concentration, strength of the electron-phonon coupling, London penetration depth, superconducting coherence length, superconducting gap, and Fermi surface topology. Together these properties provide crucial insight into the mechanism of superconductivity which is not yet available. Electrical transport and magnetic measurements are used in this project to extract the above key parameters. In addition, we search for novel superconductors with high transition temperature at lower pressures.
Our electrical transport studies require contacts to the micrometre-sized sample inside the diamond anvil pressure cell. The sample is enclosed between two diamonds and a metal gasket. Thus, access to the sample is very difficult. The project benefits from long-term expertise of the researchers in producing metal tracks on anvils as a replacement for conventional wires. The development of simple methods to produce these tracks in the small size necessary for the diamond anvils at 1 million bar has been successfully completed. A picture of such a microscopic arrangement of the electrodes is shown in Figure 1. This configuration can be used for various measurements including resistivity and Hall effect.
We have developed diamond-anvil cells to generate high pressures and to allow a wide range of measurements on individual samples. This allowed us to correlate comprehensive experimental results to obtain as clear as possible insight into the high-temperature superconductivity. In the case of hydrogen sulphide, we find that the superconductivity is represented by clean behaviour. This in turn enables us to identify with high certainty that superconductivity is driven by strong interactions of electrons with lattice vibrations and we quantify the strength of this interaction.
We conclude that the strong interactions are required to enable high-temperature superconductivity. Together with theory colleagues, we have been able to identify routes to realise strong interactions at lower pressures for instance in lanthanum hydride La4H23 where we indeed discovered superconductivity. This paves a way for the search of novel high-temperature superconductors at ambient pressure.
New superconductors with a higher transition temperature are thus very desirable for applications. Hydrogen compounds have recently achieved high transition temperatures close to 0°C. This includes hydrogen sulphide H3S with a transition temperature of -70°C found in 2015 while transition temperatures of -15°C and -45°C were found for lanthanum hydride LaH10 and yttrium hydride YH6. All these compounds are superconductors at very high pressures of 1-2 million bar only. Such high pressures are achieved with diamond anvil pressure cells where only micrometre-sized samples are produced. Whilst such high pressures are not suitable for applications, these materials provide the opportunity to study high-transition-temperature superconductors. This insight will help to design superconductors for use at room temperature and ambient pressure. This research project aims to reveal the microscopic mechanism of superconductivity in hydrogen compounds at high pressures.
Understanding the mechanism of high-temperature superconductivity is achieved through detailed studies of the properties of hydrogen-based superconductors such as H3S, LaH10 and related compounds at high pressures. We focus on several key parameters of the superconducting and normal metal states including the charge carrier concentration, strength of the electron-phonon coupling, London penetration depth, superconducting coherence length, superconducting gap, and Fermi surface topology. Together these properties provide crucial insight into the mechanism of superconductivity which is not yet available. Electrical transport and magnetic measurements are used in this project to extract the above key parameters. In addition, we search for novel superconductors with high transition temperature at lower pressures.
Our electrical transport studies require contacts to the micrometre-sized sample inside the diamond anvil pressure cell. The sample is enclosed between two diamonds and a metal gasket. Thus, access to the sample is very difficult. The project benefits from long-term expertise of the researchers in producing metal tracks on anvils as a replacement for conventional wires. The development of simple methods to produce these tracks in the small size necessary for the diamond anvils at 1 million bar has been successfully completed. A picture of such a microscopic arrangement of the electrodes is shown in Figure 1. This configuration can be used for various measurements including resistivity and Hall effect.
We have developed diamond-anvil cells to generate high pressures and to allow a wide range of measurements on individual samples. This allowed us to correlate comprehensive experimental results to obtain as clear as possible insight into the high-temperature superconductivity. In the case of hydrogen sulphide, we find that the superconductivity is represented by clean behaviour. This in turn enables us to identify with high certainty that superconductivity is driven by strong interactions of electrons with lattice vibrations and we quantify the strength of this interaction.
We conclude that the strong interactions are required to enable high-temperature superconductivity. Together with theory colleagues, we have been able to identify routes to realise strong interactions at lower pressures for instance in lanthanum hydride La4H23 where we indeed discovered superconductivity. This paves a way for the search of novel high-temperature superconductors at ambient pressure.
The work of this project included developments of experimental apparatus, novel synthesis methods of materials a high pressure, and comprehensive studies of high-temperature hydride superconductors.
We have developed diamond anvil cells specifically suited for the study of superconductors at high pressures. Our diamond anvil cells are compatible with the low-temperature resistivity and Hall effect measurements (Figure 2) and at the same time can be used for structural measurements using X-ray diffraction at synchrotron facilities and studies in high magnetic fields at the European High-Magnetic-Field facilities.
Our diamond-anvil-cell technology is now being explored for commercial exploitation. We now work towards prototypes that can be presented to industry partners and making this technology available for research and development.
Sample preparation in diamond anvil cells has been made more reliable and accessible through our development of thin-film methods. This method is naturally suited for the micro-meter sized samples in diamond anvil cells and allows to obtain a higher ratio of hydrogen in the sample. This method has been tested and used successfully for instance in the discovery of La4H23.
Comprehensive studies of hydride high-temperature superconductors have been used to correlate structural motifs with electronic and superconducting properties. In the case of La4H23, we could identify the presence of hydrogen cages to support the high-temperature superconductivity. This motif is now one of the guiding principles in the search for high-temperature superconductivity.
Our results have been presented at numerous international meetings and conferences and have been published in scientific journals in open-access format.
We have developed diamond anvil cells specifically suited for the study of superconductors at high pressures. Our diamond anvil cells are compatible with the low-temperature resistivity and Hall effect measurements (Figure 2) and at the same time can be used for structural measurements using X-ray diffraction at synchrotron facilities and studies in high magnetic fields at the European High-Magnetic-Field facilities.
Our diamond-anvil-cell technology is now being explored for commercial exploitation. We now work towards prototypes that can be presented to industry partners and making this technology available for research and development.
Sample preparation in diamond anvil cells has been made more reliable and accessible through our development of thin-film methods. This method is naturally suited for the micro-meter sized samples in diamond anvil cells and allows to obtain a higher ratio of hydrogen in the sample. This method has been tested and used successfully for instance in the discovery of La4H23.
Comprehensive studies of hydride high-temperature superconductors have been used to correlate structural motifs with electronic and superconducting properties. In the case of La4H23, we could identify the presence of hydrogen cages to support the high-temperature superconductivity. This motif is now one of the guiding principles in the search for high-temperature superconductivity.
Our results have been presented at numerous international meetings and conferences and have been published in scientific journals in open-access format.
This project has not only provided independent confirmation of hydride superconductivity but has also achieved in-depth insight into the nature of the superconducting state and identified novel superconductors at lower pressures.
Reproducing results is a cornerstone of the scientific method but high-pressure measurements of superconductivity are only available to a handful of groups around the world. We have successfully reproduced measurements of superconductivity in H3S hydrogen sulphide and established this beyond doubt through detailed cross-correlation of crystallographic and electronic measurements.
Our results establish H3S as the cleanest example of hydride superconductivity and demonstrate the relevance of strong interactions between electrons and atomic vibrations for the formation of superconductivity. This insight is now guiding the global search for high-temperature superconductivity at lower pressures.
Our discovery of high-temperature superconductivity in La4H23 is one step in the direction of superconductivity at lower pressures.
Reproducing results is a cornerstone of the scientific method but high-pressure measurements of superconductivity are only available to a handful of groups around the world. We have successfully reproduced measurements of superconductivity in H3S hydrogen sulphide and established this beyond doubt through detailed cross-correlation of crystallographic and electronic measurements.
Our results establish H3S as the cleanest example of hydride superconductivity and demonstrate the relevance of strong interactions between electrons and atomic vibrations for the formation of superconductivity. This insight is now guiding the global search for high-temperature superconductivity at lower pressures.
Our discovery of high-temperature superconductivity in La4H23 is one step in the direction of superconductivity at lower pressures.