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The absence of electrical resistance exhibited by superconducting materials would have enormous potential for applications if it existed at ambient temperature and pressure conditions. Despite decades of intense research efforts, such a state has yet to be realized . At ambient pressures, cuprates are the material class exhibiting superconductivity to the highest critical superconducting transition temperatures (T ), up to about 133 K (refs.  ). Over the past decade, high-pressure 'chemical precompression' of hydrogen-dominant alloys has led the search for high-temperature superconductivity, with demonstrated T approaching the freezing point of water in binary hydrides at megabar pressures . Ternary hydrogen-rich compounds, such as carbonaceous sulfur hydride, offer an even larger chemical space to potentially improve the properties of superconducting hydrides . Here we report evidence of superconductivity on a nitrogen-doped lutetium hydride with a maximum T of 294 K at 10 kbar, that is, superconductivity at room temperature and near-ambient pressures. The compound was synthesized under high-pressure high-temperature conditions and then-after full recoverability-its material and superconducting properties were examined along compression pathways. These include temperature-dependent resistance with and without an applied magnetic field, the magnetization (M) versus magnetic field (H) curve, a.c. and d.c. magnetic susceptibility, as well as heat-capacity measurements. X-ray diffraction (XRD), energy-dispersive X-ray (EDX) and theoretical simulations provide some insight into the stoichiometry of the synthesized material. Nevertheless, further experiments and simulations are needed to determine the exact stoichiometry of hydrogen and nitrogen, and their respective atomistic positions, in a greater effort to further understand the superconducting state of the material.

The microscopic structure of water’s surface is crucial to many natural and industrial processes, but studying its hydrogen bond (H-bond) network directly remains challenging due to the required interfacial sensitivity of experimental techniques. By leveraging advances in flat liquid sheet microjets and terawatt-scale attosecond soft X-ray pulses from the LCLS X-ray free electron laser, we employed soft X-ray second harmonic generation (SXSHG) spectroscopy to examine the liquid water/vapor interface. SXSHG combines the elemental selectivity of X-ray spectroscopies with the surface selectivity of SHG and gives access to the electronic structure of interfacial species. Here, we show the SXSHG spectrum differs from bulk water’s X-ray absorption, with its peak shifted several eV, indicating a vastly different electronic environment at the interface as compared to the bulk. First-principles electronic structure calculations show the signal is highly sensitive to H-bond interactions, such as water molecules accepting a single H-bond, which are surface abundant. Water-vapor interfaces have been studied with many techniques, yet open questions persist about their electronic and molecular structure. Here, the authors demonstrate the application of soft x-ray second harmonic generation to study the water surface by leveraging attosecond pulses at the LCLS and a flat liquid sheet microjet, providing insights on the H-bond structure.

One of the long-standing challenges in experimental physics is the observation of room-temperature superconductivity . Recently, high-temperature conventional superconductivity in hydrogen-rich materials has been reported in several systems under high pressure . An  important discovery leading to room-temperature superconductivity is the pressure-driven disproportionation of hydrogen sulfide (H S) to H S, with a confirmed transition temperature of 203 kelvin at 155 gigapascals . Both H S and CH readily mix with hydrogen to form guest-host structures at lower pressures , and are of  comparable size at 4 gigapascals. By introducing methane at low pressures into the H S + H precursor mixture for H S, molecular exchange is allowed within a large assemblage of van der Waals solids that are hydrogen-rich with H inclusions; these guest-host structures become the building blocks of superconducting compounds at extreme conditions. Here we report superconductivity in a photochemically transformed carbonaceous sulfur hydride system, starting from elemental precursors, with a maximum superconducting transition temperature of 287.7 ± 1.2 kelvin (about 15 degrees Celsius) achieved at 267 ± 10 gigapascals. The superconducting state is observed over a broad pressure range in the diamond anvil cell, from 140 to 275 gigapascals, with a sharp upturn in transition temperature above 220 gigapascals. Superconductivity is established by the observation of zero resistance, a magnetic susceptibility of up to 190 gigapascals, and reduction of the transition temperature under an external magnetic field of up to 9 tesla, with an upper critical magnetic field of about 62 tesla according to the Ginzburg-Landau model at zero temperature. The light, quantum nature of hydrogen limits the structural and stoichiometric determination of the system by X-ray scattering techniques, but Raman spectroscopy is used to probe the chemical and structural transformations before metallization. The introduction of chemical tuning within our ternary system could enable the preservation of the properties of room-temperature superconductivity at lower pressures.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The absence of electrical resistance exhibited by superconducting materials would have enormous potential for applications if it existed at ambient temperature and pressure conditions. Despite decades of intense research efforts, such a state has yet to be realized 1 , 2 . At ambient pressures, cuprates are the material class exhibiting superconductivity to the highest critical superconducting transition temperatures ( T c ), up to about 133 K (refs.  3 – 5 ). Over the past decade, high-pressure ‘chemical precompression’ 6 , 7 of hydrogen-dominant alloys has led the search for high-temperature superconductivity, with demonstrated T c approaching the freezing point of water in binary hydrides at megabar pressures 8 – 13 . Ternary hydrogen-rich compounds, such as carbonaceous sulfur hydride, offer an even larger chemical space to potentially improve the properties of superconducting hydrides 14 – 21 . Here we report evidence of superconductivity on a nitrogen-doped lutetium hydride with a maximum T c of 294 K at 10 kbar, that is, superconductivity at room temperature and near-ambient pressures. The compound was synthesized under high-pressure high-temperature conditions and then—after full recoverability—its material and superconducting properties were examined along compression pathways. These include temperature-dependent resistance with and without an applied magnetic field, the magnetization ( M ) versus magnetic field ( H ) curve, a.c. and d.c. magnetic susceptibility, as well as heat-capacity measurements. X-ray diffraction (XRD), energy-dispersive X-ray (EDX) and theoretical simulations provide some insight into the stoichiometry of the synthesized material. Nevertheless, further experiments and simulations are needed to determine the exact stoichiometry of hydrogen and nitrogen, and their respective atomistic positions, in a greater effort to further understand the superconducting state of the material. A nitrogen-doped lutetium hydride was synthesized under high-pressure high-temperature conditions and, following full recoverability, examination along compression pathways showed evidence of superconductivity at room temperature and near-ambient pressures.

Synopsis We discuss the implementation (https://commons.lbl.gov/display/csd/LBNL-AMO-MCTDHF) of Multiconfiguration Time-Dependent Hartree-Fock for polyatomic molecules using a Cartesian product grid of sinc basis functions, and present absorption cross sections and other results calculated with it.

One of the long-standing challenges in experimental physics is the observation of room-temperature superconductivity 1 , 2 . Recently, high-temperature conventional superconductivity in hydrogen-rich materials has been reported in several systems under high pressure 3 – 5 . An  important discovery leading to room-temperature superconductivity is the pressure-driven disproportionation of hydrogen sulfide (H 2 S) to H 3 S, with a confirmed transition temperature of 203 kelvin at 155 gigapascals 3 , 6 . Both H 2 S and CH 4 readily mix with hydrogen to form guest–host structures at lower pressures 7 , and are of  comparable size at 4 gigapascals. By introducing methane at low pressures into the H 2 S + H 2 precursor mixture for H 3 S, molecular exchange is allowed within a large assemblage of van der Waals solids that are hydrogen-rich with H 2 inclusions; these guest–host structures become the building blocks of superconducting compounds at extreme conditions. Here we report superconductivity in a photochemically transformed carbonaceous sulfur hydride system, starting from elemental precursors, with a maximum superconducting transition temperature of 287.7 ± 1.2 kelvin (about 15 degrees Celsius) achieved at 267 ± 10 gigapascals. The superconducting state is observed over a broad pressure range in the diamond anvil cell, from 140 to 275 gigapascals, with a sharp upturn in transition temperature above 220 gigapascals. Superconductivity is established by the observation of zero resistance, a magnetic susceptibility of up to 190 gigapascals, and reduction of the transition temperature under an external magnetic field of up to 9 tesla, with an upper critical magnetic field of about 62 tesla according to the Ginzburg–Landau model at zero temperature. The light, quantum nature of hydrogen limits the structural and stoichiometric determination of the system by X-ray scattering techniques, but Raman spectroscopy is used to probe the chemical and structural transformations before metallization. The introduction of chemical tuning within our ternary system could enable the preservation of the properties of room-temperature superconductivity at lower pressures. Room-temperature superconductivity is observed in a photochemically synthesized ternary carbonaceous sulfur hydride system at 15 °C and 267 GPa.

The expansiveness of compositional phase space is too vast to fully search using current theoretical tools for many emergent problems in condensed matter physics. The reliance on a deep chemical understanding is one method to identify local minima of relevance to investigate further, minimizing sample space. Utilizing machine learning methods can permit a deeper appreciation of correlations in higher order parameter space and be trained to behave as a predictive tool in the exploration of new materials. We have applied this approach in our search for new high temperature superconductors by incorporating models which can differentiate structural polymorphisms, in a pressure landscape, a critical component for understanding high temperature superconductivity. Our development of a representation for machine learning superconductivity with structural properties allows fast predictions of superconducting transition temperatures (\\(T_c\\)) providing a \\(r^2\\) above 0.94.