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1.
J Chem Phys ; 155(11): 114703, 2021 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-34551552

RESUMO

X-ray diffraction indicates that the structure of the recently discovered carbonaceous sulfur hydride (C-S-H) room-temperature superconductor is derived from previously established van der Waals compounds found in the H2S-H2 and CH4-H2 systems. Crystals of the superconducting phase were produced by a photochemical synthesis technique, leading to the superconducting critical temperature Tc of 288 K at 267 GPa. X-ray diffraction patterns measured from 124 to 178 GPa, within the pressure range of the superconducting phase, are consistent with an orthorhombic structure derived from the Al2Cu-type determined for (H2S)2H2 and (CH4)2H2 that differs from those predicted and observed for the S-H system at these pressures. The formation and stability of the C-S-H compound can be understood in terms of the close similarity in effective volumes of the H2S and CH4 components, and denser carbon-bearing S-H phases may form at higher pressures. The results are crucial for understanding the very high superconducting Tc found in the C-S-H system at megabar pressures.

2.
Adv Mater ; 33(39): e2103000, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-34397123

RESUMO

The competing and non-equilibrium phase transitions, involving dynamic tunability of cooperative electronic and magnetic states in strongly correlated materials, show great promise in quantum sensing and information technology. To date, the stabilization of transient states is still in the preliminary stage, particularly with respect to molecular electronic solids. Here, a dynamic and cooperative phase in potassium-7,7,8,8-tetracyanoquinodimethane (K-TCNQ) with the control of pulsed electromagnetic excitation is demonstrated. Simultaneous dynamic and coherent lattice perturbation with 8 ns pulsed laser (532 nm, 15 MW cm-2 , 10 Hz) in such a molecular electronic crystal initiates a stable long-lived (over 400 days) conducting paramagnetic state (≈42 Ωcm), showing the charge-spin bistability over a broad temperature range from 2 to 360 K. Comprehensive noise spectroscopy, in situ high-pressure measurements, electron spin resonance (ESR), theoretical model, and scanning tunneling microscopy/spectroscopy (STM/STS) studies provide further evidence that such a transition is cooperative, requiring a dedicated charge-spin-lattice decoupling to activate and subsequently stabilize nonequilibrium phase. The cooperativity triggered by ultrahigh-strain-rate (above 106 s- 1 ) pulsed excitation offers a collective control toward the generation and stabilization of strongly correlated electronic and magnetic orders in molecular electronic solids and offers unique electro-magnetic phases with technological promises.

3.
Phys Rev Lett ; 127(1): 016401, 2021 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-34270285

RESUMO

A reversible density driven insulator to metal to insulator transition in high-spin MnS_{2} is experimentally observed, leading with a colossal electrical resistance drop of 10^{8} Ω by 12 GPa. Density functional theory simulations reveal the metallization to be unexpectedly driven by previously unoccupied S_{2}^{2-} σ_{3p}^{*} antibonding states crossing the Fermi level. This is a unique variant of the charge transfer insulator to metal transition for negative charge transfer insulators having anions with an unsaturated valence. By 36 GPa the emergence of the low-spin insulating arsenopyrite (P2_{1}/c) is confirmed, and the bulk metallicity is broken with the system returning to an insulative electronic state.

4.
Phys Rev Lett ; 126(11): 117003, 2021 Mar 19.
Artigo em Inglês | MEDLINE | ID: mdl-33798352

RESUMO

The recent observation of room-temperature superconductivity will undoubtedly lead to a surge in the discovery of new, dense, hydrogen-rich materials. The rare earth metal superhydrides are predicted to have very high-T_{c} superconductivity that is tunable with changes in stoichiometry or doping. Here we report the synthesis of an yttrium superhydride that exhibits superconductivity at a critical temperature of 262 K at 182±8 GPa. A palladium thin film assists the synthesis by protecting the sputtered yttrium from oxidation and promoting subsequent hydrogenation. Phonon-mediated superconductivity is established by the observation of zero resistance, an isotope effect and the reduction of T_{c} under an external magnetic field. The upper critical magnetic field is 103 T at zero temperature.

5.
Nature ; 588(7837): E18, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-33214713

RESUMO

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

6.
Nature ; 586(7829): 373-377, 2020 10.
Artigo em Inglês | MEDLINE | ID: mdl-33057222

RESUMO

One of the long-standing challenges in experimental physics is the observation of room-temperature superconductivity1,2. Recently, high-temperature conventional superconductivity in hydrogen-rich materials has been reported in several systems under high pressure3-5. An  important discovery leading to room-temperature superconductivity is the pressure-driven disproportionation of hydrogen sulfide (H2S) to H3S, with a confirmed transition temperature of 203 kelvin at 155 gigapascals3,6. Both H2S and CH4 readily mix with hydrogen to form guest-host structures at lower pressures7, and are of  comparable size at 4 gigapascals. By introducing methane at low pressures into the H2S + H2 precursor mixture for H3S, molecular exchange is allowed within a large assemblage of van der Waals solids that are hydrogen-rich with H2 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.

7.
J Phys Chem Lett ; 10(18): 5351-5356, 2019 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-31436423

RESUMO

Many rutile-type materials are characterized by a softness in shear with pressure which is coupled to a Raman-active librational motion. Combining direct studies of anion positions in SnO2 with measurements of its electronic properties, we find a correlation between O sublattice disorder between 5 and 10 GPa and an anomalous decrease up to 4 orders of magnitude in electrical resistance. Hypotheses into the atomistic nature of the phenomenon are evaluated via ab initio calculations guided by extended X-ray absorption fine structure spectroscopy analysis, and the most likely mechanism is found to be the displacement of single anions resulting from the pressure-induced softening of the librational mode. On the basis of this mechanism, we propose that the same behavior should feature across all materials exhibiting a rutile → CaCl2 phase transition and that conductivity in other rutile-type materials could be facilitated at ambient pressure by appropriate design of devices to enhance defects of this nature.

8.
Science ; 355(6326): 715-718, 2017 02 17.
Artigo em Inglês | MEDLINE | ID: mdl-28126728

RESUMO

Producing metallic hydrogen has been a great challenge in condensed matter physics. Metallic hydrogen may be a room-temperature superconductor and metastable when the pressure is released and could have an important impact on energy and rocketry. We have studied solid molecular hydrogen under pressure at low temperatures. At a pressure of 495 gigapascals, hydrogen becomes metallic, with reflectivity as high as 0.91. We fit the reflectance using a Drude free-electron model to determine the plasma frequency of 32.5 ± 2.1 electron volts at a temperature of 5.5 kelvin, with a corresponding electron carrier density of 7.7 ± 1.1 × 1023 particles per cubic centimeter, which is consistent with theoretical estimates of the atomic density. The properties are those of an atomic metal. We have produced the Wigner-Huntington dissociative transition to atomic metallic hydrogen in the laboratory.

9.
Phys Rev Lett ; 116(14): 145501, 2016 04 08.
Artigo em Inglês | MEDLINE | ID: mdl-27104717

RESUMO

We present infrared absorption studies of solid hydrogen deuteride to pressures as high as 340 GPa (100 GPa=1 Mbar) in a diamond anvil cell and temperatures in the range 5-295 K. Above 198 GPa the HD sample transforms to a mixture of HD, H_{2}, and D_{2}, interpreted as a process of dissociation and recombination. Three new phase lines are observed, two of which differ remarkably from those of the high-pressure homonuclear species, but none are metallic. The time-dependent spectral changes are analyzed to determine the molecular concentrations as a function of time; the nucleon exchange achieves steady state concentrations in ∼20 h at ∼200 GPa.

10.
Proc Natl Acad Sci U S A ; 110(29): 11720-4, 2013 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-23818624

RESUMO

High pressure plays an increasingly important role in both understanding superconductivity and the development of new superconducting materials. New superconductors were found in metallic and metal oxide systems at high pressure. However, because of the filled close-shell configuration, the superconductivity in molecular systems has been limited to charge-transferred salts and metal-doped carbon species with relatively low superconducting transition temperatures. Here, we report the low-temperature superconducting phase observed in diamagnetic carbon disulfide under high pressure. The superconductivity arises from a highly disordered extended state (CS4 phase or phase III[CS4]) at ~6.2 K over a broad pressure range from 50 to 172 GPa. Based on the X-ray scattering data, we suggest that the local structural change from a tetrahedral to an octahedral configuration is responsible for the observed superconductivity.


Assuntos
Dissulfeto de Carbono/química , Condutividade Elétrica , Conformação Molecular , Pressão , Espalhamento de Radiação , Temperatura
11.
J Chem Phys ; 135(17): 174507, 2011 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-22070306

RESUMO

We report an unexpectedly high chemical stability of molecular solid 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) under static high pressures. In contrast to the high-pressure behavior of the majority of molecular solids, TATB remains both chemically stable and an insulator to 150 GPa--well above the predicted metallization pressure of 120 GPa. Single crystal studies have shown that TATB exhibits pressure-induced Raman changes associated with two subtle structural phase transitions at 28 and 56 GPa. These phase transitions are accompanied by remarkable color changes, from yellow to orange and to dark red with increasing pressure. We suggest that the high-stability of TATB arises as a result of its hydrogen-bonded aromatic two-dimensional (2D) layered structure and highly repulsive interlayer interaction, hindering the formation of 3D networks or metallic states.

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