What superconducts in sulfur hydrides under pressure and why

A priori crystal structure prediction techniques have been used to explore the phase diagrams of hydrides of main group elements under pressure. A number of novel phases with the chemical formulas MHn, n > 1 and M = Li, Na, K, Rb, Cs; MHn, n > 2 and M= Mg, Ca, Sr, Ba; HnI with n > 1 and PH, PH 2 , PH 3 have been predicted to be stable at pressures achievable in diamond anvil cells. The hydrogenic lattices within these phases display a number of structural motifs including H δ− 2 , H − , H − 3 , as well as one-dimensional and three-dimensional extended structures. A wide range of superconducting critical temperatures, Tcs, are predicted for these hydrides. The mechanism of metallization and the propensity for superconductivity are dependent upon the structural motifs present in these phases, and in particular on their hydrogenic sublattices. Phases that are thermodynamically unstable, but dynamically stable, are accessible experimentally. The observed trends provide insight on how to design hydrides that are superconducting at high temperatures.

Section: Introductionmentioning

confidence: 99%

Superconductivity in Hydrides Doped with Main Group Elements Under Pressure

Shamp¹,

Zurek²

2017

“…The ideas of Ashcroft have been recently confirmed by the experiments of Drozdov et al [6] and a series of theoretical papers [7][8][9][10][11][12][13][14] that confirm hydrogen-based hightemperature superconductivity is realized in the sulfur *Corresponding Author: D. A. Papaconstantopoulos: Department of Computational and Data Sciences, George Mason University, Fairfax, Virginia 22030, USA, E-mail: dpapacon@gmu.edu compound H 3 S under 200 GPa pressure. Reference [8] presents a comprehensive set of calculations for H 3 S using the GGM theory.…”

Section: Introductionmentioning

confidence: 50%

Possible High-Temperature Superconductivity in Hygrogenated Fluorine

Papaconstantopoulos¹

2017

Recent computational studies confirmed by experiment have established the occurrence of superconducting temperatures, Tc, near 200 K when the pressure is close to 200 GPa in the compound H 3 S. Motivated by these findings we investigate in this work the possibility of discovering high-temperature superconductivity in the material H 3 F. We performed linearized augmented plane wave(LAPW) calculations followed by the determination of the angular momentum components of the density of states, the scattering phase shifts at the Fermi level and the electron-ion matrix element known as the Hopfield parameter. Our calculated Hopfield parameters are much larger than those found in H 3 S suggesting that they may lead to large electron-phonon coupling constant and hence a large Tc similar or even larger than that of H 3 S. However, calculations of elastic constants are inconclusive regarding the stability of this material.

“…In particular, the electron-phonon coupling in the latter phases has been estimated to be strong enough to reproduce the experimentally observed Tc over 200 K [3,4]. They have also been shown to be the most stable thermodynamically among the HxS 1−x systems [7]. The Brought to you by | MIT Libraries Authenticated Download Date | 5/13/18 8:35 AM emergence of the H 3 S phases is thus being accepted as the most plausible scenario for the high-Tc superconductivity.…”

Section: Introductionmentioning

confidence: 80%

Emergent Magnéli-type crystal phases and their mixture in pressurized sulfur hydride

Akashi¹,

Sano²,

Arita³

et al. 2017

Abstract:The pressure-induced superconductivity in sulfur hydride has recently received tremendous amount of interest for its record-breaking transition temperature (Tc) of 203 K. We extensively discuss an infinite sequence of metastable structures of sulfur hydride under high pressure which has been recently proposed theoretically [R. Akashi et al., Phys. Rev. Lett. 117, 075503 (2016)]. The newly found structures are understood as the stacked layers of H 2 S and H 3 S, showing close similarity to the Magnéli phases formed in transition-metal oxides. The possible emergence of the "HxS Magnéli" phases are discussed as intermediate metastable phases in the formation of the high-Tc H 3 S phase. Superconducting transition temperatures and the Xray diffraction patterns are simulated with the first-principles calculations. It is demonstrated that the HxS Magnéli phases could serve as the silver bullet to explain the complicated dependences of the observed Tcs and diffraction patterns on the experimental protocol.