A superconducting critical temperature above 200 K has recently been discovered in H2S (or D2S) under high hydrostatic pressure1, 2. These measurements were interpreted in terms of a decomposition of these materials into elemental sulfur and a hydrogen-rich hydride that is responsible for the superconductivity, although direct experimental evidence for this mechanism has so far been lacking. Here we report the crystal structure of the superconducting phase of hydrogen sulfide (and deuterium sulfide) in the normal and superconducting states obtained by means of synchrotron X-ray diffraction measurements, combined with electrical resistance measurements at both room and low temperatures. We find that the superconducting phase is mostly in good agreement with theoretically predicted body-centered cubic (bcc) structure for H3S (Ref.3). The presence of elemental sulfur is also manifest in the X-ray diffraction patterns, thus proving the decomposition mechanism of H2S to H3S + S under pressure4–6.

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Template tracking is a well studied problem in computer vision which dates back to the Lucas-Kanade algorithm of 1981. Since then the paradigm has been extended in a variety of ways including: arbitrary parametric transformations of the template, and linear appearance variation. These extensions have been combined, culminating in non-rigid appearance models such as Active Appearance Models (AAMs) and Active Blobs. One question that has received very little attention is how to update the template over time so that it remains a good model of the object being tracked. This paper proposes an algorithm to update the template that avoids the "drifting" problem of the naive update algorithm. Our algorithm can be interpreted as a heuristic to avoid local minima. It can also be extended to templates with linear appearance variation. This extension can be used to convert (update) a generic, person-independent AAM into a person specific AAM.

Dynamical localization, that is, reduction of the intersite electronic transfer integral t by an alternating electric field, E(o), is a promising strategy for controlling strongly correlated systems with a competing energy balance between t and the Coulomb repulsion energy. Here we describe a charge localization induced by the 9.3 MVcm À 1 instantaneous electric field of a 1.5 cycle (7 fs) infrared pulse in an organic conductor a-(bis[ethylenedithio]-tetrathiafulvalene) 2 I 3 . A large reflectivity change of 425% and a coherent charge oscillation along the time axis reflect the opening of the charge ordering gap in the metallic phase. This optical freezing of charges, which is the reverse of the photoinduced melting of electronic orders, is attributed to the B10% reduction of t driven by the strong, high-frequency (oZt/:) electric field.

Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30–70 K in pressure range of 100–170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system.

We explore the unknown structure of phosphorus in phase IV (P-IV phase) based on first-principles calculations using the metadynamics simulation method. Starting from the simple cubic structure, we find a new modulated structure of the monoclinic lattice. The modulation is crucial to the stability of the structure. Through refining the structure further by changing the modulation period, we find the structure whose x-ray powder diffraction pattern is in best agreement with the experimental pattern. We expect that the modulation period of the structure in the P-IV phase is very close to that found in this study and probably incommensurate. DOI: 10.1103/PhysRevLett.96.095502 PACS numbers: 61.50.Ah, 62.50.+p, 64.70.Kb Recent progress in high-pressure physics has enhanced our recognition of a wide variety of crystal structures. Development of high-pressure techniques has also enabled the identification of structures that are stabilized only in a narrow pressure range. Interesting structures were found unexpectedly through high-pressure experiments. For instance, modulated structures are often found in the highpressure phases of elements. Lattice modulations have been found in group Vb elements, including As, Sb, and Bi Scarcity of experimental ultrahigh-pressure data restricts high-pressure studies. Thus, researchers often encounter difficulties in the identification of a crystal structure on the basis of experimental data alone. A theoretical approach provides additional information on the same problem. First-principles theory for determining crystal structures is believed to be sufficiently accurate. However, the limitations of computational resources sometimes impede full structure searches.We will focus on the case of phase IV of the phosphorus (P-IV) phase. Observation of the P-IV phase was first reported by Akahama et al. [8] in 1999. In the sequence of pressure-induced transformations, the simple cubic (sc) phase (P-III) appears at 10 GPa at low temperature. Akahama et al. [8] reported the appearance of a simple hexagonal (sh) phase, i.e., the P-V phase, which stabilizes above 137 GPa, and an intermediate phase, i.e., the P-IV phase, between sc and sh on the basis of x-ray diffraction data. At even higher pressures, the bcc structure (P-VI) has been theoretically predicted [9] and later identified in an experiment at 262 GPa [10]. The structure of phase IV, however, has not been identified experimentally. Ordinary Rietveld analysis based on a knowledge of the monoclinic symmetry alone has not been successful, presumably owing to the complexity of the lattice. Thus, we must guess the crystal structure or a pseudocrystal.Several structures have been tested as candidate structures for P-IV. Ahuja considered a structure of space group Imma [11]. Ehlers and Christensen studied relative stability of the Ba-IV structure against sc and sh in the pressure range from 100 to 200 GPa [12]. The Ba-IV structure is a kind of modulated structure. Despite these extensive studies, the structure of P-IV remains unidentifi...

The recent reports on 203 K superconductivity in compressed hydrogen sulfide, H3S, has attracted great interest in sulfur-hydrogen system under high pressure. Here, we investigated the superconductivity of P-doped and Cl-doped H3S using the first-principles calculations based on the supercell method, which gives more reliable results on the superconductivity in doped systems than the calculations based on the virtual crystal approximation reported earlier. The superconducting critical temperature is increased from 189 to 212 K at 200 GPa in a cubic Im3m phase by the 6.25% P doping, whereas it is decreased to 161 K by the 6.25% Cl doping. Although the Cl doping weakens the superconductivity, it causes the Im3m phase to be stabilized in a lower pressure region than that in the non-doped H3S.

The strong light-field effect of (TMTTF)2AsF6 was investigated utilizing 1.5-cycle, 7-fs infrared pulses. The ultarfast (~20 fs) and large (~40%) response of the plasma-like reflectivity edge (~0.7 eV) was analyzed by the changes in