arXiv subjects

Eugene Gregoryanz

Publications and source records attributed to Eugene Gregoryanz.

22 records · Page 2Linked to original sources

arXiv2001

Spectroscopic Studies of the Vibrational and Electronic Properties of Solid Hydrogen to 285 GPa

We report Raman scattering and visible to near-infrared absorption spectra of solid hydrogen under static pressure up to 285 GPa at 85-140 K. We obtain pressure dependences of vibron and phonon modes in agreement with previously determined to lower pressures. The results indicate the stability of the ordered molecular phase III to the highest pressure reached and provide constraints on the insulator-to-metal transition pressure.

cond-mat.mtrl-sci↗

arXiv2001

Superconductivity in the Chalcogens up to Multimegabar Pressures

Highly sensitive magnetic susceptibility techniques were used to measure the superconducting transition temperatures in S up to 231($\pm$5) GPa. S transforms to a superconductor with T$_c$ of 10 K and has a discontinuity in T_c dependence at 160 GPa corresponding to bco to beta-Po phase transition. Above this pressure T_c in S has a maximum reaching about 17.3(+/-0.5) K at 200 GPa and then slowly decreases with pressure to 15 K at 230 GPa. This trend in the pressure dependence parallels the behavior of the heavier members Se and Te. Superconductivity in Se was also observed from 15 to 25 GPa with T_c changing from 4 to 6 K and above 150 GPa with T_c of 8 K. Similiarities in the T_c dependences for S, Se, and Te, and the implications for oxygen are discussed.

cond-mat.supr-con↗

arXiv2001

High-Pressure Amorphous Nitrogen

The phase diagram and stability limits of diatomic solid nitrogen have been explored in a wide pressure--temperature range by several optical spectroscopic techniques. A newly characterized narrow-gap semiconducting phase $η$ has been found to exist in a range of 80--270 GPa and 10--510 K. The vibrational and optical properties of the $η$ phase produced under these conditions indicate that it is largely amorphous and back transforms to a new molecular phase. The band gap of the $η$ phase is found to decrease with pressure indicating possible metallization by band overlap above 280 GPa.

cond-mat.mtrl-sci↗

arXiv2001

Raman spectrum and lattice parameters of MgB2 as a function of pressure

We report Raman spectra and synchrotron x-ray diffraction measurements of lattice parameters of polycrystalline MgB2 under hydrostatic pressure conditions up to 15 GPa. An anomalously broadened Raman band at 620 cm-1 is observed that exhibits a large linear pressure shift of its frequency. The large mode damping and Gruneisen parameter indicate a highly anharmonic nature of the mode, broadly consistent with theoretical predictions for the E2g in-plane boron stretching mode. The results obtained may provide additional constraints on the electron-phonon coupling in the system.

cond-mat.supr-con↗