Warren Pickett yclept

"The modern age has a false sense of security because of the great mass of data at its disposal. But the valid issue is the extent to which people know how to form and master the material at their disposal." Goethe, 1832.

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2004's Model

H3S Fermi surface. Illustration of the topological change of the constant energy surfaces in H3S that provides the van Hove singularities that makes this simple compound the current highest temperature superconductor.

Animation of constant energy surfaces of the new high temperature superconductor H3S as the topological changes occur through the van Hove points. Our group has performed investigations into the impact of these van Hove singularities on the properties of H3S.

Description of the MnO Mott transition from insulator to metal at one million atmospheres pressure. We extended and applied the dynamical mean field theory method to obtain the magnetic and volume collapse transition. It was found Hund's rule exchange processes are important for obtaining the correct transformation pressure. Moreover, residual magnetism was obtained from the calculation, in agreement with spectroscopic data. The figure provides the current knowledge on the pressure-temperature phase diagram of MnO.

Dynamics of Superconducting H3S

In 2004 current theory (China) predicted that hydrogen sulfide H33S would become a super-high temperature superconductor at the very high pressure of 2 million atmosphers. In 2005 Eremets' group in Germany measured and found the same amazing result. One of our contributions has been to perform an ab initio molecular dynamics simulation of atomic vibrations of H3S at a temperature of 200 K and the experimental pressure. The hydrogen vibration amplitudes are very large; in a metal with normal (heavy) nuclei, the vibration would hardly be visible. Note: this video (click the title) may be slow to load.

Fermi surface & Nesting function. Superconductivity and lattice instability in compressed lithium from Fermi surface hot spots. Lithium superconducts up to 20K at high pressure, before structural phase transitions (lattice instabilities) occur, limiting higher Tc.

Heavens

Contact Warren Pickett wepickett@ucdavis.edu