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Dr. Andreas Hermann Postdoctoral Associate (Curriculum Vitae) Ph.D., Massey University (Auckland), New Zealand, 2009 Office: G44 Baker Laboratory Phone: (607) 255-0577 Email: ah736(at)cornell.edu |
Research Interests
Superconductivity was first discovered in mercury 100 years ago - since then, it has been found in a wide variety of materials, from elemental metals to highly structured and carefully doped quaternary compounds based on cuprate composites. The key variable for applicability of these systems, the transition temperature Tc to the superconducting phase, has been raised from 4 K in Kammerling-Onnes' laboratory to 133 K (or 164 K under high pressure) today. The ultimate goal is, of course, a superconductor at room temperature.
The upper left corner of the periodic
table could provide what is needed for a new class of high-Tc superconductors:
composites of H, Li, Be, and B will form metallic systems that couple
electronic degrees of freedom efficiently with ionic dynamics.
Previous work in
the groups of Profs. Hoffmann and Ashcroft has shed some light on the
interesting and surprising physics and chemistry that happens when these
seemingly simple elements are combined. I am investigating stoichiometric
ternary compounds from the elements H, Li, Be, and B, with the aim of
predicting promising candidates for new superconducting materials. A
combination of chemical intuition and evolutionary algorithms is employed to
sample the structural phase space of these compounds and find the global minima
on the density functional level of theory. The pressure variable will be varied
to explore a wider range of possible (and experimentally accessible) ground state
structures. Analysis of their respective electronic and dynamic properties will
be followed by an estimate of the electron-phonon coupling and the transition
temperature Tc using BCS theory.
Other research interests include:
- Elementary excitations in solids:
quasiparticle band structures, optical absorption spectra, phonon dispersion
relations.
- Surface physics and chemistry:
molecular adsorption on extended inorganic surfaces.
- Aqueous systems: structural and
electronic properties of water and ice.
- Ionic dynamics beyond the Born-Oppenheimer approximation.
Selected Publications
A. Hermann, P. Schwerdtfeger, "Blueshifting the Onset of Optical UV Absorption for Water Under Pressure", Phys. Rev. Lett., 106, 187403 (2011).
A. Hermann, J. Furthmüller, H.W. Gäggeler and P. Schwerdtfeger, "Spin-orbit effects in structural and electronic properties for the solid-state of group-14 elementa from Carbon to superheavy element 114", Phys. Rev. B, 82, 155116 (2010).
S. Biering, A. Hermann, J. Furthmüller and P. Schwerdtfeger, "The unusual solid state structure of mercary oxide: A first principle relastivitic density functional study for the group 12 oxides ZnO, CdO and HgO", J. Phys. Chem. A, 113, 12427 (2009).
A. Hermann and P. Schwerdtfeger, "Ground state properties of crystalline ice from periodic Hartree-Fock and a coupled-cluster-based many body decomposition of the correlation energy", Phys. Rev. Lett., 101, 183005 (2008).
A. Hermann, W.G. Schmidt and P. Schwerdtfeger, "Resolving the optical spectrum of water: Coordination and electrostatic effects", Phys. Rev. Lett., 100, 207403 (2008).
A. Hermann, M. Lein and P. Schwerdtfeger, "The search for the species with the highest coordination number", Angew. Chem. Int. Ed., 46, 2444 (2007).
A. Hermann,
W.G. Schmidt and P. Schwerdtfeger, "Opticak response of pi-conjugated
molecular monolayer adsorbed on the semiconductor Si(0001) surface: A
first principles study", Phys. Rev. B, 71, 153311 (2005).