Strong-coupling electron-phonon superconductivity in noncentrosymmetric quasi-one-dimensional K2_2Cr3_3As3_3

I study the lattice dynamics and electron-phonon coupling in non-centrosymmetric quasi-one-dimensional K$_2$Cr$_3$As$_3$ using density functional theory based first principles calculations. The phonon dispersions show stable phonons without any soft-mode behavior. They also exhibit features that point to a strong interaction of K atoms with the lattice. I find that the calculated Eliashberg spectral function shows a large enhancement around 50 cm$^{-1}$. The phonon modes that show large coupling involve in-plane motions of all three species of atoms. The $\mathbf{q}$ dependent electron-phonon coupling decreases strongly away from the $q_z = 0$ plane. The total electron-phonon coupling is large with a value of $\lambda_{\textrm{ep}} = 3.0$, which readily explains the experimentally observed large mass enhancement

Proposal for ultrafast switching of ferroelectrics using mid-infrared pulses

I propose a method for ultrafast switching of ferroelectric polarization using mid-infrared pulses. This involves selectively exciting the highest frequency $A_1$ phonon mode of a ferroelectric material with an intense mid-infrared pulse. Large amplitude oscillations of this mode provides a unidirectional force to the lattice such that it displaces along the lowest frequency $A_1$ phonon mode coordinate because of a nonlinear coupling of the type $g Q_{\textrm{P}} Q_{\textrm{IR}}^2$ between the two modes. First principles calculations show that this coupling is large in transition-metal oxide ferroelectrics, and the sign of the coupling is such that the lattice displaces in the switching direction. Furthermore, I find that the lowest frequency $A_1$ mode has a large $Q_{\textrm{P}}^3$ order anharmonicity, which causes a discontinuous switch of electric polarization as the pump amplitude is continuously increased

Research, Creative Works, and Commercialization at UAA FY15 through FY16 YTD.

The UAA Research and Commercialization trend is upward. UAA is experiencing significant growth in research, creative works, and commercialization. We are pursuing a strategic approach to fostering, supporting, and expanding faculty and student research efforts and commercialization by creating a climate of innovation and collaboration

A Prospectus on Substantive Change

Prepared for The Commission on Colleges, Northwest Association of Schools and Colleges, October 1, 1987. For consideration by the Commission on Colleges at its December 5 and 6, 1987, meeting at the Salt Lake Hilton Hotel

Orthorhombic-to-monoclinic transition in Ta2_2NiSe5_5 due to a zone-center optical phonon instability

I study dynamical instabilities in Ta$_2$NiSe$_5$ using density functional theory based calculations. The calculated phonon dispersions show two unstable optical branches. All the acoustic branches are stable, which shows that an elastic instability is not the primary cause of the experimentally observed orthorhombic-to-monoclinic structural transition in this material. The largest instability of the optical branches occurs at the zone center, consistent with the experimental observation that the size of the unit cell does not multiply across the phase transition. The unstable modes have the irreps $B_{1g}$ and $B_{2g}$. Full structural relaxations minimizing both the forces and stresses find that the monoclinic $C2/c$ structure corresponding to the $B_{2g}$ instability has the lowest energy. Electronic structure calculations show that this low-symmetry structure has a sizable band gap. This suggest that a $B_{2g}$ zone-center optical phonon instability is the primary cause of the phase transition. An observation of a softening of a $B_{2g}$ zone-center phonon mode as the transition is approached from above would confirm the mechanism proposed here. If none of the $B_{2g}$ modes present in the material soften, this would imply that the transition is caused by electronic or elastic instability

Sex Offender Treatment Program: Preliminary Description

This report provides a summary of the history of sex offender treatment in Alaska, including the current status of treatment programs offered by the Alaska Department of Corrections, a review of literature on sex offender treatment and recidivism issues, and a summary of the descriptive characteristics of individuals who came in contact with the Hiland Mountain Correctional Center from January 1987 to March 1993.Alaska Department of CorrectionsIntroduction / Sex Offender Treatment in Alaska / Literature Review / Methodology / Results / Conclusion and Recommendations / Bibliograph

Interplay between structure and chemistry of materials and their physical properties

First principles calculations provide a powerful tool for sorting out the interplay of chemical composition and structure with the physical properties of materials. In this dissertation, I discuss the physical properties and their microscopic basis within this framework for following illustrative examples. (i) The Zintl phase hydrides, where I find H is anionic and the formation of covalent sp2 bonds in the Al/Ga/Al-Si planes, which is a highly unusual bonding configuration for these elements. (ii) PbTe, which shows strong coupling between the longitudinal acoustic and transverse optic modes that may explain its low thermal conductivity. (iii) The double perovskites BiPbZnNbO6 and BiSrZnNbO6, where introducing size disorder at A-site prevents the BO6 octahedra from tiling and enhances the polar behavior. (iv) FeSe, which shares the salient electronic and magnetic features of other Fe superconductors and cannot be described as a conventional electron phonon superconductor. (v) NbFe2, which is near a magnetic quantum critical point and shows strong competition between various magnetic orderings that may explain its unusual non-Fermi liquid behavior at very low temperatures. (vi) The nickel analogues of Fe superconductors LaNiPO and BaNi2As2, where I show that superconductivity is of conventional electron-phonon type in contrast to the Fe-based superconductors. (vii) Noncentrosymmetric LaNiC2, which I find is a conventional electron-phonon superconductor with intermediate coupling