Symmetry breaking dynamical pattern in the high temperature vibrational spectrum of NaI Albert J. Sievers, Cornell University, DMR 0906491.
The continuing INS collaboration with D. L. Abernathy (Oak Ridge) has produced surprising findings in the temperature-induced dynamical changes in the vibrational spectrum of NaI.
The left panel illustrates some of the changes that occur at high temperatures. The top and bottom pictures show a k-space slice of the one phonon energy dispersion for NaI at two different temperatures. The well known low temperature dispersion curve for NaI is seen in the bottom picture while the appearance of an ILM and fragmentation of the TO mode is observed in the top one. The center picture provides a complementary display for such data.
The right panel shows how a dynamical superlattice may be formed from an ordered arrangement of ILMs.
Ordered local modes
Education and outreach:
In addition to involving two REU students in research the PI has continued a collaboration with Dickenson College. Undergrad. Paulo Candiani has submitted for publication his work on the generation of localized modes in an electrical lattice using subharmonic driving.
With Prof. M. Sato in Japan we have published the first measurements of the linear response spectra of ILMs in the bifurcation regions.
With Prof. V. Hizhnyakov in Estonia, the first prediction of ILMs in metals has been reported.
REU student K. Sullivan from Knox College measuring the IR properties of epitaxial SiC polytypes.
REU student D. Mattar from Alfred Univ. encapsulating NaI crystal for specific heat measurements.