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Special Seminar

Solid State Metathesis Reactions as a Conceptual Tool in the Synthesis of New Materials

Prof. H. -J. Meyer

by: Prof. H. -J. Meyer

Date: Friday March 25, 2011

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Solid state metathesis reactions can be used in the syntheses of inorganic solids and for strategic design of novel, eventually thermally labile materials. An explorative study of solid state metathesis reactions is presented for a number of examples, including syntheses of nitridoborates, carbodiimides, tetracyanoborates, tetracyanamidosilicates, carbon-nitride materials, and a number of other exciting compounds. This unique type of reaction is very efficient because it uses the intrinsic energy of reaction partners being involved. Desired compositions are achieved by appropriate starting materials and their relative amounts being combined into a solid state metathesis reaction. Reactions can be controlled through the heating-up procedure and by using a reactive flux, which may lower the ignition temperature of a reaction mixture and promote crystal growth of products.

Special Seminar

Magneto-Optical Properties of Graphene Layers: a Tight-Binding Study

Dr. Yen-Hung  Ho

by: Dr. Yen-Hung Ho

Date: Thursday March 10, 2011

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

A complete tight-binding model is developed to study the electronic and optical properties of graphene layers in response to magnetic field. Since the magnetic field and all atomic hoppings are simultaneously taken into account without introducing any approximation, the calculated results are accurate over a wide energy range. The wave functions and their spatial distributions appropriately characterize the Landau levels. Moreover, the concept of sublattices provides a straightforward way to clearly identify the optical spectra, including the selection rules and relative absorption rates. The spectral structures are substantially impacted by the interlayer interactions and the stacking sequence. Our numerical results can provide guideline and new spectral features for future experiments.

Special Seminar

What Kind of Stars Made the Calcium in your Bones?

Dr. Typhoon  Lee

by: Dr. Typhoon Lee

Date: Tuesday March 08, 2011

Time: 4:00 pm – 5:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

The Ca in our body were all made in other stars that contributed ejecta from their nuclearly processed interior to the proto-solar molecular cloud. The subsequent evolution will change the elemental ratios but not isotope ratios. Thus the six stable isotopes of Calcium (Ca-40, 42, 43, 44, 46, and 48 plus the radioactive Ca-41) constitute an extremely powerful tool to trace the nuclear astrophysical origin of the building material used to make our planetary system and ourselves. I will show that several processes in supernova type I and type II as well as AGB stars were involved. I will also show the most up-to-date high precision data for the earliest solid in the solar system. They not only gave us lots of insight in the late stage evolution of massive stars but also seduce us to speculate on the last minute contamination from a neaby supernova just when the planetesimals were accreting into planets.

Special Seminar

Single Impurity Problem in Ultracold Atomic Fermi Gases----Whether Fully Polarized Ferromagnetism is Possible under Repulsive Interaction

by: TcSUH Administration

Date: Thursday January 06, 2011

Time: 4:00 pm – 5:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Ultracold atomic physics have achieved great developments, in both experimental and theoretical aspects, during the past decades. In this talk, I will first give a brief introduction of cold atoms and some recent experimental developments. I will then focus on one of our recent works in understanding magnetism and correlation effects in repulsively interacting two-component Fermi gases. This is motivated by a recent expermimental work done by MIT on itinerant ferromagetism(FM) in cold fermions(Science 325, 1521(2009)). Specifically we use variational approach to study whether a fully polarized Fermi sea of ultracold atoms is energetically stable against a single spin flip.We find that for both lattice and continuum models, fully polarized FM is generally not stable even for infinite repulsive strength. However for a resonance model FM is possibly stable as long as s-wave scattering length is large and positive and the system is prepared in the metastable scattering branch.

Special Seminar

Nanostructures to Examine Strongly Correlated Materials: Magnetite

Prof. Douglas  Natelson

by: Prof. Douglas Natelson

Date: Thursday November 18, 2010

Time: 12:00 pm – 1:00 pm

Location: Houston Science Center – Building 593 — Room 102

Overview

Strongly correlated electronic materials, a huge class of materials for which single-particle band structure fails to describe their electronic properties, remain a topic of great interest. Such systems often exhibit competing electronic and magnetic phases, resulting in dramatic physical phenomena such as metal-insulator transitions and superconductivity. Magnetite, Fe3O4, is an archetypal strongly correlated transition metal oxide that, in bulk, exhibits a structural and electronic phase transition near 120 K from a moderately conducting high temperature state to a considerably more insulating low temperature state. The nature of the low temperature state remains a source of controversy after more than seven decades of investigation. Using nanostructure techniques and magnetite films, we demonstrate that it is possible to destabilize the insulating state with a sufficiently large in-plane electric field. We show that this destruction is not due to simple self-heating, and present evidence that suggests it is analogous to Landau-Zener breakdown of the correlated state, with disorder also playing an important role. Finally, we will use these studies to demonstrate that contact effects, scrupulously avoided in most experiments, provide additional insight into the conduction mechanism in this strongly correlated material.

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