TcSUH
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Special Seminar
Theoretical Understanding of Rotational Symmetry Breaking in Sodium-Doped Cuprate Superconductors
by: Dr. Y. Chen
Date: Tuesday May 22, 2007
Time: 4:00 pm – 5:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
The recent atomically resolved STM studies on strongly underdoped NaCCOC revealed a surprisingly complex pattern with the square symmetry of thelattice broken on a local scale. This has raised an interesting question about the origin of the broken local square symmetry. Our theoretical investigation shows that for reasonable parameters the single hole impurity state of t-t'-J model has a doubly degenerate ground state whose components can be represented as states with even (odd) reflection symmetry around the x(y)-axes. The conductance pattern for one state is anisotropic as the STM tip scans above the Cu-O-Cu bonds along the x(y)-axes. This strong anisotropy appears at lower voltages while much weaker anisotropy shows up at higher voltages. Our results agree qualitatively with recent experiments. In addition, we demonstrate that the satisfaction of low-energy sum rules shown in STM measurements strengthens the validity of the description of the low-energy physics by an effective single-band model instead of the three-band model. Some preliminary results will be discussed.
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Special Seminar
Bond Bending Enhanced Ferroelectricity in Multiferroic Materials
by: Prof. C. D. Hu
Date: Monday May 21, 2007
Time: 4:00 pm – 5:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
We studied transition metal oxides with spiral spin distribution. The bond bending at oxygen sites enables the hybridization of the t¬2g orbitalsof transition elements and the p-orbitals of oxygen atoms. Bloch functions are coupled due to the spiral spin distribution. The resulting wave functiongives rise to electronic distribution which has net electric polarization if spin-orbit interaction is considered.
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Special Seminar
The 1-D BOSE GAS
by: Prof. Norm Frankel
Date: Wednesday April 11, 2007
Time: 11:00 am – 12:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
The one dimensional delta function Bose gas is a classic system in the quantum many body problem. It has excited much study, with seminal contributions from theoretical physics and mathematics, over the past five decades.
The wonderful advent of exceedingly low temperature cyrogenics has brought the Bose gas into prominence. Very recently, with the application of sophisticated anisotropic traps, the Bose gas can be fashioned into a genuinely 1-D configuration, thus bringing this 1-D Bose gas into the special spotlight experimentally.
In the light of our recent works, we will focus on the density matrix and concomitantly the occupation numbers [distribution function] along with the pair correlation function and concomitantly the structure factor. These are the signature quantities of the Bose gas.
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Special Seminar
The Synthesis, Properties and Chemistry of Layered Solids
by: Prof. Simon J. Clarke
Date: Friday March 30, 2007
Time: 11:00 am – 12:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
New solid state compounds will be described which are composed of alternating transition metal oxide layers and metal sulfide or selenide layers. These compounds show a wide range of electronic, magnetic and structural features which can often be tuned by making substitutions of the cations or anions in the structures.
The lecture will focus firstly on the crystal structures and electronic and magnetic properties of compounds containing titanium, manganese, cobalt or nickel oxide layers separated by copper sulfide or selenide layers. The second part of the lecture will describe the chemical reactivity of these compounds, in particular the reversible room-temperature lithiation of many of these compounds.
A wide range of investigations will be described including diffraction, magnetometry and NMR studies. The properties will be related to the general chemistry of the elements.
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Special Seminar
Materials Science and Technology at the Naval Research Laboratory
by: Dr. Donald Gubser
Date: Wednesday March 28, 2007
Time: 11:00 am – 12:00 pm
Location: Houston Science Center – Building 593 — Room 102
Overview
A brief introduction to the Naval Research Laboratory will be given, followed by an overview of materials research topics under investigation at NRL. Topics included will be Superconductivity, Acoustic Transduction Materials, Quantum Spin Electronics, Nanocrystals, 3D Materials Visualization, Fracture Simulations, Materials Integration, and Thoracic Surrogate Materials.
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