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Wednesday, March 10th 2010

5:00 pm:

Thursday, April 1st 2010

3:00 pm:

Tuesday, April 6th 2010

4:40 pm:

Monday, April 19th 2010

4:40 pm:

Tuesday, April 20th 2010

4:40 pm:

Monday, April 26th 2010

4:40 pm:

Wednesday, April 28th 2010

4:40 pm:

Thursday, April 29th 2010

4:40 pm:

Friday, April 30th 2010

10:00 am:

Monday, May 3rd 2010

4:40 pm:

Thursday, May 6th 2010

4:40 pm:

Tuesday, May 11th 2010

1:00 pm:

Thursday, June 10th 2010

1:30 pm:

My thesis is composed of two projects. The first one is the investigation of a reversed phase sequence, which subsequently leads to the discovery of a novel Smectic-C liquid crystal phase. The 10OHFBBB1M7 (10OHF) compound, shows a reversed phase sequence with SmC_d4** phase at a higher temperature than the SmC** phase. This phase sequence is stabilized by moderate doping of 9OTBBB1M7 (C9) or 11OTBBB1M7 (C11). To further study this unique phase sequence, the mixtures of 10OHFBBB1M7 and its homologous have been characterized by optical techniques. In order to perform the resonant X-ray diffraction experiment, we have added C9 and C11 compounds to the binary mixtures and pure 10OHF. In two of the studied mixtures, a new smectic-C** liquid crystal phase with six-layer periodicity has been discovered. Upon cooling, the new phase appears between the SmC_alpha** phase having a helical structure and the SmC_d4** phase with four-layer periodicity. The SmC_d6** phase shows a distorted clock structure. Three theoretical models have predicted the existence of a six-layer phase. However,our experimental findings are not consistent with the theories.

The second project involves the mixtures of liquid crystals with different shapes. The role of different interactions in stabilizing the antiferroelectric smectic liquid crystal phases have been a long standing questions in the community. By mixing the antiferroelectric smectic liquid crystal with achiral liquid crystal molecules with rod and hockey-stick shapes, we see distinct different behaviors. In the case of the mixtures of chiral smectic liquid crystals with rod-like molecues, all the Smectic-C* variant phases vanish with small amount of doping. However, the hockey-stick molecule is much less destructive compared to the rod-like molecule. This suggest that the antiferroelectric smectic liquid crystal molecules may have a shape closer to a hockey-stick other than a rod.

Monday, June 21st 2010

1:30 pm:

My thesis investigates the effects of spin-orbit coupling on spin

transport in Ferromagnet/Semiconductor heterostructures. Spin-orbit coupling is a relativistic phenomenon that couples the spin of an electron to its momentum by means of a momentum-dependent effective magnetic field. The effects of spin-orbit coupling in bulk InGaAs are observed by measuring the direct spin Hall effect, where an applied charge current induces a perpendicular spin current. The spins are oriented perpendicular to the flow directions of both the charge current and the spin current.

This spin current leads to an out-of-plane spin accumulation that is

opposite in sign at opposite edges of the channel. The spin accumulation

is identified through the observation of a Hanle effect in the Hall

voltage measured by pairs of ferromagnetic contacts. The data are fit

using a model which includes spin diffusion, precession, and relaxation.

We use the parameters determined from the fit to calculate the spin Hall

conductivity. We find that the magnitude of the spin Hall conductivity is

in agreement with models of the extrinsic SHE due to ionized impurity

scattering. By analyzing the dependence of the spin Hall signal on channel

conductivity we determine the contributions of both skew and side jump

scattering to the total spin Hall conductivity. We calculate that the

spin-orbit coupling parameter is larger than predicted by standard k•p

perturbation theory.

Friday, July 9th 2010

1:30 pm:

Tuesday, July 13th 2010

10:30 am:

High-Tc cuprate superconductors remain the source of central intellectual challenges for condensed matter physicists two decades after their discovery. Accumulating evidence suggests possible ubiquity of coexisting superconducting and density wave correlations in the ground state of these materials. As both correlations in their spatially incoherent forms can in principle produce a pseudogap in the excitation spectrum, the nature of the pseudogap widely seen in cuprates above Tc comes to forefront of debate. I have been trying to address the relationship triangle between the pseudogap, superconductivity and density waves, by mainly using angle-resolved photoemission spectroscopy (ARPES) to study the momentum spaces of single-layer La-based (La214) and Bi-based (Bi2201) cuprates.

In this talk, I will first briefly mention our ARPES-neutron scattering joint effort (in collaboration with Tohoku University) in the stripe-ordered state of La214. We found around the 1/8 doping level a dual nature of the pseudogap (in LBCO) and a doping-dependent crossover between localized- and

itinerant-spin ground-state physics (in 1% Fe-doped LSCO). I will then focus on our ARPES findings in both the pseudogap and superconducting states of nearly optimally-doped Pb-Bi2201 obtained over unprecedented momentum, energy and temperature ranges. They suggest that the pseudogap is a broken-symmetry state that is density-wave like and distinct from homogeneous superconductivity; it explicitly coexists with coherent superconductivity below Tc, causing a striking, momentum-dependent distortion of the high-Tc ground state.

Tuesday, August 10th 2010

12:00 pm:

Wednesday, August 11th 2010

1:30 pm:

We will perform some of the more popular (and noisy) lecture demonstrations.

Thursday, August 26th 2010

08:00 am:

08:00 am:

Friday, September 24th 2010

12:00 pm:

Friday, October 15th 2010

2:30 pm:

Saturday, October 16th 2010

08:00 am:

Thursday, November 4th 2010

10:00 am:

Thursday, November 11th 2010

11:30 am:

6:30 pm:

Saturday, November 13th 2010

10:30 am:

12:00 pm:

Friday, December 10th 2010

2:30 pm:

Random matrix theories have fascinated both mathematicians and physicists since they were first introduced by Wishart and Wigner. Today we can find numerous applications and connections of random matrix theory to the following fields: probability theory, financial math, number theory, quantum chaotic system, biology, even wireless communication. In this talk, we give a short review of the main historical developments of random matrix

theory. We emphasize both the theoretical aspects, and the application of the theory, including the recent works on the universalities of random matrices.

Friday, December 31st 2010

08:00 am:

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