• Friday, September 16, 1:30 pm
Dr. Gregory Fiete
KITP, Santa Barbara
Spin incoherent effects in momentum resolved tunneling and transport in Luttinger liquids
abstract
In an electron gas at very low density a regime can be obtained where the magnetic exchange energy J between neighboring electrons is exponentially suppressed relative to the Fermi energy, E_F.  At finite temperature T, the energy hierarchy J << T << E_F can be reached, and we refer to this as the spin incoherent Luttinger liquid state. We theoretically  explore the signatures of spin incoherence in momentum resolved tunneling and in transport, and compare the results with recent experiments.   In momentum resolved tunneling the spin modes of a Luttinger liquid are thermally washed out leaving only the charge modes in the spectral function with a shift from ± k_F to ± 2k_F in momentum space.  These modes  are also broadened in momentum space by an amount of order k_F and the energy dependence of the tunneling density of states qualitatively changes from that of the spin coherent Luttinger liquid regime.  The effects of  an external magnetic field in the spin incoherent regime are also discussed.   Transport in the infinite system can be mapped onto spinless electrons and various crossovers in temperature and for finite systems connected to Fermi liquid leads are also discussed.
Host: Durst

•     Friday, September 23, 1:30 pm

          I. O. Kulik
          Quantum computation: polynomial or exponential ?
By classically simulating the quantum computational large number factorization algorithm, we have shown that despite the polynomial (in the quantity of the factorized number decimal digits) time of "quantum parallelism" evolution, the readout  of quantum register output of quantum computer may require, for classically untractable mathematical problem, more than polynomial number of times. This corroborates with the fact that quantum computer operates qubits which are  polynomial  in number (L) whereas the output spans the Hilbert space which is exponential (2^L) in its size, and the readout from the latter is a stochastic process.
Host: Likharev
• Friday, September 30, 1:30 pm CANCELED
Koichiro Umemoto
U. of Minnesota, Minneapolis, and Stony Brook
Phase transformation in CaIrO₃-type MgSiO₃ at ultra-high PTs: implications for the solar giants and terrestrial exoplanets
Host: Allen
• Friday, October 7, 1:30 pm
• Friday, October 14, 1:30 pm
• Friday, October 21, 1:30 pm
Razvan Teodorescu
Columbia University
Relaxation of nonlinear oscillations in BCS superconductivity
Recent experiments with cold, degenerate Fermi gases seem to indicate that in these systems, the parameter controlling BCS pair formation may be changed non-adiabatically, leading to coherent, non-linear dynamics of the gap parameter. Several authors derived exact oscillatory-type solutions, which share a non-physical feature: the absence of relaxation toward a steady-state at large times. We have investigated the effect that fluctuations of the single-particle spectrum have on the general solution, and obtained a universal
relaxation behavior for times much larger than the time scale of the gap parameter.
host: Abanov
• Friday, October 28, 1:30 pm
Uzi Landman
Georgia Tech
Symmetry Breaking in Quantum Dots and Traps
Landman is the Simons Lecturer for the fall.  This will be the last seminar of his one week visit.
Host: Allen
• Friday, November 4, 1:30 pm
• Friday, November 11, 1:30 pm
Ben Ocko
Brookhaven National Lab
Fundamental and Practical Aspects of Nanoscale Liquid Interfaces
This talk will explore the basic physics of equilibrium liquids on the nanoscale. The talk will start with a brief review of classical macroscopic capillarity theory. By using chemically nanopatterned substrates, the lateral size of droplets can be confined to the nanoscale. The shape of liquid drops on these surfaces differs from that predicted by classical capillary theory. This difference arises from addition, wetting studies on physically nanopatterned surfaces will be presented. As revealed by x-ray scattering studies, the wetting behavior differs from the expected power-law thickness dependence as a function of the chemical potential offset that has been predicted and observed on smooth substrates. Microscopic effects of surface induced order at liquid interfaces, such as surface freezing, will also be discussed. Finally, the macroscopic wetting effects of nanopatterned surfaces will be presented.

The author acknowledges the contribution from Antonio Checco, Yuguang Cai, Oleg Gang, Chuck Black, Julian Baumert, Moshe Deutsch, and Peter Pershan. Work supported by Materials Science Division, Basic Energy Science, DOE under contract No.DE-AC02-98CH10886.
host: Allen

• Friday, November 18, 1:30 pm
Philip Kim
Columbia University
Low-dimensional Transport Phenomena in Nanoscaled Materials
Combined with state-of-the-art device fabrication techniques, the development of new methods of nanoscale material synthesis/manipulation enable us to investigate mesoscopic transport phenomena in nanometer scales. In these length scales the nanoscaled materials have exhibited a variety of unique physical phenomena due to the enhanced quantum confinement of electrons in reduced dimensions. In this presentation, we will discuss our recent investigation of mesoscopic transport phenomena in carbon nanotubes, nanowires, and graphene, where quantum mechanically enhanced low dimensional effects are predominant. The subjects include, (1) growth/manipulation of ultralong nanotubes and electrical characterization of them, (2) electric field effect in mesoscopic thermoelectric transport in nanotubes, (3) electrical transport between nanotube-single molecular junction, (4) 1D to 3D cross-over in electric transport in multichannel nanowires, and (5) unusual quantum Hall effect and observation of Berry's phase in mesoscopic graphene.
host: Mendez
• Friday, December 2, 1:30 pm
Koichiro Umemoto
U. of Minnesota, Minneapolis, and Stony Brook
Phase transformation in CaIrO₃-type MgSiO₃ at ultra-high PTs: implications for the solar giants and terrestrial exoplanets
Host: Allen
• Friday, December 9, 1:30 pm
Yimei Zhu
Brookhaven National Lab
Revealing nano-scale electronic and magnetic structure with fast electrons
This talk is part of the monthly series of joint SBU-BNL seminars on nanoscience
A challenge in solid state physics and materials science is to accurately measure electrostatic and magnetic potentials in crystals and defects at nonometric scale.  Facing such a challenge we developed a novel quantitative electron diffraction/imaging technique that is very sensitive to charge distribution in solid and can be used to test Density Functional Theory calculations.  We present our recent work on the measurement of valence electron distribution and charge transfer in MgB2 superconductor and dielectric CaCu3Ti4O12 as well as on potential variation and space charge at the grain boundaries of Ca-doped and -undoped YBa2Cu3O7-? bicrystals.  We also report our progress towards quantitative high-resolution phase microscopy including electron holography and non-interferometric phase retrieval methods to reveal magnetic structure information.  Dynamic behavior of domains and their induction distribution during magnetization process and reversal mechanism of artificially structured Permalloy elements and arrays will be presented.  Underlying principle of the different characterization methods and their advantage and drawback will be discussed.

The author acknowledges the contribution from the members of the Advanced Electron Microscopy Group at BNL, L.Wu, JC.Zheng, R.Klie, V.Volkov, M.Schofield, M. Beleggia and J.Lau.  Work supported by Materials Science Division, Basic Energy Science, DOE under contract No.DE-AC02-98CH1-886.
Host: Allen

• Friday, December 16, 1:30 pm
 
 

Send comments to Phil Allen (substituting for Laszlo Mihaly); created 5/24/2005