Quantum over breakfast Quantum over breakfast

Spring 2012


April 13

Third meeting

Posted on 04/11/2012

Science and Technology I, Room 306, 11am (+ lunch after noon)

QOB informal talk
Prof. Chenggang Tao, Virginia Tech
Visualizing fluctuations and electron scattering in nanostructures
Nanoscale structures have high surface-to-volume ratio and are susceptible to structural fluctuations. Direct imaging at the atomic scale using scanned probe techniques allows us to quantitatively characterize fluctuations using the tools of statistical mechanics. The impact of structural fluctuations on electronic devices will be illustrated for the case of electromigration, the biased displacement of mass by electron scattering when electrical current flows through a device. Using a combination of scanning tunneling microscopy and scanning electron microscopy, we directly observed electromigration of silver and silver-C60 nanostructures. I will show how the scattering force is determined. Possible mechanisms for the large force, including current crowding, charge transfer and local heating, will be discussed.

March 30

Postponed meeting

Posted on 03/27/2012

Cancelled

QOB informal talk
Dr. Khan W. Mahmud, JQI/NIST
Dynamics of noise correlations of ultracold bosons in an optical lattice

February 10

Second meeting

Posted on 02/07/2012

Science and Technology I, Room 306, 11am (+ lunch after noon)

QOB informal talk
Dr. Satyan Bhongale, George Mason University
Satyan will discuss his recent work on dipolar condensates:
Bond order solid of two-dimensional dipolar fermions

January 20

First meeting

Posted on 01/17/2012

Science and Technology I, Room 306, 11am (+ lunch after noon)

QOB informal talk
Dr. Ehsan Khatami, Georgetown University
Finite-temperature properties and phase transitions of frustrated magnets
In frustrated magnets, lattice geometry and the nature of interactions between spins prevent simultaneous minimization of the energy on all the bonds for any configuration of spins. As a result, in the classical limit, they have an exponentially large number of ground states and a finite zero-temperature entropy. Quantum fluctuations often lead such systems with unusual low-temperature behavior to exotic ground states. In this talk, utilizing the numerical linked-cluster expansions (NLCE), we explore finite-temperature properties of the Heisenberg model on the checkerboard lattice with interactions that are antiferromagnetic between both nearest- and next-nearest-neighbor spins. We show how the proposed ground states in different parameter regions are approached as the temperature is reduced. We also study thermodynamic properties of a pinwheel-distorted Kagome lattice Heisenberg model, with a valence-bond solid (VBS) ground state, realized in Rb_2Cu_3SnF_12 material. Introducing a zero-temperature NLCE, tailored to capture the correlations of the VBS order, and by tuning a parameter that takes one from the distorted to the uniform Hamiltonian, we study the approach towards the ground state of the uniform Kagome lattice Heisenberg model. We find strong evidence that a first-order phase transition takes place before the uniform limit is reached, implying that the ground state of this model is not pinwheel dimerized and is stable to finite dimerizing perturbations.