Nathaniel Gabor, MIT

Tuesday, April 9, 2013 4:30 p.m. Galileo- Pryne – Harvey Mudd College

Graphene, an atomically thin sheet of hexagonally oriented carbon, is a zero band gap conductor (semi-metal) that exhibits extraordinary electronic behavior and broadband optical absorption. Hexagonal boron nitride, which shares a similar structure to that of graphene, is a highly insulating electronic material that does not absorb any light in the visible spectrum. By combining graphene and boron nitride into ultrathin vertical stacks, we can fabricate new optoelectronic devices that demonstrate highly sensitive optical response, yet are only as thick as the width of a DNA molecule. In this talk, I will discuss how stacking these atomically thin materials allows us to explore new types of optoelectronic devices that may ultimately lead to more efficient light energy harvesting technologies.

Hilke Schlichting, Caltech

Tuesday, April 2, 2013 4:30 p.m. Millikan Lab – Room 134

In my talk, I will discuss recent insights that we have gained into planet formation form our solar system. I will talk about the Kuiper belt, located at the outskirts of our planetary system, which provides a snapshot of earlier stages of planet formation and is therefore an ideal laboratory for testing planet formation theories. I will show how we can use the Kuiper belt size distribution to gain new insights into runaway growth during planet formation and how we can use it to constrain the initial sizes of planetesimals that are the building blocks of planets.

Robert Truehaft, JPL

Tuesday, March 26, 2013 4:30 p.m. Galileo- Pryne – Harvey Mudd College

When trees are cut down, they release their carbon to the atmosphere in CO2. After fossil fuels, deforestation is the second largest anthropogenic contributor to atmospheric CO2. Tropical forests contain about 50% of Earth’s forested biomass, and they account for most deforestation. The degree to which a forest is storing carbon or releasing it to the atmosphere can be remotely sensed by measurements of the forest 3-dimensional distribution of vegetation, particularly in the vertical direction.  For example, taller forests store more carbon than shorter ones. 3-dimensional structure measurements made regionally and globally can help to identify patterns of carbon sequestration and release, which affect the global carbon cycle.  Measurement of the distribution of vegetation in the vertical direction has only within the last 20 years been possible with the technologies of interferometric synthetic aperture radar (InSAR) and laser ranging (lidar).  InSAR and lidar measurements are made by transmitting electromagnetic waves from air or space, which scatter off the vegetated surfaces and return back to the transmitter. The time it takes for a signal to return is related to the vegetation’s height above the surface, that important vertical component. This talk explains the InSAR and lidar measurements, focusing on the basic electromagnetism needed to estimate structural characteristics from the electromagnetic returns.  For InSAR, the difference between the arrival time of a scattered signal at two ends of a baseline is the principal vertical indicator. For lidar, the time delay between transmit and receive is related to the altitude of vegetation above the surface. This talk also shows the interface between the physics of electromagnetic scattering and the biology of carbon storage in biomass. It further suggests the possibility of applying physics modes of analysis (e.g. Fourier analysis) to biomass measurement.

David Weld – UC Santa Barbara

Tuesday, March 5, 2013 4:30 p.m. Galileo- Pryne, Harvey Mudd College

Ultracold neutral atoms trapped in optical lattices represent a new frontier for the investigation of outstanding problems in many-body quantum mechanics.  These systems promise to bring the precision and control of atomic physics to bear on important problems in condensed matter physics, from nonequilibrium spin dynamics to d-wave superconductivity.   The ambit of this fast-growing field is expanding from measurement to control, and from statics to dynamics.  Breakthroughs in the ability to exert full spatiotemporal control over the evolution of cold atomic gases will enable a new generation of experiments at the boundary between condensed matter and atomic physics.

 At UCSB we are building two experimental platforms (based around ultracold lithium and strontium) which will enable the creation and study of new, highly tunable, and strongly correlated phases of matter.  Experimental goals of the lithium platform include quantum simulation of condensed matter Hamiltonians, the demonstration of effective time-reversal in a lattice-trapped gas, and the study of dynamical pseudospin ordering in higher-dimensional tilted lattices.  The rich electronic structure of strontium may enable the creation of chiral spin liquids and states exhibiting SU(10) magnetism, and the ultra-narrow intercombination transition along with the negligible scattering length of the heaviest stable strontium isotope are particularly appealing for quantum sensing experiments.

Stephon Alexander, Dartmouth University

Tuesday, February 26, 2013 4:30 pm  Millikan Lab – Room 134

Jing Xu – UC Merced

Tuesday, February 19, 2013 4:30 pm  Millikan Lab – Room 134

Experimental biophysicists build instruments to study nature’s nano-machines.  Molecular motors are nano-machines and are crucial for life: they transport materials in cells.  Motor-based transport is inherently a many body problem, and exhibits complex behavior yet to be understood.  An analytic model for multiple motor transport has been proposed, but has remained untested.  In this talk, I will discuss the construction of a single beam gradient optical trap in my laboratory. I will also discuss planned measurements using this optical trap, aimed at experimentally testing the current model and driving theory development.

Prof. Douglas Natelson, Rice University

Monday, February 11, 2013 4:30 pm  Millikan Lab – Room 134

We are all familiar with the idea that driving current through a conductor generates heat. However, when we consider the flow of current at the nanometer scale, we see that the transport of electrons is, in general, a complicated quantum mechanical process, and ideas familiar from thermal equilibrium (e.g., “temperature”) become challenging to define. I will talk about my group’s recent experiments, where we combine clever nanofabrication with electronic and optical techniques to address this question. We use metal electrodes separated at the nanometer scale to push current through molecules. These electrodes act like optical antennas, allowing us to use optical spectroscopy to watch the vibrational modes of those molecules. We can see current-driven vibrational heating, giving us new information about the flow of energy at these scales.