Apr
14
Teaser:

Electrons in free space have a well-defined mass. Recently, a new class of materials called topological insulators were discovered, where the low energy electrons have zero mass. In fact, these electrons can be described by the same massless Dirac equation that is used to describe relativistic particles travelling close to the speed of light. In this talk I will describe our recent experimental and theoretical investigations of Topological Crystalline Insulators (TCIs) [1]. TCIs belong to the newest category of topological materials...

Mar
27
Teaser:

 

 

While we would like to avoid frustration in our daily lives, frustration in condensed matter produces novel phenomena with important consequences. Materials that are geometrically frustrated cannot minimize the energy of every particle-particle interaction, even in their ground state; materials that are kinetically frustrated are trapped out of equilibrium, i.e., they cannot reach their ground state. In this talk I will review a series of experiments I have performed investigating the role of frustration in the assembly and phase behavior of colloidal systems. By tuning particle size, shape, and confinement, I systematically varied the degree of...

Mar
27
Teaser:

We use recent constraints on the star formation rate---halo mass---redshift relation to model the host halo environments where short Gamma-Ray Burst (sGRB) progenitors are created.  These halo environments set minimum energy requirements for sGRB progenitors to leave the vicinity of their original galaxy.  We find that the fraction of sGRBs which are hostless is a robust probe of the underlying velocity kick distribution for sGRB progenitors, regardless of uncertainties in the sGRB time-delay distribution and observational systematics.  We use observed constraints on the hostless fraction of sGRBs to rule out several sGRB progenitor classes which cannot supply the...

Mar
24
Teaser:

Quantum optomechanics has attracted increasing attention in recent years due to its broad applications. In 2008, we started a pioneering experiment to trap and cool a glass microsphere in vacuum towards the quantum ground state of an optical tweezer, and to create a quantum-limited microscopic detector. This novel system eliminates the physical contact inherent to clamped cantilevers and can allow ground-state cooling from room temperature. Moreover, the optical trap can be switched off, allowing a particle to undergo free-fall in vacuum after cooling. This system is ideal for studying macroscopic quantum mechanics, gravity induced quantum effects, and creating an ultrasensitive detector...

Mar
13
Teaser:

A fascinating manifestation of collective quantum phenomena in condensed matter is the emergence of elementary excitations – or quasiparticles – carrying quantum numbers that are fractions of those of a non-interacting system. Low-dimensional and frustrated magnetic materials, built from localized spins 1/2, display a diversity of such many-body phenomena. Moreover, they allow detailed experimental investigations, quantitative comparisons with theoretical predictions,...

Mar
13
Teaser:

Mar
11
Teaser:

Liquids and solids tend to stick to each other.  When a liquid droplet sticks to a solid surface we call it wetting.  When a solid particle sticks to a solid surface we call it adhesion.  The classic coarse-grained descriptions of these two phenomena are distinct from each other.  Both descriptions assume that solid objects undergo very little deformation during wetting and adhesion.  In this talk, I will show how this assumption breaks down when the solids are soft enough and how wetting and adhesion really are not that different after all.

Mar
10
Teaser:

I will present time-resolved measurements of the relaxation dynamics, in a small molecular system, following ultraviolet (UV) photoexcitation. We probe these excitations through photoionization and velocity map imaging (VMI) spectroscopy. Vacuum and extreme ultraviolet (VUV/XUV) pump and probe pulses are created by exploiting strong-field high harmonic generation (HHG) from our state-of-the-art 30 mJ, 1 kHz laser system. Three dimensional photoelectron and photoion momentum images recorded with our VMI spectrometer reveal non-Born Oppenheimer dynamics in the vicinity of a conical intersection, and allow us track the state of the...

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