Publications
Modification of the He3 phase diagram by anisotropic disorder
Motivated by the recent prediction that uniaxially compressed aerogel can stabilize the anisotropic A phase over the isotropic B phase, we measure the pressure dependent superfluid fraction of He3 entrained in 10% axially compressed, 98% porous aerogel. We observe that a broad region of the temperature-pressure phase diagram is occupied by the metastable A phase. The reappearance of the A phase on warming from the B phase, before superfluidity is extinguished at Tc, is in contrast to its absence in uncompressed aerogel.
Polarization of PAR proteins by advective triggering of a pattern-forming system
In the Caenorhabditis elegans zygote, a conserved network of partitioning-defective (PAR) polarity proteins segregates into an anterior and a posterior domain, facilitated by flows of the cortical actomyosin meshwork. The physical mechanisms by which stable asymmetric PAR distributions arise from transient cortical flows remain unclear. We present evidence that PAR polarity arises from coupling of advective transport by the flowing cell cortex to a multistable PAR reaction-diffusion system.
Pairing, ferromagnetism, and condensation of a normal spin-1 Bose gas
We find the conditions under which the normal state of a spin-1 Bose gas is unstable toward condensation, ferromagnetism, liquid crystalline-like nematicity, and Bardeen-Cooper-Schrieffer-like pairing. When the spin-dependent interactions are much weaker than the density-density interaction there is direct transition from a featureless normal state to a fully ordered Bose-Einstein condensate with either ferromagnetic or nematic order.
Low-flux measurements with Cornell's LCLS integrating pixel array detector
Next generation light sources are revolutionizing x-ray science by delivering ultra-intense, hard x-ray pulses many orders of magnitude brighter and shorter in duration than previously achievable. Maximizing the scientific potential of these light sources requires the development of suitable detectors. Experiments such as coherent x-ray imaging of single particles require detectors that can record extremely high instantaneous flux rates produced by femtosecond x-ray pulses (i.e.
Nematic order in the vicinity of a vortex in superconducting FeSe
We present a phenomenological theory of the interplay between nematic order and superconductivity in the vicinity of a vortex induced by an applied magnetic field. Nematic order can be strongly enhanced in the vortex core. As a result, the vortex cores become elliptical in shape. For the case where there is weak bulk nematic order at zero magnetic field, the field-induced eccentricity of the vortex core has a slow power-law decay away from the core. Conversely, if the nematic order is field induced, then the eccentricity is confined to the vortex core.
How Kondo-holes create intense nanoscale heavy-fermion hybridization disorder
Replacing a magnetic atom by a spinless atom in a heavy-fermion compound generates a quantum state often referred to as a "Kondo-hole". No experimental imaging has been achieved of the atomic- scale electronic structure of a Kondo-hole, or of their destructive impact [Lawrence JM, et al. (1996) Phys Rev B 53:12559-12562] [Bauer ED, et al. (2011) Proc Natl Acad Sci. 108:6857-6861] on the hybridization process between conduction and localized electrons which generates the heavy-fermion state.
Biomineralization: Micelles in a crystal
Synthetic efforts have identified a growing number of classes of organic macro-molecular impurities. Inclusion of an organic phase is believed to play a key role in enhancing the mechanical properties of the crystals, which are believed to share structural features with biogenic minerals and to have both increased hardness and fracture toughness relative to their pure, geological counterparts.
Quantum transport in mesoscopic He3 films: Experimental study of the interference of bulk and boundary scattering
We discuss the mass transport of a degenerate Fermi liquid He3 film over a rough surface, and the film momentum relaxation time, in the framework of theoretical predictions. In the mesoscopic regime, the anomalous temperature dependence of the relaxation time is explained in terms of the interference between elastic boundary scattering and inelastic quasiparticle-quasiparticle scattering within the film.
Science at the Hard X-ray Diffraction Limit (XDL2011), Part 1
There is growing excitement in the synchrotron materials science community about the potential of nearly diffraction-limited, high-repetition rate, hard X-ray sources, such as an Energy Recovery Linac (ERL) or an Ultimate Storage Ring (USR), and that these sources will pave the way to scientific insights and discoveries not possible with existing facilities. These future sources will deliver highly coherent, nearly diffraction-limited X-ray beams that will power ultra-intense, nanometer-scale X-ray probes and imaging capabilities approaching atomic resolution.