Publications
Semiclassical theory of the tunneling anomaly in partially spin-polarized compressible quantum Hall states
Electron tunneling into a system with strong interactions is known to exhibit an anomaly, in which the tunneling conductance vanishes continuously at low energy due to many-body interactions. Recent measurements have probed this anomaly in a quantum Hall bilayer of the half-filled Landau level, and shown that the anomaly apparently gets stronger as the half-filled Landau level is increasingly spin polarized.
Valley-Selective Exciton Bistability in a Suspended Monolayer Semiconductor
We demonstrate robust optical bistability, the phenomenon of two well-discriminated stable states depending upon the history of the optical input, in fully suspended monolayers of WSe2 at low temperatures near the exciton resonance. Optical bistability has been achieved under continuous-wave optical excitation that is red-detuned from the exciton resonance at an intensity level of 103 W/cm2. The observed bistability is originated from a photothermal mechanism, which provides both optical nonlinearity and passive feedback, two essential elements for optical bistability.
Mixed-valence insulators with neutral Fermi surfaces
Samarium hexaboride is a classic three-dimensional mixed valence system with a high-Temperature metallic phase that evolves into a paramagnetic charge insulator below 40 K. A number of recent experiments have suggested the possibility that the low-Temperature insulating bulk hosts electrically neutral gapless fermionic excitations.
Density and electron density of aqueous cryoprotectant solutions at cryogenic temperatures for optimized cryoprotection and diffraction contrast
The glass-phase densities at T = 77 K of aqueous solutions of the common cryoprotective agents (CPAs) methanol, ethanol, 2-propanol, glycerol, 2-methyl-2,4-pentanediol (MPD), ethylene glycol, polyethylene glycol 200 and polypropylene glycol 425 were measured as a function of CPA concentration. Individual drops with volumes as small as ∼65 pl were rapidly cooled to achieve the glass phase, and their densities at T = 77 K were determined by cryoflotation.
Electric-field switching of two-dimensional van der Waals magnets
Controlling magnetism by purely electrical means is a key challenge to better information technology 1 . A variety of material systems, including ferromagnetic (FM) metals 2-4, FM semiconductors 5, multiferroics 6-8 and magnetoelectric (ME) materials 9,10, have been explored for the electric-field control of magnetism. The recent discovery of two-dimensional (2D) van der Waals magnets 11,12 has opened a new door for the electrical control of magnetism at the nanometre scale through a van der Waals heterostructure device platform 13 .
Mechanisms of oxide growth during the combustion of Al:Zr nanolaminate foils
Reactive metal nanolaminates, most notably aluminum/zirconium composites, have been developed as fuels to aid combustion in explosive formulations. Thus far, however, their energy density is limited by incomplete oxidation. An in situ x-ray diffraction (XRD) study was performed on a 40 µm thick Al:Zr (atomic ratio 1:1) multilayer foil to track the growth of reaction products during ignition, combustion, and cooling (over approximately 5 s) to determine the mechanisms that prevent complete combustion from occurring.
Controlling surface carrier density by illumination in the transparent conductor La-doped BaSnO3
LaxBa1-xSnO3 is a promising transparent conducting oxide whose high mobility facilitates potential applications in transparent electronics, oxide electronics, and power electronics. Here, we report quantitative comparisons between angle-resolved photoemission and density functional theory, demonstrating a close agreement between calculations and the measured bulk electronic structure. Further measurements reveal upward band bending at the film-vacuum interface, while ultraviolet (UV) exposure is found to increase the surface electron density, similar to other oxides.
Nonzero Berry phase in quantum oscillations from giant Rashba-type spin splitting in LaTiO3/SrTiO3 heterostructures
The manipulation of the spin degrees of freedom in a solid has been of fundamental and technological interest recently for developing high-speed, low-power computational devices. There has been much work focused on developing highly spin-polarized materials and understanding their behavior when incorporated into so-called spintronic devices. These devices usually require spin splitting with magnetic fields. However, there is another promising strategy to achieve spin splitting using spatial symmetry breaking without the use of a magnetic field, known as Rashba-type splitting.
Dynamical susceptibility near a long-wavelength critical point with a nonconserved order parameter
We study the dynamic response of a two-dimensional system of itinerant fermions in the vicinity of a uniform (Q=0) Ising nematic quantum critical point of d-wave symmetry. The nematic order parameter is not a conserved quantity, and this permits a nonzero value of the fermionic polarization in the d-wave channel even for vanishing momentum and finite frequency: Π(q=0,Ωm)≠0.
Computation of a Theoretical Membrane Phase Diagram and the Role of Phase in Lipid-Raft-Mediated Protein Organization
Lipid phase heterogeneity in the plasma membrane is thought to be crucial for many aspects of cell signaling, but the physical basis of participating membrane domains such as "lipid rafts" remains controversial. Here we consider a lattice model yielding a phase diagram that includes several states proposed to be relevant for the cell membrane, including microemulsion - which can be related to membrane curvature - and Ising critical behavior. Using a neural-network-based machine learning approach, we compute the full phase diagram of this lattice model.