Publications
Intra-unit-cell electronic nematicity of the high-T c copper-oxide pseudogap states
In the high-transition-temperature (high-Tc) superconductors the pseudogap phase becomes predominant when the density of doped holes is reduced. Within this phase it has been unclear which electronic symmetries (if any) are broken, what the identity of any associated order parameter might be, and which microscopic electronic degrees of freedom are active. Here we report the determination of a quantitative order parameter representing intra-unit-cell nematicity: the breaking of rotational symmetry by the electronic structure within each CuO2 unit cell.
Material limitations of carbon-nanotube inertial balances: Possibility of intrinsic yoctogram mass resolution at room temperature
We present a theoretical study of the intrinsic quality factor of the fundamental flexural vibration in a carbon nanotube and its dependence on temperature, radius, length, and tension. In particular, we examine three- and four-phonon decays of the fundamental flexural mode within quantized elasticity theory.
Erratum: Cryptotomography: Reconstructing 3D Fourier intensities from randomly oriented single-shot diffraction patterns(Physical Review Letters (2010) 104 (225501))
Energy landscape of silicon systems and its description by force fields, tight binding schemes, density functional methods, and quantum Monte Carlo methods
The accuracy of the fundamental properties of the energy landscape of silicon systems obtained from density functional theory with various exchange-correlation functionals, a tight binding scheme, and force fields is studied. Depending on the application, quantum Monte Carlo or density functional theory results serve as quasiexact reference values.
Fabrication of a nanomechanical mass sensor containing a nanofluidic channel
Nanomechanical resonators operating in vacuum are capable of detecting and weighing single biomolecules, but their application to the life sciences has been limited by viscous forces that impede their motion in liquid environments. A promising approach to avoid this problem, encapsulating the fluid within a mechanical resonator surrounded by vacuum, has not yet been tried with resonant sensors of mass less than ∼100 ng, despite predictions that devices with smaller effective mass will have proportionally finer mass resolution.
Cryptotomography: Reconstructing 3D fourier intensities from randomly oriented single-shot diffraction patterns
We reconstructed the 3D Fourier intensity distribution of monodisperse prolate nanoparticles using single-shot 2D coherent diffraction patterns collected at DESY's FLASH facility when a bright, coherent, ultrafast x-ray pulse intercepted individual particles of random, unmeasured orientations. This first experimental demonstration of cryptotomography extended the expansion-maximization-compression framework to accommodate unmeasured fluctuations in photon fluence and loss of data due to saturation or background scatter.
Imaging the fano lattice to hidden order transition in URu 2 Si 2
Within a Kondo lattice, the strong hybridization between electrons localized in real space (r-space) and those delocalized in momentum-space (k-space) generates exotic electronic states called Ä€̃ heavy fermionsÄ€™. In URu 2 Si 2 these effects begin at temperatures around 55 K but they are suddenly altered by an unidentified electronic phase transition at T o = 17.5 K. Whether this is conventional ordering of the k-space states, or a change in the hybridization of the r-space states at each U atom, is unknown.
Synergistic action of RNA polymerases in overcoming the nucleosomal barrier
During gene expression, RNA polymerase (RNAP) encounters a major barrier at a nucleosome and yet must access the nucleosomal DNA. Previous in vivo evidence has suggested that multiple RNAPs might increase transcription efficiency through nucleosomes. Here we have quantitatively investigated this hypothesis using Escherichia coli RNAP as a model system by directly monitoring its location on the DNA via a single-molecule DNA-unzipping technique. When an RNAP encountered a nucleosome, it paused with a distinctive 10-base pair periodicity and backtracked by ∼10-15 base pairs.
Fractional quantum Hall states in the vicinity of Mott plateaus
We perform variational Monte Carlo calculations to show that bosons in a rotating optical lattice will form analogs of fractional quantum Hall states when the tunneling is sufficiently weak compared to the interactions, and the deviation of density from an integer is commensurate with the effective magnetic field. We compare the energies of superfluid and correlated states to one another and to the energies found in full configuration-interaction calculations on small systems.
Spin waves in a spin-1 normal Bose gas
We present a theory of spin waves in a noncondensed gas of spin-1 bosons and provide both analytic calculations of the linear theory and full numerical simulations of the nonlinear response. We highlight the role of spin-dependent contact interactions in the dynamics of a thermal gas. Although these interactions are small compared to the thermal energy, they set the scale for low-energy, long-wavelength spin waves. In particular, we find that the polar state of Rb87 is unstable to collisional mixing of magnetic sublevels even in the normal state.