24,146 research outputs found
Quantum fluctuations in the spiral phase of the Hubbard model
We study the magnetic excitations in the spiral phase of the two--dimensional
Hubbard model using a functional integral method. Spin waves are strongly
renormalized and a line of near--zeros is observed in the spectrum around the
spiral pitch . The possibility of disordered spiral states is
examined by studying the one--loop corrections to the spiral order parameter.
We also show that the spiral phase presents an intrinsic instability towards an
inhomogeneous state (phase separation, CDW, ...) at weak doping. Though phase
separation is suppressed by weak long--range Coulomb interactions, the CDW
instability only disappears for sufficiently strong Coulomb interaction.Comment: Figures are NOW appended via uuencoded postscript fil
Higher-order Stationary Phase Approximations in Semiclassical Scattering
Stationary phase approximations on differential cross section expansion for elastic particle scattering mechanic
Hybrid Superconductor-Quantum Point Contact Devices using InSb Nanowires
Proposals for studying topological superconductivity and Majorana bound
states in nanowires proximity coupled to superconductors require that transport
in the nanowire is ballistic. Previous work on hybrid nanowire-superconductor
systems has shown evidence for Majorana bound states, but these experiments
were also marked by disorder, which disrupts ballistic transport. In this
letter, we demonstrate ballistic transport in InSb nanowires interfaced
directly with superconducting Al by observing quantized conductance at
zero-magnetic field. Additionally, we demonstrate that the nanowire is
proximity coupled to the superconducting contacts by observing Andreev
reflection. These results are important steps for robustly establishing
topological superconductivity in InSb nanowires
One- and two-particle microrheology
We study the dynamics of rigid spheres embedded in viscoelastic media and
address two questions of importance to microrheology. First we calculate the
complete response to an external force of a single bead in a homogeneous
elastic network viscously coupled to an incompressible fluid. From this
response function we find the frequency range where the standard assumptions of
microrheology are valid. Second we study fluctuations when embedded spheres
perturb the media around them and show that mutual fluctuations of two
separated spheres provide a more accurate determination of the complex shear
modulus than do the fluctuations of a single sphere.Comment: 4 pages, 1 figur
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