579 research outputs found
Combining 10Be surface exposure and OSL dating to reconstruct Holocene lake-level fluctuations: a case study at Tangra Yumco (southern Tibet)
Abstract HKT-ISTP 2013
B
Kinetic Inductance of Josephson Junction Arrays: Dynamic and Equilibrium Calculations
We show analytically that the inverse kinetic inductance of an
overdamped junction array at low frequencies is proportional to the admittance
of an inhomogeneous equivalent impedance network. The bond in this
equivalent network has an inverse inductance
, where is the Josephson
coupling energy of the bond, is the ground-state phase
of the grain , and is the usual magnetic phase factor. We use this
theorem to calculate for square arrays as large as .
The calculated is in very good agreement with the low-temperature
limit of the helicity modulus calculated by conventional equilibrium
Monte Carlo techniques. However, the finite temperature structure of ,
as a function of magnetic field, is \underline{sharper} than the
zero-temperature , which shows surprisingly weak structure. In
triangular arrays, the equilibrium calculation of yields a series of
peaks at frustrations , where is an integer , consistent with experiment.Comment: 14 pages + 6 postscript figures, 3.0 REVTe
Metamagnetism in the 2D Hubbard Model with easy axis
Although the Hubbard model is widely investigated, there are surprisingly few
attempts to study the behavior of such a model in an external magnetic field.
Using the Projector Quantum Monte Carlo technique, we show that the Hubbard
model with an easy axis exhibits metamagnetic behavior if an external field is
turned on. For the case of intermediate correlations strength , we observe a
smooth transition from an antiferromagnetic regime to a paramagnetic phase.
While the staggered magnetization will decrease linearly up to a critical field
, uniform magnetization develops only for fields higher than .Comment: RevTeX 5 pages + 2 postscript figures (included), accepted for PRB
Rapid Communication
Stability of the vortex lattice in a rotating superfluid
We analyze the stability of the vortex lattice in a rotating superfluid
against thermal fluctuations associated with the long-wavelength Tkachenko
modes of the lattice. Inclusion of only the two-dimensional modes leads
formally to instability in infinite lattices; however, when the full
three-dimensional spectrum of modes is taken into account, the
thermally-induced lattice displacements are indeed finite.Comment: 16 page
Effect of disorder on the vortex-lattice melting transition
We use a three dimensional stacked triangular network of Josephson junctions
as a model for the study of vortex structure in the mixed state of high Tc
superconductors. We show that the addition of disorder destroys the first order
melting transition occurring for clean samples. The melting transition splits
in two different (continuous) transitions, ocurring at temperatures Ti and Tp
(>Ti). At Ti the perpendicular-to-field superconductivity is lost, and at Tp
the parallel-to-field superconductivity is lost. These results agree well with
recent experiments in YBaCuO.Comment: 4 pages + 2 figure
Magnetization Jump in a Model for Flux Lattice Melting at Low Magnetic Fields
Using a frustrated XY model on a lattice with open boundary conditions, we
numerically study the magnetization change near a flux lattice melting
transition at low fields. In both two and three dimensions, we find that the
melting transition is followed at a higher temperature by the onset of large
dissipation associated with the zero-field XY transition. It is characterized
by the proliferation of vortex-antivortex pairs (in 2D) or vortex loops (in
3D). At the upper transition, there is a sharp increase in magnetization, in
qualitative agreement with recent local Hall probe experiments.Comment: updated figures and texts. new movies available at
http://www.physics.ohio-state.edu:80/~ryu/jj.html. Accepted for publication
in Physical Review Letter
Charge-order transition in the extended Hubbard model on a two-leg ladder
We investigate the charge-order transition at zero temperature in a two-leg
Hubbard ladder with additional nearest-neighbor Coulomb repulsion V using the
Density Matrix Renormalization Group technique. We consider electron densities
between quarter and half filling. For quarter filling and U=8t, we find
evidence for a continuous phase transition between a homogeneous state at small
V and a broken-symmetry state with "checkerboard" [wavevector Q=(pi,pi)] charge
order at large V. This transition to a checkerboard charge-ordered state
remains present at all larger fillings, but becomes discontinuous at
sufficiently large filling. We discuss the influence of U/t on the transition
and estimate the position of the tricritical points.Comment: 4 pages, 5 figs, minor changes, accepted for publication in PRB R
Magnetism and Pairing in Hubbard Bilayers.
We study the Hubbard model on a bilayer with repulsive on-site interactions,
, in which fermions undergo both intra-plane () and inter-plane ()
hopping. This situation is what one would expect in high-temperature
superconductors such as YBCO, with two adjacent CuO planes. Magnetic and
pairing properties of the system are investigated through Quantum Monte Carlo
simulations for both half- and quarter-filled bands. We find that in all cases
inter-planar pairing with symmetry is dominant over planar
pairing with symmetry, and that for large enough pair
formation is possible through antiferromagnetic correlations. However, another
mechanism is needed to make these pairs condense into a superconducting state
at lower temperatures. We identify the temperature for pair formation with the
spin gap crossover temperature. [Submitted to Phys. Rev. B]Comment: 7 pages, uuencoded self-unpacking PS file with text and figures
First-Order Melting of a Moving Vortex Lattice: Effects of Disorder
We study the melting of a moving vortex lattice through numerical simulations
with the current driven 3D XY model with disorder. We find that there is a
first-order phase transition even for large disorder when the corresponding
equilibrium transition is continuous. The low temperature phase is an
anisotropic moving glass.Comment: Important changes from original version. Finite size analysis of
results has been added. Figure 2 has been changed. There is a new additional
Figure. To be published in Physical Review Letter
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