815 research outputs found
Coherent Inverse Photoemission Spectrum for Gutzwiller Projected Superconductors
Rigorous relations for Gutzwiller projected BCS states are derived. The
obtained results do not depend on the details of model systems, but solely on
the wave functions. Based on the derived relations, physical consequences are
discussed for strongly correlated superconducting states such as high- cuprate superconductors.Comment: 4 pages, 3 figures, to be published in Phys. Rev.
Successive phase transitions at finite temperatures of the supersolid in the three-dimensional extended Bose-Hubbard model
We study the finite temperature properties of the extended Bose-Hubbard model
on a cubic lattice. This model exhibits the so-called supersolid state. To
start with, we investigate ordering processes by quantum Monte Carlo
simulations, and find successive superfluid and solid phase transitions. There,
we find that the two order parameters compete with each other. We obtain the
finite temperature phase diagram, which contains the superfluid, the solid, the
supersolid and the disordered phase. We develop a mean-field theory to analyze
the ordering processes and compare the result with that obtained by
simulations, and discuss the mechanism of the competition of these two orders.
We also study how the supersolid region shrinks as the on-site repulsion
becomes strong.Comment: 6 pages, 6 figure
Gauge Group and Topology Change
The purpose of this study is to examine the effect of topology change in the
initial universe. In this study, the concept of -cobordism is introduced to
argue about the topology change of the manifold on which a transformation group
acts. This -manifold has a fiber bundle structure if the group action is
free and is related to the spacetime in Kaluza-Klein theory or
Einstein-Yang-Mills system. Our results revealed that fundamental processes of
compactification in -manifolds. In these processes, the initial high
symmetry and multidimensional universe changes to present universe by the
mechanism which lowers the dimensions and symmetries.Comment: 8 page
Accessing the transport properties of graphene and its multi-layers at high carrier density
We present a comparative study of high carrier density transport in mono-,
bi-, and trilayer graphene using electric-double-layer transistors to
continuously tune the carrier density up to values exceeding 10^{14} cm^{-2}.
Whereas in monolayer the conductivity saturates, in bi- and trilayer flling of
the higher energy bands is observed to cause a non-monotonic behavior of the
conductivity, and a large increase in the quantum capacitance. These systematic
trends not only show how the intrinsic high-density transport properties of
graphene can be accessed by field-effect, but also demonstrate the robustness
of ion-gated graphene, which is crucial for possible future applications.Comment: 4 figures, 4 page
Slow Relaxation Process in Ising like Heisenberg Kagome Antiferromagnets due to Macroscopic Degeneracy in the Ordered State
We study relaxation phenomena in the ferromagnetically ordered state of the
Ising-like Heisenberg kagome antiferromagnets. We introduce the "weathervane
loop" in order to characterize macroscopic degenerate ordered states and study
the microscopic mechanism of the slow relaxation from a view point of the
dynamics of the weathervane loop configuration. This mechanism may give a
possible origin of the slow relaxation reported in recent experiments.Comment: 6pages, 4figures, HFM2006 proceeding
New Seiberg Dualities from N=2 Dualities
We propose a number of new Seiberg dualities of N=1 quiver gauge theories.
The new Seiberg dualities originate in new S-dualities of N=2 superconformal
field theories recently proposed by Gaiotto. N=2 S-dual theories deformed by
suitable mass terms flow to our N=1 Seiberg dual theories. We show that the
number of exactly marginal operators is universal for these Seiberg dual
theories and the 't Hooft anomaly matching holds for these theories. These
provide strong evidence for the new Seiberg dualities. Furthermore, we study in
detail the Klebanov-Witten type theory and its dual as a concrete example. We
show that chiral operators and their non-linear relations match between these
theories. These arguments also give non-trivial consistency checks for our
proposal.Comment: 31 pages, 7 figures. v2:version to appear in JHE
Spin-Peierls transition of the first order in S=1 antiferromagnetic Heisenberg chains
We investigate a one-dimensional S=1 antiferromagnetic Heisenberg model
coupled to a lattice distortion by a quantum Monte Carlo method. Investigating
the ground state energy of the static bond-alternating chain, we find that the
instability to a dimerized chain depends on the value of the spin-phonon
coupling, unlike the case of S=1/2. The spin state is the dimer state or the
uniform Haldane state depending on whether the lattice distorts or not,
respectively. At an intermediate value of the spin-phonon coupling, we find the
first-order transition between the two states. We also find the coexistence of
the two states.Comment: 7 pages, 12 eps figures embedded in the text; corrected typos,
replaced figure
Ordered phase and phase transitions in the three-dimensional generalized six-state clock model
We study the three-dimensional generalized six-state clock model at values of
the energy parameters, at which the system is considered to have the same
behavior as the stacked triangular antiferromagnetic Ising model and the
three-state antiferromagnetic Potts model. First, we investigate ordered phases
by using the Monte Carlo twist method (MCTM). We confirmed the existence of an
incompletely ordered phase (IOP1) at intermediate temperature, besides the
completely ordered phase (COP) at low-temperature. In this intermediate phase,
two neighboring states of the six-state model mix, while one of them is
selected in the low temperature phase. We examine the fluctuation the mixing
rate of the two states in IOP1 and clarify that the mixing rate is very stable
around 1:1.
The high temperature phase transition is investigated by using
non-equilibrium relaxation method (NERM). We estimate the critical exponents
beta=0.34(1) and nu=0.66(4). These values are consistent with the 3D-XY
universality class. The low temperature phase transition is found to be of
first-order by using MCTM and the finite-size-scaling analysis
Relation of Cloud Occurrence Frequency, Overlap, and Effective Thickness Derived from CALIPSO and CloudSat Merged Cloud Vertical Profiles
A cloud frequency of occurrence matrix is generated using merged cloud vertical profile derived from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Cloud Profiling Radar (CPR). The matrix contains vertical profiles of cloud occurrence frequency as a function of the uppermost cloud top. It is shown that the cloud fraction and uppermost cloud top vertical pro les can be related by a set of equations when the correlation distance of cloud occurrence, which is interpreted as an effective cloud thickness, is introduced. The underlying assumption in establishing the above relation is that cloud overlap approaches the random overlap with increasing distance separating cloud layers and that the probability of deviating from the random overlap decreases exponentially with distance. One month of CALIPSO and CloudSat data support these assumptions. However, the correlation distance sometimes becomes large, which might be an indication of precipitation. The cloud correlation distance is equivalent to the de-correlation distance introduced by Hogan and Illingworth [2000] when cloud fractions of both layers in a two-cloud layer system are the same
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