363 research outputs found
Quasiparticles in the 111 state and its compressible ancestors
We investigate the relationship of the spontaneously inter-layer coherent
``111''state of quantum Hall bilayers at total filling factor \nu=1 to
``mutual'' composite fermions, in which vortices in one layer are bound to
electrons in the other. Pairing of the mutual composite fermions leads to the
low-energy properties of the 111 state, as we explicitly demonstrate using
field-theoretic techniques. Interpreting this relationship as a mechanism for
inter-layer coherence leads naturally to two candidate states with
non-quantized Hall conductance: the mutual composite Fermi liquid, and an
inter-layer coherent charge e Wigner crystal. The experimental behavior of the
interlayer tunneling conductance and resistivity tensors are discussed for
these states.Comment: 4 Pages, RevTe
Metamorphosis of a Quantum Hall Bilayer State into a Composite Fermion Metal
Composite fermion metal states emerge in quantum Hall bilayers at total
Landau level filling factor =1 when the tunneling gap collapses by
application of in-plane components of the external magnetic field. Evidence of
this transformation is found in the continua of spin excitations observed by
inelastic light scattering below the spin-wave mode at the Zeeman energy. The
low-lying spin modes are interpreted as quasiparticle excitations with
simultaneous changes in spin orientation and composite fermion Landau level
index.Comment: 4 pages 4 figure
Linear response of heat conductivity of normal-superfluid interface of a polarized Fermi gas to orbital magnetic field
Using perturbed Bogoliubov equations, we study the linear response to a weak
orbital magnetic field of the heat conductivity of the normal-superfluid
interface of a polarized Fermi gas at sufficiently low temperature. We consider
the various scattering regions of the BCS regime and analytically obtain the
transmission coefficients and the heat conductivity across the interface in an
arbitrary weak orbital field. For a definite choice of the field, we consider
various values of the scattering length in the BCS range and numerically obtain
the allowed values of the average and species-imbalance chemical potentials.
Thus, taking Andreev reflection into account, we describe how the heat
conductivity is affected by the field and the species imbalance. In particular,
we show that the additional heat conductivity due to the orbital field
increases with the species imbalance, which is more noticeable at higher
temperatures. Our results indicate how the heat conductivity may be controlled,
which is relevant to sensitive magnetic field sensors/regulators at the
interface.Comment: To appear in Physica B (2011
Order by disorder and spiral spin liquid in frustrated diamond lattice antiferromagnets
Frustration refers to competition between different interactions that cannot
be simultaneously satisfied, a familiar feature in many magnetic solids. Strong
frustration results in highly degenerate ground states, and a large suppression
of ordering by fluctuations. Key challenges in frustrated magnetism are
characterizing the fluctuating spin-liquid regime and determining the mechanism
of eventual order at lower temperature. Here, we study a model of a diamond
lattice antiferromagnet appropriate for numerous spinel materials. With
sufficiently strong frustration a massive ground state degeneracy develops
amongst spirals whose propagation wavevectors reside on a continuous
two-dimensional ``spiral surface'' in momentum space. We argue that an
important ordering mechanism is entropic splitting of the degenerate ground
states, an elusive phenomena called order-by-disorder. A broad ``spiral
spin-liquid'' regime emerges at higher temperatures, where the underlying
spiral surface can be directly revealed via spin correlations. We discuss the
agreement between these predictions and the well characterized spinel MnSc2S4
Temperature Dependence of Spin Correlation and Charge Dynamics in the Stripe Phase of High-T_c Superconductors
We examine the temperature dependence of the electronic states in the stripe
phase of high-Tc cuprates by using the t-J model with a potential that
stabilizes vertical charge stripes. Charge and spin-correlation functions and
optical conductivity are calculated by using finite-temperature Lanczos method.
At zero temperature, the antiferromagnetic correlation between a spin in a
charge stripe and that in a spin domain adjacent to the stripe is weak, since
the charge stripe and the spin domain are almost separated. With increasing
temperature, the correlation increases and then decreases toward high
temperature. This is in contrast to other correlations that decrease
monotonically. From the examination of the charge dynamics, we find that this
anomalous temperature dependence of the correlation is the consequence of a
crossover from one-dimensional electronic states to two-dimensional ones.Comment: 7 pages in two-column format, 6 figures, to be published in Phys.
Rev.
Spinons and triplons in spatially anisotropic frustrated antiferromagnets
The search for elementary excitations with fractional quantum numbers is a
central challenge in modern condensed matter physics. We explore the
possibility in a realistic model for several materials, the spin-1/2 spatially
anisotropic frustrated Heisenberg antiferromagnet in two dimensions. By
restricting the Hilbert space to that expressed by exact eigenstates of the
Heisenberg chain, we derive an effective Schr\"odinger equation valid in the
weak interchain-coupling regime. The dynamical spin correlations from this
approach agree quantitatively with inelastic neutron measurements on the
triangular antiferromagnet Cs_2CuCl_4. The spectral features in such
antiferromagnets can be attributed to two types of excitations: descendents of
one-dimensional spinons of individual chains, and coherently propagating
"triplon" bound states of spinon pairs. We argue that triplons are generic
features of spatially anisotropic frustrated antiferromagnets, and arise
because the bound spinon pair lowers its kinetic energy by propagating between
chains.Comment: 16 pages, 6 figure
Assisted evolution enables HIV-1 to overcome a high trim5α-imposed genetic barrier to rhesus macaque tropism
Diversification of antiretroviral factors during host evolution has erected formidable barriers to cross-species retrovirus transmission. This phenomenon likely protects humans from infection by many modern retroviruses, but it has also impaired the development of primate models of HIV-1 infection. Indeed, rhesus macaques are resistant to HIV-1, in part due to restriction imposed by the TRIM5α protein (rhTRIM5α). Initially, we attempted to derive rhTRIM5α-resistant HIV-1 strains using two strategies. First, HIV-1 was passaged in engineered human cells expressing rhTRIM5α. Second, a library of randomly mutagenized capsid protein (CA) sequences was screened for mutations that reduced rhTRIM5α sensitivity. Both approaches identified several individual mutations in CA that reduced rhTRIM5α sensitivity. However, neither approach yielded mutants that were fully resistant, perhaps because the locations of the mutations suggested that TRIM5α recognizes multiple determinants on the capsid surface. Moreover, even though additive effects of various CA mutations on HIV-1 resistance to rhTRIM5α were observed, combinations that gave full resistance were highly detrimental to fitness. Therefore, we employed an 'assisted evolution' approach in which individual CA mutations that reduced rhTRIM5α sensitivity without fitness penalties were randomly assorted in a library of viral clones containing synthetic CA sequences. Subsequent passage of the viral library in rhTRIM5α-expressing cells resulted in the selection of individual viral species that were fully fit and resistant to rhTRIM5α. These viruses encoded combinations of five mutations in CA that conferred complete or near complete resistance to the disruptive effects of rhTRIM5α on incoming viral cores, by abolishing recognition of the viral capsid. Importantly, HIV-1 variants encoding these CA substitutions and SIVmac239 Vif replicated efficiently in primary rhesus macaque lymphocytes. These findings demonstrate that rhTRIM5α is difficult to but not impossible to evade, and doing so should facilitate the development of primate models of HIV-1 infection
Identification of Lck-derived peptides applicable to anti-cancer vaccine for patients with human leukocyte antigen-A3 supertype alleles
The identification of peptide vaccine candidates to date has been focused on human leukocyte antigen (HLA)-A2 and -A24 alleles. In this study, we attempted to identify cytotoxic T lymphocyte (CTL)-directed Lck-derived peptides applicable to HLA-A11+, -A31+, or -A33+ cancer patients, because these HLA-A alleles share binding motifs, designated HLA-A3 supertype alleles, and because the Lck is preferentially expressed in metastatic cancer. Twenty-one Lck-derived peptides were prepared based on the binding motif to the HLA-A3 supertype alleles. They were first screened for their recognisability by immunoglobulin G (IgG) in the plasma of prostate cancer patients, and the selected candidates were subsequently tested for their potential to induce peptide-specific CTLs from peripheral blood mononuclear cells of HLA-A3 supertype+ cancer patients. As a result, four Lck peptides were frequently recognised by IgGs, and three of them – Lck90−99, Lck449−458, and Lck450−458 – efficiently induced peptide-specific and cancer-reactive CTLs. Their cytotoxicity towards cancer cells was mainly ascribed to HLA class I-restricted and peptide-specific CD8+ T cells. These results indicate that these three Lck peptides are applicable to HLA-A3 supertype+ cancer patients, especially those with metastasis. This information could facilitate the development of peptide-based anti-cancer vaccine for patients with alleles other than HLA-A2 and -A24
Dispersion of Ordered Stripe Phases in the Cuprates
A phase separation model is presented for the stripe phase of the cuprates,
which allows the doping dependence of the photoemission spectra to be
calculated. The idealized limit of a well-ordered array of magnetic and charged
stripes is analyzed, including effects of long-range Coulomb repulsion.
Remarkably, down to the limit of two-cell wide stripes, the dispersion can be
interpreted as essentially a superposition of the two end-phase dispersions,
with superposed minigaps associated with the lattice periodicity. The largest
minigap falls near the Fermi level; it can be enhanced by proximity to a (bulk)
Van Hove singularity. The calculated spectra are dominated by two features --
this charge stripe minigap plus the magnetic stripe Hubbard gap. There is a
strong correlation between these two features and the experimental
photoemission results of a two-peak dispersion in LaSrCuO, and
the peak-dip-hump spectra in BiSrCaCuO. The
differences are suggestive of the role of increasing stripe fluctuations. The
1/8 anomaly is associated with a quantum critical point, here expressed as a
percolation-like crossover. A model is proposed for the limiting minority
magnetic phase as an isolated two-leg ladder.Comment: 24 pages, 26 PS figure
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