157 research outputs found
Local Moment Formation in the Superconducting State of a Doped Mott Insulator
A microscopic theory is presented for the local moment formation near a
non-magnetic impurity or a copper defect in high-T_c superconductors. We use a
renormalized meanfield theory of the t-J model for a doped Mott insulator and
study the fully self-consistent, spatially unrestricted solutions of the d-wave
superconducting (SC) state in both the spin S=0 and S=1/2 sectors. We find a
transition from the singlet d-wave SC state to a spin doublet SC state when the
renormalized exchange coupling exceeds a doping dependent critical value. The
induced S=1/2 moment is staggered and localized around the impurity. It arises
from the binding of an S=1/2 nodal quasiparticle excitation to the impurity.
The local density of states spectrum is calculated and connections to NMR and
STM experiments are discussed.Comment: 4 pages, 3 figures, revised version, to be published in Phys. Rev.
Let
Phase Transitions in the Symmetric Kondo Lattice Model in Two and Three Dimensions
We present an application of high-order series expansion in the coupling
constants for the ground state properties of correlated lattice fermion
systems. Expansions have been generated up to order for and
for for certain properties of the symmetric Kondo lattice
model. Analyzing the susceptibility series, we find evidence for a continuous
phase transition from the ``spin liquid'' phase characteristic of a ``Kondo
Insulator'' to an antiferromagnetically ordered phase in dimensions as
the antiferromagnetic Kondo coupling is decreased. The critical point is
estimated to be at for square lattice and
for simple-cubic lattice.Comment: 12 pages, Revtex, replace previous corrupted fil
Non-Abelian Quantum Hall States and their Quasiparticles: from the Pattern of Zeros to Vertex Algebra
In the pattern-of-zeros approach to quantum Hall states, a set of data
{n;m;S_a|a=1,...,n; n,m,S_a in N} (called the pattern of zeros) is introduced
to characterize a quantum Hall wave function. In this paper we find sufficient
conditions on the pattern of zeros so that the data correspond to a valid wave
function. Some times, a set of data {n;m;S_a} corresponds to a unique quantum
Hall state, while other times, a set of data corresponds to several different
quantum Hall states. So in the latter cases, the patterns of zeros alone does
not completely characterize the quantum Hall states. In this paper, We find
that the following expanded set of data {n;m;S_a;c|a=1,...,n; n,m,S_a in N; c
in R} provides a more complete characterization of quantum Hall states. Each
expanded set of data completely characterize a unique quantum Hall state, at
least for the examples discussed in this paper. The result is obtained by
combining the pattern of zeros and Z_n simple-current vertex algebra which
describes a large class of Abelian and non-Abelian quantum Hall states
\Phi_{Z_n}^sc. The more complete characterization in terms of {n;m;S_a;c}
allows us to obtain more topological properties of those states, which include
the central charge c of edge states, the scaling dimensions and the statistics
of quasiparticle excitations.Comment: 42 pages. RevTeX
Spin ordering and electronic texture in the bilayer iridate SrIrO
Through a neutron scattering, charge transport, and magnetization study, the
correlated ground state in the bilayer iridium oxide SrIrO is
explored. Our combined results resolve scattering consistent with a high
temperature magnetic phase that persists above 600 K, reorients at the
previously defined K, and coexists with an electronic ground state
whose phase behavior suggests the formation of a fluctuating charge or orbital
phase that freezes below K. Our study provides a window into
the emergence of multiple electronic order parameters near the boundary of the
metal to insulator phase transition of the 5d Mott phase.Comment: Revised text and figures. 4 pages, 4 figure
Coexistence of competing orders with two energy gaps in real and momentum space in high-Tc superconductor Bi2Sr2-xLaxCuO6+delta
The superconducting phase of the high-Tc cuprates has been thought to be
described by a single d-wave pairing order parameter. Recently, there has been
growing evidence suggesting that another form of order, possibly inherited from
the pseudogap phase above Tc, may coexist with superconductivity in the
underdoped regime. Through a combined study of scanning tunneling microscopy
and angle-resolved photoemission spectroscopy, we report the observation of two
distinct gaps (a small-gap and a large-gap) that coexist both in real space and
in the anti-nodal region of momentum space in the superconducting phase of
Bi2Sr2-xLaxCuO6+delta. We show that the small-gap is associated with
superconductivity. The large-gap persists to temperatures above the transition
temperature Tc and is found to be linked to short-range charge ordering.
Remarkably, we find a strong, short-ranged correlation between the local small-
and large- gap magnitudes suggesting that the superconductivity and charge
ordering are affected by similar physical processes.Comment: 19 pages, 4 figure
Critical Conductance and Its Fluctuations at Integer Hall Plateau Transitions
Under periodic boundary condition in the transverse direction, we calculate
the averaged zero-temperature two-terminal conductance ( for ) at the critical point of
integer quantum Hall plateau transitions. We find {\it universal} values for
, and ,
where ; ; ; and
respectively. We also determine the leading finite size
scaling corrections to these observables. Comparisons with experiments will be
made.Comment: 13 pages, 3 Postscript figures included, Final version with minor
corrections, To appear in Physical Review Letter
Msh2 ATPase Activity Is Essential for Somatic Hypermutation at A-T Basepairs and for Efficient Class Switch Recombination
Somatic hypermutation (SHM) and class switch recombination (CSR) are initiated by activation-induced cytidine deaminase–mediated cytidine deamination of immunoglobulin genes. MutS homologue (Msh) 2−/− mice have reduced A-T mutations and CSR. This suggests that Msh2 may play a role in repairing activation-induced cytidine deaminase–generated G-U mismatches. However, because Msh2 not only initiates mismatch repair but also has other functions, such as signaling for apoptosis, it is not known which activity of Msh2 is responsible for the effects observed, and consequently, many models have been proposed. To further dissect the role of Msh2 in SHM and CSR, mice with a “knockin” mutation in the Msh2 gene that inactivates the adenosine triphosphatase domain were examined. This mutation (i.e., Msh2G674A), which does not affect apoptosis signaling, allows mismatches to be recognized but prevents Msh2 from initiating mismatch repair. Here, we show that, similar to Msh2−/− mice, SHM in Msh2G674A mice is biased toward G-C mutations. However, CSR is partially reduced, and switch junctions are more similar to those of postmeiotic segregation 2−/− mice than to Msh2−/− mice. These results indicate that Msh2 adenosine triphosphatase activity is required for A-T mutations, and suggest that Msh2 has more than one role in CSR
Conductance Correlations Near Integer Quantum Hall Transitions
In a disordered mesoscopic system, the typical spacing between the peaks and
the valleys of the conductance as a function of Fermi energy is called
the conductance energy correlation range . Under the ergodic hypothesis,
the latter is determined by the half-width of the ensemble averaged conductance
correlation function: . In
ordinary diffusive metals, , where is the diffusion constant
and is the linear dimension of the phase-coherent sample. However, near a
quantum phase transition driven by the location of the Fermi energy , the
above picture breaks down. As an example of the latter, we study, for the first
time, the conductance correlations near the integer quantum Hall transitions of
which is a critical coupling constant. We point out that the behavior of
is determined by the interplay between the static and the dynamic
properties of the critical phenomena.Comment: 4 pages, 4 figures, minor corrections, to appear in Phys. Rev. Let
The Effects of Electron-Electron Interactions on the Integer Quantum Hall Transitions
We study the effects of electron-electron interaction on the critical
properties of the plateau transitions in the {\it integer} quantum Hall effect.
We find the renormalization group dimension associated with short-range
interactions to be . Thus the non-interacting fixed point
(characterized and ) is stable. For the Coulomb
interaction, we find the correlation effect is a marginal perturbation at a
Hartree-Fock fixed point (, ) by dimension counting.
Further calculations are needed to determine its stability upon loop
corrections.Comment: 12 pages, Revtex, minor changes, to be published in Phys. Rev. Let
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