39 research outputs found
Effects of Randomness on the Field-Induced Phase Transition in the S=1 Bond-Alternating Spin Chain NTENP
We report novel effects of randomness in the S=1 bond-alternating
antiferromagnetic chain compound with a dimer-singlet ground state
[Ni(N,N'-bis(3-aminopropyl)propane-1,3-diamine(mu-NO2]ClO4 abbreviated as
NTENP. The 15N NMR spectra develop a continuum with sharply peaked edges at low
temperatures, indicating an inhomogeneous staggered magnetization induced by
magnetic field. We attribute this to random anisotropic interactions due to
disorder of NO2 groups in the chains. The field-induced antiferromagnetic
transition exhibits remarkably anisotropic behavior. We propose that a
field-induced incoherent magnetization is transformed into a coherent
antiferromagnetic moment with spatially fluctuating amplitude.Comment: 4pages, 5 figues, submitted to J. Phys. Soc. Jp
Possibility of spontaneous parity violation in hot QCD
We suggest that for QCD in the limit of a large number of colors, N, the
axial U(1) symmetry of massless quarks is effectively restored at the
deconfining=chiral phase transition. If the deconfining transition is of second
order, then the chiral transition is weakly first order. In this case,
metastable states in which parity is spontaneously broken appear at
temperatures below the phase transition. The production of these metastable
states would have dramatic signatures, including enhanced production of eta and
eta' mesons, which can decay through parity violating decay processes such as
eta -> pi^0 pi^0, and global parity odd asymmetries for charged pions. Using a
nonlinear sigma model, in QCD these metastable states only appear rather near
the phase transition.Comment: 4 pages, REVTe
Thermal and magnetic properties of integrable spin-1 and spin-3/2 chains with applications to real compounds
The ground state and thermodynamic properties of spin-1 and spin-3/2 chains
are investigated via exactly solved su(3) and su(4) models with physically
motivated chemical potential terms. The analysis involves the Thermodynamic
Bethe Ansatz and the High Temperature Expansion (HTE) methods. For the spin-1
chain with large single-ion anisotropy, a gapped phase occurs which is
significantly different from the valence-bond-solid Haldane phase. The
theoretical curves for the magnetization, susceptibility and specific heat are
favourably compared with experimental data for a number of spin-1 chain
compounds. For the spin-3/2 chain a degenerate gapped phase exists starting at
zero external magnetic field. A middle magnetization plateau can be triggered
by the single-ion anisotropy term. Overall, our results lend further weight to
the applicability of integrable models to the physics of low-dimensional
quantum spin systems. They also highlight the utility of the exact HTE method.Comment: 38 pages, 15 figure
Large N_c, chiral approach to M_eta' at finite temperature
We study the temperature dependence of the eta and eta' meson masses within
the framework of U(3)_L x U(3)_R chiral perturbation theory, up to
next-to-leading order in a simultaneous expansion in momenta, quark masses and
number of colours. We find that both masses decrease at low temperatures, but
only very slightly. We analyze higher order corrections and argue that large
N_c suggests a discontinuous drop of M_eta' at the critical temperature of
deconfinement T_c, consistent with a first order transition to a phase with
approximate U(1)_A symmetry.Comment: 21 pages, 6 figures. 2 footnotes added, 1 reference changed and 1
typo corrected. To be published in Phys. Rev.
One-Dimensional Quantum Liquids: Beyond the Luttinger Liquid Paradigm
For many years, the Luttinger liquid theory has served as a useful paradigm
for the description of one-dimensional (1D) quantum fluids in the limit of low
energies. This theory is based on a linearization of the dispersion relation of
the particles constituting the fluid. We review the recent progress in
understanding 1D quantum fluids beyond the low-energy limit, where the
nonlinearity of the dispersion relation becomes essential. The novel methods
which have been developed to tackle such systems combine phenomenology built on
the ideas of the Fermi edge singularity and the Fermi liquid theory,
perturbation theory in the interaction strength, and a new way of treating
finite-size integrable models. These methods can be applied to a wide variety
of 1D fluids, from 1D spin liquids to electrons in quantum wires to cold atoms
confined to a 1D trap. We review existing results for various dynamic
correlation functions, in particular the density structure factor and the
spectral function. Moreover, we show how a dispersion nonlinearity leads to
finite particle lifetimes, and discuss its impact on the transport properties
of 1D systems at finite temperatures. The conventional Luttinger liquid theory
is a special limit of the new theory, and we explain the relation between the
two.Comment: 61 pages, 18 figures, published version, minor typos correcte
Fully Gapped Single-Particle Excitations in the Lightly Doped Cuprates
The low-energy excitations of the lightly doped cuprates were studied by
angle-resolved photoemission spectroscopy. A finite gap was measured over the
entire Brillouin zone, including along the d_{x^2 - y^2} nodal line. This
effect was observed to be generic to the normal states of numerous cuprates,
including hole-doped La_{2-x}Sr_{x}CuO_{4} and Ca_{2-x}Na_{x}CuO_{2}Cl_{2} and
electron-doped Nd_{2-x}Ce_{x}CuO_{4}. In all compounds, the gap appears to
close with increasing carrier doping. We consider various scenarios to explain
our results, including the possible effects of chemical disorder, electronic
inhomogeneity, and a competing phase.Comment: To appear in Phys. Rev.
Interplay of Electron-Phonon Interaction and Electron Correlation in High Temperature Superconductivity
We study the electron-phonon interaction in the strongly correlated
superconducting cuprates. Two types of the electron-phonon interactions are
introduced in the model; the diagonal and off-diagonal interactions which
modify the formation energy of the Zhang-Rice singlet and its transfer
integral, respectively. The characteristic phonon-momentum and
electron-momentum dependence resulted from the off-diagonal coupling
can explain a variety of experiments. The vertex correction for the
electron-phonon interaction is formulated in the SU(2) slave-boson theory by
taking into account the collective modes in the superconducting ground states.
It is shown that the vertex correction enhances the attractive potential for
the d-wave paring mediated by phonon with around
which corresponds to the half-breathing mode of the oxygen
motion.Comment: 14 pages, 13 figure
Dynamical relaxation of the CP phases in next-to-minimal supersymmetry
After promoting the phases of the soft masses to dynamical fields
corresponding to Goldstone bosons of spontaneously broken global symmetries in
the supersymmetry breaking sector, the next-to-minimal supersymmetric model is
found to solve the problem and the strong CP problem simultaneously with
an invisible axion. The domain wall problem persists in the form of axionic
domain formation. Relaxation dynamics of the physical CP-violating phases is
determined only by the short-distance physics and their relaxation values are
not necessarily close to the CP-conserving points. Having observable
supersymmetric CP violation and avoiding the axionic domain walls both require
nonminimal flavor structures.Comment: 13 pp, 3 figs, published versio
Multi-criteria correlation of tephra deposits to source centres applied in the Auckland Volcanic Field, New Zealand
Angle-resolved photoemission spectroscopy of the cuprate superconductors
This paper reviews the most recent ARPES results on the cuprate
superconductors and their insulating parent and sister compounds, with the
purpose of providing an updated summary of the extensive literature in this
field. The low energy excitations are discussed with emphasis on some of the
most relevant issues, such as the Fermi surface and remnant Fermi surface, the
superconducting gap, the pseudogap and d-wave-like dispersion, evidence of
electronic inhomogeneity and nano-scale phase separation, the emergence of
coherent quasiparticles through the superconducting transition, and many-body
effects in the one-particle spectral function due to the interaction of the
charge with magnetic and/or lattice degrees of freedom. The first part of the
paper introduces photoemission spectroscopy in the context of strongly
interacting systems, along with an update on the state-of-the-art
instrumentation. The second part provides a brief overview of the scientific
issues relevant to the investigation of the low energy electronic structure by
ARPES. The rest of the paper is devoted to the review of experimental results
from the cuprates and the discussion is organized along conceptual lines:
normal-state electronic structure, interlayer interaction, superconducting gap,
coherent superconducting peak, pseudogap, electron self energy and collective
modes. Within each topic, ARPES data from the various copper oxides are
presented.Comment: Reviews of Modern Physics, in press. A HIGH-QUALITY pdf file is
available at http://www.physics.ubc.ca/~damascel/RMP_ARPES.pd