195 research outputs found
Strong-randomness infinite-coupling phase in a random quantum spin chain
We study the ground-state phase diagram of the Ashkin-Teller random quantum
spin chain by means of a generalization of the strong-disorder renormalization
group. In addition to the conventional paramagnetic and ferromagnetic (Baxter)
phases, we find a partially ordered phase characterized by strong randomness
and infinite coupling between the colors. This unusual phase acts, at the same
time, as a Griffiths phase for two distinct quantum phase transitions both of
which are of infinite-randomness type. We also investigate the quantum
multi-critical point that separates the two-phase and three-phase regions; and
we discuss generalizations of our results to higher dimensions and other
systems.Comment: 9 pages, 6 eps figures, final version as publishe
Fermi-Bose crossover using engineered disorder potential
We present the first instance of a disorder tuned Fermi-Bose crossover that
could be realized in superconducting systems. More specifically, harnessing a
non perturbative numerical technique we analyze the ground state behavior of a
two-dimensional attractive Hubbard model subjected to spin selective disorder
potential. In particular, using spectroscopic properties we provide unambiguous
evidence of the change in the Fermi surface topology as a function of the
disorder, establishing incontrovertibly a Fermi-Bose crossover. Interplay of
strong correlations and strong disorder brings out the spin selectivity in the
properties of this system giving rise to spin selective "Bose metal/insulator"
phase. We propose an experimental set-up where such disorder tuned Fermi-Bose
crossover could be observed in two-dimensional electron gas formed at oxide
interface. Finally, we speculate on the possible implication of such
spin-selective disorder on unraveling signatures of Bose-Fermi cross-over on
doped iron chalcogenide superconductors.Comment: 8 pages, 6 figure
Infinite randomness and quantum Griffiths effects in a classical system: the randomly layered Heisenberg magnet
We investigate the phase transition in a three-dimensional classical
Heisenberg magnet with planar defects, i.e., disorder perfectly correlated in
two dimensions. By applying a strong-disorder renormalization group, we show
that the critical point has exotic infinite-randomness character. It is
accompanied by strong power-law Griffiths singularities. We compute various
thermodynamic observables paying particular attention to finite-size effects
relevant for an experimental verification of our theory. We also study the
critical dynamics within a Langevin equation approach and find it extremely
slow. At the critical point, the autocorrelation function decays only
logarithmically with time while it follows a nonuniversal power-law in the
Griffiths phase.Comment: 10 pages, 2 eps figures included, final version as published
Fractional quantum Hall states in two-dimensional electron systems with anisotropic interactions
We study the anisotropic effect of the Coulomb interaction on a 1/3-filling
fractional quantum Hall system by using an exact diagonalization method on
small systems in torus geometry. For weak anisotropy the system remains to be
an incompressible quantum liquid, although anisotropy manifests itself in
density correlation functions and excitation spectra. When the strength of
anisotropy increases, we find the system develops a Hall-smectic-like phase
with a one-dimensional charge density wave order and is unstable towards the
one-dimensional crystal in the strong anisotropy limit. In all three phases of
the Laughlin liquid, Hall-smectic-like, and crystal phases the ground state of
the anisotropic Coulomb system can be well described by a family of model wave
functions generated by an anisotropic projection Hamiltonian. We discuss the
relevance of the results to the geometrical description of fractional quantum
Hall states proposed by Haldane [ Phys. Rev. Lett. 107 116801 (2011)].Comment: 8 pages, 8 figure
Winners and Losers from Enacting the Financial Modernization Statute
Previous studies of the announcement effects of relaxing administrative and legislative restraints show that signal events leading up to the enactment of the Financial Services Modernization Act (FSMA) increased the prices of several classes of financial-institution stocks. An unsettled question is whether the gains observed for these stocks arise mainly from projected increases in efficiency or from reductions in customer or competitor bargaining power. This paper documents that the value increase came at the expense of customers and competitors. The stock prices of credit-constrained customers declined during FSMA event windows and experienced significant increases in beta in the wake of its enactment. These findings reinforce evidence in the literature on bank mergers that large-bank consolidation is adversely affecting access to credit for capital-constrained firms.
Joint preservation surgery: a priority to be thought of in selective hip osteoarthritis
Femoroacetabular impingement (FAI) is one of the causes of hip arthritis. If FAI diagnosed earlier and treated properly, arthritis of hip and eventual total hip replacement (THR) can be potentially avoided. We report 48 yr male who presented with left hip severe pain, limp, restricted movements and unable do daily day activities. He is diagnosed to have pincer type of lesion in the acetabular rim and we did arthroscopic excision of the protruding fragment. The patient now has a pain free joint and able to squat and sit cross leg. His pre-operative oxford hip score was 30 which improved to 54.
Emerging criticality in the disordered three-color Ashkin-Teller model
We study the effects of quenched disorder on the first-order phase transition
in the two-dimensional three-color Ashkin-Teller model by means of large-scale
Monte Carlo simulations. We demonstrate that the first-order phase transition
is rounded by the disorder and turns into a continuous one. Using a careful
finite-size-scaling analysis, we provide strong evidence for the emerging
critical behavior of the disordered Ashkin-Teller model to be in the clean
two-dimensional Ising universality class, accompanied by universal logarithmic
corrections. This agrees with perturbative renormalization-group predictions by
Cardy. As a byproduct, we also provide support for the strong-universality
scenario for the critical behavior of the two-dimensional disordered Ising
model. We discuss consequences of our results for the classification of
disordered phase transitions as well as generalizations to other systems.Comment: 18 pages, 18 eps figures included, final version as publishe
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Promoting fair and equitable research partnerships to respond to global challenges
This report presents the findings from a programme of strategic research funded by UKRI through the GCRF. The research sought to elicit a 'partners' perspective' on participation in UKRI-funded research by generating data from three groups of partner: i) academics based in the global South; ii) civi society practitioners based in the global South; and iii) international NGOs and research capacity providers based in the UK. Drawing on this data, the report identifies eight principles for understanding and improving fair and equitable research collaboration which form the basis of a series of targeted learning modules for 6 groups of stakeholders: UK-based research funders; UK-based academics; research brokers and capacity providers; international NGOs; academics based in the global South; and civil society practitioners based in the global South
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