84 research outputs found
Efficiency, scale economies and valuation effects : evidence from bank mergers in India
Original article can be found at : http://www.inderscience.com/ Copyright Inderscience PublishersThis paper examines two important issues related to bank mergers in India. First, we estimate potential economic gains of state owned banks if they undergo consolidation. Scale economies, returns to scale and profit efficiency of state owned banks during 1986 to 2003 are estimated based on stochastic frontier analysis. We find that many Indian banks exhibit potential cost savings from mergers provided they rationalize their branch networks although profit efficiency may not rise immediately. Second we measure the realized impact of bank mergers on shareholdersâ wealth based on event study analysis. We find that in the case of forced mergers, shareholders of neither the bidder nor the target banks benefited. In the case of voluntary mergers, the bidder banksâ shareholders gained more than the target banksâ shareholders.Peer reviewe
Vortices in Superfluid Fermi Gases through the BEC to BCS Crossover
We have analyzed a single vortex at T=0 in a 3D superfluid atomic Fermi gas
across a Feshbach resonance. On the BCS side, the order parameter varies on two
scales: and the coherence length , while only variation on
the scale of is seen away from the BCS limit. The circulating current has
a peak value which is a non-monotonic function of
implying a maximum critical velocity at unitarity. The number of
fermionic bound states in the core decreases as we move from the BCS to BEC
regime. Remarkably, a bound state branch persists even on the BEC side
reflecting the composite nature of bosonic molecules.Comment: 4 Pages, 4 Figure
Relaxation of Fermionic Excitations in a Strongly Attractive Fermi Gas in an Optical Lattice
We theoretically study the relaxation of high energy single particle
excitations into molecules in a system of attractive fermions in an optical
lattice, both in the superfluid and the normal phase. In a system characterized
by an interaction scale and a tunneling rate , we show that the
relaxation rate scales as in the large
limit. We obtain explicit expressions for the exponent , both in the
low temperature superfluid phase and the high temperature phase with pairing
but no coherence between the molecules. We find that the relaxation rate
decreases both with temperature and deviation of the fermion density from
half-filling. We show that quasiparticle and phase degrees of freedom are
effectively decoupled within experimental timescales allowing for observation
of ordered states even at high total energy of the system.Comment: 5 pages, 3 figure
Preparation and detection of d-wave superfluidity in two-dimensional optical superlattices
We propose a controlled method to create and detect d-wave superfluidity with
ultracold fermionic atoms loaded in two-dimensional optical superlattices. Our
scheme consists in preparing an array of nearest-neighbor coupled square
plaquettes or ``superplaquettes'' and using them as building blocks to
construct a d-wave superfluid state. We describe how to use the coherent
dynamical evolution in such a system to experimentally probe the pairing
mechanism. We also derive the zero temperature phase diagram of the fermions in
a checkerboard lattice (many weakly coupled plaquettes) and show that by tuning
the inter-plaquette tunneling spin-dependently or varying the filling factor
one can drive the system into a d-wave superfluid phase or a Cooper pair
density wave phase. We discuss the use of noise correlation measurements to
experimentally probe these phases.Comment: 8 pages, 6 figure
Dynamical mean-field equations for strongly interacting fermionic atoms in a potential trap
We derive a set of dynamical mean-field equations for strongly interacting
fermionic atoms in a potential trap across a Feshbach resonance. Our derivation
is based on a variational ansatz, which generalizes the crossover wavefunction
to the inhomogeneous case, and the assumption that the order parameter is
slowly varying over the size of the Cooper pairs. The equations reduce to a
generalized time-dependent Gross-Pitaevskii equation on the BEC side of the
resonance. We discuss an iterative method to solve these mean-field equations,
and present the solution for a harmonic trap as an illustrating example to
self-consistently verify the approximations made in our derivation.Comment: replaced with the published versio
Crossover from adiabatic to sudden interaction quenches in the Hubbard model: Prethermalization and nonequilibrium dynamics
The recent experimental implementation of condensed matter models in optical
lattices has motivated research on their nonequilibrium behavior. Predictions
on the dynamics of superconductors following a sudden quench of the pairing
interaction have been made based on the effective BCS Hamiltonian; however,
their experimental verification requires the preparation of a suitable excited
state of the Hubbard model along a twofold constraint: (i) a sufficiently
nonadiabatic ramping scheme is essential to excite the nonequilibrium dynamics,
and (ii) overheating beyond the critical temperature of superconductivity must
be avoided. For commonly discussed interaction ramps there is no clear
separation of the corresponding energy scales. Here we show that the matching
of both conditions is simplified by the intrinsic relaxation behavior of
ultracold fermionic systems: For the particular example of a linear ramp we
examine the transient regime of prethermalization [M. Moeckel and S. Kehrein,
Phys. Rev. Lett. 100, 175702 (2008)] under the crossover from sudden to
adiabatic switching using Keldysh perturbation theory. A real-time analysis of
the momentum distribution exhibits a temporal separation of an early energy
relaxation and its later thermalization by scattering events. For long but
finite ramping times this separation can be large. In the prethermalization
regime the momentum distribution resembles a zero temperature Fermi liquid as
the energy inserted by the ramp remains located in high energy modes. Thus
ultracold fermions prove robust to heating which simplifies the observation of
nonequilibrium BCS dynamics in optical lattices.Comment: 27 pages, 8 figures Second version with small modifications in
section
Can one determine the underlying Fermi surface in the superconducting state of strongly correlated superconductors?
The question of determining the underlying Fermi surface (FS) that is gapped
by superconductivity (SC) is of central importance in strongly correlated
systems, particularly in view of angle-resolved photoemission experiments. Here
we explore various definitions of the FS in the superconducting state using the
zero-energy Green's function, the excitation spectrum and the momentum
distribution. We examine (a) d-wave SC in high Tc cuprates, and (b) the s-wave
superfluid in the BCS-BEC crossover. In each case we show that the various
definitions agree, to a large extent, but all of them violate the Luttinger
count and do not enclose the total electron density. We discuss the important
role of chemical potential renormalization and incoherent spectral weight in
this violation.Comment: 4 pages, 4 figures, version 3, Added new figures, detailed discussion
of result
System size scaling of topological defect creation in a second-order dynamical quantum phase transition
We investigate the system size scaling of the net defect number created by a
rapid quench in a second-order quantum phase transition from an O(N) symmetric
state to a phase of broken symmetry. Using a controlled mean-field expansion
for large N, we find that the net defect number variance in convex volumina
scales like the surface area of the sample for short-range correlations. This
behaviour follows generally from spatial and internal symmetries. Conversely,
if spatial isotropy is broken, e.g., by a lattice, and in addition long-range
periodic correlations develop in the broken-symmetry phase, we get the rather
counterintuitive result that the scaling strongly depends on the dimension
being even or odd: For even dimensions, the net defect number variance scales
like the surface area squared, with a prefactor oscillating with the system
size, while for odd dimensions, it essentially vanishes.Comment: 20 pages of IOP style, 6 figures; as published in New Journal of
Physic
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