2,637 research outputs found
Romanian commercial banks and credit risk in financing SME
Romania’s integration in the European Union brought about some major changes in our banking system. One of the direct consequences is the fierce competition between banks for supremacy on the market. According to this, the Romanian banks saw in the SMEs sector a true potential for reaching their goal and they proceeded to conquer it by conceiving unique products, specially designed to reach the financial needs of this segment. Moreover, banks often come up with new attractive offers and cost reductions for the SMEs (Small and Mediu Sized Enterprises) sector. In this context, some answers need to be done: the effective risk banks accept to take by providing the offers, specific risks in financing this sector, the problem of the balance between risk and profit return (or market share increase).credit risk, risk management, financing SME, bank policies
Holstein polaron: the effect of multiple phonon modes
We generalize the Momentum Average approximations MA and MA
to study the effects of coupling to multiple optical phonons on the properties
of a Holstein polaron. As for a single phonon mode, these approximations are
numerically very efficient. They become exact for very weak or very strong
couplings, and are highly accurate in the intermediate regimes, {\em e.g.} the
spectral weights obey exactly the first six, respectively eight, sum rules. Our
results show that the effect on ground-state properties is cumulative in
nature. In particular, if the effective coupling to one mode is much larger
than to the others, this mode effectively determines the GS properties.
However, even very weak coupling to a second phonon mode has important
non-perturbational effects on the higher energy spectrum, in particular on the
dispersion and the phonon statistics of the polaron band
Hidden Symmetries of Electronic Transport in a Disordered One-Dimensional Lattice
Correlated, or extended, impurities play an important role in the transport
properties of dirty metals. Here, we examine, in the framework of a
tight-binding lattice, the transmission of a single electron through an array
of correlated impurities. In particular we show that particles transmit through
an impurity array in identical fashion, regardless of the direction of
transversal. The demonstration of this fact is straightforward in the continuum
limit, but requires a detailed proof for the discrete lattice. We also briefly
demonstrate and discuss the time evolution of these scattering states, to
delineate regions (in time and space) where the aforementioned symmetry is
violated
DC conductivity of twisted bilayer graphene: Angle-dependent transport properties and effects of disorder
The in-plane DC conductivity of twisted bilayer graphene (TBLG) is calculated
using an expansion of the real-space Kubo-Bastin conductivity in terms of
Chebyshev polynomials. We investigate within a tight-binding (TB) approach the
transport properties as a function of rotation angle, applied perpendicular
electric field and vacancy disorder. We find that for high-angle twists, the
two layers are effectively decoupled, and the minimum conductivity at the Dirac
point corresponds to double the value observed in monolayer graphene. This
remains valid even in the presence of vacancies, hinting that chiral symmetry
is still preserved. On the contrary, for low twist angles, the conductivity at
the Dirac point depends on the twist angle and is not protected in the presence
of disorder. Furthermore, for low angles and in the presence of an applied
electric field, we find that the chiral boundary states emerging between AB and
BA regions contribute to the DC conductivity, despite the appearance of
strongly localized states in the AA regions. The results agree with recent
conductivity experiments on twisted bilayer graphene
Topological phase transitions in small mesoscopic chiral p-wave superconductors
Spin-triplet chiral p-wave superconductivity is typically described by a
two-component order parameter, and as such is prone to unique emergent effects
when compared to the standard single-component superconductors. Here we present
the equilibrium phase diagram for small mesoscopic chiral p-wave
superconducting disks in the presence of magnetic field, obtained by solving
the microscopic Bogoliubov-de Gennes equations self-consistently. In the
ultra-small limit, the cylindrically-symmetric giant-vortex states are the
ground state of the system. However, with increasing sample size, the
cylindrical symmetry is broken as the two components of the order parameter
segregate into domains, and the number of fragmented domain walls between them
characterizes the resulting states. Such domain walls are topological defects
unique for the p-wave order, and constitute a dominant phase in the mesoscopic
regime. Moreover, we find two possible types of domain walls, identified by
their chirality-dependent interaction with the edge states
Using magnetic stripes to stabilize superfluidity in electron-hole double monolayer graphene
Experiments have confirmed that double monolayer graphene cannot generate
finite temperature electron-hole superfluidity. This has been shown to be due
to very strong screening of the electron-hole pairing attraction. The linear
dispersing energy bands in monolayer graphene prevent attempts to reduce the
strength of the screening. We propose a new hybrid device in which the two
sheets of monolayer graphene are placed in a modulated periodic perpendicular
magnetic field. Such a magnetic field preserves the isotropic Dirac cones of
the original monolayers but it reduces the slope of the cones so that the
monolayer Fermi velocity is smaller. We show that with current
experimental techniques, this reduction in can sufficiently weaken the
screening to permit electron-hole superfluidity at measurable temperatures.Comment: Revised version. MultiSuper collaboration: http://www.multisuper.or
Quantum mechanics of spin transfer in coupled electron-spin chains
The manner in which spin-polarized electrons interact with a magnetized thin
film is currently described by a semi-classical approach. This in turn provides
our present understanding of the spin transfer, or spin torque phenomenon.
However, spin is an intrinsically quantum mechanical quantity. Here, we make
the first strides towards a fully quantum mechanical description of spin
transfer through spin currents interacting with a Heisenberg-coupled spin
chain. Because of quantum entanglement, this requires a formalism based on the
density matrix approach. Our description illustrates how individual spins in
the chain time-evolve as a result of spin transfer.Comment: 4 pages, 3 (colour) figure
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