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$^{(0)}$ and MA$^{(1)}$ 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 $v_F$ is smaller. We show that with current experimental techniques, this reduction in $v_F$ 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