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C. P. Moca

Publications and source records attributed to C. P. Moca.

31 records · Page 2Linked to original sources
arXiv2007

Finite-size Effects in a Two-Dimensional Electron Gas with Rashba Spin-Orbit Interaction

Within the Kubo formalism, we estimate the spin-Hall conductivity in a two-dimensional electron gas with Rashba spin-orbit interaction and study its variation as a function of disorder strength and system size. The numerical algorithm employed in the calculation is based on the direct numerical integration of the time-dependent Schrodinger equation in a spin-dependent variant of the particle source method. We find that the spin-precession length, L_s controlled by the strength of the Rashba coupling, establishes the critical lengthscale that marks the significant reduction of the spin-Hall conductivity in bulk systems. In contrast, the electron mean free path, inversely proportional to the strength of disorder, appears to have only a minor effect.

cond-mat.mes-hall↗
arXiv2003

Specific heat behavior of high temperature superconductors in the pseudogap regime

Experimental data obtained from thermodynamic measurements in underdoped high temperature superconductors show unusual anomalies in the temperature dependence of the electronic specific heat both in the normal state and at the critical point associated to the superconducting phase transition. The observed deviations from the standard behavior are probably linked with the opening of a pseudogap in the energy spectrum of the single-particle excitations associated with the normal state. Based on a phenomenological description of the pseudogap phase we perform analytical and numerical calculations for the temperature dependence of the specific heat for both the superconducting and normal state. The reduced specific heat jump at the transition point can be explained by a modified electronic single particle contribution to the specific heat in the presence of the normal state pseudogap. The hump observed in the normal state specific heat can be explained by the electronic pair contribution associated with strong fluctuations of the order parameter in the critical region. The obtained theoretical results are discussed in connection with experimental data for cuprates.

cond-mat.supr-con↗
arXiv2002

Signatures of interband scattering in spectroscopic experiments on $MgB_2$

Within a two-band, strong coupling model we analyze SIS-tunneling conductance, Raman scattering and optical conductivity measured on $MgB_2$ samples. We find that features observed in tunneling and Raman spectroscopy at intermediate energies $ω=Δ_σ+Δ_π\simeq 8÷10meV$ can be consistently explained when incoherent scattering between $σ$ and $π$ band is considered. We calculate the optical conductivity and find that strong coupling effects are important for explaining the presently available data, and predict the location and magnitude of interband scattering features for this spectroscopic probe as well.

cond-mat.supr-con↗
arXiv2001

The electronic specific heat in the pairing pseudogap regime

When pairing correlations in a quasi two dimensional electron system induce a pseudogap in the single particle density of states, the specific heat must also contain a sizeable pair contribution. The theoretically calculated specific heat for such a system is compared to the experimental results of Loram and his collaborators for underdoped YBa_2Cu_3O_{6+x} and La_{2-x}Sr_{x}CuO_4 samples. The size and doping dependence of the extracted pseudogap energy scale for both materials is comparable to the values obtained from a variety of other experiments.

cond-mat.supr-con↗
arXiv2001

Transport Properties Calculation in the Superconducting State for a Quasi-Twodimensional System

We performed a self-consistent calculation of the transport properties of a d-wave superconductor. We used for calculations the T-matrix approximation. The coresponding equations were evaluated numerically directly on the real frequecy axis. We studied the ab-plane charge dynamics in the coherent limit. For the c-axis charge dynamics, we considered both, the coherent and the incoherent limit. We also have calculated the penetration depth in this model.

cond-mat.str-el↗
arXiv2000

Transport Properties Calculation for a Quasi-Bidimensional System using T-Matrix Approximation

We performed a self-consistent calculation using T-Matrix approximation for a quasi-bidimensional system. We calculated the one particle spectrum function A(k,ω) in the presence of strong d-wave attractive interaction. The c-axis charge dynamics was studied by considering incoherent interlayer hopping and ab-plane charge dynamics was studied in the coherent limit. It is shown that the c-axis charge dynamics is mainly governed by the scattering from the in plane fluctuations. We also present results for c-axis and ab-plane resistivity and for thermopower coefficient.

cond-mat.str-el↗
arXiv2000

Ginsburg-Landau Expansion in a non-Fermi Superconductor

We study the Ginsburg-Landau expansion for the non-Fermi model proposed by Anderson. We analyze the deviations of the main properties of a non-Fermi superconductor from the isotropic s-wave bidimensiona superconductor.

cond-mat.str-el↗
arXiv1999

Field-Theoretical description of the crossover between BCS and BEC in a non-Fermi superconductor

Using the field-theoretical methods we studied the evolution from BCS description of a non-Fermi superconductor to that of Bose-Einstein condensation (BEC) in one loop approximation. We showed that the repulsive interaction between composite bosons is determined by the exponent $α$ of the Anderson propagator in a two dimensional model. For $\a\neq 0$ the crossover is also continous and for $\a=0$ we obtain the case of the Fermi liquid.

cond-mat.str-el↗
arXiv1999

Non-Fermi behavior of the disorder electronic system

We showed that an electronic system with weak disorder considered in the finite-charge infinite U Hubbard model can present a non-Fermi behavior. The imaginary pert of the self-energy has been calculated and a linear temperature dependence was obtained. This result is in agreement with the non-Fermi behavior observed at the insulator-metal crossover in La_{2-x}Sr_xCuO_4.

cond-mat.str-el↗
arXiv1999

Renormalization group approach of itinerant electron systems near the Lifshitz point

Using the renormalization approach proposed by Millis for the itinerant electron systems we calculated the specific heat coefficient $γ(T)$ for the magnetic fluctuations with susceptibility $χ^{-1}\sim |δ+ω|^α+f(q)$ near the Lifshitz point. The constant value obtained for $α=4/5$ and the logarithmic temperature dependence, specific for the non-Fermi behavior, have been obtained in agreement with the experimental dat.

cond-mat.str-el↗
arXiv1998

Electron-fluctuation interaction in a non-Fermi superconductor

We studied the influence of the amplitude fluctuations of a non-Fermi superconductor on the energy spectrum of the 2D Anderson non-Fermi system. The classical fluctuations give a temperature dependence in the pseudogap induced in the fermionic excitations.

cond-mat.supr-con↗
arXiv1998

Flow-Equation method for a superconductor with magnetic correlations

The flow equation method has been used to calculate the energy of single impurity in a superconductor for the Anderson model with $U \neq 0$. We showed that the energy of the impurity depends only of the $Δ^{2}_{R}$ (renormalized order parameter) which depends on the renormalized Hubbard repulsion$U^R$. For a strong Hubbard repulsion $U^R = U$ and $Δ^R = Δ^I$ the effect of the $s-d$ interactions are nonrelevant, a result which is expected for this model.

cond-mat↗