arXiv subjects

Victor Galitski

Publications and source records attributed to Victor Galitski.

170 records · Page 10Linked to original sources

arXiv2003

Divergence of the effective mass near a density wave instability in a MOSFET system

We study the renormalization of the Fermi-liquid parameters in the vicinity of a density wave quantum phase transition, which should occur in MOSFET systems at low densities. First, using a perturbative RPA treatment of fluctuations, we calculate the electronic self-energy and show that the effective mass diverges at the density wave transition point. Second, we go beyond perturbation theory, making use of the exact Pitaevskii identities. Within this exact analysis, we also find a divergence of the effective mass, which occurs at higher densities in the fluctuation region, as compared to the perturbation theory. This result signals the break-down of conventional Fermi-liquid description in the vicinity of the transition point. The divergence of the effective mass gives rise to a singular behavior of the electronic compressibility. We suggest that the experimentally observed enhancement of the effective mass is a precursor to a second order thermodynamic phase transition into a glassy density wave state.

cond-mat.str-el↗

arXiv2003

Kohn-Luttinger pseudo-pairing in a two-dimensional Fermi-liquid

We consider possible superconducting instabilities in a two-dimensional Fermi system with short-ranged repulsive interactions between electrons. The possibility of an unusual superconducting paring due to the Kohn-Luttinger mechanism is examined. The quasiparticle scattering amplitude is shown to possess an attractive harmonic in second-order perturbation theory for finite values of the energy transfer. The corresponding singularity in the pairing vertex leads to a superconducting pairing of the electron excitations with finite energies. We identify the energy transfer in the Cooper channel as the binding energy of the excited pair. At low enough temperatures, the Fermi system is a mixture of normal electron excitations and fluctuating d-wave Cooper pairs possessing a finite gap.

cond-mat.supr-con↗

arXiv2003

Renormalization of the upper critical field by superconducting fluctuations

We study the effect of superconducting fluctuations on the upper critical field of a disordered superconducting film at low temperatures. The first order fluctuation correction is found explicitly. In the framework of the perturbative analysis, superconducting fluctuations are shown to shift the upper critical field line toward lower fields and do not lead to an upward curvature. Higher order corrections to the quadratic term coefficient in the Ginzburg-Landau free energy functional are studied. We extract a family of the mostly divergent diagrams and formulate a general rule of calculating a diagram of an arbitrary order. We find that the singularity gets more severe with increasing perturbation theory order. We conclude that the renormalization of the Ginzburg-Landau coefficients by superconducting fluctuations is an essentially non-perturbative effect. As a result, the genuine transition line may be strongly shifted from the classical mean-field curve in a two-dimensional superconductor.

cond-mat.supr-con↗

arXiv2002

Spin glass versus superconductivity

A superconductor with interacting paramagnetic impurities is considered. The impurities are coupled via the Ruderman-Kittel-Kasuya-Yoshida interaction. At a temperature Tg, the system of magnetic impurities forms a spin-glass state. We study the effect of the spin-spin interactions on the superconducting transition point at T<Tg. We show that superconducting properties depend on the state of the spin system via spin-spin autocorrelation functions. With the help of the Keldysh technique, a general nonequilibrium Gor'kov equation is derived. Possible ageing effects in the superconducting transition point are discussed. The equilibrium superconducting transition point is found explicitly and shown to be shifted towards higher temperatures and impurity concentrations compared to the classical Abrikosov-Gor'kov's curve. The corresponding shift of the superconducting quantum critical point is quite small (about 10%). A method of calculating spin-spin correlation function is suggested. The method combines the ideas of random mean-field method and virial expansion. We calculate analytically the first virial term for the spin-spin correlator for the quantum Heisenberg spin glass with the RKKY interactions in the quasiequilibrium regime.

cond-mat.supr-con↗

arXiv2001

Symmetry properties of the large-scale solar magnetic field

We investigate symmetry properties of the solar magnetic field in the framework of the linear Parker's migratory dynamo model. We show that the problem can be mapped onto the well-known quantum-mechanical double-well problem. Using the WKB approximation, we construct analytical solutions for the dipole and quadrupole configurations of the generated magnetic field. Our asymptotic analysis within the equatorial region indicates the existence of an additional weak dynamo wave which violates the Hale's polarity law. We estimate the spatial decay decrement of this wave. We also calculate explicitly the splitting of the eigenvalues corresponding to the dipole and quadrupole modes. The real part of the dipole eigenvalue is shown to exceed the quadrupole one. A sufficiently long time after generation the dipole mode should dominate the quadrupole one. The relevant observational evidences of the properties obtained are discussed.

astro-ph↗

arXiv2001

Kinematic dynamo wave in the vicinity of the solar poles

We consider a dynamo wave in the solar convective shell for the kinematic $αω$-dynamo model. The spectrum and eigenfunctions of the corresponding equations are derived analytically with the aid of the WKB method. Our main aim here is to investigate the dynamo wave behavior in the vicinity of the solar poles. Explicit expressions for the incident and reflected waves are obtained. The reflected wave is shown to be relatively weak in comparison to the incident wave. The phase shifts and the ratio of amplitudes of the two waves are found.

astro-ph↗

arXiv2001

Disorder and Quantum Fluctuations in Superconducting Films in Strong Magnetic Fields

We find that the upper critical field in a two-dimensional disordered superconductor can increase essentially at low temperatures. This happens due to the formation of local superconducting islands weakly coupled via the Josephson effect. The distribution of the superconducting islands is derived. It is shown that the value of the critical field is determined by the interplay of the proximity effect and quantum phase fluctuations. We find that the shift of the upper critical field is connected with the pinning properties of a superconductor.

cond-mat.supr-con↗

arXiv2000

Superconducting fluctuations at low temperature

The effect of fluctuations on the transport and thermodynamic properties of two-dimensional superconductors in a magnetic field is studied at low temperature. The fluctuation conductivity is calculated in the framework of the perturbation theory with the help of usual diagram technique. It is shown that in the dirty case the Aslamazov-Larkin, Maki-Thomson and Density of States contributions are of the same order. At extremely low temperature, the total fluctuation correction to the normal conductivity is negative in the dirty limit and depends on the external magnetic field logarithmically. In the non-local clean limit, the Aslamazov-Larkin contribution to conductivity is evaluated with the aid of the Helfand-Werthamer theory. The longitudinal and Hall conductivities are found. The fluctuating magnetization is calculated in the one-loop and two-loop approximations.

cond-mat.supr-con↗