arXiv subjects

V. P. Mineev

Publications and source records attributed to V. P. Mineev.

89 records · Page 5Linked to original sources

arXiv2004

Theory of polarized Fermi liquid

The dispersion law of transverse spin waves known in the Stoner-Hubbard model of itinerant ferromagnetism corresponds to that is well known in more broder and well controlled approach of Fermi-liquid theory. Making use the quantum-field theoretical approach we derive the dispersion law for the transverse spin waves in a weakly polarized Fermi liquid at T=0. Along with the dissipationless part inversely proportional to the polarization it contains also the finite zero-temperature damping. It is shown that similar derivation for "ferromagnetic Fermi liquid" taking into consideration the divergency of static transverse susceptibility also leads to the same attenuating spin wave spectrum. Hence, in both cases we deal in fact with spin polarized Fermi liquid but not with isotropic itinerant ferromagnet where the zero temperature atenuation is prohibited by Goldstone theorem. It demonstrates, the troubles of the Fermi liquid formulation of a theory of itinerant ferromagnetic systems.

cond-mat.str-el↗

arXiv2004

Paramagnetic limit of superconductivity in a crystal without inversion center

The theory of paramagnetic limit of superconductivity in metals without inversion center is developed. There is in general the paramagnetic suppression of superconducting state. The effect is strongly dependent on field orientation in respect to crystal axes. The reason for this is that the degeneracy of electronic states with opposite momenta forming of Cooper pairs is lifted by magnetic field but for some field directions this lifting can be small or even absent.

cond-mat.supr-con↗

arXiv2004

Superconductivity in ferromagnetic metals and in compounds without inversion centre

The symmetry properties and the general overview of the superconductivity theory in the itinerant ferromagnets and in materials without space parity are presented. The basic notions of unconventional superconductivity are introduced in broad context of multiband superconductivity which is inherent property of ferromagnetic metals or metals without centre of inversion.

cond-mat.supr-con↗

arXiv2004

On the theory of polarized Fermi liquid

The transport equation for transverse vibrations of magnetization in spin polarized Fermi liquid is derived from integral equation for the vertex function. The dispersion law for the transverse spin waves is established. The existance of zero-temperature spin-waves attenuation is confirmed. The problem of similar derivation in ferromagnetic "Fermi liquid" is discussed.

cond-mat.stat-mech↗

arXiv2004

Transverse spin dynamics in a spin-polarized Fermi liquid

The linear equations for transverse spin dynamics in weakly polarised degenerate Fermi liquid with arbitrary relationship between temperature and polarization are derived from Landau-Silin phenomenological kinetic equation with general form of two-particle collision integral. The temperature and polarization dependence of the spin current relaxation time is established. It is found in particular that at finite polarization transverse spin wave damping has a finite value at T=0. The analogy between temperature dependences of spin waves attenuation and ultrasound absorption in degenerate Fermi liquid at arbitrary temperature is presented. We also discuss spin-polarized Fermi liquid in the general context of the Fermi-liquid theory and compare it with "Fermi liquid" with spontaneous magnetization.

cond-mat.stat-mech↗

arXiv2004

On the theory of superconductivity in ferromagnetic superconductors with triplet pairing

We point out that ferromagnetic superconductors with triplet pairing and strong spin-orbit coupling are even in the simplest case at least two-band superconductors. The Gor'kov type formalism for such superconductors is developed and the Ginzburg-Landau equations are derived. The dependence of the critical temperature on the concentration of ordinary point-like impurities is found. Its nonuniversality could serve as a qualitative measure of the two-band character of ferromagnetic superconductors. The problem of the upper critical field determination is also discussed.

cond-mat.supr-con↗

arXiv2003

Pressure dependence of magnetism in URu2Si2

Neutron-scattering and specific-heat measurements of the heavy-fermion superconductor URu2Si2 under hydrostatic pressure and with Rh-doping [U(Ru{0.98}Rh{0.02})2Si2] show the existence of two magnetic phase transitions. At the second-order phase transition Tm ≈ 17.5 K, a tiny ordered moment is established, while at TM < Tm, a first-order phase transition (under pressure or doping) gives rise to a large moment. The results can be understood in terms of a hidden OP Psi coupled to the ordered moment m, where m and Psi have the same symmetry.

cond-mat.str-el↗

arXiv2003

Giant Quantum Oscillations of the Longitudinal Magnetoresistance in Quasi two-dimensional Metals

We have investigated in frame of the quantum transport theory the magnetic quantum oscillations of the longitudinal magnetoresistance $ρ_{zz}$ in quasi two-dimensional metals for a magnetic field perpendicular to the layers. Giant Shubnikov-de Haas oscillations are found when the cyclotron energy $\hbar ω_{c}$ is much larger than the interlayer transfer integral $t$ (the two-dimensional limit). In large magnetic fields and at low temperatures, the minima of the magnetoconductivity $σ_{zz}=ρ_{zz}^{-1}$ exhibit a thermally activated behavior in presence of negligibly small chemical potential oscillations, as observed in the organic layered conductor $β''\mathrm{-(BEDT-TTF)}_{2}\mathrm{SF}_{5}\mathrm{CH}_{2}\mathrm{CF}_{2}\m athrm{SO}_{3}$. The questions concerning the absence of strong chemical potential oscillations in such compound and the impurity self-energy are discussed.

cond-mat↗

arXiv2003

Comment on ``London Theory for Superconducting Phase Transitions in External Magnetic Fields: Application to $\text{UPt}_{3}$''

The authors of the Letter PRL 89, 017004 (2002) predict nontrivial flux lattice structures in UPt3 in vicinity of the superconducting transition between the A and B phases for low magnetic fields, an important conclusion for motivating future experiments. We show that the approach and the conclusions of this Letter are wrong. The transitions between the different superconducting phases in the mixed state are pointed out to be rather crossovers than real second-order phase transitions within the most popular theoretical models of a two-component superconducting order parameter for UPt3.

cond-mat.supr-con↗

arXiv2002

Magnetic Quantum Oscillations of the Longitudinal Conductivity $σ_{zz}$ in Quasi two-dimensional Metals

We derive an analytical expression for the longitudinal magnetoconductivity $σ_{zz}$ in layered conductors in presence of a quantizing magnetic field perpendicular to the layers and for short-range in-plane impurity scattering in frame of the quantum transport theory. Our derivation points out quite unusual temperature and magnetic field dependences for Shubnikov-de Haas oscillations in the two-dimensional limit, i.e. $\hbar ω_{c} \gg 4 πt$, where $t$ is the interlayer hopping integral for electrons, and $ω_{c}$ the cyclotron frequency. In particular, when $\hbar ω_{c} \gg 4 πt$ and $\hbar ω_{c} \geq 2 πΓ_μ$ (here $Γ_μ$ is the value of the imaginary part of the impurity self-energy at the chemical potential $μ$), a pseudo-gap centered on integer values of $μ/\hbarω_{c}$ appears in the zero-temperature magnetoconductivity function $σ_{zz}(μ/\hbarω_{c})$. At low temperatures, this high-field regime is characterized by a thermally activated behavior of the conductivity minima (when chemical potential $μ$ lies between Landau levels) in correspondence with the recent observation in the organic conductor $β''\text{-(BEDT-TTF)}_{2}\text{SF}_{5}\text{CH}_{2}\text{CF}_{2}\text{SO}_ {3}$.

cond-mat↗

arXiv2002

Superconducting states in ferromagnetic metals

The symmetry of the superconducting states arising directly from ferromagnetic states in the crystals with cubic and orthorombic symmetries is described. The symmetry nodes in the quasiparticle spectra of such the states are pointed out if they exist. The superconducting phase transition in the ferromagnet is accompanied by the formation of superconducting domain structure consisting of complex conjugate states imposed on the ferromagnet domain structure with the opposite direction of the magnetization in the adjacent domains. The interplay between stimulation of a nonunitary superconducting state by the ferromagnetic moment and supression of the superconductivity by the diamagnetic orbital currents is established.

cond-mat.supr-con↗

arXiv2002

Upper critical field in a trigonal unconventional superconductor UPt_3

A theory of the upper critical field in a trigonal superconductor with a two-component order-parameter is developed. We demonstrate the existence of sixfold modulations of the upper critical field in the basal plane. The form of the angular dependence of H_c2 in the plane of the main symmetry axis is studied in the whole range of phenomenological rigidity coefficients. A qualitative dependence of these coefficients on the form of the Fermi surface is established. The results obtained are discussed in connection with the measurements of the direction dependence of H_c2 in the heavy fermion superconductor UPt_3 that has been recently found to possess trigonal crystalline structure. PACS numbers: 74.20.De, 74.70.Tx

cond-mat.supr-con↗

arXiv2001

Effects of dipolar field in the spin dynamics of a Fermi liquid

We study spin dynamics of a normal Fermi liquid taking into account the demagnetizing field produced by the spin system itself. Linear solutions of the spin dynamics equations in the form of standing spin waves in a finite volume of liquid are found. At almost all known experimental conditions the influence of demagnetizing field can be satisfactorily described by the first order of perturbation theory. We carried out perturbational calculations for two geometries of experimental cell -- spherical and finite-cylindrical. We performed also exact numerical simulations of the spin wave spectra in a spherical cell at an arbitrary strength of the demagnetizing field. The obtained results are applied in particular to conditions of recent experiment (G.Vermeulen and A.Roni, Phys. Rev. Lett. 86, 248 (2001)) related to the problem of zero temperature transverse relaxation in a polarized Fermi liquid. We found that not taking into account demagnetizing field leads to negligible errors in the measured relaxation time, thus supporting the conclusion of the absence of zero temperature spin wave damping.

cond-mat↗

arXiv2001

Spin susceptibility of the superfluid $^{3}$He-B in aerogel

The temperature dependence of paramagnetic susceptibility of the superfluid ^{3}He-B in aerogel is found. Calculations have been performed for an arbitrary phase shift of s-wave scattering in the framework of BCS weak coupling theory and the simplest model of aerogel as an aggregate of homogeneously distributed ordinary impurities. Both limiting cases of the Born and unitary scattering can be easily obtained from the general result. The existence of gapless superfluidity starting at the critical impurity concentration depending on the value of the scattering phase has been demonstrated. While larger than in the bulk liquid the calculated susceptibility of the B-phase in aerogel proves to be conspicuously smaller than that determined experimentally in the high pressure region.

cond-mat↗

arXiv2000

De Haas-van Alphen effect in two- and quasi two-dimensional metals and superconductors

An analytical form of the quantum magnetization oscillations (de Haas-van Alphen effect) is derived for two- and quasi two-dimensional metals in normal and superconducting mixed states. The theory is developed under condition that the chemical potential is much greater than the cyclotron frequency, which is proved to be valid for using grand canonical ensemble in the systems of low dimensionality. Effects of impurity, temperature, spin-splitting and vortex lattice - in the case of superconductors of type II -, are taken into account. Contrary to the three dimensional case, the oscillations in sufficiently pure systems of low dimensionality and at sufficiently low temperatures are characterized by a saw-tooth wave form, which smoothened with temperature and concentration of impurities growth. In the normal quasi two-dimensional systems, the expression for the magnetization oscillations includes an extra factor expressed through the transfer integral between the layers. The additional damping effect due to the vortex lattice is found. The criterion of proximity to the upper critical field for the observation of de Haas-van Alphen effect in the superconducting mixed state is established.

cond-mat.stat-mech↗

arXiv2000

Upper critical field in layered superconductors

The theoretical statements about a restoration of a superconductivity at magnetic fields higher than the quasiclassical upper critical field and a reentrance of superconductivity at temperatures $T_c(H)\approx T_c(0)$ in the superconductors with open Fermi surfaces are reinvestigated taking into account a scattering of quasiparticles on the impurities. The system of integral equations for determination of the upper critical field parallel to the conducting planes in a layered conventional and unconventional superconductors with impurities are derived. The $H_{c2}(T)$ values for the "clean" case in the Ginzburg-Landau regime and at any temperature in the "dirty" case are found analytically. The upper limit of the superconductor purity when the upper critical field definately has a finite value is established.

cond-mat.supr-con↗

arXiv1999

Phase transition into superconducting mixed state and de Haas - van Alphen effect

The Landau expansion for the free energy of the superconducting mixed state near the upper critical field in powers of the square modulus of the order parameter averaged over Abrikosov lattice is derived. The analytical calculations has been carried out in frame of Gor'kov formalism for 3-dimensional isotropic BCS model beyond the limits of quasiclassical approximation, another words with Landau quantization of the quasiparticle energy levels taken into consideration. The derivation is performed at low temperature and high enough but finite crystal's purity. The effect of Pauli paramagnetic terms is taken into account. The quantum oscillations of the critical temperature, the order parameter's amplitude and the magnetization (de Haas-van Alphen effect) in the mixed state are found. The limitation of validity of a mean field approach due to critical fluctuations (Ginzburg criterion) for the phase transition under consideration is established.

cond-mat.supr-con↗