Index of content:
Volume 37, Issue 10, October 2011

Angular magnetostriction oscillations in layered conductors with multisheet Fermi surfaces
View Description Hide DescriptionThe dependence of the electrical conductivity of layered conductors with a quasitwo dimensional electron energy spectrum on the orientation of an external magnetic field is studied. The oscillatory dependence of the magnetostriction of conductors with a multisheet Fermi surface (FS) on the angle of inclination of a strong magnetic field to the layers is found to contain valuable information on the shape of the FS. In particular, the period of the oscillations can be used to determine the magnitude of the corrugation in a plane sheet of the Fermi surface.

New features of magnetoresistance in highly anisotropic layered metals
View Description Hide DescriptionThe angular and magneticfield variations of the interlayer magnetoresistance calculated in the limits of high magnetic field and very high anisotropy manifest several unusual properties. The monotonic part of the interlayer magnetoresistance increases with rising magnetic field along the current, which contradicts the standard theory and changes the angular dependence of the magnetoresistance. The Dingle temperature increases with magnetic field, dampens the magnetic quantum oscillations, and changes the field dependence of their amplitudes.

New lowdimensional molecular conductors: α′′(BEDOTTF)_{2}Cl·3H_{2}O and θ(BDHTTP)_{2}(Br_{0.67}Cl_{0.33})·3H_{2}O
View Description Hide DescriptionXray singlecrystal diffraction studies of two new molecular conductors α′′(BEDOTTF)_{2}Cl·3H_{2}O and θ(BDHTTP)_{2}(Br_{0.67}Cl_{0.33})·3H_{2}O are reported. Both crystals have a layered structure in which conducting layers of organic BEDOTTF or BDHTTP πelectron donors are separated by complex anion layers. The anion layers consist of honeycomb networks of Cl^{−} (Br^{−}) halogen anions and water molecules, which are stable owing to the formation of hydrogen bonds. Calculations of the electron band structure of these crystals show that metallic conductivity is to be expected in the organic α′′(BEDOTTF) and θ(BDHTTP) layers.

Magnetoresistance oscillations up to 32 K in the organic metal β″(ET)_{4}(H_{3}O)[Fe(C_{2}O_{4})_{3}] · C_{6}H_{4}Cl_{2}
View Description Hide DescriptionThe magnetic torque and magnetoresistance of the quasitwodimensional charge transfer salt β″(ET)_{4}(H_{3}O)[Fe(C_{2}O_{4})_{3}] · C_{6}H_{4}Cl_{2} have been investigated in pulsed magnetic fields of up to 55 T. As opposed to de Haas–van Alphen oscillations, Shubnikov–de Haas oscillations are observed up to temperatures as high as 32 K at ambient pressure despite significant thermal damping in the lowtemperature range. This feature, which is also observed under applied pressure, is interpreted in terms of the coexistence of a closed orbit and a quantum interference path with the same cross section.

Angle dependent magnetothermopower of α(ET)_{2}KHg(SCN)_{4}
View Description Hide DescriptionThe magnetic field and angle dependences of the thermopower and Nernst effect for the quasitwo dimensional (q2D) organic conductor α(ET)_{2}KHg(SCN)_{4} are measured at temperatures below (4 K) and above (9 K) the transition temperature in fields of up to 31 T. In addition, a theoretical model involving a magnetic breakdown effect between the q1D and q2D bands is proposed in order to simulate the data. Analysis of the background components of the thermopower and Nernst effect imply that at low temperatures, in the CDW state, the properties of α(ET)_{2}KHg(SCN)_{4} are determined mostly by the orbits on new, open Fermi sheets. The quantum oscillations observed in both thermoelectric effects at fields above 8 T are caused only by the α orbit.

Fieldinduced chargedensitywave transitions in the organic metal α(BEDTTTF)_{2}KHg(SCN)_{4} under pressure
View Description Hide DescriptionSuccessive magneticfieldinduced chargedensitywavetransitions in the layered molecular conductor α(BEDTTTF)_{2}KHg(SCN)_{4} are studied in a hydrostatic pressure regime in which the zero field chargedensitywave(CDW) state is completely suppressed. It is shown that the orbital effect of the magnetic field restores the density wave, while orbital quantization induces transitions between different CDW states as the field strength is varied. The latter show up as distinct anomalies in the magnetoresistance as a function of field. The interplay between the orbital and Pauli paramagnetic effects, which act, respectively, to enhance and to suppress the CDW instability, is particularly manifest in the angular dependence of the fieldinduced anomalies.

Valentin Peschansky and the puzzles of magnetotransport
View Description Hide DescriptionSince the 1950’s, the Kharkov school of theoretical physics has been a world leader in the theory of metals. In particular, the research by V. G. Peschansky for many years has focused on the relationship between the magnetic field dependence of components of the resistivity and the electron energy spectrum. Peschansky developed an elegant theory of magnetoresistance that took surface scattering of electrons into account. The physics of bulk 3D metals was almost exhausted by the end of 1970’s and Peschansky extended his research to lowdimensional electron systems. Throughout his scientific life, V. G. Peschansky has advocated the idea that magnetoresistance is a powerful tool for exploring the rich physics of electron systems. The many experimental and theoretical studies of magnetoresistance behavior in various systems, from simple to the most complex, have, by now, confirmed the fruitfulness of this idea.

Different forms of the Kadanoff–Baym equations in quantum statistical mechanics
View Description Hide DescriptionA new form of the Kadanoff–Baym equations for a system of interacting particles is offered on the basis of the retarded and advanced quantum Green’s functions. The comparison of the traditional and the offered forms of the equations allows to analyze the question to what extent Landau–Silin kinetic equations for the neutral Fermiliquid and for the electron liquid of normal metals take into account quickly varying in space and time disturbances.

Collective modes in quantum Fermi liquid
View Description Hide DescriptionLandau’s theory of Fermi liquids is generalized by incorporating the de Broglie waves diffraction. A newly derived kinetic equation of the Fermi particles is used to derive a general dispersion relation and the excitation of zero sound is studied. A new mode is found due to the quantum correction. It is shown that the zero sound can exist even in an ideal Fermi gas. We also disclose a new branch of frequency spectrum due to the weak interaction.

Nonrelativistic quantum theory of induced Cherenkov radiation and Compton scattering in plasma
View Description Hide DescriptionThe role of quantum effects in the theory of Langmuir waves in collisionless plasma is discussed. It is shown that quantum effects do can be significant at resonant interactions between flows of quantum particles and plasma eigenmodes.

On chemical bonding and helium distribution in hcp beryllium
View Description Hide DescriptionThe electron densities of states and spatial distribution of electron density in the system hcp berylliumhelium were investigated by means of abinitio methods of simulation. It was found that contrary to predictions of the “jelly” model, the energetically more favorable configuration is that where a helium atom is located at the most restricted position, on a triangular face of two adjacent tetrahedrons, and where the charge density of electrons is maximal. It is established that this occurs due to hybridization of electron states of helium and nearest beryllium atom. The helium binding energy is about 5.6 eV. The spatial distribution of the charge density is investigated in details. Calculation of solution energy of helium in hcp beryllium was performed. The helium location at lattice sites in different interstitial positions and in divacancy complexes were considered. It is found that helium implemented into hcp beryllium favors formation of divacancies.

Spontaneous spin polarization of systems with impurity hybridized electron states in conduction band of crystals
View Description Hide DescriptionA theoretical description of spontaneous spin polarization in systems of hybridized electron states on donor impurities with low concentration in a conduction band of a crystal is developed. On the base of general equations for the energy of spin splitting of the electron spectrum, formulated within the framework of the Fermiliquid approach, it is shown that in systems of such a type the spin ordering mechanism of conduction electrons, which is more efficient than the usually considered mechanism of an exchange interaction with magnetic impurities, takes place. The possible realization of spontaneous spin ordering of electrons in hybridized states is substantiated for the case of total polarization of the system within the model of Fermiliquid constants. Possibilities of finding manifestations of spontaneous spin polarization of an electron impurity system in thermodynamic properties (heat capacity and elastic moduli) are discussed. Evidences of such manifestations are presented from an analysis of available experimental data.

Negative ions at an interface between liquid helium mixtures
View Description Hide DescriptionThe properties of electron bubbles electrostatically forced against an interface between liquid^{3}He and saturated ^{4}He–^{3}He mixture were determined at low temperatures. The equilibrium state of such objects is characterized by the binding energy of 6.5 K and oscillatory spectrum of first excitations with a frequency of 0.6·10^{10 }s^{–1}. The shifting electric field E = 100 V/cm at the temperature T = 0.2 K leads to decaying the bound bubble state with the lifetime τ ≈ 1 s. The experimental study of bubble electron states can appear to be useful for determining properties of an interface between liquid helium mixtures.

Oscillations of kinks on dislocation lines in crystals and lowtemperature transport anomalies as a “passport” of newlyinduced defects
View Description Hide DescriptionThe possible interpretation of experimental data on lowtemperature anomalies in weakly deformed metallic crystals prepared form ultrapure lead, copper, and silver, as well as in crystals of ^{4}He is discussed within the previously proposed theoretical picture of dislocations with dynamical kinks. In the case of pure metals the theoretical predictions give a general picture of interaction of conduction electrons in a sample with newlyintroduced dislocations, containing dynamic kinks in the Peierls potential relief. In the field of random stresses appearing due to plastic deformation of a sample, kinks on the dislocation line form a set of onedimensional oscillators in potential wells of different shapes. In the low temperature region at low enough density of defects pinning kinks the inelastic scattering of electrons on kinks should lead to deviations from the WiedemannFranz law. In particular, the inelastic scattering on kinks should result in a quadratic temperature dependence of the thermal conductivity in a metallic sample along preferential directions of dislocation axes. In the plane normal to the dislocation axis the elastic largeangle scattering of electrons is prevalent. The kink pinning by a point defect or by additional dislocations as well as the sample annealing leading to the disappearance of kinks should induce suppression of transport anomalies. Thus, the energy interval for the spectrum of kink oscillations restricted by characteristic amplitude of the Peierls relief is a “passport of deformation history” for each specific sample. For instance, in copper the temperature/energy region of the order of 1 K corresponds to it. It is also planned to discuss in the other publication applicability of mechanism of phonon scattering on mobile dislocationkinks and pinning of kinks by impurities in order to explain anomalies of phonon thermal conductivity of ^{4}He crystals and deformed crystals of pure lead in a superconducting state.

Rosensweig instability in ferrofluids
View Description Hide DescriptionWe propose a simple model to analyze stability of the free surface of horizontally unbound ferrofluid in a vertical magnetic field. With respect to the well known Rosensweig instability (see e.g., R. E. Rosensweig, Ferrohydrodynamics, Cambridge University Press, Cambridge (1993) and references therein) we go one step further to include into consideration coupling of surface displacements to nonmagnetic degree of freedoms. We show that the coupling can lead to a considerable reduction of the critical magnetic field and as well yields to nontrivial depletion layering near the surface.

Quantum oscillations in a tunable graphene bilayer
View Description Hide DescriptionThe oscillations of forbidden gap, chemical potential and carrier concentration on a graphene bilayer in the quasiclassical magnetic field and in the transverse electric field created by the gate voltage are considered.

Magnetoresistance of nanocarbon materials based on carbon nanotubes
View Description Hide DescriptionThe results of experimental investigations of magnetoresistance in nanocarbon material (NCM) containing carbon nanotubes in magnetic field up to 5 T and at temperature up to 0.54 K are reported. The obtained experimental magnetoresistance curves of NCM are described satisfactorily within the framework of the shrinkage effect of wave function of localized state in a magnetic field along with the spinpolarization mechanism.

Heat capacity of an electron gas at the surface of a nanotube with its superlattice in a magnetic field
View Description Hide DescriptionThe effect of modulating potential at the surface of a nanotube in a longitudinal magnetic field on heat capacity of a degenerate and nondegenerate electron gas is considered. The heat capacity is represented by monotonic and oscillating terms. Heat capacity of a degenerate electron gas exhibits de Haasvan Alphen type oscillations, dependent on density of electrons, and AharonovBohm type oscillation dependent on the intensity of the magnetic field going through the nanotube cross section.

Twodimensional Pauli operator in a magnetic field
View Description Hide DescriptionThe twodimensional purely magnetic Schrödinger operator for the nonrelativistic particle with a spin of ½ in a magnetic field has some remarkable properties, that were discovered in the late 70s: its strongly degenerate in the ground state and it admits supersymmetry. In the present work we investigate the special case where the magnetic flux of the periodic field through the elementary cell equals zero. This case has not been covered in the previous publications. An interesting connection with the theory of solitons, in particular with Burgerslike systems and their twodimensional analogues, is revealed. Their linearizability properties are simpler than some famous systems, such as KdV and KP. Members of the AharonovBohmtype system with quantized magnetic flux play a special role in the investigation of this case.