Acoustoelectric current through a quantum wire containing a point impurity

A dc electric current due to a flow of ultrasonic phonons through a quantum wire containing an isolated point impurity is analyzed theoretically. An explicit expression for the acoustoelectric (AE) current is obtained and its dependence on the chemical potential of the electron gas and the induction of the external magnetic field is investigated. It is shown that a point impurity may lead to a partial or complete destruction of the steplike structure of the AE current as a function of the chemical potential.     

Acoustoelectric current through a ballistic microconstriction

The behavior of an acoustoelectric current through a three-dimensional quantum microconstriction placed in a longitudinal uniform magnetic field is studied theoretically in the ballistic transport regime. The oscillation periods of the acoustoelectric current are studied in detail as functions of the chemical potential and the magnetic field induction. The temperature effect is taken into account. It is shown that the acoustoelectric current as a function of the chemical potential can exhibit a steplike behavior. The limits for the existence of a steplike structure are determined.     

Electronic properties of a quantum dot formed by the potentials associated with the surface acoustic wave and constrictions

The electronic structure of dynamic quantum dots formed by surface acoustic waves potential and the confinement potential produced by gate voltage has been investigated within the spin-density-functional theory. We found the addition energy of this kind quantum dot in general decreases as the electron number increases, so the basic feature of the quantized acoustoelectric current with multi-plateaus can be reproduced. The addition energy needed for a second electron entering into the dynamic quantum dot is found to be about 2.21 meV, which is in good agreement with experimental estimations. Moreover, the formation of the Wigner molecule-like states is observed when the number of electrons in the dot exceeds three. By the calculated addition energy and the evolution of the electron density in the presence of a magnetic field, we also explained the influence of the magnetic field on the acoustoelectric current appeared in the experiments.     

Transverse acoustoelectric effect in ferromagnetic superconductors

A longitudinal ultrasonic wave in a type-II superconductor with a ferromagnetic subsystem and negligible Hall effect carries the vortex structure in its propagation direction and generates a constant transverse electric (acoustoelectric) field. This field has a maximum in temperature and external magnetic field. The magnitudes and positions of these maxima depend on the magnitude and direction of the internal ferromagnetic moment of the superconductor. It is shown that experimental investigation of the temperature dependence of the acoustoelectric field in a fixed external magnetic field or at a fixed temperature on the external magnetic field strength makes it possible to measure the magnetic moment and magnetic susceptibility of the superconductor ferromagnetic subsystem and the viscosity coefficient of the vortex structure.     

On the electrostatic potential distribution in a screened Corbino disk carrying a transport current under conditions of the quantum Hall effect

It is shown that the characteristic features of the chemical potential for 2D electrons in a magnetic field, which lead to sharp dips in the magnetic field dependence of the capacitance of a 2D system, also affect the electrostatic potential distribution in the direction of the transport current flowing through a 2D Corbino disk under conditions of integral magnetic filling factor. The associated details of the temperature dependence of the electrostatic potential distribution, the distances to the screening electron, and the transport potential difference at the Corbino edges are investigated. The possibilities of experimentally observing these features of the electrostatic potential distribution along a Corbino disk with a transport current under conditions of the quantum Hall effect are discussed. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 8, 545–550 (25 October 1997)     

Oscillating sign of drag in high Landau levels

Motivated by experiments, we study the sign of the Coulomb drag voltage in a double layer system in a strong magnetic field. We show that the commonly used Fermi golden rule approach implicitly assumes a linear dependence of intralayer conductivity on density, and is thus inadequate in strong magnetic fields. Going beyond this approach, we show that the drag voltage commonly changes sign with density difference between the layers. We find that, in the quantum Hall regime, the Hall and longitudinal drag resistivities may be comparable. Our results are also relevant for pumping and acoustoelectric experiments.     

The sign change of the acoustoelectric effect in type-II superconductors

The acoustoelectric effect is studied in normal and mixed superconducting states of an anisotropic metal. We find that if the superconducting gap is anisotropic and the Fermi surface contains both electron-like and holelike parts, then the acoustoelectric voltage can sharply change sign when transited from the normal to superconducting state. The affect of superconducting fluctuations on the acoustoelectric current is also investigated.     

Acoustoelectric effects in carbon nanotubes

We report observations of acoustoelectric effects in carbon nanotubes. We excite sound in &mgr;m long ropes of single walled carbon nanotubes suspended between two metallic contacts by applying radio-frequency electric field. The sound is detected by measuring either the dc resistance of the tubes in a region of strong temperature dependence (in the vicinity of superconducting or metal-insulator transition), or their critical current. We show that, depending on the excitation power, the vibrations produce either electron heating or phase coherence breaking.     

Surface acoustic wave propagation and acoustoelectric interaction in multilayered piezoelectric semiconductors

In the past years, the acoustoelectric interaction has been used in a number of different devices such as acoustic amplifiers, acoustoelectric convolvers and acoustic coupled transport devices. Recent developments in synthesized semiconductor superlattices with high quality heterostructures have been found to be useful in a new generation of high performance devices such as the High Electron Mobility Transistor. The objective of this paper is to extend the use of these superlattices to acoustoelectric devices. A complete theory of acoustoelectric interaction in layered piezoelectric semiconductor has been developed. The acoustic propagation equations have been solved together with the continuity, transport and Poisson equations. The free carrier transport properties are accounted for using a mobility tensor to describe the two-dimensional behavior. The acoustical and electrical boundary conditions have been used to obtain mechanical displacement and electric field expressed in terms of Bloch functions. The effect of longitudinal D.C. applied field on SAW attenuation or amplification is also considered.     

Orbital and spin magnetism and dielectric response of electrons in metals

A survey is given of the theory of orbital and spin magnetism of electrons in metals, and of the relation of this to dielectric response theory. In particular, the orbital magnetic behaviour of Bloch electrons in a static but spatially varying magnetic field is discussed. It is shown that the treatment of Hebborn and Sondheimer can be generalized to include this spatial dependence of the applied magnetic field and that the result may be written compactly in terms of the zero field canonical density matrix, or Green function.

It is further shown that the frequency dependence of both the orbital and spin susceptibility can be obtained, again from the density matrix, by calculating the current. The connection with neutron scattering is exhibited and for the case of nickel the way in which such experiments can lead to estimates of the role of the electron interactions is discussed.

The effect of a magnetic field on phonon spectra in metals is considered briefly. Finally it is suggested that it may be of interest to study the effect of the magnetic field on the periodic potential usually employed to calculate energy levels of electrons in magnetic fields. Some modifications of pair forces between ions is to be expected in very high fields.     

Chiral magnetic effect in lattice QCD with a chiral chemical potential

We perform a first lattice QCD simulation including a two-flavor dynamical fermion with a chiral chemical potential. Because the chiral chemical potential gives rise to no sign problem, we can exactly analyze a chirally imbalanced QCD matter by Monte Carlo simulation. By applying an external magnetic field to this system, we obtain a finite induced current along the magnetic field, which corresponds to the chiral magnetic effect. The obtained induced current is proportional to the magnetic field and to the chiral chemical potential, which is consistent with an analytical prediction.     

Effect of strong magnetic field on chemical potential and electron capture in magnetar

The chemical potential of electrons in a strong magnetic field is investigated. It is shown that the magnetic field has only a slight effect on electron chemical potential when B 〈 10^11 T, but electron chemical potential will decrease greatly when B 〉 10^11 T. The effects of a strong magnetic field on electron capture rates for ^60Fe are discussed, and the result shows that the electron capture sharply decreases because of the strong magnetic field.     

Fermi energy and energy band occupation for a relativistic degenerate electron gas in a quantizing magnetic field

We examine the influence of a quantizing magnetic field on the occupation of the energy bands for a relativistic electron gas, whose magnetic moments are parallel or antiparallel to the field. The field dependence of not only the chemical potential, but also the Fermi energy of the gas, is determined for a series of magnetic field strengths.Brestek State Teachers Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 3–7, September, 1993.     

Magnetization reversal process at atomic scale in systems with itinerant electrons

The magnetic response of itinerant electrons systems to an external magnetic field is investigated on the basis of a microscopic Hamiltonian from which the spin-polarized electronic structure is determined. The magnetic moment and grand thermodynamic potential of the d-electronic subsystem on a particular atomic site in the presence of the external field are calculated as a function of the moment's orientation for fixed electron configuration of its local environment. Self-consistent magnetic solutions strongly depend on the d-electron number, determined by the position of the d level relative to the Fermi energy. For parameters corresponding to α-Fe, two branches of self-consistent solutions with high and low magnetic moments are found. For parameters corresponding to bulk Cr, a Fe impurity in the Cr matrix and a Cr impurity in the Fe matrix, there are only low-spin solutions. The theory is also applied for describing magnetization reversal processes in exchange spring magnets. A slab of Fe was considered as a soft magnetic layer. The influence of the hard magnet is modeled by the inclusion of an external magnetic field applied to the interface Fe layers. The dependence of the hysteresis loop on the thickness of the Fe slab and on the value of the interface field is investigated.     

Current–current correlation function in the presence of chemical potential and magnetic field

A (2+1)-dimensional electronic system is considered, in which the relation between the Green functions and the conductivity is used. A current–current correlation function, Π_μν(B), of the fermion system was obtained in the presence of nonquantized fermion magnetic field B, chemical potential η and gap m. Using this function one can obtain an expression for polarization operator calculated without the magnetic field. The result obtained can be applied for graphene.     

Vortex dynamics in Pb-doped Hg-1234 superconductor by AC susceptibility response

The general equation that describes the AC magnetic susceptibility response of the superconducting system due to the change of varying AC field has been reviewed. By using the AC susceptibility measurements, the temperature, magnetic field and current density dependence of the effective pinning potential U(T, H, J) for our Pb-doped Hg-1234 superconductor has been determined. It is found that the fast drop of the effective pinning potential with current density is due to the large value of the characteristic exponent μ which depends on the existing types of non-superconducting phases that form the intergrowth structures with the dominant matrix. The characteristic curve of electric field E(J) against the current density J has been obtained from the AC susceptibility technique. For consideration of current relaxation due to the presence of giant flux creep, we have studied and determined the temperature dependence of the critical current density J_c for our specimen.     

Influence of super-strong magnetic field on the electron chemical potential and β decay in the stellar surroundings

In this paper, considering the quantum effect of electrons in a super-strong magnetic field, the influence of a super-strong magnetic field on the chemical potential of a non-zero temperature electron is analyzed, the rates of β decay under the super-strong magnetic field are studied, and then we compare them with the case without a magnetic field. Here, the nucleus 63Co is investigated in detail as an example. The results show that a magnetic field that is less than 1010 T has little effect on the electron chemical potential and β decay rates, but the super-strong magnetic field that is greater than 1010 T depresses the electron chemical potential and improves the β decay rates clearly.     

Particle motion and electromagnetic fields of rotating compact gravitating objects with gravitomagnetic charge

The exact solution for the electromagnetic field occuring when the Kerr–Taub–NUT compact object is immersed (i) in an originally uniform magnetic field aligned along the axis of axial symmetry (ii) in dipolar magnetic field generated by current loop has been investigated. Effective potential of motion of charged test particle around Kerr–Taub–NUT gravitational source immersed in magnetic field with different values of external magnetic field and NUT parameter has been also investigated. In both cases presence of NUT parameter and magnetic field shifts stable circular orbits in the direction of the central gravitating object. Finally we find analytical solutions of Maxwell equations in the external background spacetime of a slowly rotating magnetized NUT star. The star is considered isolated and in vacuum, with monopolar configuration model for the stellar magnetic field.     

Field dependent specific heat and longitudinal magnetization of the quantum magnet layer Cs2CuCl4: Anisotropy effects

We have addressed the specific heat and magnetization of an anisotropic spin-1/2 triangular Heisenberg antiferromagnet Cs₂CuCl₄ in the presence of magnetic field at finite temperature. We have investigated the behavior of thermodynamic properties by means of excitation spectrum in terms of a hard core bosonic representation. The effect of in-plane anisotropy on thermodynamic properties has also been studied via the bosonic model by Green’s function approach. This anisotropy is considered for exchange constants that couple spin components perpendicular to magnetic field direction. We have found the temperature dependence of the specific heat and longitudinal magnetization in the gapped field induced spin-polarized phase for various magnetic fields and anisotropy parameters. Furthermore we have studied the magnetic field dependence of specific heat and magnetization for various anisotropy parameters. Our results show temperature dependence of specific heat includes a peak so that its temperature position goes to higher temperature with increase of magnetic field. We have found the magnetic field dependence of specific heat shows a monotonic decreasing behavior for various magnetic fields due to increase of energy gap in the excitation spectrum.     

Electronic spectrum and ballistic transport in a helical nanotube

A model of a helical nanotube permitting analytical calculation of the spectrum and wave functions is proposed and studied. It is shown that the specific character of the symmetry of the Hamiltonian results in an electronic spectrum having no band structure despite the periodicity of the potential along the system axis. A two-dimensional ribbon rolled into a helix and a quasi-one-dimensional helix in a magnetic field are considered as limiting cases of the model. It is shown that the presence of additional local minima in the subbands of the electronic spectrum leads to a nonmonotonic dependence of the ballistic conductance of the system on the chemical potential.