Total control over ultracold interactions via electric and magnetic fields

The scattering length is commonly used to characterize the strength of ultracold atomic interactions, since it is the leading parameter in the low-energy expansion of the scattering phase shift. Its value can be modified via a magnetic field, by using a Feshbach resonance. However, the effective range term, which is the second parameter in the phase shift expansion, determines the width of the resonance and gives rise to important properties of ultracold gases. Independent control over this parameter is not possible by using a magnetic field only. We demonstrate that a combination of magnetic and electric fields can be used to get independent control over both parameters, which leads to full control over elastic ultracold interactions.     

Noninteracting electron gas in high magnetic fields

A closed-form expression is obtained for a free electron gas in a magnetic field. The resulting formulation is valid for fields less than 10⁸ gauss and temperatures where de Haas-Van Alphen effects can be neglected.     

Critical currents of type ii superconductors in non-transversal magnetic fields

The force on flux lines near narrow defects elongated in the direction of the transport current is calculated. This force, together with the maximum interaction forcek _m on the central flux line element, gives the volume pinning forceF _p on the flux line lattice. The dependence ofk _m (and of the critical current densityj _c ) on the angle between the magnetic field and the transport current is calculated for different defect dimensions (with respect to the coherence length of the superconductor) and compared with the experimental results. We obtainj _c sin^–n , where 1n3 in dependence on the defect dimensions and on the angle interval. The possibility of testing theF _p k _m ² dependence of the statistical theory of pinning is proposed.     

Measuring magnetic fields generated by DC currents in receive-only coils

DC decoupling currents applied to receive-only coils during radiofrequency transmission can create stray magnetic fields capable of changing the resonant frequency of nearby nuclei. It is difficult to measure these fields with conventional field-mapping techniques because the fields are not present when the signal is acquired. The stray fields can be measured empirically with cardiac tags.     

Hot electron transverse conductivity in quantizing magnetic fields

In this work the general expression of the electron transverse conductivity tensor of an electron-phonon system being in crossed strong electric and quantizing magnetic fields is considered starting from the Kubo-Kalashnikov formula. An explicit formula for the hot electron transverse conductivity σ _xx is obtained and it is compared to a Titeica-type formula with the temperature of electrons replaced by an effective electron temperature depending on the electric field.     

Itinerant electron transport in microscopically inhomogeneous magnetic fields

We report on magnetoresistance measurements in thin nickel films modulated by a periodic magnetic field emanating from micromagnetic arrays fabricated at the film surface. By increasing the strength of the magnetic potential using nickel and dysprosium micromagnets, we are able to quench the anisotropic magnetoresistance (AMR) in the film.     

Quantization of persistent currents in quantum dot at strong magnetic fields

We investigate equilibrium electron currents and magnetization in an ideal two-dimensional disc of radius R placed in a strong magnetic field H. The most striking results emerge when the conditions for the existence of edge and bulk states are met, namely . When the Fermi energy is locked on a Landau level, the current as a function of electron density is quantized in units of , where ω_c is the cyclotron frequency. We argue that this effect survives against weak disorder. It is also shown that the persistent current has an approximately periodic dependence on 1/H.     

Modification of field-emission currents from tungsten by external magnetic fields

Experimental work is described on the changes produced by an external magnetic field on field emission currents from tungsten needles held at helium temperatures. A steady decrease with field above a critical field is reported together with oscillatory variations of the order of 10 – 15%.     

Quenching of non-local electron transport in tilted magnetic fields

A variety of transport phenomena observed at laterally confined two- dimensional electron systems (2DES) prove the occurrence of non-local contributions to the electronic conductance in these systems. However, this non-local regime accompanied by a non-equilibrium population of the edge states with respect to the 2D bulk state is quenched at rather low values of current-driving electric fields.We analyse the non-Ohmic behaviour of SdH oscillations at GaAs/GaAlAs Quantum Hall conductors on the basis of a model including edge and bulk conduction and deduce the non-equilibrium population of edge and bulk states quantitatively.The spatial separation between edge and bulk states was changed by tilting the samples with respect to the magnetic field. The resulting angular dependences of equilibration parameters could be quantitatively explained by the change of the ratio of spin splitting to cyclotron energy being present in 2DES in tilted magnetic fields.PACS index numbers: 73.20.Dx; 73.40.Hm     

Hyperfine magnetic fields at rare-earth elements in ferromagnetic transition metals

Hyperfine magnetic fields for such probes as:¹⁵²SmFe,¹⁵²SmCo,¹⁵²SmNi,¹⁵⁵GdFe,¹⁷²YbFe,¹⁷²YbCo and¹⁷²YbNi have been measured using PAC method. The quantitative analysis of components of these fields has been also performed.     

Semiclassical theory of electron drag in strong magnetic fields

We present a semiclassical theory for electron drag between two parallel two-dimensional electron systems in a strong magnetic field, which provides a transparent picture of the most salient qualitative features of anomalous drag phenomena observed in recent experiments, especially the striking sign reversal of drag at mismatched densities. The sign of the drag is determined by the curvature of the effective dispersion relation obeyed by the drift motion of the electrons in a smooth disorder potential. Localization plays a role in explaining the activated low temperature behavior but is not crucial for anomalous drag per se.     

On envelope equations for electron beams in magnetic fields

A self-similarity approach is used to obtain envelope equations for an annular beam propagating along a magnetic field, and also an electron beam injected at an angle to a magnetic field. An exact solution is constructed for the self-consistent problem of transverse oscillations of a cold annular beam in a magnetic field, and a comparison is made with approximate results from the method of envelope equations. Zh. Tekh. Fiz. 68, 103–107 (January 1998)     

The magnetic hyperfine fields of rare earth ions in metals

Data for the magnetic dipole hyperfine interaction of essentially single rare earth ions in metals, measured with different experimental methods, are collected and discussed. Depending on the host, the magnetic hyperfine field of these paramagnetic ions remains undisturbed by the environment, or it is enlarged, or weakened or can even become completely lost. If there are magnetic ions in the neighbourhood, the magnetic interaction can enlarge the hyperfine field of the single ion by a transferred hyperfine field. The reason of the demagnetization effect may be crystal field splitting and hybridization. The core polarization field of the free rare earth ions is redetermined from measurements of the hyperfine interaction in nonmagnetic metals at low magnetic ion concentration.     

Dynamic rheological properties of viscoelastic magnetic fluids in uniform magnetic fields

The dynamic rheological properties of viscoelastic magnetic fluids in externally applied uniform magnetic fields are investigated by a laboratory-made cone-plate rheometer in this study. In particular, the effects of the magnetic field on the viscoelastic properties (the complex dynamic modulus) of the viscoelastic magnetic fluids are studied. In the investigation, three viscoelastic magnetic fluids are made by mixing a magnetic fluid and a viscoelastic fluid with different mass ratios. As a supplementation to the experimental investigation, a theoretical analysis is also presented. The present study shows that the viscosity and elasticity of the viscoelastic magnetic fluids are significantly influenced by the magnetic field and the concentrations of the magnetic particles in the test fluids. Theoretical analysis qualitatively explains the present findings.     

Out-of-plane bipolar and quadrupolar magnetic fields generated by shear flows in two-dimensional resistive reconnection

Shear flows perpendicular to the anti-parallel reconnecting magnetic field are often observed in magnetosphere and interplanetary plasmas, and in laboratory plasmas toroidal differential rotations can also be generated in magnetic confinement devices. Our study finds that such shear flows can generate bipolar or quadrupolar out-of-plane magnetic field perturbations in a two-dimensional resistive MHD reconnection without the Hall effects. The quadrupolar structure has otherwise been thought a typical Hall MHD reconnection feature caused by the in-plane electron convection. The results will challenge the conventional understanding and satellite observations of the signature of reconnection evidences in space plasmas.     

Theory of electron spin resonance of magnetic ions in metals

Reviewed at both a relatively elementary and more advanced level is the interpretative theory of the electron spin resonance of magnetic ions in metals. The various theoretical possibilities are illustrated by experimental examples wherever possible. Initially the development is based upon the Bloch-Hasegawa equations. The relationship of the advanced theory to this more elementary theory is emphasized. Multimagnetic-impurity experiments, the skin depth problem, the analysis of exchange, hyperfine and crystal field parameters, Redfield theory, ionic and virtual bound state models and the Kondo effect, all in relation to E.S.R. in metals, are each covered in some detail. A discussion of some outstanding problems and projections for the future are also included.     

De Rham currents,extended singularities of fields and magnetic monopoles

We apply De Rham's concept of “currents” to the treatment of extended singularities or discontinuities of physical fields in a coordinate independent way. In particular, we obtain a generalization of the theory of magnetic monopoles when applied to the electromagnetic field.