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G. P. Mikitik

Publications and source records attributed to G. P. Mikitik.

32 records · Page 2Linked to original sources
arXiv2011

Oscillations of the Nernst coefficient in bismuth

We calculate the magnetic-field dependence (oscillations) of the Nernst coefficient in bismuth at low temperatures for the case when the magnetic field is directed along the trigonal axis of the crystal. In the calculations we take into account the scattering of the electrons and holes in bismuth on impurities and the dependence of this scattering on the magnetic field. The results of these calculations are compared with the experimental data recently published.

cond-mat.mes-hall↗
arXiv2009

Nanomechanics of an individual vortex in an anisotropic type-II superconductor

As shown in recent experiments [Auslaender et al., Nature Physics 5, 35 (2009)] magnetic force microscopy permits one not only to image but also to manipulate an individual vortex in type-II superconductors, and this manipulation provides a new powerful tool to study vortex dynamics and pinning. We derive equations that describe the deformation of an individual vortex in an anisotropic biaxial type-II superconductor under the action of the microscope's magnetic tip. These equations take into account the driving force generated by the tip, the elastic force caused by the vortex deformation, and the pinning force exerted by point defects. Using these equations, we reproduce the main features of the experimental data obtained by Auslaender et al.

cond-mat.supr-con↗
arXiv2009

Transport Properties of Vortex Matter Governed by the Edge Inductance of Superconducting Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ Single Crystals

We study the distribution of transport current across superconducting Bi$_2$Sr$_2$CaCu$_2$O$_8$ crystals and the vortex flow through the sample edges. We show that the $T_x$ transition is of electrodynamic rather than thermodynamic nature, below which vortex dynamics is governed by the edge inductance instead of the resistance. This allows measurement of the resistance down to two orders of magnitude below the transport noise. By irradiating the current contacts the resistive step at vortex melting is shown to be due to loss of c-axis correlations rather than breakdown of quasi-long-range order within the a-b planes.

cond-mat.supr-con↗
arXiv2007

Electron energy spectrum and the Berry phase in graphite bilayer

We emphasize that there exist four Dirac-type points in the electron-energy spectrum of a graphite bilayer near the point K of its Brillouin zone. One of the Dirac points is at the point K, and three Dirac points lie nearby. Each of these three points generates the Berry phase $π$, while the Dirac point at K gives the phase $-π$. It is these four points that determine the Berry phase in the bilayer. If an electron orbit surrounds all these points, the Berry phase is equal to $2π$.

cond-mat.mtrl-sci↗
arXiv2007

"Unusual" critical states in type-II superconductors

We give a theoretical description of the general critical states in which the critical currents in type-II superconductors are not perpendicular to the local magnetic induction. Such states frequently occur in real situations, e.g., when the sample shape is not sufficiently symmetric or the direction of the external magnetic field changes in some complex way. Our study is restricted to the states in which flux-line cutting does not occur. The properties of such general critical states can essentially differ from the well-known properties of the usual Bean critical states. To illustrate our approach, we analyze several examples. In particular, we consider the critical states in a slab placed in a uniform perpendicular magnetic field and to which two components of the in-plane magnetic field are then applied successively. We also analyze the critical states in a long thin strip placed in a perpendicular magnetic field which then is tilted towards the axis of the strip.

cond-mat.supr-con↗
arXiv2006

Self field of ac current reveals voltage-current law in type-II superconductors

The distribution of ac magnetic fields in a thin superconducting strip is calculated when an ac current is applied to the sample. The edge barrier of the strip to flux penetration and exit is taken into account. The obtained formulas provide a basis to extract voltage-current characteristics in the bulk and at the edges of superconductors from the measured ac magnetic fields. Based on these results, we explain the spatial and temperature dependences of the profiles of the ac magnetic field measured in a Bi2Sr2CaCu2O8 strip [D.T. Fuchs et al., Nature 91, 373 (1998)].

cond-mat.supr-con↗
arXiv2006

Band-Contact Lines in Electron Energy Spectrum of Graphite

We discuss the known experimental data on the phase of the de Haas -van Alphen oscillations in graphite. These data can be understood if one takes into account that four band-contact lines exist near the HKH edge of the Brillouin zone of graphite.

cond-mat.other↗
arXiv2006

Pinning in nonmagnetic borocarbides

The field dependences of the Labush parameter in nonmagnetic borocarbides are measured by a method that does not require achieving a critical state. The expected values of the critical current are estimated. The values obtained are two order of magnitude greater than the results of "direct" measurements performed on the basis of transport (magnetic) experiments. A giant peak effect, which the collective pinning model describes quantitavely well, is observed in the field dependences of the Labush parameter in Y-based borocarbides.

cond-mat.supr-con↗
arXiv2005

Anisotropic superconducting strip in an oblique magnetic field

The critical state of a thin superconducting strip in an oblique applied magnetic field H_a is analyzed without any restrictions on the dependence of the critical current density j_c on the local magnetic induction {\bf B}. In such a strip, j_c is not constant across the thickness of the sample and differs from J_c/d, where J_c is the critical sheet current. It is shown that in contrast to the case of {\bf B}-independent j_c, the profiles H_z(x) of the magnetic-field component perpendicular to the strip plane generally depend on the in-plane component H_{ax} of the applied magnetic field H_a, and on how H_a is switched on. On the basis of this analysis, we explain how and under what conditions one can extract j_c({\bf B}) from the magnetic-field profiles H_z(x) measured by magneto-optical imaging or by Hall-sensor arrays at the upper surface of the strip.

cond-mat.supr-con↗
arXiv2005

Asymmetry of magnetic-field profiles in superconducting strips

We analyze the magnetic-field profiles H_z(x) at the upper (lower) surface of a superconducting strip in an external magnetic field, with z perpendicular to the plane of the strip and x along its width. The external magnetic field H_a is perpendicular or inclined to the plane of the strip. We show that an asymmetry of the profiles H_z(x) appears in an oblique magnetic field H_a and also in the case when the angular dependence of the critical current density j_c in the superconductor is not symmetric relative to the z axis. The asymmetry of the profiles is related to the difference ΔH_z(x) of the magnetic fields at the upper and lower surfaces of the strip, which we calculate. Measurement of this difference or, equivalently, of the asymmetry of the profiles can be used as a new tool for investigation of flux-line pinning in superconductors.

cond-mat.supr-con↗
arXiv2004

Berry phase and de Haas - van Alphen effect in LaRhIn$_5$

We explain the experimental data on the magnetization of $LaRhIn_5$ recently published by R. G. Goodrich et al. in Phys. Rev.Lett. {\bf 89}, 026401 (2002). We show that the magnetization of a small electron group associated with a band-contact line was detected in that paper. These data provide the first observation of the Berry phase of electrons in metals via the de Haas - van Alphen effect.

cond-mat.mtrl-sci↗
arXiv2004

Superconducting strip in an oblique magnetic field

As an example for a seemingly simple but actually intricate problem, the Bean critical state is studied in a superconducting strip of finite thickness d and width 2w >> d placed in an oblique magnetic field. The analytical solution is obtained to leading order in the small parameter d/w. The critical state depends on how the applied magnetic field is switched on, e.g., at constant tilt angle, or first the perpendicular and then the parallel field component. For these two basic scenarios the distributions of current density and magnetic field are obtained in the critical states. In particular, we find the shapes of the flux-free core and of the lines separating regions with opposite direction of the critical currents, the detailed magnetic field lines (along the vortex lines), and both components of the magnetic moment. The component of the magnetic moment parallel to the strip plane is a nonmonotonic function of the applied magnetic field.

cond-mat.supr-con↗
arXiv2003

Effect of pinning on the vortex-lattice melting line in type-II superconductors

The vortex-lattice melting line in three-dimensional type-II superconductors with pinning is derived by equating the free energies of the vortex system in the solid and liquid phases. We account for the elastic and pinning energies and the entropy change that originates from the disappearance of the phonon shear modes in the liquid. The pinning is assumed to be caused by point defects and to be not too strong so that the melting line lies inside the so-called bundle-pinning region. We show that the derived equation for the melting line is equivalent to some Lindemann criterion, which however differs from that used previously. Estimating the effect of pinning on the entropy jump at melting, we find the upper critical point of the melting line from the condition that this jump vanishes. We also consider the H-T phase diagrams of type-II superconductors for different strengths and types of pinning and analyze the two recently discussed scenarios how the melting line and the order--disorder line merge.

cond-mat.supr-con↗