105 research outputs found
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.Comment: 5 pages, 2 fifures. To appear in Physical Review B (B15
Berry phase and de Haas - van Alphen effect in LaRhIn
We explain the experimental data on the magnetization of 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.Comment: 4 pages, 2 figure
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 , while the Dirac point at K
gives the phase . 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 .Comment: 4 pages, 2 figures, submitted to Phys. Rev. B ; expande
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.Comment: 7 pages with 4 figure
Critical state in type-II superconductors of arbitrary shape
The well-known Bean critical state equations in general are not sufficient to
describe the critical state of type-II superconductors when the sample shape is
not symmetric. We show how one can find the critical state in superconductors
of arbitrary shape. Analyzing a simple example of nonsymmetry, we demonstrate
that in the general case, a perturbation of the current distribution in the
critical state propagates into the sample smoothly in a diffusive way. This is
in contrast to the usual Bean critical state where the current distribution
changes abruptly at a narrow front.Comment: 4 pages, 1 figure, appears in Phys. Rev. B 71, issue 1 (2005
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.Comment: 11 pages, 13 figure
- …