435 research outputs found
Electronic spectrum and tunnelling properties of multi-wall carbon nanotubes
We develop a general approach to calculations of the electron spectrum of
metallic multi-wall carbon nanotubes (MWNT) with arbitrary number of coaxial
layers. It is based on the model with singular attractive potential of
equidistant conductive cylinders. The knowledge of one-electron spectrum allows
to construct the corresponding Green function and then to calculate the entropy
and density of states for MWNT. We analyze the tunnelling between the nanotube
and normal metal electrode. The possibility of direct determination of
one-electron density of states by measurements of the tunnelling conductivity
at low temperatures is proved and the necessary restrictions on temperature are
formulated. We discuss briefly the conflicting experimental observations of
electronic properties of MWNT.Comment: 14 pages, 1 figur
Absence of singular superconducting fluctuation corrections to thermal conductivity
We evaluate the superconducting fluctuation corrections to thermal
conductivity in the normal state which diverge as T approaches T_c. We find
zero total contribution for one, two and three-dimensional superconductors for
arbitrary impurity concentration. The method used is diagrammatic many-body
theory, and all contributions -- Aslamazov-Larkin (AL), Maki-Thompson (MT), and
density-of-states (DOS) -- are considered. The AL contribution is convergent,
whilst the divergences of the DOS and MT diagrams exactly cancel.Comment: 4 pages text; 2 figure
The Ferromagnetism in the Vicinity of Lifshitz Topological Transitions
We show that the critical temperature of a ferromagnetic phase transition in
a quasi-two-dimensional hole gas confined in a diluted magnetic semiconductor
quantum well strongly depends on the hole chemical potential and hole density.
The significant variations of the the Curie temperature occur close to the
Lifshitz topological transition points where the hole Fermi surface acquires
additional components of topological connectivity due to the filling of excited
size-quantization subbands. The model calculations demonstrate that the Curie
temperature can be doubled by a small variation of the gate voltage for the
CdMnTe/CdMgTe quantum well based device
Entropy per particle spikes in the transition metal dichalcogenides
We derive a general expression for the entropy per particle as a function of
chemical potential, temperature and gap magnitude for the single layer
transition metal dichalcogenides. The electronic excitations in these materials
can be approximately regarded as two species of the massive or gapped Dirac
fermions. Inside the smaller gap there is a region with zero density of states
where the dependence of the entropy per particle on the chemical potential
exhibits a huge dip-and-peak structure. The edge of the larger gap is
accompanied by the discontinuity of the density of states that results in the
peak in the dependence of the entropy per particle on the chemical potential.
The specificity of the transition metal dichalcogenides makes possible the
observation of these features at rather high temperatures order of 100 K. The
influence of the uniaxial strain on the entropy per particle is discussed.Comment: 6 pages, 4 figures; Special Issue to the 90th birthday of A.A.
Abrikoso
Spherical functions on the de Sitter group
Matrix elements and spherical functions of irreducible representations of the
de Sitter group are studied on the various homogeneous spaces of this group. It
is shown that a universal covering of the de Sitter group gives rise to
quaternion Euler angles. An explicit form of Casimir and Laplace-Beltrami
operators on the homogeneous spaces is given. Different expressions of the
matrix elements and spherical functions are given in terms of multiple
hypergeometric functions both for finite-dimensional and unitary
representations of the principal series of the de Sitter group.Comment: 40 page
Gaussian superconducting fluctuations, thermal transport, and the Nernst effect
We calculate the contribution of superconducting fluctuations to thermal
transport in the normal state, for low magnetic fields. We do so in the
Gaussian approximation to their critical dynamics which is also the
Aslamazov-Larkin approximation in the microscopics. Our results for the thermal
conductivity tensor and the transverse thermoelectric response are new. The
latter compare favorably with the data of Ong and collaborators on the Nernst
effect in the cuprates.Comment: 4 pages, 1 figure; improved introduction, minor changes; published
versio
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