Zener transitions between dissipative Bloch bands. II: Current Response at Finite Temperature

We extend, to include the effects of finite temperature, our earlier study of the interband dynamics of electrons with Markoffian dephasing under the influence of uniform static electric fields. We use a simple two-band tight-binding model and study the electric current response as a function of field strength and the model parameters. In addition to the Esaki-Tsu peak, near where the Bloch frequency equals the damping rate, we find current peaks near the Zener resonances, at equally spaced values of the inverse electric field. These become more prominenent and numerous with increasing bandwidth (in units of the temperature, with other parameters fixed). As expected, they broaden with increasing damping (dephasing).Comment: 5 pages, LateX, plus 5 postscript figure

Newton's law for Bloch electrons, Klein factors and deviations from canonical commutation relations

The acceleration theorem for Bloch electrons in a homogenous external field is usually presented using quasiclassical arguments. In quantum mechanical versions the Heisenberg equations of motion for an operator $\hat {\vec k}(t)$ are presented mostly without properly defining this operator. This leads to the surprising fact that the generally accepted version of the theorem is incorrect for the most natural definition of $\hat {\vec k}$. This operator is shown not to obey canonical commutation relations with the position operator. A similar result is shown for the phase operators defined via the Klein factors which take care of the change of particle number in the bosonization of the field operator in the description of interacting fermions in one dimension. The phase operators are also shown not to obey canonical commutation relations with the corresponding particle number operators. Implications of this fact are discussed for Tomonaga-Luttinger type models.Comment: 9 pages,1 figur

Landau-Zener transitions in a linear chain

We present an exact asymptotic solution for electron transition amplitudes in an infinite linear chain driven by an external homogeneous time-dependent electric field. This solution extends the Landau-Zener theory for the case of infinite number of states in discrete spectrum. In addition to transition amplitudes we calculate an effective diffusion constant.Comment: 3 figure

Nuclear spin-lattice relaxation in ferrimagnetic clusters and chains: A contrast between zero and one dimensions

Motivated by ferrimagnetic oligonuclear and chain compounds synthesized by Caneschi et al., both of which consist of alternating manganese(II) ions and nitronyl-nitroxide radicals, we calculate the nuclear spin-lattice relaxation rate 1/T_1 employing a recently developed modified spin-wave theory. 1/T_1 as a function of temperature drastically varies with the location of probe nuclei in both clusters and chains, though the relaxation time scale is much larger in zero dimension than in one dimension. 1/T_1 as a function of an applied field in long chains forms a striking contrast to that in finite clusters, diverging with decreasing field like inverse square root at low temperatures and logarithmically at high temperatures.Comment: to be published in Phys. Rev. B 68 August 01 (2003

Localized time-dependent perturbations in metals : formalism and simple examples

Methods introduced by Keldysh to treat non-equilibrium problems are applied to strong, localized time-dependent perturbations in metals. After having introduced the formalism, we treat simple examples which are linked to the dynamics of atoms near surfaces : ionization probabilities of atoms leaving a metallic surface and friction coefficients of atoms near a metallic surface.La méthode introduite par Keldysh pour traiter les problèmes hors d'équilibre est appliquée au cas de fortes perturbationes, localisées, dépendant du temps, dans les métaux. Après avoir introduit le formalisme, nous traitons quelques exemples simples qui sont liés à la dynamique des atomes près des surfaces : probabilités d'ionisation d'atomes quittant une surface métallique, coefficients de frottement d'atomes au voisinage d'une surface métallique

``Pseudo-Casimir'' effect in liquid crystals

URL: http://www-spht.cea.fr/articles/T92/010International audienc

Carbon nanotubes as heat dissipaters in microelectronics

We review our recent modelling work of carbon nanotubes as potential candidates for heat dissipation in microelectronics cooling. In the first part, we analyze the impact of nanotube defects on their thermal transport properties. In the second part, we investigate the loss of thermal properties of nanotubes in presence of an interface with various substances, including air and water. Comparison with previous works is established whenever is possible.Comment: 14 pages, 21 figures, 5 table