H. Pastawski | Universidad Nacional de Córdoba (original) (raw)

Papers by H. Pastawski

We show that due to interference effects quantum diffusion near a surface occurs more rapidly tha... more We show that due to interference effects quantum diffusion near a surface occurs more rapidly that in bulk. We discuss possible observation on exciton dynamics and progation of spin excitations in linear chains.

Here, we extend the fomalization in term of Keldysh-Kadanoff-Baym formulation of the Quantum Fiel... more Here, we extend the fomalization in term of Keldysh-Kadanoff-Baym formulation of the Quantum Fields Theory applied to electronic transport. Following the previous paper we show that time dependent transport follows from this form of D'Amato-Pastawski model. Time dependences for tunneling through barriers and resonant tunneling follow in this formalism as a for of Wigner delay times and can be represented as an effective impedance or delay. We prove the effect of decoherence processes on a.c. response.

We show that low dimensionality of asymmetric complexes is enhanced by Quantum Zeno Effect, as a ... more We show that low dimensionality of asymmetric complexes is enhanced by Quantum Zeno Effect, as a stronger interaction in one direction quenches diffusion in the other. This serve to explain the present experiments where small molecular asymmetries induce strong dimensional crossover of spin diffusion from 2d to 1d like.

We show that the D'Amato-Pastawski model, which conserves probability in presence of inelastic an... more We show that the D'Amato-Pastawski model, which conserves probability in presence of inelastic and decoherent processes provides the natural frame to solve a Keldysh-Kadanoff-Baym quantum fields theory by possing in the form a linearized set of equations that we solve analytically in a number of cases. Those extend from the non-Ohmic, purely quantum, regime dominated by interferences to smooth classical transport of the Ohm's Law.

Using a model well fitted to describe electron transfer between a donor and an acceptor bridged t... more Using a model well fitted to describe electron transfer between a donor and an acceptor bridged through an intermediary molecule or conductance in a multiply connected system we show how the Hamiltonian can be decimated it a two centre problem. We discuss the appearance of antiresonaces or destructive interferences among different bridging pathways.

We present an interpretation of the periodicity in the magnetoresistance in terms of the flux dep... more We present an interpretation of the periodicity in the magnetoresistance in terms of the flux dependence of the position of the antiresonces, which being an interference phenomena that depends of the flux is responsible for the change of the conductance. This is one of the first appearances of the concept of antiresonance (a form of Fano resonance) in transport properties.

This is the D'Amato-Pastawski model where inelastic and decoherence processes are incorporated in... more This is the D'Amato-Pastawski model where inelastic and decoherence processes are incorporated in a Hamiltonian description through the Fermi Golden Rule mean life they produce in charge conserving description which is a generalization of the Büttiker's voltage probe model. Thus, the drawback that would result from a non-Hermitian Hamiltonian is fully solved.

A calculation of the b4 and b6 crystal field parameters for Dy 3+ impurities in Cu is presented w... more A calculation of the b4 and b6 crystal field parameters for Dy 3+ impurities in Cu is presented within a rigid band model scheme. In our model the "crystal field" results from the direct and exchange contribution due to the Coulomb interaction of the 4f electrons with those in the band states. These states are obtained with the augmented plane wave method, which are assumed to penetrate the ion. The contributions to b4 and b6 obtained at different k-points within the Brillouin zone
are examined and we find that for almost all band states the exchange contribution dominates the direct one. We obtain crystal field parameters with the right sign and order of magnitude, which result from a balance between the fully occupied bands of d character and the half occupied s band.

We show that half-flux oscillations arise from an oscillations of the energy spectrum of cylinder... more We show that half-flux oscillations arise from an oscillations of the energy spectrum of cylinders which for certain half-flux show a tendency to degeneration.

Because of separation of variables the electronic structure of hypercubes have a well defined nes... more Because of separation of variables the electronic structure of hypercubes have a well defined nesting structure. This is used to show that the Polish Fractal Dimension obtained from the bandwidth is natural way to characterize how well the hypercube fill the hyperspace.

The decay of the ensemble averaged Green's function in a disordered system gives the phase cohere... more The decay of the ensemble averaged Green's function in a disordered system gives the phase coherence length or mean-free-path, not the localization length. This last is obtained from decay with length of the average of the square modulus.

We introduce the Polish Fractal Dimension to characterize the electronic bands and hence the gap ... more We introduce the Polish Fractal Dimension to characterize the electronic bands and hence the gap of an amorphous semiconductor.

A concise method is developed to show the following in one dimension: (a) If there is a sharp met... more A concise method is developed to show the following in one dimension: (a) If there is a sharp metal-inmhtor transition in an ideal sinusoidal incommensurate structure then W/V = 2. Co) There is an infinite dc conductivity of electrons in an ideal incommensurate structure for T = 0 if W/V < 2. (c) Addition of impurities which scatter between all pairs of k values may lead to a finite conductivity for W/V < 2. (It tends to zero as L-* =). The concept of duality used by Aubry is then extended to the general problem of localization and the breakdown of extended states is illustrated.

We show that due to interference effects quantum diffusion near a surface occurs more rapidly tha... more We show that due to interference effects quantum diffusion near a surface occurs more rapidly that in bulk. We discuss possible observation on exciton dynamics and progation of spin excitations in linear chains.

Here, we extend the fomalization in term of Keldysh-Kadanoff-Baym formulation of the Quantum Fiel... more Here, we extend the fomalization in term of Keldysh-Kadanoff-Baym formulation of the Quantum Fields Theory applied to electronic transport. Following the previous paper we show that time dependent transport follows from this form of D'Amato-Pastawski model. Time dependences for tunneling through barriers and resonant tunneling follow in this formalism as a for of Wigner delay times and can be represented as an effective impedance or delay. We prove the effect of decoherence processes on a.c. response.

We show that low dimensionality of asymmetric complexes is enhanced by Quantum Zeno Effect, as a ... more We show that low dimensionality of asymmetric complexes is enhanced by Quantum Zeno Effect, as a stronger interaction in one direction quenches diffusion in the other. This serve to explain the present experiments where small molecular asymmetries induce strong dimensional crossover of spin diffusion from 2d to 1d like.

We show that the D'Amato-Pastawski model, which conserves probability in presence of inelastic an... more We show that the D'Amato-Pastawski model, which conserves probability in presence of inelastic and decoherent processes provides the natural frame to solve a Keldysh-Kadanoff-Baym quantum fields theory by possing in the form a linearized set of equations that we solve analytically in a number of cases. Those extend from the non-Ohmic, purely quantum, regime dominated by interferences to smooth classical transport of the Ohm's Law.

Using a model well fitted to describe electron transfer between a donor and an acceptor bridged t... more Using a model well fitted to describe electron transfer between a donor and an acceptor bridged through an intermediary molecule or conductance in a multiply connected system we show how the Hamiltonian can be decimated it a two centre problem. We discuss the appearance of antiresonaces or destructive interferences among different bridging pathways.

We present an interpretation of the periodicity in the magnetoresistance in terms of the flux dep... more We present an interpretation of the periodicity in the magnetoresistance in terms of the flux dependence of the position of the antiresonces, which being an interference phenomena that depends of the flux is responsible for the change of the conductance. This is one of the first appearances of the concept of antiresonance (a form of Fano resonance) in transport properties.

This is the D'Amato-Pastawski model where inelastic and decoherence processes are incorporated in... more This is the D'Amato-Pastawski model where inelastic and decoherence processes are incorporated in a Hamiltonian description through the Fermi Golden Rule mean life they produce in charge conserving description which is a generalization of the Büttiker's voltage probe model. Thus, the drawback that would result from a non-Hermitian Hamiltonian is fully solved.

A calculation of the b4 and b6 crystal field parameters for Dy 3+ impurities in Cu is presented w... more A calculation of the b4 and b6 crystal field parameters for Dy 3+ impurities in Cu is presented within a rigid band model scheme. In our model the "crystal field" results from the direct and exchange contribution due to the Coulomb interaction of the 4f electrons with those in the band states. These states are obtained with the augmented plane wave method, which are assumed to penetrate the ion. The contributions to b4 and b6 obtained at different k-points within the Brillouin zone
are examined and we find that for almost all band states the exchange contribution dominates the direct one. We obtain crystal field parameters with the right sign and order of magnitude, which result from a balance between the fully occupied bands of d character and the half occupied s band.

We show that half-flux oscillations arise from an oscillations of the energy spectrum of cylinder... more We show that half-flux oscillations arise from an oscillations of the energy spectrum of cylinders which for certain half-flux show a tendency to degeneration.

Because of separation of variables the electronic structure of hypercubes have a well defined nes... more Because of separation of variables the electronic structure of hypercubes have a well defined nesting structure. This is used to show that the Polish Fractal Dimension obtained from the bandwidth is natural way to characterize how well the hypercube fill the hyperspace.

The decay of the ensemble averaged Green's function in a disordered system gives the phase cohere... more The decay of the ensemble averaged Green's function in a disordered system gives the phase coherence length or mean-free-path, not the localization length. This last is obtained from decay with length of the average of the square modulus.

We introduce the Polish Fractal Dimension to characterize the electronic bands and hence the gap ... more We introduce the Polish Fractal Dimension to characterize the electronic bands and hence the gap of an amorphous semiconductor.

A concise method is developed to show the following in one dimension: (a) If there is a sharp met... more A concise method is developed to show the following in one dimension: (a) If there is a sharp metal-inmhtor transition in an ideal sinusoidal incommensurate structure then W/V = 2. Co) There is an infinite dc conductivity of electrons in an ideal incommensurate structure for T = 0 if W/V < 2. (c) Addition of impurities which scatter between all pairs of k values may lead to a finite conductivity for W/V < 2. (It tends to zero as L-* =). The concept of duality used by Aubry is then extended to the general problem of localization and the breakdown of extended states is illustrated.