Debendranath Sahoo

Aharonov-Bohm oscillations and spin-polarized transport in a mesoscopic ring with a magnetic impurity

We present a detailed analysis of Aharonov-Bohm (AB) interference oscillations manifested through transmission of an electron in a mesoscopic ring with a magnetic impurity atom inserted in one of its arms. Spin-polarized transport is also studied. The electron interacts with the impurity through exchange interaction, leading to spin-flip scattering. Transmission in the spin-flipped and -unflipped channels are explicitly calculated. We show that entanglement between electron and spin-flipper states leads to reduction of AB oscillations in spite of the absence of any inelastic scattering. The spin conductance (related to spin-polarized transmission coefficient) is asymmetric under flux reversal, as opposed to the two-probe conductance, which is symmetric. We point out certain limitations of this model in regard to the general notion of dephasing in quantum mechanics.

Gauge theory of defects in the elastic continuum

A gauge theory of defects in an elastic continuum is developed after providing the necessary background in continuum elasticity and gauge theories. The gauge group is the three-dimensional (3D) Euclidean group [semi-direct product of the translation group T (3) with the rotation group SO (3)]. We obtainboth dislocations and disclinations by breaking of the translational invariance. Breaking of the rotational invariance is shownnot to lead to any interesting effects in a linear analysis. These results are shown to be consistent with the topological analysis which is briefly discussed at the end of the paper. Any defect given by the present theory acquires acore which removes the singularity of the stress field at the origin. The stress field agrees with the continuum result asymptotically, as is expected. Geometrical aspects of the deformed state of condensed matter are also briefly touched upon.

Mixing quantum and classical mechanics and uniqueness of Planck's constant

Observables of quantum or classical mechanics form algebras called quantum or classical Hamilton algebras (HAs), respectively (Grgin and Petersen 1974 J. Math. Phys. 15 764, Sahoo 1977 Pramana 8 545). We show that the tensor product of two quantum HAs, each characterized by a different Plancks constant (PC), is an algebra of the same type characterized by yet another PC. The algebraic structure of mixed quantum and classical systems is then analysed by taking the limit of vanishing PC in one of the component algebras. This approach provides new insight into failures of various formalisms dealing with mixed quantum?classical systems. It shows that in the interacting mixed quantum?classical description, there can be no back-reaction of the quantum system on the classical system. A natural algebraic requirement involving restriction of the tensor product of two quantum HAs to their components proves that PC is unique.

ROLE OF QUANTUM ENTANGLEMENT DUE TO A MAGNETIC IMPURITY ON CURRENT MAGNIFICATION EFFECT IN MESOSCOPIC OPEN RINGS

We study the current magnification effect in presence of exchange scattering of electron from a magnetic impurity placed in one arm of an open mesoscopic ring. The exchange interaction causes entanglement of electron spin and impurity spin. Earlier studies have shown that such an entanglement causes reduction or loss of interference in the Aharonov–Bohm oscillations leading to decoherence. We find however, that this entanglement, in contradiction to the naive expectation of a reduction in current magnification leads to enhancement as well as suppression of the effect. We also observe additional novel features like new resonances and current reversals.

Modeling of stochastic absorption in a random medium

We report a detailed and systematic study of wave propagation through a stochastic absorbing random medium. Stochastic absorption is modeled by introducing an attenuation constant per unit length

Algebraic structure of Nambu mechanics

\ensuremath{\alpha}

Force between two parallel screw dislocations — gauge theory result

in the free propagation region of the one-dimensional disordered chain of delta-function scatterers. The average value of the logarithm of transmission coefficient decreases linearly with the length of the sample. The localization length is given by

Elastic continuum theories of lattice defects: a review

\ensuremath{\xi}={\ensuremath{\xi}}_{w}{\ensuremath{\xi}}_{\ensuremath{\alpha}}/({\ensuremath{\xi}}_{w}+{\ensuremath{\xi}}_{\ensuremath{\alpha}}),

Light scattering from a fluid in a nonequilibrium steady state: plane Couette flow

where

Tensor product composition of algebras in Bose and Fermi canonical formalism

{\ensuremath{\xi}}_{w}