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S. S. Z. Ashraf

Publications and source records attributed to S. S. Z. Ashraf.

3 recordsLinked to original sources

Derivation of the deformed Heisenberg algebra from discrete spacetime

Although the deformation of the Heisenberg algebra by a minimal length has become a central tool in quantum gravity phenomenology, it has never been rigorously obtained and is often derived using heuristic reasoning. In this study, we move beyond the heuristic derivation of the deformed Heisenberg algebra and explicitly derive it using a model of discrete spacetime, which is motivated by quantum gravity. Initially, we investigate the effects of the leading order Planckian lattice corrections and demonstrate that they precisely match those suggested by the heuristic arguments commonly used in quantum gravity phenomenology. Furthermore, we rigorously obtain deformations from the higher-order Planckian lattice corrections. In contrast to the leading-order corrections, these higher-order corrections are model dependent. We select a specific model that breaks the rotational symmetry, as the importance of such rotational symmetry breaking lies in the relationship between CMB anisotropies and quantum gravitational effects. Based on the mathematical similarity of the Planckian lattice used here with the graphene lattice, we propose that graphene can serve as an analogue system for the study of quantum gravity. Finally, we examine the deformation of the covariant form of the Heisenberg algebra using a four-dimensional Euclidean lattice.

gr-qc↗

Acoustoelectric current in graphene due to electron deformation potential and piezoelectric phonon couplings

Recent studies strongly indicate that graphene can be used as a channel material for converting surface acoustic waves to acoustoelectric current, which is a resource for various exciting technological applications. On the theoretical side, studies on phonon amplification/attenuation and acoustoelectric current at low temperatures in graphene have reported approximate analytical results under exceedingly simplifying conditions using the Boltzmann transport equation. Overcoming the earlier simplifying assumptions, we investigate both numerically and analytically the governing kinetic equations for amplification/attenuation and acoustoelectric current, taking into account the piezoelectric and deformation potential electron phonon coupling mechanism in the semi classical Boltzmann transport formalism approach, and obtain analytical results that are in reasonable agreement with the reported experimental results.

cond-mat.mes-hall↗

Inelastic scattering and cooling of photoexcited electrons through coupling with acoustic, optic and surface polar optic phonons in graphene

The acoustic, optic, and surface polar optic phonons are the three important intrinsic and extrinsic phononic modes that increasingly populate graphene on a substrate with rising temperatures; the coupling of which with photoexcited hot carriers in the equipartition regime provides significant pathways for electron-phonon relaxation. In this paper, we theoretically investigate the relative significance of the three phononic modes in electron scattering and cooling phenomena in single layer graphene, including their comparison with supercollision driven power loss, and obtain analytical formulae on the energy dependence of electron-phonon scattering rate and cooling power in the Boltzmann transport formalism. The obtained analytical solutions not only closely reproduce the results for scattering rate and cooling power, as that obtained from the earlier reported numerically tractable integral forms, but also enable us to derive closed-form formulae of the cooling time and thermal conductance. The important role of Pauli blocking that prevents transition to filled energy states has also been elucidated in the estimation of the scattering rate and cooling power density for all the three modes. The obtained formulae provide a better insight into the dynamics of hot electron phenomena giving an explicit view on the interplay of the different variables that affect the transport quantities under investigation. The formulae can also be potentially useful for performance optimization of transport quantities in numerical optimization methods since the first and second-order derivatives are easily deducible from these formulae.

cond-mat.mes-hall↗