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Kyriienko O.,University of Iceland | Shelykh I.A.,University of Iceland | Shelykh I.A.,International Institute of Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We consider effective interactions in a two-dimensional (2D) hybrid polariton-electron system and calculate dispersion of elementary excitations by accounting for the spin degrees of freedom of the particles. Due to the crucial role played by the exchange term in polariton-electron interactions the dispersions of this system become spin dependent and show unusual behavior. The coupling of the excitations of the condensate with 2D plasmons can result in the appearance of roton minimum in the dispersion and destruction of the condensate for close enough situated quantum wells with electrons and excitons. © 2011 American Physical Society. Source


Downing C.A.,University of Exeter | Stone D.A.,University of Exeter | Portnoi M.E.,University of Exeter | Portnoi M.E.,International Institute of Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We present exact analytical zero-energy solutions for a class of smooth-decaying potentials, showing that the full confinement of charge carriers in electrostatic potentials in graphene quantum dots and rings is indeed possible without recourse to magnetic fields. These exact solutions allow us to draw conclusions on the general requirements for the potential to support fully confined states, including a critical value of the potential strength and spatial extent. © 2011 American Physical Society. Source


Hartmann R.R.,University of Exeter | Shelykh I.A.,University of Iceland | Portnoi M.E.,University of Exeter | Portnoi M.E.,International Institute of Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We calculate the exciton binding energy in single-walled carbon nanotubes with narrow band gaps, accounting for the quasirelativistic dispersion of electrons and holes. Exact analytical solutions of the quantum relativistic two-body problem are obtained for several limiting cases. We show that the binding energy scales with the band gap, and conclude on the basis of the data available for semiconductor nanotubes that there is no transition to an excitonic insulator in quasimetallic nanotubes and that their THz applications are feasible. © 2011 American Physical Society. Source


Stone D.A.,University of Exeter | Downing C.A.,University of Exeter | Portnoi M.E.,International Institute of Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Using the variable phase method, we reformulate the Dirac equation governing the charge carriers in graphene into a nonlinear first-order differential equation from which we can treat both confined-state problems in electron waveguides and above-barrier scattering problems for arbitrary-shaped potential barriers and wells, decaying at large distances. We show that this method agrees with a known analytic result for a hyperbolic secant potential and go on to investigate the nature of more experimentally realizable electron waveguides, showing that when the Fermi energy is set at the Dirac point, truly confined states are supported in pristine graphene. In contrast to exponentially decaying potentials, we discover that the threshold potential strength at which the first confined state appears is vanishingly small for potentials decaying at large distances as a power law; but nonetheless, further confined states are formed when the strength and spread of the potential reach a certain threshold. © 2012 American Physical Society. Source


Alexeev A.M.,University of Exeter | Portnoi M.E.,University of Exeter | Portnoi M.E.,International Institute of Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Magneto-oscillations of the electric dipole moment are predicted and analyzed for a single-electron nanoscale ring pierced by a magnetic flux (an Aharonov-Bohm ring) and subjected to an electric field in the ring's plane. These oscillations are accompanied by periodic changes in the selection rules for interlevel optical transitions in the ring allowing control of polarization properties of the associated terahertz radiation. © 2012 American Physical Society. Source

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