Institut für Theoretische Physik III

Allgemeine Beschreibung des Teilprojekts

Projekt: Photon-assisted quantum coherent phenomena in graphene n-p and n-p-n junctions:
Quantum transport in graphene based arrays of nanocrystals
Prof. K. Efetov
Theoretische Physik III

Ruhr-Universität Bochum
Universitätstrasse 150
44780 Bochum

Tel.: (02 34) 32 - 2 37 37
Fax: (02 34) 32 - 1 44 48

This project is aimed on a detailed theoretical study of quantum-mechanical effects in the charge transport of graphene based diverse micro- and nanostructures.
Setup A key point of our proposal is to explore a possibility of photon-assisted quantum interference effects in lateral n-p and n-p-n junctions formed in monolayer and bilayer graphene, graphene nanoribbons, exposed to an externally applied electromagnetic field (EF) [1-3] (see Fig. 1).
These quantum interference effects result from the combination of two graphene properties: a gapless two bands spectrum of quasiparticles in the graphene and a local resonant interaction of quasiparticles with EF allowing to re-distribute particles between bands. The quantum interference effects manifest themselves, e.g., by large oscillations in the dependence of dc current on the gate voltage (see Fig. 2) [3].
These oscillations present a particular realization of the Ramsey quantum beating ("Ramsey fringes") or Stueckelberg oscillations well known in atomic physics.

We will focus also on the quantum phenomena in the transport of graphene based arrays of nanocrystals, i.e. the arrays of quantum dots incorporated in graphene nanoribbons, graphene nanoflakes embedded into an insulator/metal matrix.
Figure 3 The quantum effects in such systems are due to interplay of the specific electron spectrum of graphene, quantum-mechanical tunneling between nanocrystals, quantum fluctuations, Coulomb interactions, and disorder [4-5]. The electronic transport in such systems can vary from the insulator behavior to a good metal one (see Fig. 3). We will theoretically study temperature dependencies of the conductivity close to the metal-insulator transition and the co-tunneling regime of linear and nonlinear electronic transport, the gate voltage influence on the transport.

The obtained results can be important for the field of Quantum information processing in graphene based nanostructures.

1. M. V. Fistul and K. B. Efetov, "Electromagnetic-Field-Induced Suppression of Transport through n-p Junctions in Graphene", Phys. Rev. Lett. 98, 256803 (2007).

2. S. V. Syzranov, M. V. Fistul, and K. B. Efetov, "Effect of radiation on transport in graphene", Phys. Rev. B 78, 045407 (2008).

3. M. V. Fistul, S. V. Syzranov, A. M. Kadigrobov, and K. B. Efetov, “Radiation-induced quantum interference in low-dimensional n-p junctions”, Phys. Rev. B, 78, 045407 (2008).

4. I. S. Beloborodov, A. V. Lopatin, V. M. Vinokur, and K. B. Efetov, “ Granular electronic systems “, Rev. Mod. Phys. 79, 469 (2007).

5. I. L. Aleiner and K. B. Efetov, “ Effect of Disorder on Transport in Graphene” , Phys. Rev. Lett. 97, 236801 (2006)