D. Yu. Ivanov

Vector meson electroproduction at next-to-leading order

The process of light neutral vector meson electroproduction is studied in the framework of QCD factorization in which the amplitude factorizes in a convolution of the nonperturbative meson distribution amplitude and generalized parton densities with perturbatively calculable hard-scattering amplitudes. We derive a complete set of hard-scattering amplitudes at next-to-leading order (NLO) for the production of vector mesons, V=ρ0, ω, ϕ.

PHOTON-REGGEON INTERACTION VERTICES IN THE NLA

We calculate the effective vertices for the quark-antiquark and the quark-antiquark-gluon production in the virtual-photon-Reggeized gluon interaction. The last vertex is considered at the Born level; for the first one the one-loop corrections are obtained. These vertices have a number of applications; in particular, they are necessary for calculation of the virtual photon impact factor in the next-to-leading logarithmic approximation.

Orbital quantization in a system of edge Dirac fermions in nanoperforated graphene

The dependence of the electric resistance R of nanoperforated graphene samples on the position of the Fermi level EF, which is varied by the gate voltage Vg, has been studied. Nanoperforation has been performed by irradiating graphene samples on a Si/SiO2 substrate by heavy (xenon) or light (helium) ions. A series of regular peaks have been revealed on the R(Vg) dependence at low temperatures in zero magnetic field. These peaks are attributed to the passage of EF through an equidistant set of levels formed by orbitally quantized states of edge Dirac fermions rotating around each nanohole. The results are in agreement with the theory of edge states for massless Dirac fermions.

Nonlinear electron transport in normally pinched-off quantum wire

Nonlinear electron transport in normally pinched-off quantum wires was studied. The wires were fabricated from AlGaAs/GaAs heterostructures with high-mobility two-dimensional electron gas by electron beam lithography and following wet etching. At certain critical source-drain voltage the samples exhibited a step rise of the conductance. The differential conductance of the open wires was noticeably lower than e2/h as far as only part of the source-drain voltage dropped between source contact and saddle point of the potential relief along the wire. The latter limited the electron flow injected to the wire. At high enough source-drain voltages the decrease of the differential conductance due to the real space transfer of electrons from the wire in GaAs to the doped AlGaAs layer was found. In this regime the sign of the differential magnetoconductance was changed with reversing the direction of the current in the wire or the magnetic field, when the magnetic field lies in the heterostructure plane and is directed perpendicular to the current. The dependence of the differential conductance on the magnetic field and its direction indicated that the real space transfer events were mainly mediated by the interface scattering.

Probing the electronic properties of disordered two-dimensional systems by means of resonant tunnelling

We investigate resonant tunnelling in GaAs/(AlGa)As double-barrier resonant-tunnelling diodes in which a single layer of InAs self-assembled quantum dots is embedded in the centre of the GaAs quantum well. The dots provide a well-defined and controllable source of disorder in the well and we use resonant tunnelling to study the effect of this disorder on the electronic properties of the well.

Conductance anomalies in gated V-groove quantum wires

We present transconductance measurements on gated V-groove GaAs/AlGaAs quantum wire heterostructures grown by metal-organic chemical vapour deposition. The results show anomalously large negative magnetoresistance for a magnetic field perpendicular to the current, and oscillations in conductance with the field oriented along the width of the wire. Clear steps in conductance versus gate voltage are also observed and these are consistent with the charging of a nearby `droplet with each step corresponding to a change in the occupation of a single electron.

Conductivity and persistent photoconductivity in GaAs epitaxial films containing single and double delta-doped layers

Electrophysical parameters of single and double delta-doped layers in GaAs epitaxial films grown by the metal-organic chemical vapor deposition have been systematically investigated in the temperature range of 4.2 to 300 K. The 2D electron gas density distribution is affected by the overlap of wave functions in neighboring quantum wells, as a result of which the peak on the curve of the Hall mobility in the 2D electron gas versus the separation between the quantum wells shifts. The persistent photoconductivity in delta-doped layers is due to the change in the surface potential caused by the neutralization of the negative charge of surface states by photoexcited holes. A method for comparing delta-doped layers grown under different conditions at different depths from the sample surface has been suggested.

Magnetic field induced linear Coulomb gap in tunnelling between disordered two-dimensional electron systems

We have investigated equilibrium tunnelling between disordered two-dimensional electron systems at temperatures below 0:3 K over a wide range of magneticeld, B, applied perpendicular to the electron layers. In zeroeld, we observe a narrow conductance peak of about 1 mV width at zero bias. As B is increased, this is transformed into a narrow linear gap in the tunnel spectrum. The existence of the linear gap is discussed in terms of many-electron interaction e7ects. ? 2002 Elsevier Science B.V. All rights reserved. PACS: 73.20.Dx; 73.40.Gk; 72.15.Rn

Tunnel gaps in the two-dimensional electron system in a magnetic field

We have studied the near-equilibrium tunnelling between identical two-dimensional electron systems at 0.3 K over a wide range of magnetic field applied normal to the electron layers. The magnetic field suppresses the electron tunnelling. Our results are consistent with the co-existence of two types of tunneling gap. Moreover, at ν < 2 additional features arise in the tunneling spectra, which we interpret in terms of the emission of some as yet unidentified quasiparticle.

Magneto-tunnelling spectroscopy of the electron states in the quantum well with embedded self assembled quantum dots: studies in magnetic field up to 28 T

We have studied magneto-oscillations of the tunnelling current through a quantum well (QW) incorporating InAs self-assembled quantum dots in magnetic fields up to 28 T applied normal to the QW plane. We find evidence for the strong modification of the Landau levels in the host GaAs quantum well in the presence of dots embedded at the center of the well, which we attribute to electron-electron interactions.