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113


Numbers of donors and acceptors from transport measurements in graphene

Novikov, D. S.
A method is suggested to separately determine the surface density of positively and negatively charged impurities that limit the mobility in a graphene monolayer. The method is based on the exact result for the transport cross section, according to which the massless carriers are scattered more strongly when they are attracted to a charged impurity than when they are repelled from it. (c) 2007 American Institute of Physics.
ISI:000249322900023
ISSN: 0003-6951
CID: 3856512

Transverse field effect in graphene ribbons

Novikov, D S
It is shown that a graphene ribbon, a ballistic strip of carbon monolayer, may serve as a quantum wire whose electronic properties can be continuously and reversibly controlled by an externally applied transverse voltage. The electron bands of armchair-edge ribbons undergo dramatic transformations: The Fermi surface fractures, Fermi velocity and effective mass change sign, and excitation gaps are reduced by the transverse field. These effects are manifest in the conductance plateaus, van Hove singularities, thermopower, and activated transport. The control over one-dimensional bands may help enhance effects of electron correlations, and be utilized in device applications.
PMID: 17930776
ISSN: 1079-7114
CID: 3856492

Two-dimensional holes in GaAsHIGFETs: Fabrication methods and transport measurements

Huang, Jian; Novikov, D. S.; Tsui, D. C.; Pfeiffer, L. N.; West, K. W.
We present a fabrication process and results of transport measurements of a number of p-channel heterojunction-insulated-gate field-effect transistors (HIGFETs). Without intentional doping in HIGFETs, the disorder is likely to be less than that in the modulation-doped samples. We established a process that eliminates the well-known gate leakage problem. The hole density in our devices can be continuously tuned down to a record low value of 7 x 10(8) cm(-2). Remarkably, such a dilute system (with Fermi wavelength approaching 1 mu m) exhibits a non-activated conductivity that grows with temperature approximately as a power law at sufficiently low temperatures. We contrast it with the activated transport found in more disordered samples and discuss possible transport mechanisms in this strongly-interacting regime.
ISI:000251988900015
ISSN: 0217-9792
CID: 3856502

Nonactivated transport of strongly interacting two-dimensional holes in GaAs

Huang, Jian; Novikov, D. S.; Tsui, D. C.; Pfeiffer, L. N.; West, K. W.
We report on the transport measurements of two-dimensional holes in GaAs field-effect transistors with record low densities down to 7x10(8) cm(-2). Remarkably, such a dilute system (with Fermi wavelength approaching 1 mu m) exhibits a nonactivated conductivity that grows with temperature approximately as a power law at sufficiently low temperatures. We contrast it with the activated transport found in more disordered samples and discuss possible transport mechanisms in this strongly interacting regime.
ISI:000242409400004
ISSN: 1098-0121
CID: 3856412

Energy anomaly and polarizability of carbon nanotubes

Novikov, D S; Levitov, L S
The energy of Fermi sea perturbed by an external potential is analyzed with the help of an energy anomaly. Using an example of massive Dirac fermions on a circle, we illustrate how the anomaly accounts for the contribution of the deep-lying states. The energy anomaly is a universal function of the applied field and is related to known field-theoretic anomalies. Applied to the transverse polarizability of carbon nanotubes, the anomaly reveals universality and scale invariance of the response dominated by electrons. The electron band transformation in a strong field-effect regime is predicted.
PMID: 16486742
ISSN: 0031-9007
CID: 3856482

Correlated electron states and transport in triangular arrays

Novikov, DS; Kozinsky, B; Levitov, LS
We study correlated electron states in frustrated geometry of a triangular lattice. The interplay of long-range interactions and finite residual entropy of a classical system gives rise to unusual effects in equilibrium ordering as well as in transport. A correlated fluid phase is identified in a wide range of densities and temperatures above freezing into commensurate solid phases. The charge dynamics in the correlated phase is described in terms of a height field, its fluctuations, and topological defects. We demonstrate that the height field fluctuations give rise to a "free" charge flow and finite dc conductivity. We show that freezing into the solid phase, controlled by the long-range interactions, manifests itself in singularities of transport properties.
ISI:000234336000087
ISSN: 2469-9950
CID: 3856392

Electron properties of carbon nanotubes in a periodic potential

Novikov, DS
A periodic potential applied to a nanotube is shown to lock electrons into incompressible states that can form a devil's staircase. Electron interactions result in spectral gaps when the electron density (relative to a half-filled carbon pi band) is a rational number per potential period, in contrast to the single-particle case where only the integer-density gaps are allowed. When electrons are weakly bound to the potential, incompressible states arise due to Bragg diffraction in the Luttinger liquid. Charge gaps are enhanced due to quantum fluctuations, whereas neutral excitations are governed by an effective SU(4)similar or equal to O(6) Gross-Neveu Lagrangian. In the opposite limit of the tightly bound electrons, effects of exchange are unimportant, and the system behaves as a single fermion mode that represents a Wigner crystal pinned by the external potential, with the gaps dominated by the Coulomb repulsion. The phase diagram is drawn using the effective spinless Dirac Hamiltonian derived in this limit. Incompressible states can be detected in the adiabatic transport setup realized by a slowly moving potential wave, with electron interactions providing the possibility of pumping of a fraction of an electron per cycle (equivalently, in pumping at a fraction of the base frequency).
ISI:000234336000116
ISSN: 2469-9950
CID: 3856402

Devil's staircase of incompressible electron states in a nanotube

Novikov, Dmitry S
It is shown that a periodic potential applied to a nanotube can lock electrons into incompressible states. Depending on whether electrons are weakly or tightly bound to the potential, excitation gaps open up either due to the Bragg diffraction enhanced by the Tomonaga-Luttinger correlations, or via pinning of the Wigner crystal. Incompressible states can be detected in a Thouless pump setup, in which a slowly moving periodic potential induces quantized current, with a possibility to pump on average a fraction of an electron per cycle as a result of interactions
PMID: 16090966
ISSN: 0031-9007
CID: 146361

Levy statistics and anomalous transport in quantum-dot arrays

Novikov, DS; Drndic, M; Levitov, LS; Kastner, MA; Jarosz, MV; Bawendi, MG
A model of transport is proposed to explain power-law current transients and memory phenomena observed in partially ordered arrays of semiconducting nanocrystals. The model describes electron transport by a stationary Levy process of transmission events and thereby requires no time dependence of system properties. The waiting time distribution with a characteristic long tail gives rise to a nonstationary response in the presence of a voltage pulse. We report on noise measurements that agree well with the predicted non-Poissonian fluctuations in current, and discuss possible mechanisms leading to this behavior.
ISI:000231564500096
ISSN: 2469-9950
CID: 3856382

Anomalous transport and memory in quantum dot arrays [Meeting Abstract]

Novikov, DS; Drndic, M; Levitov, LS; Kastner, MA; Jarosz, MV; Bawendi, MG
We address anomalous transport phenomena in arrays of semiconductor nanocrystals (quantum dots): Transient power-law decay of current as a response to a step in large bias voltage applied across the array, as well as memory effects observed after successive applications of the bias voltage. A novel phenomenological model of transport in such systems is proposed, capable of rationalizing both anomalous transport and memory. The model describes electron transport by a stationary Levy process of transmission events and therefore requires no time dependence of system properties. The long tail in the waiting time distribution gives rise to a nonstationary response in the presence of a voltage pulse. Noise measurements agree well with the predicted non-Poissonian fluctuations in current. We briefly discuss possible microscopic mechanisms that could cause the anomalous statistics in transmission.
ISI:000231241600017
ISSN: 0277-786x
CID: 3856532