571 research outputs found
Magnetoconductance of the Corbino disk in graphene
Electron transport through the Corbino disk in graphene is studied in the
presence of uniform magnetic fields. At the Dirac point, we observe conductance
oscillations with the flux piercing the disk area , characterized by
the period , where () is the outer
(inner) disk radius. The oscillations magnitude increase with the radii ratio
and exceed 10% of the average conductance for in the case
of the normal Corbino setup, or for in the case of the
Andreev-Corbino setup. At a finite but weak doping, the oscillations still
appear in a limited range of , away from which
the conductance is strongly suppressed. At large dopings and weak fields we
identify the crossover to a normal ballistic transport regime.Comment: RevTeX, 5 pages, 3 figures. New version with minor revisions and
references added; to be published in Phys. Rev.
Strain-induced transitions to quantum chaos and effective time-reversal symmetry breaking in triangular graphene nanoflakes
We investigate the effect of strain-induced gauge fields on statistical
distribution of energy levels of triangular graphene nanoflakes with zigzag
edges. In the absence of strain fields but in the presence of weak potential
disorder such systems were found in Ref. [1] to display the spectral statistics
of the Gaussian unitary ensemble (GUE) due to the effective time-reversal
(symplectic) symmetry breaking. Here show that, in the absence of disorder,
strain fields may solely lead to spectral fluctuations of GUE providing a
nanoflake is deformed such that all its geometric symmetries are broken. In a
particular case when a single mirror symmetry is preserved the spectral
statistics follow the Gaussian orthogonal ensemble (GOE) rather then GUE. The
corresponding transitions to quantum chaos are rationalized by means of
additive random-matrix models and the analogy between strain-induced gauge
fields and real magnetic fields is discussed.Comment: Minor revisions, typos corrected, references and acknowledgments
added. RevTeX, 10 pages, 10 figure
Aharonov-Bohm and relativistic Corbino effects in graphene: A comparative study of two quantum interference phenomena
This is an analytical study of magnetic fields effects on the conductance,
the shot noise power, and the third charge-transfer cumulant for Aharonov-Bohm
rings and Corbino disks in graphene. The two distinct physical mechanisms lead
to very similar magnetotransport behaviors. Differences are unveiled when
discussing the third-cumulant dependence on magnetic fields.Comment: Typos corrected. A version to be published in Acta Physica Polonica
A. Presented during "The European Conference: Physics of Magnetism 2011"
(PM'11), June 27 - July 1, 2011 Poznan, Polan
Conductance of a double quantum dot with correlation-induced wave function renormalization
The zero-temperature conductance of diatomic molecule, modelled as a
correlated double quantum dot attached to noninteracting leads is investigated.
We utilize the Rejec-Ramsak formulas, relating the linear-response conductance
to the ground-state energy dependence on magnetic flux within the framework of
EDABI method, which combines exact diagonalization with ab initio calculations.
The single-particle basis renormalization leads to a strong particle-hole
asymmetry, of the conductance spectrum, absent in a standard parametrized model
study. We also show, that the coupling to leads V=0.5t (t is the hopping
integral) may provide the possibility for interatomic distance manipulation due
to the molecule instability.Comment: Presented on the The International Conference on Strongly Correlated
Electron Systems SCES'05, July 26-30th 2005, Vienna, Austria. An abbreviated
version will appear in Physica
Pseudodiffusive conductance, quantum-limited shot noise, and Landau-level hierarchy in biased graphene bilayer
We discuss, by means of mode-matching analysis for the Dirac equation, how
splittings of the Landau-level (LL) degeneracies associated with spin, valley,
and layer degrees of freedom affect the ballistic conductance of graphene
bilayer. The results show that for wide samples () the
Landauer-B\"{u}ttiker conductance reaches the maximum
at the resonance via each LL, with the
prefactor varying from if all three degeneracies are preserved, to
if all the degeneracies are split. In the absence of bias between the layers,
the degeneracies associated with spin and layer degrees of freedom may be split
by manipulating the doping and magnetic field; the conductance at the zeroth LL
is twice as large, while the conductance at any other LL equals to the
corresponding conductance of graphene monolayer. The presence of bias potential
allows one also to split the valley degeneracy. Our results show that the
charge transfer at each LL has pseudodiffusive character, with the second and
third cumulant quantified by and (respectively).
In case the electrochemical potential is allowed to slowly fluctuate in a
finite vicinity of LL, the resulting charge-transfer characteristics are still
quantum-limited, with and in the
limit of large fluctuations. The above values of and are
also predicted to be approached in the limit of high source-drain voltage
difference applied. The possible effects of indirect interlayer hopping
integrals are also briefly discussed.Comment: Minor revisions, refs. added; new Section V describing the possible
effects of indirect hoppings between the layers. Figure files optimized for
the faster download. RevTeX, 13 pages, 10 figure
Minimal conductivity and signatures of quantum criticality in ballistic graphene bilayer
We study the ballistic conductivity of graphene bilayer in the presence of
next-nearest neighbor hoppings between the layers. An undoped and unbiased
system was found in Ref. [1] to show a nonuniversal (length-dependent)
conductivity , approaching the value of
for large . Here we demonstrate
one-parameter scaling and determine the scaling function
. The scaling flow has an attractive
fixed point [, ] reproducing
the scenario predicted for random impurity scattering of Dirac fermions with
Coulomb repulsion, albeit the system considered is perfectly ballistic and
interactions are not taken into account. The role of electrostatic bias between
the layers is also briefly discussed.Comment: RevTeX, 5 pages, 4 figure
Magnetoconductance of the Corbino disk in graphene: Chiral tunneling and quantum interference in the bilayer case
Quantum transport through an impurity-free Corbino disk in bilayer graphene
is investigated analytically, by the mode-matching method for effective Dirac
equation, in the presence of uniform magnetic fields. Similarly as in the
monolayer case (see Refs. [1,2]), conductance at the Dirac point shows
oscillations with the flux piercing the disk area characterized by the
period , where () is the outer (inner) disk radius. The oscillations magnitude depends
either on the radii ratio or on the physical disk size, with the condition for
maximal oscillations reading (for ),
where is the interlayer hopping integral, is the Fermi velocity
in graphene, and is an {\em even} integer. {\em Odd}-integer values of
correspond to vanishing oscillations for the normal Corbino setup, or to
oscillations frequency doubling for the Andreev-Corbino setup. At higher Landau
levels (LLs) magnetoconductance behaves almost identically in the monolayer and
bilayer cases. A brief comparison with the Corbino disk in 2DEG is also
provided in order to illustrate the role of chiral tunneling in graphene.Comment: Typos corrected; acknowledgment added. RevTeX, 13 pages, 7 figure
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