47 research outputs found
Coulomb drag as a measure of trigonal warping in doped graphene
I suggest to use the effect of Coulomb drag between two closely positioned
graphite monolayers (graphene sheets) for experimental measurement of the
strength of weak non-linearities of the spectrum in graphene. I consider
trigonal warping as a representative mechanism responsible for the drag effect.
Since graphene is relatively defect-free, I evaluate the drag conductivity in
the ballistic regime and find that it is proportional to the fourth power of
the warping strength.Comment: 4 pages, 1 figur
Van der Waals Frictional Drag induced by Liquid Flow in Low- Dimensional Systems
We study the van der Waals frictional drag force induced by liquid flow in
low-dimensional systems (2D and 1D electron systems, and 2D and 1D channels
with liquid). We find that for both 1D and 2D systems, the frictional drag
force induced by liquid flow may be several orders of magnitude larger than the
frictional drag induced by electronic current.Comment: 10 pages, 4 figure
Effective Drag Between Strongly Inhomogeneous Layers: Exact Results and Applications
We generalize Dykhne's calculation of the effective resistance of a 2D
two-component medium to the case of frictional drag between the two parallel
two-component layers. The resulting exact expression for the effective
transresistance, , is analyzed in the limits when the resistances
and transresistances of the constituting components are strongly different -
situation generic for the vicinity of the {\em classical} (percolative)
metal-insulator transition (MIT). On the basis of this analysis we conclude
that the evolution of across the MIT is determined by the type
of correlation between the components, constituting the 2D layers. Depending on
this correlation, in the case of two electron layers, changes
either monotonically or exhibits a sharp maximum. For electron-hole layers
is negative and exhibits a sharp minimum at the
MIT.Comment: 7 pages, 3 figure
On the temperature dependence of ballistic Coulomb drag in nanowires
We have investigated within the theory of Fermi liquid dependence of Coulomb
drag current in a passive quantum wire on the applied voltage across an
active wire and on the temperature for any values of . We assume
that the bottoms of the 1D minibands in both wires almost coincide with the
Fermi level. We come to conclusions that 1) within a certain temperature
interval the drag current can be a descending function of the temperature ;
2) the experimentally observed temperature dependence of the drag
current can be interpreted within the framework of Fermi liquid theory; 3) at
relatively high applied voltages the drag current as a function of the applied
voltage saturates; 4) the screening of the electron potential by metallic gate
electrodes can be of importance.Comment: 7 pages, 1 figur
Intershell resistance in multiwall carbon nanotubes: A Coulomb drag study
We calculate the intershell resistance R_{21} in a multiwall carbon nanotube
as a function of temperature T and Fermi level (e.g. a gate voltage), varying
the chirality of the inner and outer tubes. This is done in a so-called Coulomb
drag setup, where a current I_1 in one shell induces a voltage drop V_2 in
another shell by the screened Coulomb interaction between the shells neglecting
the intershell tunnelling. We provide benchmark results for R_{21}=V_2/I_1
within the Fermi liquid theory using Boltzmann equations. The band structure
gives rise to strongly chirality dependent suppression effects for the Coulomb
drag between different tubes due to selection rules combined with mismatching
of wave vector and crystal angular momentum conservation near the Fermi level.
This gives rise to orders of magnitude changes in R_{21} and even the sign of
R_{21} can change depending on the chirality of the inner and outer tube and
misalignment of inner and outer tube Fermi levels. However for any tube
combination, we predict a dip (or peak) in R_{21} as a function of gate
voltage, since R_{21} vanishes at the electron-hole symmetry point. As a
byproduct, we classified all metallic tubes into either zigzag-like or
armchair-like, which have two different non-zero crystal angular momenta m_a,
m_b and only zero angular momentum, respectively.Comment: 17 pages, 10 figure
Coulomb drag between ballistic quantum wires
We develop a kinetic equation description of Coulomb drag between ballistic
one-dimensional electron systems, which enables us to demonstrate that
equilibration processes between right- and left-moving electrons are crucially
important for establishing dc drag. In one-dimensional geometry, this type of
equilibration requires either backscattering near the Fermi level or scattering
with small momentum transfer near the bottom of the electron spectrum.
Importantly, pairwise forward scattering in the vicinity of the Fermi surface
alone is not sufficient to produce a nonzero dc drag resistivity , in contrast to a number of works that have studied Coulomb drag due to
this mechanism of scattering before. We show that slow equilibration between
two subsystems of electrons of opposite chirality, "bottlenecked" by inelastic
collisions involving cold electrons near the bottom of the conduction band,
leads to a strong suppression of Coulomb drag, which results in an activation
dependence of on temperature---instead of the conventional power
law. We demonstrate the emergence of a drag regime in which does
not depend on the strength of interwire interactions, while depending strongly
on the strength of interactions inside the wires.Comment: 41 pages, 11 figures, more extended discussion, figures adde
Coulomb Drag for Strongly Localized Electrons: Pumping Mechanism
The mutual influence of two layers with strongly loclized electrons is
exercised through the random Coulomb shifts of site energies in one layer
caused by electron hops in the other layer. We trace how these shifts give rise
to a voltage drop in the passive layer, when a current is passed through the
active layer. We find that the microscopic origin of drag lies in the time
correlations of the occupation numbers of the sites involved in a hop. These
correlations are neglected within the conventional Miller-Abrahams scheme for
calculating the hopping resistance.Comment: 5 pages, 3 figure
Density imbalance effect on the Coulomb drag upturn in an electron-hole bialyer
A low-temperature upturn of the Coulomb drag resistivity measured in an
undoped electron-hole bilayer (uEHBL) device, possibly manifesting from exciton
formation or condensation, was recently observed. The effects of density
imbalance on this upturn are examined. Measurements of drag as a function of
temperature in a uEHBL with a 20 nm wide AlGaAs barrier layer
at various density imbalances are presented. The results show drag increasing
as the density of either two dimensional system was reduced, both within and
above the upturn temperature regime. A comparison of the data with numerical
calculations of drag in the presence of electron-hole pairing fluctuations,
which qualitatively reproduce the drag upturn behavior, is also presented. The
calculations, however, predict a peak in drag at matched densities, which is
not reflected by the measurements.Comment: 4 pages, 4 figures, submitted to PRB Rapi
Frictional drag between quantum wells mediated by fluctuating electromagnetic field
We use the theory of the fluctuating electromagnetic field to calculate the
frictional drag between nearby two-and three dimensional electron systems. The
frictional drag results from coupling via a fluctuating electromagnetic field,
and can be considered as the dissipative part of the van der Waals interaction.
In comparison with other similar calculations for semiconductor two-dimensional
system we include retardation effects. We consider the dependence of the
frictional drag force on the temperature , electron density and separation
. We find, that retardation effects become dominating factor for high
electron densities, corresponding thing metallic film, and suggest a new
experiment to test the theory. The relation between friction and heat transfer
is also briefly commented on.Comment: 14 pages, 4 figure
Coulomb Drag at the Onset of Anderson Insulators
It is shown that the Coulomb drag between two identical layers in the
Anderson insulting state indicates a striking difference between the Mott and
Efros-Shklovskii (ES) insulators. In the former, the trans-resistance
is monotonically increasing with the localization length ; in the latter,
the presence of a Coulomb gap leads to an opposite result: is enhanced
with a decreasing , with the same exponential factor as the single layer
resistivity. This distinction reflects the relatively pronounced role of
excited density fluctuations in the ES state, implied by the enhancement in the
rate of hopping processes at low frequencies. The magnitude of drag is
estimated for typical experimental parameters in the different cases. It is
concluded that a measurement of drag can be used to distinguish between
interacting and non-interacting insulating state.Comment: 15 pages, revte