arXiv subjects

V. S. Khrapai

Publications and source records attributed to V. S. Khrapai.

53 records · Page 3Linked to original sources

arXiv2012

Pair Scattering of Electrons in Edge Channels of Opposite Chiralities in the Presence of a Disorder Potential

The nonequilibrium transfer of the energy between electrons of counter-propagating quasi-one-dimensional systems has been perturbatively calculated for edge channels in a two-dimensional system in the integer quantum Hall effect. The processes involving two electrons that are allowed only in the system with disorder have been taken into account. Expressions for the cases of Coulomb scattering and transfer of nonequilibrium phonons have been obtained. The energy transferred per unit time has a quasi-threshold dependence on the degree of nonequilibrium of the hot channel. According to numerical estimates for electrons in GaAs, Coulomb scattering processes dominate in the energy transfer and the expected effect can be experimentally observed.

cond-mat.mes-hall↗

arXiv2010

Acoustic phonon-based interaction between coplanar quantum circuits in magnetic field

We explore the acoustic phonon-based interaction between two neighboring coplanar circuits containing semiconductor quantum point contacts in a perpendicular magnetic field B. In a drag-type experiment, a current flowing in one of the circuits (unbiased) is measured in response to an external current in the other. In moderate B the sign of the induced current is determined solely by the polarity of B. This indicates that the spatial regions where the phonon emission/reabsorption is efficient are controlled by magnetic field. The results are interpreted in terms of non-equilibrium transport via skipping orbits in two-dimensional electron system.

cond-mat.mes-hall↗

arXiv2010

Shot noise measurements in a wide-channel transistor near pinch-off

We study a shot noise of a wide channel gated high-frequency transistor at temperature of 4.2K near pinch-off. In this regime, a transition from the metallic to the insulating state is expected to occur, accompanied by the increase of the partition noise. The dependence of the noise spectral density on current is found to be slightly nonlinear. At low currents, the differential Fano factor is enhanced compared to the universal value 1/3 for metallic diffusive conductors. We explain this result by the effect of thermal fluctuations in a nonlinear regime near pinch-off, without calling for the enhanced partition noise.

cond-mat.mes-hall↗

arXiv2008

Nonequilibrium interactions between two quantum circuits

We briefly overview our recent results on nonequilibrium interactions between neighboring electrically isolated nanostructures. One of the nanostructures is represented by an externally biased quantum point contact (drive-QPC), which is used to supply energy quanta to the second nanostructure (detector). Absorption of these nonequilibrium quanta of energy generates a dc-current in the detector, or changes its differential conductance. We present results for a double quantum dot, a single quantum dot or a second QPC placed in the detector circuit. In all three cases a detection of quanta with energies up to ~1 meV is possible for bias voltages across the drive-QPC in the mV range. The results are qualitatively consistent with an energy transfer mechanism based on nonequilibrium acoustic phonons.

cond-mat.mes-hall↗

arXiv2008

Nonequilibrium phenomena in adjacent electrically isolated nanostructures

We report on nonequilibrium interaction phenomena between adjacent but electrostatically separated nanostructures in GaAs. A current flowing in one externally biased nanostructure causes an excitation of electrons in a circuit of a second nanostructure. As a result we observe a dc current generated in the unbiased second nanostructure. The results can be qualitatively explained in terms of acoustic phonon based energy transfer between the two mutually isolated circuits.

cond-mat.mes-hall↗

arXiv2008

Filling factor dependence of the fractional quantum Hall effect gap

We directly measure the chemical potential jump in the low-temperature limit when the filling factor traverses the nu = 1/3 and nu = 2/5 fractional gaps in two-dimensional (2D) electron system in GaAs/AlGaAs single heterojunctions. In high magnetic fields B, both gaps are linear functions of B with slopes proportional to the inverse fraction denominator, 1/q. The fractional gaps close partially when the Fermi level lies outside. An empirical analysis indicates that the chemical potential jump for an IDEAL 2D electron system, in the highest accessible magnetic fields, is proportional to q^{-1}B^{1/2}.

cond-mat.str-el↗

arXiv2007

Counterflow of electrons in two isolated quantum point contacts

We study the interaction between two adjacent but electrically isolated quantum point contacts (QPCs). At high enough source-drain bias on one QPC, the drive QPC, we detect a finite electric current in the second, unbiased, detector QPC. The current generated at the detector QPC always flows in the opposite direction than the current of the drive QPC. The generated current is maximal, if the detector QPC is tuned to a transition region between its quantized conductance plateaus and the drive QPC is almost pinched-off. We interpret this counterflow phenomenon in terms of an asymmetric phonon-induced excitation of electrons in the leads of the detector QPC.

cond-mat.mes-hall↗

arXiv2007

Direct measurements of the fractional quantum Hall effect gaps

We measure the chemical potential jump across the fractional gap in the low-temperature limit in the two-dimensional electron system of GaAs/AlGaAs single heterojunctions. In the fully spin-polarized regime, the gap for filling factor nu=1/3 increases LINEARLY with magnetic field and is coincident with that for nu=2/3, reflecting the electron-hole symmetry in the spin-split Landau level. In low magnetic fields, at the ground-state spin transition for nu=2/3, a correlated behavior of the nu=1/3 and nu=2/3 gaps is observed.

cond-mat.str-el↗

arXiv2006

A double-dot quantum ratchet driven by an independently biased quantum point contact

We study a double quantum dot (DQD) coupled to a strongly biased quantum point contact (QPC), each embedded in independent electric circuits. For weak interdot tunnelling we observe a finite current flowing through the unbiased Coulomb blockaded DQD in response to a strong bias on the QPC. The direction of the current through the DQD is determined by the relative detuning of the energy levels of the two quantum dots. The results are interpreted in terms of a quantum ratchet phenomenon in a DQD energized by a nearby QPC.

cond-mat.mes-hall↗

arXiv2006

Spin ordering: two different scenarios for the single and double layer structures in the fractional and integer quantum Hall effect regimes

We investigate the ground state competition at the transition from the spin unpolarized to spin ordered phase at filling factor $ν=2/3$ in single layer heterostructure and at $ν=2$ in double layer quantum well. To trace the quantum Hall phase we use the minimum in the dissipative conductivity $σ_{xx}$. We observe two different transition scenarios in two investigated situations. For one of them we propose a qualitative explanation, based on the domain structure evolution in the vicinity of the transition point. The origin for the second scenario, corresponding to the experimental situation at $ν=2$ in double layer 2DES, still remains unclear.

cond-mat.mes-hall↗

arXiv2005

Spin gap in the 2D electron system of GaAs/AlGaAs single heterojunctions in weak magnetic fields

We study the interaction-enhanced spin gaps in the two-dimensional electron gas confined in GaAs/AlGaAs single heterojunctions subjected to weak magnetic fields. The values are obtained from the chemical potential jumps measured by magnetocapacitance. The gap increase with parallel magnetic field indicates that the lowest-lying charged excitations are accompanied with a single spin flip at the odd-integer filling factor nu=1 and nu=3, in disagreement with the concept of skyrmions.

cond-mat.str-el↗

arXiv2003

Screening and inplane magnetoresistance of anisotropic two-dimensional gas

In order to split the influence of the orbital and spin effects on the inplane magnetoresistance of a quasi two-dimensional gas we derive its linear response function and dielectric function for the case of anisotropic effective mass. This result is used for the calculation of elastic transport relaxation time of a quasi two dimensional system in a parallel magnetic field. The relaxation time is proved to be isotropic in the low density limit for the case of charged impurity scattering, allowing to separate the two contributions.

cond-mat↗

arXiv2003

Direct measurements of the spin and the cyclotron gaps in a 2D electron system in silicon

Using magnetocapacitance data in tilted magnetic fields, we directly determine the chemical potential jump in a strongly correlated two-dimensional electron system in silicon when the filling factor traverses the spin and the cyclotron gaps. The data yield an effective g-factor that is close to its value in bulk silicon and does not depend on filling factor. The cyclotron splitting corresponds to the effective mass that is strongly enhanced at low electron densities.

cond-mat.str-el↗

arXiv2002

Strong enhancement of the valley splitting in a 2D electron system in silicon

Using magnetocapacitance data, we directly determine the chemical potential jump in a strongly correlated 2D electron system in silicon when the filling factor traverses the valley gap at ν=1 and ν=3. The data yield a valley gap that is strongly enhanced compared to the single-particle value and increases LINEARLY with magnetic field. This result has not been explained by existing theories.

cond-mat↗

arXiv2000

Response of the two-dimensional electron gas of AlGaAs/GaAs heterostructures to parallel magnetic field

We study the transport properties of the two-dimensional electron gas in AlGaAs/GaAs heterostructures in parallel to the interface magnetic fields at low temperatures. The magnetoresistance in the metallic phase is found to be positive and weakly anisotropic with respect to the orientation of the in-plane magnetic field and the current through the sample. At low electron densities ($n_s< 5\times 10^{10}$ cm$^{-2}$) the experimental data can be described adequately within spin-related approach while at high $n_s$ the magnetoresistance mechanism changes as inferred from $n_s$-independence of the normalized magnetoresistance.

cond-mat.mes-hall↗

arXiv2000

Opening an energy gap in an electron double layer system at integer filling factor in a tilted magnetic field

We employ magnetocapacitance measurements to study the spectrum of a double layer system with gate-voltage-tuned electron density distributions in tilted magnetic fields. For the dissipative state in normal magnetic fields at filling factor $ν=3$ and 4, a parallel magnetic field component is found to give rise to opening a gap at the Fermi level. We account for the effect in terms of parallel-field-caused orthogonality breaking of the Landau wave functions with different quantum numbers for two subbands.

cond-mat.mes-hall↗

arXiv1999

Canted antiferromagnetic phase in a double quantum well in a tilted quantizing magnetic field

We investigate the double-layer electron system in a parabolic quantum well at filling factor $ν=2$ in a tilted magnetic field using capacitance spectroscopy. The competition between two ground states is found at the Zeeman splitting appreciably smaller than the symmetric-antisymmetric splitting. Although at the transition point the system breaks up into domains of the two competing states, the activation energy turns out to be finite, signaling the occurrence of a new insulator-insulator quantum phase transition. We interpret the obtained results in terms of a predicted canted antiferromagnetic phase.

cond-mat.mes-hall↗