V. S. Khrapai

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 tunneling we observe a finite current flowing through the 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.

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 nu=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.

Strong enhancement of the valley splitting in a two-dimensional electron system in silicon

Using magnetocapacitance data, we directly determine the chemical potential jump in a strongly correlated two-dimensional electron system in silicon when the filling factor traverses the valley gap at

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

\ensuremath{\nu}=1

Local noise in a diffusive conductor.

and

Tunable Nonequilibrium Luttinger Liquid Based on Counterpropagating Edge Channels

\ensuremath{\nu}=3.

Direct measurements of fractional quantum Hall effect gaps.

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.

Spin gap in the two-dimensional electron system of Ga As ∕ Al x Ga 1 − x As single heterojunctions in weak magnetic fields

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 the filling factor. The cyclotron splitting corresponds to the effective mass that is strongly enhanced at low electron densities.

Filling factor dependence of the fractional quantum Hall effect gap.

The control and measurement of local non-equilibrium configurations is of utmost importance in applications on energy harvesting, thermoelectrics and heat management in nano-electronics. This challenging task can be achieved with the help of various local probes, prominent examples including superconducting or quantum dot based tunnel junctions, classical and quantum resistors, and Raman thermography. Beyond time-averaged properties, valuable information can also be gained from spontaneous fluctuations of current (noise). From these perspective, however, a fundamental constraint is set by current conservation, which makes noise a characteristic of the whole conductor, rather than some part of it. Here we demonstrate how to remove this obstacle and pick up a local noise temperature of a current biased diffusive conductor with the help of a miniature noise probe. This approach is virtually noninvasive for the electronic energy distributions and extends primary local measurements towards strongly non-equilibrium regimes.

Counterflow of Electrons in Two Isolated Quantum Point Contacts

We investigate the energy transfer between counterpropagating quantum Hall edge channels (ECs) in a two-dimensional electron system at a filling factor of