Lev G. Mourokh

High spatial resolution thermal conductivity of bulk ZnO (0001)

We measured high spatial/depth resolution 300 K thermal conductivity κ of the Zn and O surfaces of two bulk n-type ZnO (0001) samples, grown by a vapor-phase transport method, using scanning thermal microscopy (SThM). The thermal investigation was performed in both point-by-point (∼2 μm resolution) and area-scan modes. On the first sample κ=1.16±0.08 (Zn face)/1.10±0.09 (O face) W/cm K while for the second material κ=1.02±0.07 (Zn face)/0.98±0.08 (O face) W/cm K. These are the highest κ values reported on ZnO. A correlation between SThM area-scan readings and surface topography was established by simultaneously performing atomic force microscopy scans. The influence of surface roughness on the effective thermal conductivity (i.e., heat flow) is discussed.

Optical Aharonov-Bohm effect in stacked type-II quantum dots

Excitons in vertically stacked type-II quantum dots experience the topological magnetic phase and demonstrate the Aharonov-Bohm oscillations in the emission intensity. Photoluminescence of vertically stacked ZnTe/ZnSe quantum dots is measured in magnetic fields up to 31 T. The Aharonov-Bohm oscillations are found in the magnetic-field dependence of emission intensity. The positions of the peaks of the emission intensity are in a good agreement with numerical simulations of excitons in stacked quantum dots.

Probing the microscopic structure of bound states in quantum point contacts

Using an approach that allows us to probe the electronic structure of strongly pinched-off quantum point contacts (QPCs), we provide evidence for the formation of self-consistently realized bound states (BSs) in these structures. Our approach exploits the resonant interaction between closely coupled QPCs, and demonstrates that the BSs may give rise to a robust confinement of single spins, which show clear Zeeman splitting in a magnetic field.

Nonequilibrium fluctuations and decoherence in nanomechanical devices coupled to the tunnel junction

We analyze the dynamics of a nanomechanical oscillator coupled to an electrical tunnel junction with an arbitrary voltage applied to the junction and arbitrary temperature of electrons in leads. We obtain the explicit expressions for the fluctuations of oscillator position, its damping/decoherence rate, and the current through the structure. It is shown that quantum heating of the oscillator results in nonlinearity of the current-voltage characteristics. The effects of mechanical vacuum fluctuations are also discussed.

Terahertz response of quantum point contacts

We measure a clear terahertz response in the low-temperature conductance of a quantum point contact at 1.4 and 2.5THz. We show that this photoresponse does not arise from a heating effect, but that it is instead excellently described by a classical model of terahertz-induced gate-voltage rectification. This effect is distinct from the rectification mechanisms that have been studied previously, being determined by the phase-dependent interference of the source drain and gate voltage modulations induced by the terahertz field.

Modelling chemical reactions using semiconductor quantum dots

We propose the use of semiconductor quantum dots for simulating chemical reactions, as electrons are redistributed among such artificial atoms. We show that it is possible to achieve various reaction regimes and obtain different reaction products by varying the speed of voltage changes applied to the gates forming quantum dots. Considering the simplest possible reaction, H2+H→H+H2, we show how the necessary initial state can be obtained and what voltage pulses should be applied to achieve a desirable final product. Our calculations have been performed using the Pechukas gas approach, which can be extended for more complicated reactions.

Detection of Local-Moment Formation Using the Resonant Interaction between Coupled Quantum Wires

We study the influence of many-body interactions on the transport characteristics of a pair of quantum wires that are coupled to each other by means of a quantum dot. Under conditions where a local magnetic moment is formed in one of the wires, tunnel coupling to the other gives rise to an associated peak in its density of states, which can be detected directly in a conductance measurement. Our theory is therefore able to account for the key observations in the recent study of T. Morimoto et al. [Appl. Phys. Lett., ()]], and demonstrates that coupled quantum wires may be used as a system for the detection of local magnetic-moment formation.

Semiconductor superlattice in a biharmonic field: Absolute negative conductivity and static electric-field generation

We analyze the transport properties of a semiconductor superlattice in the presence of a biharmonic electric field. The modification of current-voltage characteristics induced by the biharmonic radiation is obtained. The conditions for absolute negative conductivity and for the spontaneous generation of a significant static electric field are determined. We also show that a simple harmonic field can experience nonlinear amplification even when the differential superlattice dc conductivity is positive, and we determine the corresponding range of parameters.

Negative high-frequency differential conductivity in semiconductor superlattices

We examine the high-frequency differential conductivity response properties of semiconductor superlattices having various miniband dispersion laws. Our analysis shows that the anharmonicity of Bloch oscillations (beyond tight-binding approximation) leads to the occurrence of negative high-frequency differential conductivity at frequency multiples of the Bloch frequency. This effect can arise even in regions of positive static differential conductivity. The influence of strong electron scattering by optic phonons is analyzed. To achieve terahertz field amplification, we propose employing structures having minibands with effective electron mass that decreases as the electron energy increases.

Vertically coupled quantum wires in a longitudinal magnetic field

The authors examine analytically the energy subband structure for two vertically stacked quantum wires separated by a tunneling barrier in the presence of a longitudinal magnetic field. For identical harmonic confining potentials, they show that the tunnel splitting between formed symmetric and antisymmetric subbands decreases exponentially with increasing magnetic field and, moreover, the tunnel coupling disappears at appropriate values of the magnetic field in agreement with experimental data. They propose to achieve a controllable coupling of quantum wires with the decoupling magnetic field and with nanomagnets providing coupling windows, which can be used for quantum computation purposes.