M. Yu. Melnikov

Effective electron mass in high-mobility SiGe/Si/SiGe quantum wells

The effective mass m* of the electrons confined in high-mobility SiGe/Si/SiGe quantum wells has been measured by the analysis of the temperature dependence of the Shubnikov-de Haas oscillations. In the accessible range of electron densities, ns, the effective mass has been found to grow with decreasing ns, obeying the relation m*/mb = ns/(ns − nc), where mb is the electron band mass and nc ≈ 0.54 × 1011 cm−2. In samples with maximum mobilities ranging between 90 and 220 m2/(V s), the dependence of the effective mass on the electron density has been found to be identical suggesting that the effective mass is disorder-independent, at least in the most perfect samples.

Ultra-high mobility two-dimensional electron gas in a SiGe/Si/SiGe quantum well

We report the observation of an electron gas in a SiGe/Si/SiGe quantum well with maximum mobility up to 240 m^2/Vs, which is noticeably higher than previously reported results in silicon-based structures. Using SiO, rather than Al_2O_3, as an insulator, we obtain strongly reduced threshold voltages close to zero. In addition to the predominantly small-angle scattering well known in the high-mobility heterostructures, the observed linear temperature dependence of the conductivity reveals the presence of a short-range random potential.

Indication of band flattening at the Fermi level in a strongly correlated electron system

Using ultra-high quality SiGe/Si/SiGe quantum wells at millikelvin temperatures, we experimentally compare the energy-averaged effective mass, m, with that at the Fermi level, mF, and verify that the behaviours of these measured values are qualitatively different. With decreasing electron density (or increasing interaction strength), the mass at the Fermi level monotonically increases in the entire range of electron densities, while the energy-averaged mass saturates at low densities. The qualitatively different behaviour reveals a precursor to the interaction-induced single-particle spectrum flattening at the Fermi level in this electron system.

Nonlinear transport and noise thermometry in quasiclassical ballistic point contacts

We study nonlinear transport and non-equilibrium current noise in quasi-classical point contacts (PCs) defined in a low-density high-quality two-dimensional electron system in GaAs. At not too high bias voltages

Influence ofe-escattering on the temperature dependence of the resistance of a classical ballistic point contact in a two-dimensional electron system

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Observation of two relaxation mechanisms in transport between spin split edge states at high imbalance

across the PC the noise temperature is determined by a Joule heat power and almost independent on the PC resistance that can be associated with a self-heating of the electronic system. This commonly accepted scenario breaks down at increasing

Manifestation of the bulk phase transition in the edge energy spectrum in a two-dimensional bilayer electron system

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Unusual anisotropy of inplane field magnetoresistance in ultra-high mobility SiGe/Si/SiGe quantum wells

, where we observe extra noise accompanied by a strong decrease of the PCs differential resistance. The spectral density of the extra noise is roughly proportional to the nonlinear current contribution in the PC

Classical Effects in the Weak-Field Magnetoresistance of InGaAs/InAlAs Quantum Wells

\delta S\approx2F^*|e\delta I|\sim V^2

Fractional Quantum Hall Effect in SiGe/Si/SiGe Quantum Wells in Weak Quantizing Magnetic Fields

with the effective Fano factor