Back gating of a two-dimensional hole gas in a SiGe quantum well

A device comprising a low-resistivity, n-type, Si substrate as a back gate to a p-type (boron), remote-doped, SiGe quantum well has been fabricated and characterized. Reverse and forward voltage biasing of the gate with respect to the two-dimensional hole gas in the quantum well allows the density of holes to be varied from 8 × 1011 cm–2 down to a measurement-limited value of 4 × 1011 cm–2. This device is used to demonstrate the evolution with decreasing carrier density of a re-entrant insulator state between the integer quantum Hall effect states with filling factors 1 and 3

Spin-orbit-induced correlations of the local density of states in two-dimensional electron gas

We study the local density of states (LDOS) of two-dimensional electrons in the presence of spin-orbit (SO) coupling. Although SO coupling has no effect on the average density of states, it manifests itself in the correlations of the LDOS. Namely, the correlation function acquires two satellites centered at energy difference equal to the SO splitting, $2\omega_{SO}$, of the electron Fermi surface. For a smooth disorder the satellites are well separated from the main peak. Weak Zeeman splitting $\omega_{Z} \ll \omega_{SO}$ in a parallel magnetic field causes an anomaly in the shape of the satellites. We consider the effect of SO-induced satellites in the LDOS correlations on the shape of the correlation function of resonant-tunneling conductances at different source-drain biases, which can be measured experimentally. This shape is strongly sensitive to the relation between $\omega_{SO}$ and $\omega_{Z}$.Comment: 10 pages, 4 figure

Fractional quantum Hall effect without energy gap

In the fractional quantum Hall effect regime we measure diagonal ($\rho_{xx}$) and Hall ($\rho_{xy}$) magnetoresistivity tensor components of two-dimensional electron system (2DES) in gated GaAs/Al$_{x}$Ga$_{1-x}$As heterojunctions, together with capacitance between 2DES and the gate. We observe 1/3- and 2/3-fractional quantum Hall effect at rather low magnetic fields where corresponding fractional minima in the thermodynamical density of states have already disappeared manifesting complete suppression of the quasiparticle energy gaps.Comment: 4 pages, 4 figure

Microwave induced magnetoresistance oscillations at the subharmonics of the cyclotron resonance

The magnetoresistance oscillations, which occur in a two-dimensional electron system exposed to strong microwave radiation when the microwave frequency $\omega$ coincides with the n-th subharmonic of the cyclotron frequency $\omega_c$ have been investigated for n = 2, 3 and 4. It is shown that these subharmonic features can be explained within a non-equilibrium energy distribution function picture without invoking multi-photon absorption processes. The existence of a frequency threshold above which such oscillations disappear lends further support to this explanation.Comment: 5 pages, 5 figure

Nonlinear theory of fractional microwave-induced magnetoresistance oscillations in a dc-driven two-dimensional electron system

Microwave-induced nonlinear magnetoresistance in a dc-driven two-dimensional electron system is examined using a multi-photon-assisted transport scheme direct controlled by the current. It is shown that near the 2nd subharmonic of the cyclotron resonance, the frequency of the resistivity oscillation with the magnetic-field-normalized current-density is double that at the cyclotron resonance and its harmonics, in excellent agreement with recent experimental findings by Hatke {\it et al.} [Phys. Rev. Lett. {\bf 101}, 246811 (2008)]. The current-induced alternative emergence of resonant two-photon and single-photon processes is responsible for this frequency doubling. Near the third subharmonic of the cyclotron resonance, the current-induced consecutive appearance of resonant 0-/3-photon, two-photon, and single-photon processes may lead to the frequency tripling of the resistivity oscillation.Comment: 6 pages, 2 figures, published versio

Microwave photoresponse in the 2D electron system caused by intra-Landau level transitions

The influence of microwave radiation on the DC-magnetoresistance of 2D-electrons is studied in the regime beyond the recently discovered zero resistance states when the cyclotron frequency exceeds the radiation frequency. Radiation below 30 GHz causes a strong suppression of the resistance over a wide magnetic field range, whereas higher frequencies produce a non-monotonic behavior in the damping of the Shubnikov-de Haas oscillations. These observations are explained by the creation of a non-equilibrium electron distribution function by microwave induced intra-Landau level transitions.Comment: 4 pages, 5 figure

Calcium Orthophosphate Bioceramics

The present review is intended to point the readers’ attention to the important subject of calcium orthophosphate bioceramics. Calcium orthophosphates by one-selves appear to be of a special significance for the human beings because they represent the inorganic part of calcified tissues of mammals. Therefore, many types of calcium orthophosphate-based bioceramics possess remarkable biocompatibility and bioactivity. Materials scientists extensively use this property in attempts to construct artificial bone grafts those are either entirely made of or only surface-coated by calcium orthophosphate bioceramics. Namely, self-setting calcium orthophosphate cements are very helpful in filling voids in damaged bones, while metallic implants covered by a surface layer of calcium orthophosphate bioceramics are widely used for hip joint endoprostheses and tooth substitutes. Porous bioceramicscaffolds made of calcium orthophosphates are very promising tools for tissue engineering applications. In this paper, an overview on the current knowledge on calcium orthophosphate bioceramics has been provided

Wigner Crystalization in the Lowest Landau Level for ν≥1/5\nu \ge 1/5

By means of exact diagonalization we study the low-energy states of seven electrons in the lowest Landau level which are confined by a cylindric external potential modelling the rest of a macroscopic system and thus controlling the filling factor $\nu$. Wigner crystal is found to be the ground state for filling factors between $\nu = 1/3$ and $\nu = 1/5$ provided electrons interact via the bare Coulomb potential. Even at $\nu =1/5$ the solid state has lower energy than the Laughlin's one, although the two energies are rather close. We also discuss the role of pseudopotential parameters in the lowest Landau level and demonstrate that the earlier reported gapless state, appearing when the short-range part of the interaction is suppressed, has nothing in common with the Wigner crystalization in pure Coulomb case.Comment: 9 pages, LaTex, 8 figure