Nonlocal transport near the charge neutrality point in a two-dimensional electron-hole system

Nonlocal resistance is studied in a two-dimensional system with a simultaneous presence of electrons and holes in a 20 nm HgTe quantum well. A large nonlocal electric response is found near the charge neutrality point (CNP) in the presence of a perpendicular magnetic field. We attribute the observed nonlocality to the edge state transport via counter propagating chiral modes similar to the quantum spin Hall effect at zero magnetic field and graphene near Landau filling factor $\nu=0$Comment: 5 pages, 4 figure

Giant microwave-induced BB-periodic magnetoresistance oscillations in a two-dimensional electron gas with a bridged-gate tunnel point contact

We have studied the magnetoresistance of the quantum point contact fabricated on the high mobility two-dimensional electron gas (2DEG) exposed to microwave irradiation. The resistance reveals giant $B$-periodic oscillations with the relative amplitude $\Delta R/R$ of up to $700$\% resulting from the propagation and interference of the edge magnetoplasmons (EMPs) in the sample. This giant photoconductance is attributed to the considerably large local electron density modulation in the vicinity of the point contact. We have also analyzed the oscillation periods $\Delta B$ of the resistance oscillations and, comparing the data with the EMP theory, extracted the EMP interference length $L$. We have found that the length $L$ substantially exceeds the distance between the contact leads but rather corresponds to the distance between metallic contact pads measured along the edge of the 2DEG. This resolves existing controversy in the literature and should help to properly design highly sensitive microwave and terahertz spectrometers based on the discussed effect.Comment: 5 pages, 5 figure

Electron transport through antidot superlattices in Si/SiGeSi/SiGe heterostructures: new magnetoresistance resonances in lattices with large diameter antidots

In the present work we have investigated the transport properties in a number of Si/SiGe samples with square antidot lattices of different periods. In samples with lattice periods equal to 700 nm and 850 nm we have observed the conventional low-field commensurability magnetoresistance peaks consistent with the previous observations in GaAs/AlGaAs and Si/SiGe samples with antidot lattices. In samples with a 600 nm lattice period a new series of well-developed magnetoresistance oscillations has been found beyond the last commensurability peak which are supposed to originate from periodic skipping orbits encircling an antidot with a particular number of bounds.Comment: To appear in EuroPhys. Let

Quantum corrections to the conductivity and Hall coefficient of a 2D electron gas in a dirty AlGaAs/GaAs/AlGaAs quantum well: transition from diffusive to ballistic regime

We report an experimental study of the quantum corrections to the longitudinal conductivity and the Hall coefficient of a low mobility, high density two-dimensional two-dimensional electron gas in a AlGaAs/GaAs/AlGaAs quantum well in a wide temperature range (1.5 K - 110 K). This temperature range covers both the diffusive and the ballistic interaction regimes for our samples. It was therefore possible to study the crossover region for the longitudinal conductivity and the Hall effect

Transport properties of a 3D topological insulator based on a strained high mobility HgTe film

We investigated the magnetotransport properties of strained, 80nm thick HgTe layers featuring a high mobility of mu =4x10^5 cm^2/Vs. By means of a top gate the Fermi-energy is tuned from the valence band through the Dirac type surface states into the conduction band. Magnetotransport measurements allow to disentangle the different contributions of conduction band electrons, holes and Dirac electrons to the conductivity. The results are are in line with previous claims that strained HgTe is a topological insulator with a bulk gap of ~15meV and gapless surface states.Comment: 11 pages (4 pages of main text, 6 pages of supplemental materials), 8 figure