arXiv subjects

E. B. Olshanetsky

Publications and source records attributed to E. B. Olshanetsky.

At least 19 recordsLinked to original sources

arXiv2024

Interaction-controlled transport in a two-dimensional massless-massive Dirac system: Transition from degenerate to nondegenerate regimes

The resistivity of two-dimensional (2D) metals generally exhibits insensitivity to electron-electron scattering. However, it's worth noting that Galilean invariance may not hold true in systems characterized by a spectrum containing multiple electronic branches or in scenarios involving electron-hole plasma. In the context of our study, we focus on 2D electrons confined within a triple quantum well (TQW) based on HgTe. This system displays a coexistence of energy bands featuring both linear and parabolic-like spectra at low energy and, therefore, lacks the Galilean invariance. This research employs a combined theoretical and experimental approach to investigate the transport properties of this two-component system across various regimes. By manipulating carrier density and temperature, we tune our system from a fully degenerate regime, where resistance follows a temperature-dependent behavior proportional to $T^2$, to a regime where both types of electrons adhere to Boltzmann statistics. In the non-degenerate regime, electron interactions lead to resistance that is weakly dependent on temperature. Notably, our experimental observations closely align with the theoretical predictions derived in this study. This work establishes the HgTe-based TQW as a promising platform for exploring different interaction dominant scenarios for the massless-massive Dirac system.9 pages, 8 figures

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arXiv2024

Electron-hole scattering-induced temperature behaviour of HgTe-based semimetal quantum well

The semimetal quantum well (QW) based on HgTe structures exhibiting unusual transport properties at low temperature is examined experimentally. It demonstrates either a linear or quadratic growth of resistance with temperature at different top-gate voltages in the semimetal regime. We develop a theoretical model of HgTe-based semimetal QW resistance temperature dependence based on electron-hole scattering processes at low temperatures. We apply the Boltzmann transport equation approach to study the effect of electron-hole scattering in a semimetal QW. The calculated temperature behavior of 2D semimetal resistivity demonstrates an excellent agreement with experimental findings.

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arXiv2024

Interaction dominated transport in 2D conductors: from degenerate to partially-degenerate regime

In this study, we investigate the conductivity of a two-dimensional (2D) system in HgTe quantum well comprising two types of carriers with linear and quadratic spectra, respectively. The interactions between the two-dimensional Dirac holes and the heavy holes lead to the breakdown of Galilean invariance, resulting in interaction-limited resistivity. Our exploration of the transport properties spans from low temperatures, where both subsystems are fully degenerate, to higher temperatures, where the Dirac holes remain degenerate while the heavy holes follow Boltzmann statistics, creating a partially degenerate regime. Through a developed theory, we successfully predict the behavior of resistivity as $ρ\sim T^2$ and $ρ\sim T^{3}$ for the fully degenerate and partially degenerate regimes, respectively, which is in reasonable agreement with experimental observations. Notably, at elevated temperatures, the interaction-limited resistivity surpasses the resistivity caused by impurity scattering by a factor of 5-6. These findings imply that the investigated system serves as a versatile experimental platform for exploring various interaction-limited transport regimes in two component plasma.

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arXiv2021

Engineering topological phases in triple HgTe/CdTe quantum wells

Quantum wells formed by layers of HgTe between Hg$_{1-x}$Cd$_x$Te barriers lead to two-dimensional (2D) topological insulators, as predicted by the BHZ model. Here, we theoretically and experimentally investigate the characteristics of triple HgTe quantum wells. We describe such heterostructure with a three dimensional $8\times 8$ Kane model, and use its eigenstates to derive an effective 2D Hamiltonian for the system. From these we obtain a phase diagram as a function of the well and barrier widths and we identify the different topological phases composed by zero, one, two, and three sets of edge states hybridized along the quantum wells. The phase transitions are characterized by a change of the spin Chern numbers and their corresponding band inversions. Complementary, transport measurements are experimentally investigated on a sample close to the transition line between the phases with one and two sets of edges states. Accordingly, for this sample we predict a gapless spectrum with low energy bulk conduction bands given by one parabolic and one Dirac band, and with edge states immersed in the bulk valance bands. Consequently, we show that under these conditions, local and non-local transport measurements are inconclusive to characterize a sole edge state conductivity due to bulk conductivity. On the other hand, Shubnikov-de Haas (SdH) oscillations show an excellent agreement with our theory. Particularly, we show that the measured SdH oscillation frequencies agrees with our model and show clear signatures of the coexistence of a parabolic and Dirac bands.

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arXiv2021

Transport through the network of topological channels in HgTe based quantum well

Topological insulators represent a new quantum state of matter which is characterized by edge or surface states and an insulating band gap in the bulk. In a two dimensional (2D) system based on the HgTe quantum well (QW) of critical width random deviations of the well width from its average value result in local crossovers from zero gap 2D Dirac fermion system to either the 2D topological insulator or the ordinary insulator, forming a complicated in-plane network of helical channels along the zero-gap lines. We have studied experimentally the transport properties of the critical width HgTe quantum wells near the Dirac point, where the conductance is determined by a percolation along the zero-gap lines. The experimental results confirm the presence of percolating conducting channels of a finite width. Our work establishes the critical width HgTe QW as a promising platform for the study of the interplay between topology and localization.

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arXiv2021

Magnetohydrodynamics and electro-electron interaction of massless Dirac fermions

The magnetotransport properties of massless Dirac fermions in a gapless HgTe quantum well are investigated. In samples with narrow channels, a large negative magnetoresistance with a Lorentzian profile is observed, which is interpreted as a manifestation of electron viscosity due to electron-electron interaction. Comparison of experiment with theory yields the shear stress relaxation time of the Dirac fermions caused by electron-electron scattering.

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arXiv2021

Multiple crossing of Landau levels of two-dimensional fermions in double HgTe quantum wells

The double quantum well systems consisting of two HgTe layers separated by a tunnel-transparent barrier are expected to manifest a variety of phase states including two-dimensional gapless semimetal and two-dimensional topological insulator. The presence of several subbands in such systems leads to a rich filling factor diagram in the quantum Hall regime. We have performed magnetotransport measurements of the HgTe-based double quantum wells in both gapless and gapped state and observed numerous crossings between the Landau levels belonging to different subbands. We analyze the Landau level crossing patterns and compare them to the results of theoretical calculations.

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arXiv2020

Topological insulators based on HgTe

The most interesting experimental results obtained in studies of 2D and 3D topological insulators (TIs) based on HgTe quantum wells and films are reviewed. In the case of 2D TIs, these include the observation of nonlocal ballistic and diffusion transport, the magnetic breakdown of 2D TIs, and an anomalous temperature dependence of edge-channel resistance. In 3D TIs, a record-setting high mobility of surface two-dimensional Dirac fermions (DFs) has been attained. This enabled determining all the main TI parameters (the bulk gap and the density of DFs on both of its surfaces) and provided information on the phase of the Shubnikov - de Haas oscillations of DFs, which indicates the rigid topological coupling between the fermion spin and momentum. Prospects for further research are discussed in the conclusion.

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arXiv2020

Two-dimensional topological insulator state in double HgTe quantum well

The two-dimensional topological insulator phase has been observed previously in single HgTe-based quantum wells with inverted subband ordering. In double quantum wells (DQWs), coupling between the layers introduces additional degrees of freedom leading to a rich phase picture. By studying local and nonlocal resistance in HgTe-based DQWs, we observe both the gapless semimetal phase and the topological insulator phase, depending on parameters of the samples and according to theoretical predictions. Our work establishes the DQWs as a promising platform for realization of multilayer topological insulators.

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arXiv2019

Mesoscopic transport in two-dimensional topological insulators

Topological states of matter have attracted a lot of attention due to their many intriguing transport properties. In particular, two-dimensional topological insulators (2D TI) possess gapless counter propagating conducting edge channels, with opposite spin, that are topologically protected from backscattering. Two basic features are supposed to confirm the existence of the ballistic edge channels in the submicrometer limit: the 4-terminal conductance is expected to be quantized at the universal value $2e^{2}/h$, and a nonlocal signal should appear due to a net current along the sample edge, carried by the helical states. On the other hand for longer channels the conductance has been found to deviate from the quantized value. This article reviewer the experimental and theoretical work related to the transport in two-dimensional topological insulators (2D-TI), based on HgTe quantum wells in zero magnetic field. We provide an overview of the basic mechanisms predicting a deviation from the quantized transport due to backscattering (accompanied by spin-flips) between the helical channels. We discuss the details of the model, which takes into account the edge and bulk contribution to the total current and reproduces the experimental results.

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arXiv2019

Electronic thermal conductivity in 2D topological insulator in a HgTe quantum well

We have measured the differential resistance in a two-dimensional topological insulator (2DTI) in a HgTe quantum well, as a function of the applied dc current. The transport near the charge neutrality point is characterized by a pair of counter propagating gapless edge modes. In the presence of an electric field, the energy is transported by counter propagating channels in the opposite direction. We test a hot carrier effect model and demonstrate that the energy transfer complies with the Wiedemann Franz law near the charge neutrality point in the edge transport regime.

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arXiv2018

Thermoelectric transport in two-dimensional topological insulator state based on HgTe quantum well

The thermoelectric response of HgTe quantum wells in the state of two-dimensional topological insulator (2D TI) has been studied experimentally. Ambipolar thermopower, typical for an electron-hole system, has been observed across the charge neutrality point, where the carrier type changes from electrons to holes according to the resistance measurements. The hole-type thermopower is much stronger than the electron-type one. The thermopower linearly increases with temperature. We present a theoretical model which accounts for both the edge and bulk contributions to the electrical conductivity and thermoelectric effect in a 2D TI, including the effects of edge to bulk leakage. The model, contrary to previous theoretical studies, demonstrates that the 2D TI is not expected to show anomalies of thermopower near the band conductivity threshold, which is consistent with our experimental results. Based on the experimental data and theoretical analysis, we conclude that the observed thermopower is mostly of the bulk origin, while the resistance is determined by both the edge and bulk transport.

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arXiv2018

Thermopower of a Two-Dimensional Semimetal in a HgTe Quantum Well

The thermopower in a two-dimensional semimetal existing in HgTe quantum wells 18-21 nm thick has been studied experimentally and theoretically for the first time. It has been found theoretically and experimentally that the thermopower has two components - diffusion and phonon drag and that the second component is several times larger than the first. It has been concluded that the electron-hole scattering plays an important role in both mechanisms of the thermopower.

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arXiv2017

Two-dimensional semimetal in HgTe quantum well under hydrostatic pressure

We report results of systematic measurements of charge transport properties of the 20.5nm wide HgTe-based quantum well in perpendicular magnetic field, performed under hydrostatic pressures up to 15.1 kbar. At ambient pressure transport is well described by the two-band semiclassical model.In contrast, at elevated pressure, we observed non-monotonic pressure dependence of resistivity at CNP. For pressures lower than $\approx9$ kbar, resistivity grows with pressure, in accord with expectations from the band structure calculations and the model incorporating effects of disorder on transport in 2D semimetals with indirect band overlap. For higher pressures, the resistivity saturates and starts decreasing upon further increase of pressure. Above $\approx14$ kbar the resistance and hopping transport character sharply change, which may indicate formation of the excitonic insulator state. The data also reveals strong influence of disorder on transport in 2D electron-hole system with a small band overlap.

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arXiv2017

Two dimensional topological insulator in quantizing magnetic fields

The effect of quantizing magnetic field on the electron transport is investigated in a two dimensional topological insulator (2D TI) based on a 8 nm (013) HgTe quantum well (QW). The local resistance behavior is indicative of a metal-insulator transition at $B\approx 6$ T. On the whole the experimental data agrees with the theory according to which the helical edge states transport in a 2D TI persists from zero up to a critical magnetic field $B_c$ after which a gap opens up in the 2D TI spectrum.

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arXiv2015

Persistence of two-dimensional topological insulator state in wide HgTe quantum well

Our experimental studies of electron transport in wide (14 nm) HgTe quantum wells confirm persistence of a two-dimensional topological insulator state reported previously for narrower wells, where it was justified theoretically. Comparison of local and nonlocal resistance measurements indicate edge state transport in the samples of about 1 mm size at temperatures below 1 K. Temperature dependence of the resistances suggests an insulating gap of the order of a few meV. In samples with sizes smaller than 10 $μ$m a quasiballistic transport via the edge states is observed.

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arXiv2013

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.

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arXiv2013

Transition from insulating to metallic phase induced by in-plane magnetic field in HgTe quantum wells

We report transport measurements in HgTe-based quantum wells with well width of 8 nm, corresponding to quantum spin Hall state, subject to in-plane magnetic field. In the absence of the magnetic field the local and nonlocal resistances behave very similar, which confirms the edge state transport in our system. In the magnetic field, we observe a monotonic decrease of the resistance with saturation of local resistance, while nonlocal resistance disappears completely, independent of the gate voltage. We believe that these evidences of metallic behavior indicate a transition to a gapless two-dimensional phase, according to theoretical predictions. The influence of disorder on resistivity properties of HgTe quantum wells under in-plane magnetic field is discussed.

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