arXiv subjects

S. S. Krishtopenko

Publications and source records attributed to S. S. Krishtopenko.

27 records · Page 2Linked to original sources

arXiv2018

Realistic picture of helical edge states in HgTe quantum wells

We propose a minimal effective two-dimensional Hamiltonian for HgTe/CdHgTe quantum wells (QWs) describing the side maxima of the first valence subband. By using the Hamiltonian, we explore the picture of helical edge states in tensile and compressively strained HgTe QWs. We show that both dispersion and probability density of the edge states can differ significantly from those predicted by the Bernevig-Hughes-Zhang (BHZ) model. Our results pave the way towards further theoretical investigations of HgTe-based quantum spin Hall insulators with direct and indirect band gaps beyond the BHZ model.

cond-mat.mes-hall↗

arXiv2018

Temperature-induced topological phase transition in HgTe quantum wells

We report a direct observation of temperature-induced topological phase transition between trivial and topological insulator in HgTe quantum well. By using a gated Hall bar device, we measure and represent Landau levels in fan charts at different temperatures and we follow the temperature evolution of a peculiar pair of "zero-mode" Landau levels, which split from the edge of electron-like and hole-like subbands. Their crossing at critical magnetic field $B_c$ is a characteristic of inverted band structure in the quantum well. By measuring the temperature dependence of $B_c$, we directly extract the critical temperature $T_c$, at which the bulk band-gap vanishes and the topological phase transition occurs. Above this critical temperature, the opening of a trivial gap is clearly observed.

cond-mat.mtrl-sci↗

arXiv2017

Large gap quantum spin Hall insulator, massless Dirac fermions and bilayer graphene analogue in InAs/Ga(In)Sb heterostructures

The quantum spin Hall insulator (QSHI) state has been demonstrated in two semiconductor systems - HgTe/CdTe quantum wells (QWs) and InAs/GaSb QW bilayers. Unlike the HgTe/CdTe QWs, the inverted band gap in InAs/GaSb QW bilayers does not open at the $Γ$ point of the Brillouin zone, preventing the realization of massless Dirac fermions. Here, we propose a new class of semiconductor systems based on InAs/Ga(In)Sb multilayers, hosting a QSHI state, a graphene-like phase and a bilayer graphene analogue, depending on their layer thicknesses and geometry. The QSHI gap in the novel structures can reach up to 60 meV for realistic design and parameters. This value is twice as high as the thermal energy at room temperature and significantly extends the application potential of III-V semiconductor-based topological devices.

cond-mat.mtrl-sci↗

arXiv2017

Temperature-driven single-valley Dirac fermions in HgTe quantum wells

We report on temperature-dependent magnetospectroscopy of two HgTe/CdHgTe quantum wells below and above the critical well thickness $d_c$. Our results, obtained in magnetic fields up to 16 T and temperature range from 2 K to 150 K, clearly indicate a change of the band-gap energy with temperature. The quantum well wider than $d_c$ evidences a temperature-driven transition from topological insulator to semiconductor phases. At the critical temperature of 90 K, the merging of inter- and intra-band transitions in weak magnetic fields clearly specifies the formation of gapless state, revealing the appearance of single-valley massless Dirac fermions with velocity of $5.6\times10^5$ m$\times$s$^{-1}$. For both quantum wells, the energies extracted from experimental data are in good agreement with calculations on the basis of the 8-band Kane Hamiltonian with temperature-dependent parameters.

cond-mat.mtrl-sci↗

arXiv2016

Pressure and temperature driven phase transitions in HgTe quantum wells

We present theoretical investigations of pressure and temperature driven phase transitions in HgTe quantum wells grown on CdTe buffer. Using the 8-band \textbf{k$\cdot$p} Hamiltonian we calculate evolution of energy band structure at different quantum well width with hydrostatic pressure up to 20 kBar and temperature ranging up 300 K. In particular, we show that in addition to temperature, tuning of hydrostatic pressure allows to drive transitions between semimetal, band insulator and topological insulator phases. Our realistic band structure calculations reveal that the band inversion under hydrostatic pressure and temperature may be accompanied by non-local overlapping between conduction and valence bands. The pressure and temperature phase diagrams are presented.

cond-mat.mtrl-sci↗

arXiv2016

Temperature-dependent magnetospectroscopy of HgTe quantum wells

We report on magnetospectroscopy of HgTe quantum wells in magnetic fields up to 45 T in temperature range from 4.2 K up to 185 K. We observe intra- and inter-band transitions from zero-mode Landau levels, which split from the bottom conduction and upper valence subbands, and merge under the applied magnetic field. To describe experimental results, realistic temperature-dependent calculations of Landau levels have been performed. We show that although our samples are topological insulators at low temperatures only, the signature of such phase persists in optical transitions at high temperatures and high magnetic fields. Our results demonstrate that temperature-dependent magnetospectroscopy is a powerful tool to discriminate trivial and topological insulator phases in HgTe quantum wells.

cond-mat.mes-hall↗

arXiv2016

Phase transitions in two tunnel-coupled HgTe quantum wells. Bilayer graphene analogy and beyond

HgTe quantum wells possess remarkable physical properties as for instance the quantum spin Hall state and the 'single-valley' analog of graphene, depending on their layer thicknesses and barrier composition. However, double HgTe quantum wells yet contain more fascinating and still unrevealed features. Here we report on the study of the quantum phase transitions in tunnel-coupled HgTe layers separated by CdTe barrier. We demonstrate that this system has a 3/2 pseudo spin degree of freedom, which features a number of particular properties associated with the spin-dependent coupling between HgTe layers. We discover a specific metal phase arising in a wide range of HgTe and CdTe layer thicknesses, in which a gapless bulk and a pair of helical edge states coexist. This phase holds some properties of bilayer graphene such as an unconventional quantum Hall effect and an electrically-tunable band gap. In this 'bilayer graphene' phase, electric field opens the band gap and drives the system into the quantum spin Hall state. Furthermore, we discover a new type of quantum phase transition arising from a mutual inversion between second electron- and hole-like subbands. This work paves the way towards novel materials based on multi-layered topological insulators.

cond-mat.mes-hall↗

arXiv2016

Temperature-driven massless Kane fermions in HgCdTe crystals: verification of universal velocity and rest-mass description

It has recently been shown that the electronic states in bulk gapless HgCdTe offer another realization of pseudo-relativistic three-dimensional particles in a condensed matter system. These single valley relativistic states, referred to as massless Kane fermions, cannot be described by any other well-known relativistic massless particles. Furthermore, the HgCdTe band structure can be continuously tailored by modifying either the cadmium content or temperature. At the critical concentration or temperature, the bandgap, Eg, collapses as the system undergoes a semimetal-to-semiconductor topological phase transition between the inverted and normal alignments. Here, using far-infrared magneto-spectroscopy we explore the continuous evolution of band structure of bulk HgCdTe as temperature is tuned across the topological phase transition. We demonstrate that the rest-mass of the Dirac-like Kane fermions, m changes sign at the critical temperature, while their velocity, c remains constant. The relation Eg = 2mc2 with the universal value of c = (1.07 +- 0.05)10x6 m/s remains valid in a broad range of temperatures and Cd concentrations, indicating a striking universality of the pseudo-relativistic description of the Dirac-like Kane fermions in HgCdTe.

cond-mat.mtrl-sci↗

arXiv2013

Many-body corrections to ESR energy and spin-wave excitations in two-dimensional systems with Bychkov-Rashba spin splitting

We report effects of electron-electron (\emph{e-e}) interaction on electron spin resonance (ESR) in perpendicular magnetic field in two-dimensional (2D) systems with Bychkov-Rashba spin splitting induced by spin-orbit interaction (SOI) and structural inversion asymmetry (SIA). Using the Hartree-Fock approximation, we demonstrate that the SIA results in non-zero many-body corrections to the ESR energy and the energy of spin wave excitations. We discover that the \emph{e-e} interaction in 2D systems with SIA not only can enhance the ESR energy but can also lead to the ESR energy reduction. The magnitude of this effect exhibits remarkable features in a wide range of parameters relevant to experiment: it is found to be rather sensitive to the sign of g-factor and the filling factor of Landau levels $ν$. We derive analytical expressions for many-body corrections to ESR energy and the dispersion of spin wave excitations for the case of $ν\leq 2$. We have found out that \emph{e-e} interaction does not affect the ESR energy in the case of filling of the lowest Landau level ($ν\leq 1$) in 2D systems with positive g-factors even at arbitrarily large values of Bychkov-Rashba constant. The many-body renormalization of ESR energy in the case of fractional Quantum Hall effect is also discussed.

cond-mat.mes-hall↗