Publications (108)253.45 Total impact
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ABSTRACT: We present a theory of the electron structure and the Zeeman effect for the helical edge states emerging in twodimensional topological insulators based on HgTe/HgCdTe quantum wells with strong natural interface inversion asymmetry. The interface inversion asymmetry, reflecting the real atomistic structure of the quantum well, drastically modifies both bulk and edge states. For the inplane magnetic field, this asymmetry leads to a strong anisotropy of the edgestate effective $g$factor which becomes dependent on the edge orientation. The interface inversion asymmetry also couples the counter propagating edge states in the outofplane magnetic field leading to the opening of the gap in the edgestate spectrum by arbitrary small fields. 
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ABSTRACT: We uncover the fine structure of a silicon vacancy in isotopically purified silicon carbide (4H$^{28}$SiC) and find extra terms in the spin Hamiltonian, originated from the trigonal pyramidal symmetry of this spin3/2 color center. These terms give rise to additional spin transitions, which are otherwise forbidden, and lead to a level anticrossing in an external magnetic field. We observe a sharp variation of the photoluminescence intensity in the vicinity of this level anticrossing, which can be used for a purely alloptical sensing of the magnetic field. We achieve dc magnetic field sensitivity of 87 nT Hz$^{1/2}$ within a volume of $3 \times 10^{7}$ mm$^{3}$ at room temperature and demonstrate that this contactless method is robust at high temperatures up to at least 500 K. As our approach does not require application of radiofrequency fields, it is scalable to much larger volumes. For an optimized lighttrapping waveguide of 3 mm$^{3}$ the projection noise limit is below 100 fT Hz$^{1/2}$.  [Show abstract] [Hide abstract]
ABSTRACT: The driving of charge carriers confined in a quantum well lacking the center of space inversion by an alternating electric field leads to the formation of a direct electric current. We develop a microscopic theory of such a quantum ratchet effect for quantum wells subjected to a static magnetic field. We show that the ratchet current emerges for a linearly polarized alternating electric field as well as a rotating electric field and drastically increases at the cyclotron resonance conditions. For the magnetic field tilted with respect to the quantum well normal, the ratchet current contains an additional resonance at the first subharmonic of the cyclotron resonance. 
Dataset: 658

Dataset: 658
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ABSTRACT: We study the polarization optical properties of microcavities with embedded (110)oriented quantum wells. The spin dynamics of exciton polaritons in such structures is governed by the interplay of the spinorbit splitting of exciton states, which is odd in the inplane momentum, and the longitudinaltransverse splitting of cavity modes, which is even in the momentum. We demonstrate the generation of polariton spin currents by linearly polarized optical pump and analyze the arising polariton spin textures in the cavity plane. Tuning the excitation spot size, which controls the polariton distribution in the momentum space, one obtains symmetric or asymmetric spin textures.  [Show abstract] [Hide abstract]
ABSTRACT: We develop a theory of thermal fluctuations of spin density emerging in a twodimensional electron gas. The spin fluctuations probed at spatially separated spots of the sample are correlated due to Brownian motion of electrons and spinobit coupling. We calculate the spatiotemporal correlation functions of the spin density for both ballistic and diffusive transport of electrons and analyze them for different types of spinorbit interaction including the isotropic Rashba model and persistent spin helix regime. The measurement of spatial spin fluctuations provides direct access to the parameters of spinorbit coupling and spin transport in conditions close to the thermal equilibrium.  [Show abstract] [Hide abstract]
ABSTRACT: We report on the observation of cyclotron resonance induced photocurrents, excited by continuous wave terahertz radiation, in a 3D topological insulator (TI) based on an 80 nm strained HgTe film. The analysis of the photocurrent formation is supported by complimentary measurements of magnetotransport and radiation transmission. We demonstrate that the photocurrent is generated in the topologically protected surface states. Studying the resonance response in a gated sample we examined the behavior of the photocurrent, which enables us to extract the mobility and the cyclotron mass as a function of the Fermi energy. For high gate voltages we also detected cyclotron resonance (CR) of bulk carriers, with a mass about two times larger than that obtained for the surface states. The origin of the CR assisted photocurrent is discussed in terms of asymmetric scattering of TI surface carriers in the momentum space. Furthermore, we show that studying the photocurrent in gated samples provides a sensitive method to probe the effective masses and the mobility of 2D Dirac surface states, when the Fermi level lies in the bulk energy gap or even in the conduction band.  [Show abstract] [Hide abstract]
ABSTRACT: We report on a magnetophotoluminescence (PL) study of Mn modulationdoped InAs/InGaAs/InAlAs quantum wells. Two PL lines corresponding to the radiative recombination of photoelectrons with free and boundonMn holes have been observed. In the presence of a magnetic field applied in the Faraday geometry both lines split into two circularly polarized components. While temperature and magnetic field dependences of the splitting are well described by the Brillouin function, providing an evidence for exchange interaction with spin polarized manganese ions, the value of the splitting exceeds the expected value of the giant Zeeman splitting by two orders of magnitude for a given Mn density. Possible reasons of this striking observation are discussed.  [Show abstract] [Hide abstract]
ABSTRACT: The valley degeneracy of electron states in graphene stimulates intensive research of valleyrelated optical and transport phenomena. While many proposals on how to manipulate valley states have been put forward, experimental access to the valley polarization in graphene is still a challenge. Here, we develop a theory of the second optical harmonic generation in graphene and show that this effect can be used to measure the degree and sign of the valley polarization. We show that, at the normal incidence of radiation, the second harmonic generation stems from imbalance of carrier populations in the valleys. The effect has a specific polarization dependence reflecting the trigonal symmetry of electron valley and is resonantly enhanced if the energy of incident photons is close to the Fermi energy.  [Show abstract] [Hide abstract]
ABSTRACT: The highfrequency (ac) conductivity of a high quality modulation doped GeSi/Ge/GeSi single quantum well structure with hole density $p$=6$\times$10$^{11}$cm$^{2}$ was measured by the surface acoustic wave (SAW) technique at frequencies of 30 and 85~MHz and magnetic fields $B$ of up to 18 T in the temperature range of 0.3  5.8 K. The acoustic effects were also measured as a function of the tilt angle of the magnetic field with respect to the normal of the twodimensional channel at $T$=0.3 K. It is shown, that at the minima of the conductivity oscillations, holes are localized on the Fermi level, and that there is a temperature domain in which the highfrequency conductivity in the bulk of the quantum well is of the activation nature. The analysis of the temperature dependence of the conductivity at odd filling factors enables us to determine the effective $g_z$ factor. It is shown that the inplane component of the magnetic field leads to an increase of the cyclotron mass and to a reduction of the $g_z$ factor. We developed a microscopic theory of these effects for the heavyhole states of the complex valence band in quantum wells which describes well the experimental findings.  [Show abstract] [Hide abstract]
ABSTRACT: We describe the fine structure of Dirac states in HgTe/CdHgTe quantum wells of critical and closetocritical thickness and demonstrate the formation of an anticrossing gap between the tips of the Dirac cones driven by interface inversion asymmetry. By combining symmetry analysis, atomistic calculations, and kp theory with interface terms, we obtain a quantitative description of the energy spectrum and extract the interface mixing coefficient. The zeromagneticfield splitting of Dirac cones can be experimentally revealed in studying magnetotransport phenomena, cyclotron resonance, Raman scattering, or THz radiation absorption. 
Conference Paper: AC Transport in pGe/GeSi Quantum Well in High Magnetic Fields
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ABSTRACT: The contactless surface acoustic wave technique is implemented to probe the highfrequency conductivity of a highmobility pGe/GeSi quantum well structure in the regime of integer quantum Hall effect (IQHE) at temperatures 0.35.8 K and magnetic fields up to 18 T. It is shown that, in the IQHE regime at the minima of conductivity, holes are localized and ac conductivity is of hopping nature and can be described within the "twosite" model. The analysis of the temperature and magneticfieldorientation dependence of the ac conductivity at odd filing factors enables us to determine the effective hole gfactor, vertical bar g(zz)vertical bar approximate to 4.5. It is shown that the inplane component of the magnetic field leads to a decrease in the gfactor as well as increase in the cyclotron mass, which is explained by orbital effects in the complex valence band of germanium.  [Show abstract] [Hide abstract]
ABSTRACT: We study the orbital and spin dynamics of charge carriers induced by nonoverlapping linearly polarized light pulses in semiconductor quantum wells (QWs). It is shown that such an optical excitation with coherent pulses leads to a spin orientation of photocarriers and an electric current. The effects are caused by the interference of optical transitions driven by individual pulses. The distribution of carriers in the spin and momentum spaces depends on the QW crystallographic orientation and can be efficiently controlled by the pulse polarizations, time delay and phase shift between the pulses, as well as an external magnetic field.  [Show abstract] [Hide abstract]
ABSTRACT: Photoluminescence (PL) and highly circularlypolarized magnetoPL (up to 50% at 6 T) from twostep bandgap InAs/InGaAs/InAlAs quantum wells (QWs) are studied. Bright PL is observed up to room temperature, indicating a high quantum efficiency of the radiative recombination in these QW. The sign of the circular polarization indicates that it stems from the spin polarization of heavy holes caused by the Zeeman effect. Although in magnetic field the PL line are strongly circularly polarized, no energy shift between the counterpolarized PL lines was observed. The results suggest that the electron and the hole gfactor to be of the same sign and close magnitudes.  [Show abstract] [Hide abstract]
ABSTRACT: We study the tunneling of conduction electrons through a (110)oriented singlebarrier heterostructure grown from IIIV semiconductor compounds. It is shown that, due to low spatial symmetry of such a barrier, the tunneling current through the barrier leads to an electron spin polarization. The inverse effect, generation of a direct tunneling current by spin polarized electrons, is also predicted. We develop the microscopic theory of the effects and show that the spin polarization emerges due to the combined action of the Dresselhaus spinorbit coupling within the barrier and the Rashba spinorbit coupling at the barrier interfaces.  [Show abstract] [Hide abstract]
ABSTRACT: We report on the observation of magnetic quantum ratchet effect in metaloxidesemiconductor fieldeffecttransistors on silicon surface (SiMOSFETs). We show that the excitation of an unbiased transistor by ac electric field of terahertz radiation at normal incidence leads to a direct electric current between the source and drain contacts if the transistor is subjected to an inplane magnetic field. The current rises linearly with the magnetic field strength and quadratically with the ac electric field amplitude. It depends on the polarization state of the ac field and can be induced by both linearly and circularly polarized radiation. We present the quasiclassical and quantum theories of the observed effect and show that the current originates from the Lorentz force acting upon carriers in asymmetric inversion channels of the transistors.  [Show abstract] [Hide abstract]
ABSTRACT: We study the electron spin relaxation in both symmetric and asymmetric GaAs/AlGaAs quantum wells (QWs) grown on (110) substrates in an external magnetic field B applied along the QW normal. The spin polarization is induced by circularly polarized light and detected by timeresolved Kerr rotation technique. In the asymmetric structure, where a {\delta}doped layer on one side of the QW produces the Rashba contribution to the conductionband spinorbit splitting, the lifetime of electron spins aligned along the growth axis exhibits an anomalous dependence on B in the range 0<B<0.5 T; this results from the interplay between the Dresselhaus and Rashba effective fields which are perpendicular to each other. For larger magnetic fields, the spin lifetime increases, which is the consequence of the cyclotron motion of the electrons and is also observed in (001)grown quantum wells. The experimental results are in agreement with the calculation of the spin lifetimes in (110) grown asymmetric quantum wells described by the point group Cs where the growth direction is not the principal axis of the spinrelaxationrate tensor. 
Conference Paper: Spin structure of electron subbands in (110)grown quantum wells
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ABSTRACT: We present the theory of fine structure of electron states in symmetric and asymmetric zincblendetype quantum wells with the (110) crystallographic orientation. By combining the symmetry analysis, sp 3 d 5 s* tightbinding method, and envelopefunction approach we obtain quantitative description of inplane wave vector, well width and applied electric field dependencies of the zeromagneticfield spin splitting of electron subbands and extract spinorbitcoupling parameters.
Publication Stats
1k  Citations  
253.45  Total Impact Points  
Top Journals
Institutions

2015

Saint Petersburg State University
SanktPeterburg, St.Petersburg, Russia


20012015

Ioffe Physical Technical Institute
 Centre of Nanoheterostructure Physics
SanktPeterburg, St.Petersburg, Russia


19982014

Russian Academy of Sciences
 Ioffe PhysicalTechnical Institute
Moskva, Moscow, Russia


2013

Imperial College London
Londinium, England, United Kingdom
