Professor Dr. Yurii E. Lozovik

Curriculum vitae and main results
 

Institute for Spectroscopy,

Russian Academy of Sciences.

Troitsk, Moscow region

142190, Russia.

Skype: lozovik_yurii

E-mail: lozovik@isan.troitsk.ru, lozovik@mail.ru

Head of Laboratory of Spectroscopy of Nanostructures of Institute for Spectroscopy and also Professor of Physics in Moscow Institute of Physics and Technology – Technological University

Awards:

The Russian State Fellowship for Outstanding Scientists, prize for best publication in Russian scientific journals. According to Web of Science one of the most cited scientists of Russia (more than 5000 citations, h-index=33).

Scientific results:

More than 500 published papers (including 10 reviews and collective monographs) devoted to electron properties of nanostructures, low-dimensional electron systems, nanooptics, different aspects of solid state physics, cluster physics, nanotechnology, and ultrafast optics .

Teaching:

Tutor of 35 PhD theses. Lecture courses: Quantum nanostructures, Nanophotonics and Quantum Electrodynamics, Solid State Physics, Computer Simulations in Physics etc.

Conferences:

Invited and plenary talks at International conferences on nanostructures, photonics, laser physics. Lectures at Fermi School (Italy), Goteborg University etc.
The member of Organizing and International Advisory Committees of different International conferences(Nano and Giga Challenges in Electronics and Photonics; 15-th, 16-th International Conferences on the Electronic Properties of Two-Dimensional Systems, Int. Conf. on Excitonic coherent systems, Conferences on Physics of Clusters, etc.).
 

Member of Editorial Boards:

“Solid State Communications”, “Nanostructures.Mathematical Physics and Modelling” (Rus.) .
Societies Yu. Lozovik is fellow member of European Academy of Science.
 

Main recent scientific results

Recent results for graphene

• Plasmon and magnetoplasmon excitations in graphene and bilayer graphene were analyzed.

• Nanoelectromechanical systems based on relative motion and interaction of graphene layers: theory and simulation.

• Multiscale modeling of fluctuations, dissipation and diffusion in graphene based systems was developed. Diffusion of a graphene flake on a graphene was analyzed and a new diffusion mechanism was proposed , namely rotational transition of the flake from commensurate to incommensurate states with subsequent simultaneous rotation and translational motion until the another commensurate state is reached again, and so on.

• Collective effects of massless electrons and holes in graphene was analyzed. BCS-like state of massless Dirac fermions in two independently gated graphene layers separated by a barrier was considered. The essential distinctions from ordinary coupled quantum wells are particularly due to Berry phase in graphene and different screening properties. The energy gap in one-particle excitation spectrum for different interlayer distances and carrier concentrations is calculated. Influence of disorder is discussed. At large dielectric susceptibility of surrounding medium, the weak coupling regime holds even at arbitrarily small carrier concentrations contrary to the case of nonzero effective masses. Strong-coupling regime is discussed. Localized electron-hole pairs are absent in graphene, thus the behavior of the system versus coupling strength is cardinally different from usual BCS-BEC crossover. The e-h condensation can be observed through essential rise of e-h drag.

• One and coupled graphene layers in strong perpendicular magnetic field was considered. Magnetoexciton spectra and their effective magnetic mass in one and coupled graphene layers is studied in detail. The energy spectrum of collective excitations and quasi-condensation is studied.

• The possibility of superconducting pairing of electrons in doped graphene due to in-plane and out-of-plane phonons was studied. The sign and magnitude of contribution of each phonon mode to effective electron–electron interaction turns out to depend on both the symmetry of phonon mode and the structure of the order parameter. Unconventional orbital–spin symmetry of the order parameter is found.

• A novel type of photonic crystal formed by embedding a periodic array of constituent stacks of alternating graphene and dielectric discs into a background dielectric medium is proposed. The photonic band structure and transmittance of such photonic crystal are calculated. The advantages of the graphene-based photonic crystal are discussed.
 

Recent results for bilayer electron-hole system

• Effects of strong correlations in 2D exciton system on spectra, roton minimum formation and pair correlation function were studied in detail. Quantum crystal phase formation of dipolar excitons was studied.

• Supersolid phase in mesoscopic exciton systems which possesses simultaneously transverse elasticity and superfluidity (or diagonal and nondiagonal orders) was studied for the first time.

• New nonlinear optical effects for exciton coherent phase, laser stimulated backscattering and anomalous transmission were predicted. Quantum optics of coherent phase of excitons has been studied. The presence of angular correlation of photons due to coherent recombination of two or several excitons from Bose-condensate which can be studied in Hanbury Brown-Twiss- type experiments has been predicted.

• BCS-type instability of a bilayer (electron) system of composite fermions (at half Landau level filling) has been considered. The influence of composite fermion marginality due to strong correlation effects (the absence of weakly damping excitations near the Fermi surface) on BCS pairing has been analyzed. The competition of (composite) spatially separated electron-hole with electron-electron pairing controlled by interlayer separation was analyzed. Quantum phase transition controlled by interlayer separation is predicted.

Recent results for cavity polaritons Bose condensation

• The phase transition of the quasi-equilibrium system of exciton polaritons in optical microcavity with embedded quantum well was analyzed. As a result of exciton-cavity photon resonance interaction composite particles, exciton-polaritons, superposition of microcavity photons and excitons are formed in the system. Although the system contains two types of bosons, cavity photons and excitons undergoing mutual transformations, only one Kosterlitz-Thouless phase transition to the superfluid state with the quasi-long-range order takes place in this two-dimensional system. We derived an expression for the effective low-energy action for thermodynamic phase fluctuations and simultaneously obtain the expression for “superfluid density” of the cavity polariton system in terms of the current–current correlation function. In result the transition temperature to “superfluid state” of polaritons was found as the function of exciton-photon detuning. A new physical system—excitons in a photon crystal—has been proposed for the Bose condensation of exciton polaritons. 2D trap for cavity polariton was analyzed. The spatial distribution of photons and excitons in Bose-condensed polaritons in the trap was obtained.

• The drag effects in the system of spatially separated electrons and excitons in an optical microcavity are predicted. It is shown that at low temperature an electron current induces the polariton flow, therefore, a transport of photons along the cavity. However, the superfluid polariton component does not contribute to the electron drag.

• Traps for cavity polaritons were analyzed, spatial profiles of coupled photon and exciton Bose-condensates were calculated as function of pumping.

Nanostructures.1.Electron-hole systems

1. The superfluidity, Josephson-type effects (in nonsuperconducting systems), drag effects, anomalous behavior in external magnetic fields, some unusual coherent optical properties and phase diagram for the spatially separated electron-hole systems were predicted for the first time. The theory of Bose-condensation and superfluidity of 2D excitons in traps and in random fields was developed. These papers open the perspective physics of coherent phenomena in exciton system in coupled quantum wells and dipole excitons in single quantum wells in strong normal electric field. Theory of strongly correlated exciton liquid in the form of generalized DFT theory with spontaneous breaking of symmetry. Now in this region of investigation very interesting experimental results were obtained.

2. The theory of two-dimensional electron-hole system in strong magnetic fields was developed. Theory of two-dimensional magnetoexcitons was developed. The exact solution for the many-body problem of 2D electron-hole system in strong magnetic field was obtained: the ground state at any Landau level filling and any form of interaction (e.g. on taking into account image forces) due to supersymmetry is Bose condensed ideal (!) gas of magnetoexcitons. The class of exact solutions for analogous systems were obtained. Phase diagram, excitations and thermodynamics of the system were studied. The thermodynamics, excitations and some other properties of nonideal system (when interaction between electrons and holes are slightly nonsymmetrical or due to (small at high magnetic fields) contribution of virtual transitions to higher Landau levels) was studied. The papers occurred to be starting point for a set of brilliant experimental and theoretical works in the field.

3. Bose condensation and effects of strong correlations of exciton systems in traps, quantum dots, coupled quantum dots (quantum dot molecules) etc., in particular, in strong magnetic fields were considered. Strongly correlated phases were analyzed. Phase diagram of mesoscopic quantum exciton system was studied.

4. Dispersion curves of two-dimensional magnetoexcitons were analyzed for the first time. It was shown that at asymptotically high magnetic fields magnetoexcitons effective mass is proportional to square root of magnetic field and it does not depend on bare electron and hole effective masses but determined only by electron-hole interaction. It was shown also that excited magnetoexciton dispersion curve is nonmonotonous function of (magnetic) momentum, i.e. “roton” minima were predicted for magnetoexciton dispersion curve. These results are in agreement with later experiments.

5. The dispersion engineering of interwell excitons and luminescence control by parallel magnetic field were proposed and experimentally realized. This gives the possibility to determine experimentally the exciton dispersion law (with the help of fluorescence) and the dependence of the exciton mass on the magnetic field. It was shown that in strong magnetic fields, in accordance with our theory the magnetoexciton effective mass at high magnetic fields is much greater than sum of the electron and hole band masses. The instant transformation of exciton in weak fixed magnetic field to magnetoexciton (corresponding to high effective magnetic field regime) with the increase of the exciton momentum was studied.

6. Dispersion engineering of spatially indirect excitons in the coupled quantum wells by external electric and magnetic fields in order to generate coherent acoustic phonons, to control exciton luminescence and to detect Bose condensate of excitons was proposed.

7. The system of interacting spatially-separated excitons and electrons, particularly in the presence of Bose-condensate of excitons was analyzed. The kinetic properties of the system connected with electron-exciton drag effects have been studied. The expressions for linear response coefficients of the electron subsystem to the quantities magnitudes determining nonequlibrium state in the subsystem of excitons have been obtained. Experimental observation of these drag effects can give new information about the phase state of excitons by study the electric response in the electron layer and, moreover, give a new way of control of excitons with the use of electrons transport.

Nanostructures. 2.Electron systems

1. Magnetic field induced electron crystallization in 2D system based on suppression of zero-point oscillation by the field was predicted for the first time. The phase diagram and the oscillation spectra for 2D Wigner crystal in high magnetic field was calculated both from first principles and phenomenologically and also by computer simulations. Image forces influence on the phase diagram was analyzed. The set of these papers gave the first example of the influence of magnetic field on phases of 2D electron system and initiated many interesting theoretical and experimental works in physics of 2D electron gas.

2. Crystallization of mesoscopic electron systems was studied in detail. Many-stage phase transitions, intershell orientational melting and subsequent radial shell melting were revealed for the first time. The connection of these phenomena with smallness of energy barriers relative to intershell rotation relative to intershell electron jump was revealed.

3. The ground state and one-particle excitations, composite fermions at half-filled Landau level for two-dimensional electron gas with anisotropic band-mass tensor were studied. Using asymptotic Ward identities of Chern-Simons theory it was shown that the composite fermions Fermi surface is not renormalized by infrared gauge fluctuations. Thus its form is identical to that of an anisotropic electron Fermi surface in the absence of the magnetic field.

4. Quantum Hall effect has been considered in drift approach. The connection between quantized Hall conductance and geometrical topological invariant in the system has been revealed. The drift resonance in 2D system of electrons in strong magnetic fields connected with resonance excitation of drift boundary currents along external and internal boundaries of the system was analyzed in detail. It has been shown that it represents the properties of fractal contours of random potential.

5. The BCS-type instability of a bilayer system of composite fermions (at half Landau level filling) has been considered. The influence of composite fermion marginality due to strong correlation effects (the absence of weakly damping excitations near the Fermi surface) on BCS pairing has been analyzed. The competition of (composite) spatially separated electron-hole with electron-electron pairing controlled by interlayer separation was analyzed.

Solid State Physics. General Problems.

1. Weak localization of excitons, plasmons and their spectra in disordered systems was considered.

2. Weak localization of particles with random effective mass was studied.

3. New methods for the phonon laser creation were studied.

4. The self-consistent theory of anharmonic crystals and their melting was developed. The theory take into account skeleton diagrams which have the same order on Lindemann parameter. The ab initio theory predicts melting points and behavior of transverse phonons as function of the temperature and quantum parameter. The results obtained are in good agreement with the numerical simulations for 2D crystals and with experimental results for Wigner and dipole crystals. The existence of some almost universal parameters (such as Lindemann parameter etc.) for crystal was explained. Empirical melting criterion, particularly Lindemann criterion was generalized and proved for the two-dimensional systems (usual Lindemann criterion is of no use for two dimensions, because the mean squared displacement of a particle from the crystal site diverges in thermodynamical limit ).

Superfluidity

1. Strongly correlated phase, mesoscopic supersolid was considered for atoms with induced dipoles or dipole excitons confined in a trap.

2. The system of mesoscopic traps with Bose-condensate of atoms (or excitons) with Josephson coupling was considered in detail.

3. The Bose-condensation of atoms and strong-correlation in Tonks regime in the quasi-one-dimensional traps was considered.

4. The drag effects in two vertically coupled traps with Bose-condensed atoms were studied.

Quantum electrodynamics in a cavity

1. Lamb shift controlling for atom in a cavity was studied. “Dynamic Lamb effect” ( the parametric, photonless atom excitation in nonstationary cavity due to nonadiabatic modulation of Lamb shift by cavity modulation) ¬was predicted. The effect has no relation to the dynamical Casimir effect and thus should be considered as a new vacuum quantum electrodynamical effect.

2. Distribution and squeezing of photons generated in nonstationary cavity was calculated interaction of modes in nonstationary cavity being taken into account.

3. The experimental realization of dynamical Casimir effect, parametric excitation of photons in a cavity due to instantaneous change of boundary conditions induced by laser pulses or electron injection is proposed.

Atoms, molecules

1. Anapole (toroidal) moment of atom electron shell induced by parity nonconservation due to weak interactions effects was predicted.

2. Spectra of atoms, molecules and biexcitons in strong magnetic fields were studied. Paramagnetism of many-electron atoms in strong magnetic fields was considered. Thomas-Fermi equation for atoms was generalized for nonhomogeneously magnetized electron liquid in strong magnetic fields. Magnetic dissociation of molecules (or biexcitons) and change of the binding type in high magnetic field was predicted. This phenomena was observed experimentally for biexcitons. Magnetic field induced van der Waals binding was considered.

3. Channelling of molecules and atoms in light fields was studied by means of computer simulation. The results can be useful to control atomic and molecular motions for driving nanolocal chemical reaction and also for nanotechnological applications.

Computer Simulations

1. Computer simulations of set of physical systems (low-dimensional systems, clusters, cooled atoms etc. with different interparticle interactions ) study of their spectra, thermodynamical properties and phase transitions were performed by molecular dynamics, classical and quantum Monte Carlo, Path Integral Quantum Monte Carlo, Wigner quantum dynamics and other techniques.

2. Computer simulation and design of different photonic crystals by FDTD, LKKR, plane wave methods. New type of photonic crystal, superconducting photonic crystals (with photonic band spectra controlled by temperature and/or magnetic field) was studied

3. Computer design of new materials (esp., nanomaterials and materials for photonics).

4. Ab initio DFT simulation of nanotubes etc. Study of energy barriers, elastic and electronic properties of nanotubes.

5. New methods of simulations of quantum systems based on quantum tomography and also Wigner formulation of quantum mechanics were developed and used in a set of physical problems: wave packet tunneling, weak localization etc. Time arrival of wave packet after passage through the tunneling barrier was studied in detail.

6. The multiscale computer method to model the elements of optical chemosensors based on the phonic crystals was developed.

General problems

1. General analysis of phase transitions in 2D systems using conformal theories was fulfilled.

2. Equation of state for anyons (quasiparticles with fractional statistics) was analyzed.

3. Analytical, nonperturbative approaches to few-body quantum systems based on -expansion near the space dimension d=2, as well as the 1/d-expansion, where d is the space dimensionality were developed.

4. Mechanism of quark confinement was proposed based on stochastic behavior of gluon field and Anderson localization in corresponding disordered effective potential.

Nanotechnology.

1. Nanolithography and nanolocal optical study based on irradiation of tip of scanning tunneling microscope by ultrashort laser pulses were studied. The method demonstrates the possibility of ultradense laser writing (λ/40 where λ is wavelength). Detailed calculations of local resonances and spatial distributions of optical fields near tip of STM were performed . The method uses nanolocal “bright spot” under STM tip originated from “lightning rod” effect and excitation of local plasmon resonance. It is proposed to use this effect also for providing nanolocal chemical reactions, for nanolocal coherent control of molecules and biological objects, for linear and nonlinear optical and spectroscopy study with high spatial resolution.

Quantum dots.

1. New topological phase (new Berry phase) for 2D quantum dots with odd number of electrons is revealed. The theory is in agreement with experiments on q dots with three electrons in strong magnetic field.

2. The consistent microscopic theory of collective excitations in quantum dos and arrays of quantum dots in strong magnetic fields based on generalized RPA (taking into account all diagrams of the same order on small dimensionless parameter characterizing the dot) has been developed. The phenomena of drift resonance in that system on the example of Fermi equipotentials of random potential on Fermi level has been predicted.

3. Strong correlated electron liquid state in quantum dot based on summing of expansion on deviation from electron crystallized state was studied.

4. Spin state transformation of quantum dot molecules was studied

NEMS.

1. Nanomechanics connected with relative motion of nanotube shells was developed. Regimes of work of NEMS (nanoelectromechanical systems) were analyzed.

2. New types of NEMS based on nanotubes were proposed: nanothermometer, nanovaristor, nanoswitch, memory elements etc.

Clusters, nanoparticles, nanotubes

1. Computer simulations and theory phase transition-like phenomena in nanoscale systems.

2. Shell structure and structural rearrangement in different clusters were analyzed in detail. Two-stage melting was discovered in classical and quantum many-shell clusters (orientational melting, which leads to relative reorientation of “crystallized” shells and then radial melting, resulting in disappearance of shells). Potential barriers for relative rotation of shells of carbon nanoparticles and many-shell nanotubes have been studied. It was found that two-stage melting is connected with smallness of potential barrier between neighbor shells (originated from their incommensurability) in comparison with potential barrier relating to jump of particle between the shells.

3. Computer simulations of spectra, thermodynamic and phase transitions of two-dimensional electronic, dipole, van der Waals and other extended systems, quantum wells, quantum dots and clusters were performed by molecular dynamics, classical and diffusional quantum Monte Carlo, Path Integral Quantum Monte Carlo, Wigner quantum dynamics and Quantum tomography.

4. Topological classification of spherical molecules and clusters was developed.

5. Mechanisms of the formation of new carbon molecules - fullerenes, nanoparticles, nanotubes and cones have been analyzed in detail.

6. The size dependent anomalous high diamagnetism or paramagnetism of clusters was studied.

Plasmon optics. Nanooptics.

1. New surface-sensitive method of time-resolved surface plasmon optics was proposed and experimentally realized. The nonlinear optical response connected with the synchronized excitation of two surface plasmon-polariton waves, their nonlinear interaction and photon generation with the sum frequency was studied. The dependence of this process versus the temporal delay between two laser pulses and the mutual spatial overlapping of the laser beams on the surface were studied.

2. Anomalous scattering of electromagnetic waves on composite media consisting from particles with magnetic shell was predicted. The possibility of creation of “invisible” covering of this type was analyzed.

3. Light backscattering in disordered 2D media due to weak localization phenomena was studied.

4. Properties of new types of photonic crystal, superconducting photonic crystals and graphene based photonic crystals were studied.

5. The Borrmann-type effect, which is related to the microscopic distribution of the electromagnetic field inside the primitive cell, was studied in photonic and magnetophotonic crystals. This effectis responsible for the enhancement or suppression of various linear and nonlinear optical effects when the incidence angle and/or the frequency change. It is shown that by design of the primitive cell of photonic crystal this effect can be suppressed and even inverted.

Ultrafast Optics.

1. Damping of quasiparticles near the Fermi surface, Fermi-liquid properties and possible deviation from Landau description in strongly correlated electron systems (in underdoped oxide superconductors) were studied by femtosecond pump-supercontinuum probe method.

2. The temporal evolution of superconducting state after femtosecond laser pulse excitation was studied in detail by time- resolved, femtosecond laser spectroscopy (by pump-supercontinuum probe method).

3. New method for determination of mobility edge in disordered materials by femtosecond pump-supercontinuum probe spectroscopy was proposed and experimentally realized. The method is based on the determination of the spectral dependence of a stretched exponential relaxation in a wide probing spectral range. The method was demonstrated for porous silicon. The spectral dependence of stretched exponential index gives the unique information about existence and position of the mobility edge in disordered materials, and thus may be used as effective tool in manifestation of the transition from localized to delocalized relaxation regime on the femtosecond time scale.

4. Our femtosecond laser spectroscopy studies open the door for highly efficient relaxation time spectroscopy which can be sensitive tool in the cases when ordinary stationary spectroscopy can not reveal any specific behavior (e.g. near Fermi level position in metals, near mobility edge in disordered semiconductor etc.).