arXiv subjects

Ilya Grigorenko

Publications and source records attributed to Ilya Grigorenko.

17 recordsLinked to original sources

arXiv2014

Superfluidity in asymmetric electron-hole systems

The pairing in a system of electrons and holes in two spatially separated parallel planes is studied in the case of electron-hole asymmetry caused by the difference in the carriers masses and their chemical potentials. It is found that the superfluid state is possible in a wide range of the asymmetry parameters, because the asymmetries can effectively compensate each other. It is predicted that the system may exhibit two critical temperatures for some asymmetry parameters. The lower critical temperature corresponds to the superfluid transition induced by thermal fluctuations. In the asymmetric system a coexistence of the normal and superfluid states is possible even at zero temperature.

cond-mat.mes-hall↗

arXiv2013

The electron-hole superfluidity in two coaxial nanotubes

The superfluid phase and Coulomb drag effect caused by the pairing in the system of spatially separated electrons and holes in two coaxial cylindrical nanotubes are predicted. It is found that the drag resistance as a function of temperature experiences a jump at the critical temperature and can be used for the manifestation of the superfluid transition. It is demonstrated that at sufficiently low temperatures the order parameter and free energy density exhibit a kink due to the electron-hole asymmetry that is controlled by the radii of the nanotubes.

cond-mat.supr-con↗

arXiv2013

Evolutionary search for new high-k dielectric materials: methodology and applications to hafnia-based oxides

High-k dielectric materials are important as gate oxides in microelectronics and as potential dielectrics for capacitors. In order to enable computational discovery of novel high-k dielectric materials, we propose a fitness model (energy storage density) that includes the dielectric constant, bandgap, and intrinsic breakdown field. This model, used as fitness function in conjunction with first-principles calculations and global optimization evolutionary algorithm USPEX, efficiently leads to practically important results. We found a number of high-fitness structures of SiO2 and HfO2, some of which correspond to known phases and some are new. The results allow us to propose characteristics (genes) common to high-fitness structures - these are the coordination polyhedra and their degree of distortion. Our variable-composition searches in the HfO2-SiO2 system uncovered several high-fitness states. This hybrid algorithm opens up a new avenue of discovering novel high-k dielectrics with both fixed and variable compositions, and will speed up the process of materials discovery.

cond-mat.mtrl-sci↗

arXiv2011

Non-equilibrium local pair potential enhancement

We propose a new mechanism for the local pair potential enhancement with the help of electromagnetic control fields. The mechanism is based on the creation of non-equilibrium, spatially localized Bogoliubov quasiparticle excitations, which result in a significant enhancement of the local pair potential and the local transition temperature T_c.

cond-mat.supr-con↗

arXiv2011

Fractal nanostructures with the Hilbert curve geometry as a SERS substrate

We suggest a new type of substrates for the Surface Enhanced Raman Scattering measurements with the geometry based on self-similar fractal space filling curves. As an example, we have studied theoretically the dielectric response properties of doped semiconductor nanostructures, where the conducting electrons are trapped in the effective potential having the geometry of the Hilbert curve. We have found that the system may exhibit the induced charge distribution specific for either two dimensional or one dimensional systems, depending on the frequency of the external applied field. We have demonstrated that with the increasing of the depth of the trapping potential the resonance of the system counterintuitively shifts to lower frequencies.

cond-mat.mes-hall↗

arXiv2011

Superconductivity in bundles of a mixture of doped carbon nanotubes

Using inhomogeneous Bogoliubov-de Gennes formalism we study superconducting properties of bundles of single wall carbon nanotubes, consisting of a mixture of metallic and semiconducting nanotubes, having different critical transition temperatures. We investigate how the averaged superconducting order parameter and the critical transition temperature depend on the fraction of semiconducting carbon nanotubes in the bundle.

cond-mat.supr-con↗

arXiv2009

Strategies for optimal design for electrostatic energy storage in quantum multiwell heterostructures

The physical principles are studied for the optimal design of a quantum multiwell heterostructure working as an electrostatic energy storage device. We performed the search for an optimal multiwell trapping potential for electrons that results in the maximum static palarizability of the system. The response of the heterostructure is modeled quantum mechanically using nonlocal linear response theory. Three main design strategies are identified, which lead to the maximization of the stored energy. We found that the efficiency of each strategy crucially depends on the temperature and the broadening of electron levels. The energy density for optimized heterostructures can exceed the nonoptimized value by a factor more than $400$. These findings provide a basis for the development of new nanoscale capacitors with high energy density storage capabilities.

cond-mat.mes-hall↗

arXiv2009

Plasmonic Excitations in Tight-Binding Nanostructures

We explore the collective electromagnetic response in atomic clusters of various sizes and geometries. Our aim is to understand, and hence to control, their dielectric response, based on a fully quantum-mechanical description which captures accurately their relevant collective modes. The electronic energy levels and wave functions, calculated within the tight-binding model, are used to determine the non-local dielectric response function. It is found that the system shape, the electron filling and the driving frequency of the external electric field strongly control the resonance properties of the collective excitations in the frequency and spatial domains. Furthermore, it is shown that one can design spatially localized collective excitations by properly tailoring the nanostructure geometry.

cond-mat.str-el↗

arXiv2009

Optimal control of the local electromagnetic response of nanostructured materials: optimal detectors and quantum disguises

We consider the problem of optimization of an effective trapping potential in a nanostructure with a quasi-one-dimensional geometry. The optimization is performed to achieve certain target optical properties of the system. We formulate and solve the optimization problem for a nanostructure that serves either as a single molecule detector or as a "quantum disguise" for a single molecule.

cond-mat.mtrl-sci↗

arXiv2008

Coherent control near metallic nanostructures

We study coherent control in the vicinity of metallic nanostructures. Unlike in the case of control in gas or liquid phase, the collective response of electrons in a metallic nanostructure can significantly enhance different frequency components of the control field. This enhancement strongly depends on the geometry of the nanostructure and can substantially modify the temporal profile of the local control field. The changes in the amplitude and phase of the control field near the nanostructure are studied using linear response theory. The inverse problem of finding the external electromagnetic field to generate the desired local control field is considered and solved.

cond-mat.mes-hall↗

arXiv2008

Optimization of the design of superconducting inhomogeneous nanowires

We study optimization of superconducting properties of inhomogeneous nanowires. The main goal of this research is to find an optimized geometry that allows one to maximize the desired property of superconductors, such as the maximum value of local superconducting gap or total condensation energy. We consider axially symmetric design of multi-layered nanowires with possibility to adjust and change the layers thickness. We use numerical solution of the Bogoliubov-de Gennes equations to obtain the local superconducting gap for different arrangements of the inhomogeneous structures. The value of the optimized properties can be up to 300% greater compared to a non-optimized geometry. The optimized configuration of multilayers strongly depends on the desired property one wants to optimize and on the number of layers in the nanowire.

cond-mat.supr-con↗

arXiv2008

Design of resonators using materials with negative refractive index

By optimizing the design we show that inhomogeneous electromagnetic resonators with almost uniform field intensity and up to twice the energy density of conventional structures are possible by exploiting the properties of negative refractive index materials. materials. We demonstrate that using negative refractive index materials it is possible to make full width at half maximum (FWHM) of the transmission coefficient independent from cavity length L.

physics.optics↗

arXiv2008

Analytical solution for optimal squeezing of wave packet of a trapped quantum particle

Optimal control problem with a goal to squeeze wave packet of a trapped quantum particle is considered and solved analytically using adiabatic approximation. The analytical solution that drives the particle into a highly localized final state is presented for a case of an infinite well trapping potential. The presented solution may be applied to increase the resolution of atom lithography.

quant-ph↗

arXiv2008

Formation of collective excitations in quasi-one dimensional metallic nanostructures: size and density dependance

We investigate theoretically the formation of collective excitations in atomic scale quasi-one dimensional metallic nanostructures. The response of the system is calculated within the linear response theory and random phase approximation. For uniform nanostructures a transition from quantum single particle excitations to classical plasmon scaling is observed, depending on the system length and electron density. We find crucial differences in the scaling behavior for quasi-one dimensional and three-dimensional nanostructures. The presence of an additional modulating on-site potential is shown to localize electrons, leading to the response function that is highly sensitive to the number of electrons at low fillings.

cond-mat.mes-hall↗

arXiv2008

Optimal control of electromagnetic field using metallic nanoclusters

The dielectric properties of metallic nanoclusters in the presence of an applied electromagnetic field are investigated using non-local linear response theory. In the quantum limit we find a non-trivial dependence of the induced field and charge distribution on the spatial separation between the clusters and on the frequency of the driving field. Using a genetic algorithm, these quantum functionalities are exploited to custom-design sub-wavelength lenses with a frequency controlled switching capability.

cond-mat.mes-hall↗

arXiv2007

Bogoliubov angle and visualization of particle-hole mixture in superconductors

Superconducting excitations --Bogoliubov quasiparticles -- are the quantum mechanical mixture of negatively charged electron (-e) and positively charged hole (+e). Depending on the applied voltage bias in STM one can sample the particle and hole content of such a superconducting excitation. Recent Scanning Tunneling Microscope (STM) experiments offer a unique insight into the inner workings of the superconducting state of superconductors. We propose a new observable quantity for STM studies that is the manifestation of the particle-hole dualism of the quasiparticles. We call it a {\em Bogoliubov angle}. This angle measures the relative weight of particle and hole amplitude in the superconducting (Bogoliubov) quasiparticle. We argue that this quantity can be measured locally by comparing the ratio of tunneling currents at positive and negative biases. This Bogoliubov angle allows one to measure directly the energy and position dependent particle-hole admixture and therefore visualize robustness of superconducting state locally. It may also allow one to measure the particle-hole admixture of excitations in normal state above critical temperature and thus may be used to measure superconducting correlations in pseudogap state.

cond-mat.supr-con↗

arXiv2006

Electromagnetic response of broken-symmetry nano-scale clusters

A microscopic, non-local response theory is developed to model the interaction of electromagnetic radiation with inhomogeneous nano-scale clusters. The breakdown of classical continuum-field Mie theory is demonstrated at a critical coarse-graining threshold, below which macroscopic plasmon resonances are replaced by molecular excitations with suppressed spectral intensity.

cond-mat.str-el↗