Spatial distribution of local density of states in vicinity of impurity on semiconductor surface

We present the results of detailed theoretical investigations of changes in local density of total electronic surface states in 2D anisotropic atomic semiconductor lattice in vicinity of impurity atom for a wide range of applied bias voltage. We have found that taking into account changes in density of continuous spectrum states leads to the formation of a downfall at the particular value of applied voltage when we are interested in the density of states above the impurity atom or even to a series of downfalls for the fixed value of the distance from the impurity. The behaviour of local density of states with increasing of the distance from impurity along the chain differs from behaviour in the direction perpendicular to the chain. The article is published in the original.     

Controlling Fano resonance of nanowire surface plasmons

We theoretically study the effect of the applied magnetic field on the scattering properties of the nanowire surface plasmons coupled to two quantum dots. The dispersion relations of the surface plasmon are found to be upwardly displaced in the presence of an applied magnetic field. The symmetric double peaks in the transmission spectrum resulting from the interference between the localized and delocalized channels of the surface plasmon can combine together and the associated Fano lineshape will be smeared out when increasing the magnitude of the magnetic field.     

Fano resonance in the impurity photoconductivity spectrum of InP doped with shallow donors

The Fano resonances in the impurity photoconductivity spectra of n-InP are investigated theoretically and experimentally. It is shown that the calculations describe the experimental data with an accuracy of up to 20%.     

Spin-flip induction of Fano resonance upon electron tunneling through atomic-scale spin structures

The inclusion of inelastic spin-dependent electron scatterings by the potential profiles of a single magnetic impurity and a spin dimer is shown to induce resonance features due to the Fano effect in the transport characteristics of such atomic-scale spin structures. The spin-flip processes leading to a configuration interaction of the system’s states play a fundamental role for the realization of Fano resonance and antiresonance. It has been established that applying an external magnetic field and a gate electric field allows the conductive properties of spin structures to be changed radically through the Fano resonance mechanism.     

Effect of spin-orbit interaction on a magnetic impurity in the vicinity of a surface

We propose a new mechanism for surface-induced magnetic anisotropy to explain the thickness dependence of the Kondo resistivity of thin films of dilute magnetic alloys. The surface anisotropy energy, generated by spin-orbit coupling on the magnetic impurity itself, is an oscillating function of the distance d from the surface and decays as 1/d2. Numerical estimates based on simple models suggest that this mechanism, unlike its alternatives, gives rise to an effect of the desired order of magnitude.     

Scanning tunneling microscopy of the nonequilibrium interaction of impurity states at semiconductor surfaces

Interaction of two localized impurity states of Si atoms at a GaAs surface was studied by scanning tunneling microscopy and spectroscopy. The effects of a twofold “switching” on and off of the states of each of the interacting atoms, the tunneling-interaction-induced mutual level pulling of these states, and the level stabilization near E _F were observed. These effects are explained in terms of the extended Anderson model.     

The influence of tunneling matrix element modification due to on-site Coulomb interaction on local tunneling conductivity

Interplay between changes of energy levels and tunneling amplitudes caused by localized electrons’ on-site Coulomb interaction depending on non-equilibrium electron filling numbers is analyzed. Specific features of local tunneling conductivity spectra for different positions of localized states’ energy relative to the Fermi level have been investigated by means of self-consistent mean field approximation in the presence of non-equilibrium effects. The conditions when modifications of tunneling transfer amplitude due to changes of electron filling numbers in the presence of on-site Coulomb interaction should be taken into account in tunneling conductivity spectra have been revealed.     

Fano resonance analysis in a pair of semiconductor quantum dots coupling to a metal nanowire

We investigate theoretically a surface plasmon transport in the metal nanowire coupling to a pair of quantum dots. The Fano-type transmission spectrum is analyzed. The phase shift and group velocity delay of the transmitted surface plasmon are explored. The electromagnetically-induced-transparency-type transmission spectrum is also discussed.     

Quantum discreteness effects and flicker fluctuations in tunneling conductivity

An analysis of events in the tunneling junction shows that the interaction of one-electron processes in a many-electron system may be a source of scale-invariant low-frequency fluctuations of conductivity (the interaction consists in that the quantum probability of an electron transition depends on fast random changes in the environment in the course of the transition, including the changes caused by analogous transitions). The theory relates flicker fluctuations in the tunneling conductivity to the discrete character of the spectrum of electron states and explains the nonlinearity of the noise-current characteristic observed in nanocomposites.     

High-sensitivity Bloch surface wave sensor with Fano resonance in grating-coupled multilayer structures

A new type of device consisting of a lithium niobate film coupled with a distributed Bragg reflector (DBR) was theoretically proposed to explore and release Bloch surface waves for applications in sensing and detection. The film and grating made of lithium niobate (LiNbO₃) were placed on both sides of the DBR and a concentrated electromagnetic field was formed at the film layer. By adjusting the spatial incidence angle of the incident light, two detection and analysis modes were obtained, including surface diffraction detection and guided Bloch detection. Surface diffraction detection was used to detect the gas molecule concentrations, while guided Bloch detection was applied for the concentration detection of biomolecule-modulated biological solutions. According to the drift of the Fano curve, the average sensor sensitivities from the analysis of the two modes were 1560 °/RIU and 1161 °/RIU, and the maximum detection sensitivity reached 2320 °/RIU and 2200 °/RIU, respectively. This study revealed the potential application of LiNbO₃ as a tunable material when combined with DBR to construct a new type of biosensor, which offered broad application prospects in Bloch surface wave biosensors.     

Signature of a Fano resonance in a plasmonic metamolecule's local density of optical states

We present measurements on plasmonic metamolecules under local excitation using cathodoluminescence which show a spatial redistribution of the local density of optical states at the same frequency where a sharp spectral Fano feature in extinction has been observed. Our analytical model shows that both near- and far-field effects arise due to interference of the same two eigenmodes of the system. We present quantitative insights both in a bare state, and in a dressed state picture that describe Fano interference either as near-field amplitude transfer between coupled bare states, or as interference of uncoupled eigenmodes in the far field. We identify the same eigenmode causing a dip in extinction to strongly enhance the radiative local density of optical states, making it a promising candidate for spontaneous emission control.     

Minimizing finite-size effects in artificial resonance tunneling structures

We consider finite-size effects in coupled cavity structures. Starting with microring resonator structures well described by transfer matrices, we obtain conditions that lead to the minimization of finite-size effects. Our approach does not require numerical optimization and requires only slight modification of design parameters guided by closed-form analytical expressions. Using a Breit-Wigner scattering formalism, we demonstrate that the scheme can be used to minimize finite-size effects in a general class of coupled cavity structures. The strength of the present technique lies in its simplicity and its applicability to a wide variety of structures described by tight-binding formalisms.     

First-principles calculation of the single impurity surface Kondo resonance

We perform first-principles calculations of the surface and bulk wave functions of the Cu(111) surface and their hybridization energies to a Co adatom, including the potential scattering from the Co. By analyzing the calculated hybridization energies, we find the bulk states dominate the contribution to the Kondo temperature, in agreement with recent experiments. Furthermore, we also calculate the tunneling conductance of a scanning tunneling microscope and compare our results with recent experiments of Co impurities in the Cu(111) surface. Good quantitative agreement is found at short parallel impurity-tip distances (<6 A). Our results indicate the need for a new formulation of the problem at larger distances.     

Structural control of Fano resonances in semiconductor heterostructures

Structural control of quantum interference in the optical intrasubband absorption spectrum of GaAs/AlGaAs multi-quantum wells is investigated theoretically. Our study shows that pronounced Fano resonances are in general difficult to obtain in quantum well heterostructures, with a presence of distinct Fano resonance features being the exception rather than the rule. Guided by an analogy to Young’s double-slit experiment, we design increasingly improved structures to display Fano resonances. Best results are achieved in structures where there is strong overlap between the ground-state wavefunction and scattering states associated with the uncoupled continuum. Alternatively one may use ionization via two or more resonances. In this case, resonances should not be separated by more than 25 meV to give significant effects. Moreover, we show that resonance features may also be induced without potential barriers to a continuum merely via orthogonality between bound and excited states.     

Scanning tunneling spectroscopy of charge effects on semiconductor surfaces and atomic clusters

We have used scanning tunneling microscopy and scanning tunneling spectroscopy at liquid helium temperature to study the electronic structure of in situ cleaved, (110) oriented surfaces of InAs single crystals. Both unperturbed, atomically flat areas and areas with an atomic-size defect cluster have been investigated. We show that the anomalous behavior of the local tunneling conductivity, which indicates a pronounced enhancement of the semiconductor band gap for the flat areas, is consistent with band bending induced by charges localized at the apex of the tip. Atomic-size defect clusters contain additional charges which modify the band bending; this explains the different behavior of the tunneling conductivity near the defect cluster. The experimentally observed oscillations of the tunneling conductivity near the band gap edges can be directly related to resonant tunneling through quantized surface states which appear because of the band bending. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 130–135 (25 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Femtosecond relaxation dynamics of surface plasmon-polaritons in the vicinity of fano-type resonance

JETP Letters - Temporal modification of femtosecond laser pulses reflected from planar periodic metal nanostructures with resonant excitation of surface plasmon-polaritons is experimentally...     

Femtosecond relaxation dynamics of surface plasmon-polaritons in the vicinity of fano-type resonance

Temporal modification of femtosecond laser pulses reflected from planar periodic metal nanostructures with resonant excitation of surface plasmon-polaritons is experimentally studied. Spectral time-resolved measurements of the second-order cross-correlation function performed with the pulse duration comparable with the surface plasmon-polariton relaxation time (about 100 fs) show the strong spectral dependence of the envelope of the reflected femtosecond pulse described by Fano-resonance parameters.