arXiv subjects

Andrei G. Borisov

Publications and source records attributed to Andrei G. Borisov.

11 recordsLinked to original sources

arXiv2026

Clocking and controlling attosecond currents in a scanning tunnelling microscope

Quantum tunnelling of electrons can be confined to the sub-cycle time scale of strong light fields, contributing decisively to the extreme time resolution of attosecond science. Because tunnelling also enables atomic-scale spatial resolution in scanning tunnelling microscopy (STM), integrating STM with light pulses has long been a key objective in ultrafast microscopy, spanning the picosecond and femtosecond domains, with first signatures of attosecond dynamics. However, while sub-cycle dynamics on the attosecond time scale are routinely controlled and determined with high precision, controlling the direction of attosecond currents and determining their duration have remained elusive in STM. Here, we induce STM tunnelling currents using two-colour laser pulses and dynamically control their direction, relying solely on the sub-cycle waveform of the pulses. Projecting our measurement data onto one-electron and many-body theory descriptions reveals a three-step transport process in the non-adiabatic tunnelling regime as the physical mechanism, with a theory-derived current burst duration of 860 as. Despite working under ambient conditions but free of thermal artifacts, we achieve sub-angström topographic sensitivity and a lateral spatial resolution of 2 nm. This unprecedented capability to directionally control attosecond bursts will enable triggering and imaging ultrafast charge dynamics at the spatio-temporal microscopy frontier of lightwave electronics.

quant-ph↗

arXiv2026

Ultrafast optically induced tunneling in narrow metallic gaps from the time dependent density functional perspective

In this work, using the time-dependent density functional theory, we address the electron tunneling triggered by short (single-cycle and several-cycle) optical pulses in narrow metallic gaps under conditions relevant for actual experiments. We identify photon-assisted tunneling with one-photon, two-photon, and higher-order photon absorption, and we discuss the effect of the tunneling barrier, applied bias, and strength of the optical field on transition from photon-assisted tunneling (weak optical fields) to the optical field emission at strong optical fields. The numerical single-electron calculations and an analytical strong-field theory model are used to gain deeper insights into the results of the time-dependent density functional theory calculations. Additionally, our parameter-free calculations allow us to retrieve and explain recent experimental results on optically induced transport in narrow metallic gaps under an applied dc bias.

physics.optics↗

arXiv2025

Roadmap on Nonlocality in Photonic Materials and Metamaterials

Photonic technologies continue to drive the quest for new optical materials with unprecedented responses. A major frontier in this field is the exploration of nonlocal (spatially dispersive) materials, going beyond the local, wavevector-independent assumption traditionally made in optical material modeling. On one end, the growing interest in plasmonic, polaritonic and quantum materials has revealed naturally occurring nonlocalities, emphasizing the need for more accurate models to predict and design their optical responses. This has major implications also for topological, nonreciprocal, and time-varying systems based on these material platforms. Beyond natural materials, artificially structured materials--metamaterials and metasurfaces--can provide even stronger and engineered nonlocal effects, emerging from long-range interactions or multipolar effects. This is a rapidly expanding area in the field of photonic metamaterials, with open frontiers yet to be explored. In the case of metasurfaces, in particular, nonlocality engineering has become a powerful tool for designing strongly wavevector-dependent responses, enabling enhanced wavefront control, spatial compression, multifunctional devices, and wave-based computing. Furthermore, nonlocality and related concepts play a critical role in defining the ultimate limits of what is possible in optics, photonics, and wave physics. This Roadmap aims to survey the most exciting developments in nonlocal photonic materials, highlight new opportunities and open challenges, and chart new pathways that will drive this emerging field forward--toward new scientific discoveries and technological advancements.

cond-mat.mes-hall↗

arXiv2023

Fluorescent single-molecule STM probe

The plasmonic tip of a scanning tunnelling microscope (STM) is functionalized with a single fluorescent molecule and is scanned on a plasmonic substrate. The tunneling current flowing through the tip-molecule-substrate junction generates a narrow-line emission of light corresponding to the fluorescence of the negatively charged molecule suspended at the apex of the tip, i.e., the emission of the excited molecular anion (trion). The fluorescence of this molecular probe is recorded for tip-substrate nanocavities featuring different plasmonic resonances, for different tip-substrate distances and applied bias voltages, and on different substrates. We demonstrate that the width of the emission peak can be used as a probe of the trion-plasmon coupling strength and that the energy of the emitted photons is governed by the molecule interactions with its electrostatic environment. Additionally, we theoretically elucidate why the direct contact of the suspended molecule with the metallic tip does not totally quench the radiative emission of the molecule.

cond-mat.mes-hall↗

arXiv2021

Mapping Lamb, Stark and Purcell effects at a chromophore-picocavity junction with hyper-resolved fluorescence microscopy

The interactions between the excited states of a single chromophore with static and dynamic electric fields confined to a plasmonic cavity of picometer dimensions are investigated in a joint experimental and theoretical effort. In this configuration, the spatial extensions of the confined fields are smaller than the one of the molecular exciton, a property that is used to generate fluorescence maps of the chromophores with intra-molecular resolution. Theoretical simulations of the electrostatic and electrodynamic interactions occurring at the chromophore-picocavity junction are able to reproduce and interpret these hyper-resolved fluorescence maps, and reveal the key role played by subtle variations of Purcell, Lamb and Stark effects at the chromophore-picocavity junction.

cond-mat.mes-hall↗

arXiv2005

Wave packet propagation by the Faber polynomial approximation in electrodynamics of passive media

Maxwell's equations for propagation of electromagnetic waves in dispersive and absorptive (passive) media are represented in the form of the Schrödinger equation $i\partial Ψ/\partial t = {H}Ψ$, where ${H}$ is a linear differential operator (Hamiltonian) acting on a multi-dimensional vector $Ψ$ composed of the electromagnetic fields and auxiliary matter fields describing the medium response. In this representation, the initial value problem is solved by applying the fundamental solution $\exp(-itH)$ to the initial field configuration. The Faber polynomial approximation of the fundamental solution is used to develop a numerical algorithm for propagation of broad band wave packets in passive media. The action of the Hamiltonian on the wave function $Ψ$ is approximated by the Fourier grid pseudospectral method. The algorithm is global in time, meaning that the entire propagation can be carried out in just a few time steps. A typical time step is much larger than that in finite differencing schemes, $Δt_F \gg \|H\|^{-1}$. The accuracy and stability of the algorithm is analyzed. The Faber propagation method is compared with the Lanczos-Arnoldi propagation method with an example of scattering of broad band laser pulses on a periodic grating made of a dielectric whose dispersive properties are described by the Rocard-Powels-Debye model. The Faber algorithm is shown to be more efficient. The Courant limit for time stepping, $Δt_C \sim \|H\|^{-1}$, is exceeded at least in 3000 times in the Faber propagation scheme.

physics.comp-ph↗

arXiv2004

Electromagnetic Pulse Propagation in Passive Media by the Lanczos Method

Maxwell's equations are cast in the form of the Schrödinger equation. The Lanczos propagation method is used in combination with the fast Fourier pseudospectral method to solve the initial value problem. As a result, a time-domain, unconditionally stable, and highly efficient numerical algorithm is obtained for the propagation and scattering of broad-band electromagnetic pulses in dispersive and absorbing media. As compared to conventional finite-difference time-domain methods, an important advantage of the proposed algorithm is a dynamical control of accuracy: Variable time steps or variable computational costs per time step with error control are possible. The method is illustrated with numerical simulations of extraordinary transmission and reflection in metal and dielectric gratings with rectangular and cylindrical geometry.

physics.comp-ph↗

arXiv2004

Lanczos Pseudospectral Propagation Method for Initial-Value Problems in Electrodynamics of Passive Media

Maxwell's equations for electrodynamics of dispersive and absorptive (passive) media are written in the form of the Schrödinger equation with a non-Hermitian Hamiltonian. The Lanczos time-propagation scheme is modified to include non-Hermitian Hamiltonians and used, in combination with the Fourier pseudospectral method, to solve the initial-value problem. The time-domain algorithm developed is shown to be unconditionally stable. Variable time steps and/or variable computational costs per time step with error control are possible. The algorithm is applied to study transmission and reflection properties of ionic crystal gratings with cylindric geometry in the infra-red range.

physics.comp-ph↗

arXiv2003

Applications of the wave packet method to resonant transmission and reflection gratings

Scattering of femtosecond laser pulses on resonant transmission and reflection gratings made of dispersive (Drude metals) and dielectric materials is studied by a time-domain numerical algorithm for Maxwell's theory of linear passive (dispersive and absorbing) media. The algorithm is based on the Hamiltonian formalism in the framework of which Maxwell's equations for passive media are shown to be equivalent to the first-order equation, $\partial Ψ/\partial t = {\cal H}Ψ$, where ${\cal H}$ is a linear differential operator (Hamiltonian) acting on a multi-dimensional vector $Ψ$ built of the electromagnetic inductions and auxiliary matter fields describing the medium response. The initial value problem is then solved by means of a modified time leapfrog method in combination with the Fourier pseudospectral method applied on a non-uniform grid that is constructed by a change of variables and designed to enhance the sampling efficiency near medium interfaces. The algorithm is shown to be highly accurate at relatively low computational costs. An excellent agreement with previous theoretical and experimental studies of the gratings is demonstrated by numerical simulations using our algorithm. In addition, our algorithm allows one to see real time dynamics of long leaving resonant excitations of electromagnetic fields in the gratings in the entire frequency range of the initial wide band wave packet as well as formation of the reflected and transmitted wave fronts.

physics.comp-ph↗

arXiv2003

An application of interpolating scaling functions to wave packet propagation

Wave packet propagation in the basis of interpolating scaling functions (ISF) is studied. The ISF are well known in the multiresolution analysis based on spline biorthogonal wavelets. The ISF form a cardinal basis set corresponding to an equidistantly spaced grid. They have compact support of the size determined by the underlying interpolating polynomial that is used to generate ISF. In this basis the potential energy matrix is diagonal and the kinetic energy matrix is sparse and, in the 1D case, has a band-diagonal structure. An important feature of the basis is that matrix elements of a Hamiltonian are exactly computed by means of simple algebraic transformations efficiently implemented numerically. Therefore the number of grid points and the order of the underlying interpolating polynomial can easily be varied allowing one to approach the accuracy of pseudospectral methods in a regular manner, similar to high order finite difference methods. The results of numerical simulations of an H+H_2 collinear collision show that the ISF provide one with an accurate and efficient representation for use in the wave packet propagation method.

physics.atom-ph↗

arXiv2001

The wave packet propagation using wavelets

It is demonstrated that the wavelets can be used to considerably speed up simulations of the wave packet propagation in multiscale systems. Extremely high efficiency is obtained in the representation of both bound and continuum states. The new method is compared with the fast Fourier algorithm. Depending on ratios of typical scales of a quantum system in question, the wavelet method appears to be faster by a few orders of magnitude.

physics.comp-ph↗