arXiv subjects

D. Konstantinov

Publications and source records attributed to D. Konstantinov.

13 recordsLinked to original sources

arXiv2024

Delocalized low-frequency magnetoplasmon in a two-dimensional electron fluid with cylindrical symmetry

The properties of a two-dimensional (2D) electron system can be drastically altered by a magnetic field applied perpendicular to the 2D plane. In particular, the frequency of its bulk collective excitations becomes gaped at the cyclotron frequency, while the low-frequency localized excitations, the edge magnetoplasmon (EMP), appear near the system's edge. A new type of the delocalized low-frequency excitations, the gradient magnetoplasmon (GMP), was recently shown to exist in a 2D electron system with a linear density gradient that breaks the system's cylindrical symmetry [Phys. Rev. B \textbf{103}, 075420 (2021)]. Like EMP, these new excitations are gapless and chiral, and originate from the classical Hall effect. Here we show that a similar magnetoplasmon mode can exist in a system with strongly-inhomogeneous radial distribution of the electron density that preserves the cylindrical symmetry. This is experimentally demonstrated in a pristine system of surface electrons on liquid helium and is confirmed by a numerical simulation. This result extends the variety of known collective excitations in a 2D charge system and presents electrons on helium as a promising model system for their study.

cond-mat.mes-hall↗

arXiv2020

Motional Quantum States of Surface Electrons on Liquid Helium in a Tilted Magnetic Field

The Jaynes-Cummings model (JCM), one of the paradigms of quantum electrodynamics, was introduced to describe interaction between light and a fictitious two-level atom. Recently it was suggested that the JCM Hamiltonian can be invoked to describe the motional states of electrons trapped on the surface of liquid helium and subjected to a constant uniform magnetic field tilted with respect to the surface [Yunusova et al. Phys. Rev. Lett. 122, 176802 (2019)]. In this case, the surface-bound (Rydberg) states of an electron are coupled to the electron cyclotron motion by the in-plane component of tilted field. Here we investigate, both theoretically and experimentally, the spectroscopic properties of surface electrons in a tilted magnetic field and demonstrate that such a system exhibits a variety of phenomena common to the light dressed states of atomic and molecular systems. This shows that electrons on helium realize a prototypical atomic system where interaction between components can be engineered and controlled by simple means and with high accuracy, and which therefore can be potentially used as a new flexible platform for quantum experiments. Our work introduces a pure condensed-matter system of electrons on helium into the context of atomic, molecular and optical physics.

quant-ph↗

arXiv2020

Many-electron system on helium and the color center spectroscopy

Electrons on the helium surface display sharp resonant absorption lines related to the transitions between the subbands of quantized motion transverse to the surface. A magnetic field parallel to the surface strongly affects the absorption spectrum. We show that the effect comes from admixing the out-of-plane motion to the in-plane quantum dynamics of the strongly correlated electron liquid or a Wigner crystal. This is similar to the admixing electron transitions in color centers to phonons. The spectrum permits a direct characterization of the many-electron dynamics and also enables testing the theory of color centers in a system with a controllable coupling.

cond-mat.mes-hall↗

arXiv2020

GeantV: Results from the prototype of concurrent vector particle transport simulation in HEP

Full detector simulation was among the largest CPU consumer in all CERN experiment software stacks for the first two runs of the Large Hadron Collider (LHC). In the early 2010's, the projections were that simulation demands would scale linearly with luminosity increase, compensated only partially by an increase of computing resources. The extension of fast simulation approaches to more use cases, covering a larger fraction of the simulation budget, is only part of the solution due to intrinsic precision limitations. The remainder corresponds to speeding-up the simulation software by several factors, which is out of reach using simple optimizations on the current code base. In this context, the GeantV R&D project was launched, aiming to redesign the legacy particle transport codes in order to make them benefit from fine-grained parallelism features such as vectorization, but also from increased code and data locality. This paper presents extensively the results and achievements of this R&D, as well as the conclusions and lessons learnt from the beta prototype.

physics.comp-ph↗

arXiv2020

Unidirectional ripplopolaron charge transport in a three-terminal microchannel device

We study the transport of surface electrons on superfluid helium through a microchannel structure in which the charge flow splits into two branches, one flowing straight and one turned at 90 degrees. According to Ohm law, an equal number of charges should flow into each branch. However, when the electrons are dressed by surface excitations (ripplons) to form polaron-like particles with sufficiently large effective mass, all the charge follows the straight path due to momentum conservation. This surface-wave induced transport is analogous to the motion of electrons coupled to surface acoustic waves in semiconductor 2DEGs.

cond-mat.mes-hall↗

arXiv2019

Coupling between Rydberg states and Landau levels of electrons trapped on liquid helium

We investigate the coupling between Rydberg states of electrons trapped on a liquid Helium surface and Landau levels induced by a perpendicular magnetic field. We show that this realises a prototype quantum system equivalent to an atom in a cavity, where their coupling strength can be tuned by a parallel magnetic field. We determine experimentally the renormalisation of the atomic transition energies induced by the coupling to the cavity, which can be seen as an analogue of the Lamb shift. When the coupling is sufficiently strong the transition between the ground and first excited Rydberg states splits into two resonances corresponding to dressed states with vacuum and one photon in the cavity. Our results are in quantitative agreement with the energy shifts predicted by the effective atom in a cavity model where all parameters are known with high accuracy.

cond-mat.mes-hall↗

arXiv2018

Sliding of Electron Crystal of Finite Size on the Surface of Superfluid He-4 Confined in a Microchannel

We present a new study of the nonlinear transport of a two-dimensional electron crystal on the surface of liquid helium confined in a 10 micrometer-wide channel in which the effective length of the crystal can be varied from 10 to 215 micrometers. At low driving voltages, the moving electron crystal is strongly coupled to deformation of the liquid surface arising from resonant excitation of surface capillary waves, ripplons, while at higher driving voltages the crystal decouples from the deformation. We find strong dependence of the decoupling threshold of the driving electric field acting on the electrons, on the size of the crystal. In particular, the threshold electric field significantly decreases when the length of the crystal becomes shorter than 25 micrometers. We explain this effect as arising from weakening of surface deformations due to radiative loss of resonantly-excited ripplons from an electron crystal of finite size, and we account for the observed effect using an instructive analytical model.

cond-mat.mes-hall↗

arXiv2018

Transport properties of a quasi-1D Wigner Solid on liquid helium confined in a microchannel with periodic potential

We present transport measurements in a quasi-1D system of surface electrons on liquid helium confined in a 101-$μ$m long and 5-$μ$m wide microchannel where an electrostatic potential with periodicity of $1$-$μ$m along the channel is introduced. In particular, we investigate the influence of such a potential on the nonlinear transport of quasi-1D Wigner Solid (WS) by varying the amplitude of the periodic potential in a wide range. At zero and small values of amplitude, quasi-1D WS in microchannel shows expected features such as the Bragg-Cherenkov scattering of ripplons and reentrant melting. As the amplitude of potential increases, the above features are strongly suppressed. This behavior suggests loss of the long-range positional order in the electron system, which is reminiscent of the re-entrant melting behaviour due to the lateral confinement of WS in the channel.

cond-mat.mes-hall↗

arXiv2018

On the nonlinear NMR and magnon BEC in antiferromagnetic materials with coupled electron-nuclear spin precession

We present a new study of nonlinear NMR and Bose-Einstein Condensation (BEC) of nuclear spin waves in antiferromagnetic MnCO3 with coupled electron and nuclear spins. In particular, we show that the observed behaviour of NMR signals strongly contradicts the conventional description of paramagnetic ensembles of noninteracting spins based on the phenomenological Bloch equations. We present a new theoretical description of the coupled electron-nuclear spin precession, which takes into account an indirect relaxation of nuclear spins via the electron subsystem. We show that the magnitude of the nuclear magnetization is conserved for arbitrary large excitation powers, which is drastically different from the conventional heating scenario derived from the Bloch equations. This provides strong evidence that the coherent precession of macroscopic nuclear magnetization observed experimentally can be identified with BEC of nuclear spin waves with k=0.

cond-mat.other↗

arXiv2017

Circular-Polarization-Dependent Study of Microwave-Induced Conductivity Oscillations in a Two-Dimensional Electron Gas on Liquid Helium

The polarization dependence of photoconductivity response at cyclotron-resonance harmonics in a nondegenerate two-dimensional (2D) electron system formed on the surface of liquid helium is studied using a setup in which a circular polarization of opposite directions can be produced. Contrary to the results of similar investigations reported for semiconductor 2D electron systems, for electrons on liquid helium, a strong dependence of the amplitude of magnetoconductivity oscillations on the direction of circular polarization is observed. This observation is in accordance with theoretical models based on photon-assisted scattering and, therefore, it solves a critical issue in the dispute over the origin of microwave-induced conductivity oscillations.

cond-mat.mes-hall↗

arXiv2017

Ripplonic Lamb shift for electrons on liquid helium

We study the shift of the energy levels of electrons on helium surface due to the coupling to the quantum field of surface vibrations. As in quantum electrodynamics, the coupling is known, and it is known to lead to an ultraviolet divergence of the level shifts. We show that there are diverging terms of different nature and use the Bethe-type approach to show that they cancel each other, to the leading-order. This resolves the long-standing theoretical controversy and explains the existing experiments. The results allow us to study the temperature dependence of the level shift. The predictions are in good agreement with the experimental data.

cond-mat.mes-hall↗

arXiv2016

Strong coupling of the cyclotron motion of surface electrons on liquid helium to a microwave cavity

The strong coupling regime is observed in a system of two-dimensional electrons whose cyclotron motion is coupled to an electro-magnetic mode in a Fabry-Perot cavity resonator. The Rabi splitting of eigenfrequencies of coupled motion is observed both in the cavity reflection spectrum and ac current of electrons, the latter probed by measuring their bolometric photoresponse. Despite the fact that similar observations of the Rabi splitting in many-particle systems have been described as a quantum-mechanical effect, we show that the observed splitting can be explained completely by a model based on the classical electrodynamics.

cond-mat.mes-hall↗

arXiv2015

Photo-Conductivity Response at Cyclotron-Resonance Harmonics in a Non-Degenerate 2D Electron Gas on Liquid Helium

We report the first observation of an oscillatory photo-conductivity response at the cyclotron-resonance harmonics in a non-degenerate 2D electron system formed on the free surface of liquid helium. The dc conductivity oscillations are detected for electrons occupying the ground surface subband. Their period is governed by the ratio of the microwave frequency to the cyclotron frequency. Theoretical analysis of the photo-response in a strongly interacting electron system indicates that the observation can be explained by an oscillatory correction to the electron distribution function that appears for a large inelastic relaxation time because of photon-assisted scattering.

cond-mat.mes-hall↗