arXiv subjects

V. Yu. Kachorovskii

Publications and source records attributed to V. Yu. Kachorovskii.

At least 19 recordsLinked to original sources

arXiv2026

Tunable massive and acoustic plasmons in two-dimensional plasmonic crystals

We theoretically investigate dispersion of plasma waves propagating in a lateral plasmonic crystal based on a two-dimensional electron system with grating gates. Two specific configurations are analyzed: a system with single grating gate having ungated gaps and a double-grating-gate system. We calculate the dispersion relations for the fundamental and several higher-order plasma modes, classifying them as either ${\it bright}$ or ${\it dark}$ excitations. At the boundaries of the Brillouin zones, the dispersion of both types of excitations is shown to be quadratic, justifying introduction of effective bright and dark plasmon masses. In the low-frequency limit, the plasmonic crystal spectrum exhibits an acoustic plasma mode characterized by a certain velocity. We demonstrate that the effective plasmon mass and acoustic velocity are highly sensitive to both the crystal geometry (specifically the lattice filling factor) and the gate voltages, enabling wide-range tunability.

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arXiv2026

Ratchet effect in lateral plasmonic crystal: Giant enhancement due to interference of "bright" and "dark" modes

We develop a theory of the ratchet effect in a lateral plasmonic crystal (LPC) formed by a two dimensional electron gas under a periodic dual-grating gate. The system is driven by terahertz radiation, and the spatial asymmetry required for the generation of dc photocurrent is introduced by a phase shift between the radiation's near-field modulation and the static electron density profile. In contrast to the commonly used perturbative "minimal model" of the ratchet effect, which assumes weak density modulation, we solve the problem exactly with respect to the static gate-induced potential while treating the radiation field perturbatively. This approach reveals a dramatic enhancement of the plasmonic contribution to the ratchet current due to the interference of "bright" and "dark" plasmon modes, which are excited on an equal footing in the asymmetric LPC. Specifically, we predict a parametric growth of the plasmonic peak as compared with the Drude peak with increasing coupling, and the appearance of a dense super-resonant structure when the spacing between plasmonic sub-bands becomes larger than the damping rate. Hence, the dc response exhibits both resonant and super-resonant regimes observed in recent experiments on the radiation transmission through the LPC. The interplay of bright and dark modes, together with their interference, provides a powerful mechanism for controlling the magnitude and sign of the photocurrent by gate voltages and the radiation frequency.

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arXiv2025

Shot noise in Aharonov-Bohm interferometers: Comparison of helical and conventional setups

We study tunneling transport through quantum Aharonov-Bohm (AB) interferometers and demonstrate that interference effects strongly modify shot noise of the current. We discuss in detail two simplest setups: conventional single-channel spinless interferometer and interferometer formed by helical edge states of two-dimensional topological insulator. We demonstrate that both in the conventional and the helical case the interference dramatically changes the Fano factor and its magnetic field dependence. For weak tunneling coupling, the Fano factor of both setups exhibits a periodic series of sharp AB peaks depending on the magnetic flux piercing the system. Our key finding is that the Fano factor in the helical interferometer provides information about the presence of backscattering defects violating topological protection. In particular, the amplitude of AB peaks in the helical setup is proportional to the strength of the defect in contrast to conventional setup, where peaks have finite amplitude even in the ballistic case.

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arXiv2025

A non-magnetic mechanism of backscattering in helical edge states

We study interaction-induced backscattering mechanism for helical edge states of a two-dimensional topological insulator which is tunnel-coupled to a puddle located near the edge channel. The mechanism does not involve inelastic scattering and is due to the zero-mode fluctuations in a puddle. We discuss in detail a simple model of a puddle - a cavity in the bulk of the topological insulator. Such a cavity also has helical edge states with tunneling coupling to helical states encompassing the topological insulator. We analyze effect of the edge current in the puddle. Although averaged value of this current is equal to zero, its zero-mode fluctuations act, in the presence of electron-electron interaction, similar to magnetic flux thus allowing backscattering processes, which involve tunneling through the puddle. Rectification of these fluctuations leads to a finite probability of backscattering. This effect is further enhanced due to dephasing process which is also dominated by zero-mode fluctuations. Remarkably, for temperature exceeding level spacing in the puddle, the rate of backscattering does not depend on temperature in a good agreement with recent experiments.

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arXiv2024

Lateral plasmonic crystals: Tunability, dark modes, and weak-to-strong coupling transition

We study transmission of the terahertz radiation through a two-dimensional electron gas with a concentration controlled by grating gate electrodes. Voltage applied to these electrodes creates a lateral plasmonic crystal with a gate-tunable band structure. We find that only a part of plasmonic modes of such a crystal is seen in the transmission spectrum for the case of homogeneous excitation (so-called bright modes), while there also exist dark modes which show up only in a case of inhomogeneous excitation. We develop a theory that describes both weak- to strong- coupling transition in the crystal with increasing depth of the density modulation and a transition from resonant to super-resonant regime with increasing quality factor of the structure. We discuss very recent experiment, where transmission of the terahertz radiation through GaN/AlGaN based grating gate periodic structures was studied. We argue that this experiment represents an evidence of formation of the lateral plasmonic crystal with the band structure fully controlled by the gate electrodes, in a full agreement with developed theory

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arXiv2024

Thermoelectric and viscous contributions to the hydrodynamic ratchet effect

We study thermoelectric and viscous contributions to the ratchet effect, i.e. radiation-induced generation of the direct electric current, $J_{\rm rat},$ in asymmetric dual-grating gate structure without inversion center. Previously [E.Mönch et al, Phys. Rev. B {\bf 105}, 045404 (2022)], it was demonstrated that frequency dependence of the $J_{\rm rat}$ is essentially different within hydrodynamic (HD) and drift-diffusion (DD) regimes of the electron transport: $ J_{\rm rat}^{\rm HD} \propto 1/ω^6 $ and $ J_{\rm rat}^{\rm DD} \propto 1/ω^2 $ for $ω\to \infty.$ Here we analyze previously neglected thermoelectric contribution and find that it yields high-frequency asymptotic $1/ω^2$ even in the HD regime and can change sign of the response. Account of the finite viscosity of the electron liquid yields contribution which scales at high frequency as $1/ω^4.$ We also find plasmonic resonances in the $J_{\rm rat},$ and demonstrate that asymmetry of the structure allows for excitation of the so-called directional travelling plasmons.

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arXiv2024

Lateral plasmonic superlattice in strongly dissipative regime

We calculate transmission coefficient, $\mathcal T,$ of terahertz radiation through lateral plasmonic superlattice with a unit cell consisting of two regions with different plasma wave velocities, $s_1$ and $s_2$ ($s_1 > s_2$). We generalize theory developed earlier for resonant case to the non-resonant regime, when the scattering rate, $γ,$ is large compared to fundamental gate-tunable frequencies $ω_{1,2}$ of plasma oscillations in both regions. We find that absorption, and consequently $\mathcal T$, strongly depends on density modulation amplitude and on the frequency of the incoming radiation. We describe evolution of the absorption with increasing of radiation frequency from the quasi-static regime of very low frequency to the high-frequency regime, identify several dissipation regimes and find analytical expression for absorption, and, accordingly, for $\mathcal T,$ in these regimes. A general phase diagram of non-resonant regime in the plane $(ω,ω_2)$ for fixed $ω_1$ is constructed. Most importantly, $\mathcal T$ sharply depends on the gate voltages and frequency. In particular, for $ω_2 \ll ω_1,$ $\mathcal T$ strongly varies on the very small frequency scale, $δω\ll γ,$ determined by the Maxwell relaxation, $δω\sim ω_1^2/γ,$ so that the superlattice shows high responsivity within the frequency band $δω.$

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arXiv2023

Narrowing of the flexural phonon spectral line in stressed crystalline two-dimensional materials

We develop the microscopic theory for the attenuation of out-of-plane phonons in stressed flexible two-dimensional crystalline materials. We demonstrate that the presence of nonzero tension strongly reduces the relative magnitude of the attenuation and, consequently, results in parametrical narrowing of the phononspectral line. We predict the specific power-law dependence of the spectral-line width on temperature and tension. We speculate that suppression of the phonon attenuation by nonzero tension might be responsible for high quality factors of mechanical nanoresonators based on flexural two-dimensional materials.

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arXiv2023

Tunable helical crystals

We consider a superlattice formed by tunnel-connected identical holes, periodically placed in a two-dimensional topological insulator. We study tunneling transport through helical edges of these holes and demonstrate that the band structure of such helical crystal can be controlled by both gate electrodes and external magnetic filed. For integer and half-integer values of dimensionless magnetic flux through the holes, the spectrum possesses Dirac points whose positions and velocities can be tuned by gates. The deviation of magnetic flux from these special values by $δϕ$ makes the Dirac cones massive, with the gap value $Δ\propto |δϕ|$. At certain gate-dependent values of $δϕ$ different Dirac points converge to a double Dirac point and then disappear with further increase of $δϕ.$ Interaction between carriers may lead to strong renormalization of parameters $α$ and $β$ controlling total tunnel coupling between holes and spin flip tunneling processes, respectively. We plot the renormalization flow in the plane $(α,β)$ and demonstrate multicritical behavior of the crystal -- there is a multicritical fully unstable fixed point separating three different phases: independent rings, independent shoulders, and perfect spin-flip channels. We also find that defects in the crystal may lead to a formation of topologically protected qubits which are not destroyed by temperature and can be also manipulated both by gates and by magnetic field. The possibility of purely electrical high-temperature control of the qubits opens a wide avenue for applications in the area of quantum computing.

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arXiv2023

Effective Hamiltonian of topologically protected qubit in a helical crystal

We study a superlattice formed by tunnel-coupled identical antidots periodically situated in a two-dimensional topological insulator placed in a magnetic field. The superlattice spectrum can be controlled by gate electrodes or by changing the magnetic flux through the antidots. We demonstrate that a topologically protected qubit appears at the boundary between two regions with different fluxes. The qubit properties depend on the value of the flux jump on the boundary and can be controlled by the gate voltage. We derive the effective Hamiltonian of such a qubit and analyze the dependence of its properties on the main parameters of the superlattice: the tunnel coupling between antidots, and the probability of jumps with the spin flip.

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arXiv2022

Disorder-driven transition to tubular phase in anisotropic two-dimensional materials

We develop a theory of anomalous elasticity in disordered two-dimensional flexible materials with orthorhombic crystal symmetry. Similar to the clean case, we predict existence of infinitely many flat phases with anisotropic bending rigidity and Young's modulus showing power-law scaling with momentum controlled by a single universal exponent the very same as in the clean isotropic case. With increase of temperature or disorder these flat phases undergo crumpling transition. Remarkably, in contrast to the isotropic materials where crumpling occurs in all spatial directions simultaneously, the anisotropic materials crumple into tubular phase. In distinction to clean case in which crumpling transition happens at unphysically high temperatures, a disorder-induced tubular crumpled phase can exist even at room-temperature conditions. Our results are applied to anisotropic atomic single layers doped by adatoms or disordered by heavy ions bombarding.

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arXiv2022

The effect of elastic disorder on single electron transport through a buckled nanotube

We study transport properties of a single electron transistor based on elastic nanotube. Assuming that an external compressive force is applied to the nanotube, we focus on the vicinity of the Euler buckling instability. We demonstrate that in this regime the transport through the transistor is extremely sensitive to elastic disorder. In particular, built-in curvature (random or regular) leads to the ``elastic curvature blockade'': appearance of threshold bias voltage in the $I$-$V$ curve which can be larger than the Coulomb-blockade-induced one. In the case of a random curvature, an additional plateau in dependence of the average current on a bias voltage appears.

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arXiv2021

Coherent spin transport through helical edge states of topological insulator

We study coherent spin transport through helical edge states of topological insulator tunnel-coupled to metallic leads. We demonstrate that unpolarized incoming electron beam acquires finite polarization after transmission through such a setup provided that edges contain at least one magnetic impurity. The finite polarization appears even in the fully classical regime and is therefore robust to dephasing. There is also a quantum magnetic field-tunable contribution to the polarization, which shows sharp identical Aharonov-Bohm resonances as a function of magnetic flux - with the period $hc/2e$ - and survives at relatively high temperature. We demonstrate that this tunneling interferometer can be described in terms of ensemble of flux-tunable qubits giving equal contributions to conductance and spin polarization. The number of active qubits participating in the charge and spin transport is given by the ratio of the temperature and the level spacing. The interferometer can effectively operate at high temperature and can be used for quantum calculations. In particular, the ensemble of qubits can be described by a single Hadamard operator. The obtained results open wide avenue for applications in the area of quantum computing.

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arXiv2021

Emergent continuous symmetry in anisotropic flexible two-dimensional materials

We develop the theory of anomalous elasticity in two-dimensional flexible materials with orthorhombic crystal symmetry. Remarkably, in the universal region, where characteristic length scales are larger than the rather small Ginzburg scale ${\sim} 10\, {\rm nm}$, these materials possess an infinite set of flat phases which are connected by emergent continuous symmetry. This hidden symmetry leads to the formation of a stable line of fixed points corresponding to different phases. The same symmetry also enforces power law scaling with momentum of the anisotropic bending rigidity and Young's modulus, controlled by a single universal exponent -- the very same along the whole line of fixed points. These anisotropic flat phases are uniquely labeled by the ratio of absolute Poisson's ratios. We apply our theory to monolayer black phosphorus (phosphorene).

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arXiv2021

Beatings of ratchet current magneto-oscillations in GaN-based grating gate structures: manifestation of spin-orbit band splitting

We report on the study of the magnetic ratchet effect in AlGaN/GaN heterostructures superimposed with lateral superlattice formed by dual-grating gate structure. We demonstrate that irradiation of the superlattice with terahertz beam results in the dc ratchet current, which shows giant magneto-oscillations in the regime of Shubnikov de Haas oscillations. The oscillations have the same period and are in phase with the resistivity oscillations. Remarkably, their amplitude is greatly enhanced as compared to the ratchet current at zero magnetic field, and the envelope of these oscillations exhibits large beatings as a function of the magnetic field. We demonstrate that the beatings are caused by the spin-orbit splitting of the conduction band. We develop a theory which gives a good qualitative explanation of all experimental observations and allows us to extract the spin-orbit splitting constant α_{\rm SO}= 7.5 \pm 1.5 meV \unicode{x212B}. We also discuss how our results are modified by plasmonic effects and show that these effects become more pronounced with decreasing the period of the gating gate structures down to sub-microns.

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arXiv2021

Spin and charge transport through helical Aharonov-Bohm interferometer with strong magnetic impurity

We discuss transport through an interferometer formed by helical edge states of the quantum spin Hall insulator. Focusing on effects induced by a strong magnetic impurity placed in one of the arms of interferometer, we consider the experimentally relevant case of relatively high temperature as compared to the level spacing. We obtain the conductance and the spin polarization in the closed form for arbitrary tunneling amplitude of the contacts and arbitrary strength of the magnetic impurity. We demonstrate the existence of quantum effects which do not show up in previously studied case of weak magnetic disorder. We find optimal conditions for spin filtering and demonstrate that the spin polarization of outgoing electrons can reach 100%.

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arXiv2020

Hydrodynamic Inverse Faraday Effect in Two Dimensional Electron Liquid

We show that a small conducting object, such as a nanosphere or a nanoring, embedded into or placed in the vicinity of the two-dimensional electron liquid (2DEL) and subjected to a circularly polarized electromagnetic radiation induces ``twisted'' plasmonic oscillations in the adjacent 2DEL. The oscillations are rectified due to the hydrodynamic nonlinearities leading to the helicity sensitive circular dc current and to a magnetic moment. This hydrodynamic inverse Faraday effect (HIFE) can be observed at room temperature in different materials. The HIFE is dramatically enhanced in a periodic array of the nanospheres forming a resonant plasmonic coupler. Such a coupler exposed to a circularly polarized wave converts the entire 2DEL into a vortex state. Hence, the twisted plasmonic modes support resonant plasmonic-enhanced gate-tunable optical magnetization. Due to the interference of the plasmonic and Drude contributions, the resonances have an asymmetric Fano-like shape. These resonances present a signature of the 2DEL properties not affected by contacts and interconnects and, therefore, providing the most accurate information about the 2DEL properties. In particular, the widths of the resonances encode direct information about the momentum relaxation time and viscosity of the 2DEL.

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arXiv2020

Giant ratchet magneto-photocurrent in graphene lateral superlattices

We report on the observation of the magnetic quantum ratchet effect in graphene with a lateral dual-grating top gate (DGG) superlattice. We show that the THz ratchet current exhibits sign-alternating magneto-oscillations due to the Shubnikov-de Haas effect. The amplitude of these oscillations is greatly enhanced as compared to the ratchet effect at zero magnetic field. The direction of the current is determined by the lateral asymmetry which can be controlled by variation of gate potentials in DGG. We also study the dependence of the ratchet current on the orientation of the terahertz electric field (for linear polarization) and on the radiation helicity (for circular polarization). Notably, in the latter case, switching from right- to left-circularly polarized radiation results in an inversion of the photocurrent direction. We demonstrate that most of our observations can be well fitted by the drift-diffusion approximation based on the Boltzmann kinetic equation with the Landau quantization fully encoded in the oscillations of the density of states.

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