arXiv subjects

I. V. Kukushkin

Publications and source records attributed to I. V. Kukushkin.

At least 19 recordsLinked to original sources

arXiv2026

Spin Polarization of a Two-Dimensional Electron Liquid

We show experimentally that the longitudinal resistance of a strongly correlated two-dimensional electron system provides a quantitative measure of its spin polarization. Using electrically detected electron spin resonance to independently calibrate the spin state, we establish a parameter-free relation between magnetotransport and spin polarization, allowing the latter to be determined from transport alone. This approach enables the magnetic state of the electron liquid to be mapped across a broad range of carrier densities and magnetic fields.

cond-mat.str-el↗

arXiv2026

Magnetoplasma excitations in interacting GaAs disks

We investigate the effect of inter-disk coupling on the magnetoplasmon dispersion in a square lattice of two-dimensional electron system (2DES) disks etched from a GaAs quantum well. Using magneto-optical terahertz (THz) spectroscopy, we track the evolution of the collective modes as disk lattice period is systematically reduced, thereby increasing the coupling strength. At large distances, the system exhibits magnetoplasma modes corresponding to individual excitations in disks. As the inter-disk distance decreases, we observe a modification to magnetoplasma dispersion.

cond-mat.mes-hall↗

arXiv2026

Novel SuperLattice Plasmon Mode in a Grating of 2D Electron Strips

We investigate GaAs/AlGaAs heterostructure membranes with a metasurface made up of a grating of two-dimensional electron system (2DES) strips. Experiments have revealed a strong plasma resonance in the transmission of the metasurface. We have found that a collective effect from the superlattice, along with lateral screening between the strips, leads to the emergence of a new plasmon mode in the metasurface under study. Furthermore, we develop an analytical approach that accurately describes the behavior of the discovered superlattice plasmon mode, providing new insights into the fundamental physics of plasmonic metasurface systems.

cond-mat.mes-hall↗

arXiv2025

Discovery of Slot Plasma Excitations in a AlGaN/GaN Plasmonic Crystal

We experimentally investigate the terahertz spectrum of plasma excitations in a plasmonic crystal based on AlGaN/GaN two-dimensional electron system (2DES). While screened plasmon modes with linear dispersion are readily observed in the plasmonic crystals, the existence of unscreened modes localized in the slots between the gates has remained unobserved until now. We discover this slot plasma excitation exhibiting square-root dispersion. It turned out that these slot plasmons follow an unconventional wave-vector quantization rule, $q_u=(N + 1/4) \times π/l_u$ for even integers $N$, and require the condition for excitation $q_u h \ll 1$, where $h$ is the gate-to-2DES distance and $l_u$ is the slot width. We develop an analytical model that accurately captures the found dispersion and relaxation, revealing a non-trivial $-π/4$ phase shift upon plasmon reflection at the gate edge. Experiments demonstrate that the slot plasmons persist up to room temperature, thereby enabling a broad range of opportunities for the advancement of plasmonic devices.

cond-mat.mes-hall↗

arXiv2025

On the Nature of the Fundamental Plasma Excitation in a Plasmonic Crystal

We report on the experimental study of the spectrum of plasma excitations in a plasmonic crystal fabricated from the two-dimensional electron system in an AlGaAs/GaAs semiconductor heterostructure. We perform a comprehensive research on the mode frequency and relaxation as a function of the gate width across different plasmonic crystal periods. Importantly, we develop an analytical approach that accurately describes the behavior of plasma excitations in plasmonic crystals, providing new insights into the fundamental physics of plasmonic systems.

cond-mat.mes-hall↗

arXiv2025

Resonant Photoluminescence of Quantum Incompressible Liquids

We investigate resonant photoluminescence arising from incompressible quantum liquids formed in two-dimensional electron systems. We demonstrate that, for excitons composed of a photoexcited electron occupying the upper spin sublevel of the zeroth Landau level and a valence-band hole, the influence of disorder potential fluctuations on optical recombination is strongly suppressed, indicating complete screening of the disorder. We identify an optical invariant quantity that is insensitive to excitation energy yet strongly dependent on the electron temperature, serving as a probe of exciton recombination in quantum liquids. Analysis of this quantity reveals that quantum-liquid formation initiates at (n = 1/3) as the electron temperature decreases, consistent with the Laughlin state. Upon further cooling, the range of filling factors exhibiting quantum-liquid behavior expands continuously from (n = 1/3) toward (n = 1/2). Transitions between distinct incompressible quantum-liquid states occur smoothly, without well-defined phase boundaries separating insulating and conducting regimes. Locally, the system retains quantum-liquid characteristics even as bulk transport measurements indicate finite conductivity. Finally, we present a phase diagram delineating the stability region of incompressible quantum liquids relative to conductive phases.

cond-mat.mes-hall↗

arXiv2023

Non-linear optical response of the excited Laughlin liquid

An ensemble of neutral excitations is constructed experimentally in the Laughlin liquid at the electron filling factor 1/3. The excitations are found to induce a nonlinear optical response, manifested as a quadratic dependence of the reflection signal on the excitation power. The reported experimental results indicate that the observed effect is due to the contribution of the coherent anti-Stokes-Stokes scattering of light from the excited Laughlin liquid.

cond-mat.str-el↗

arXiv2022

Plasmons in a Square of Two-Dimensional Electrons

Microwave absorption spectra of a single square of two-dimensional electrons (2DES) have been investigated using an optical detection technique. Fundamental dipole and harmonic quadrupole plasmon modes have been identified and compared to those in the disk geometry. In the square-shaped 2DES, a strong interaction is discovered between the neighboring plasmon modes, whereas no such hybridization is observed in the disk-shaped geometry. We establish a rigid theoretical platform to analytically describe the magneto-optical response of confined two-dimensional systems. The developed theory provides a proper description of the obtained experimental results.

cond-mat.mes-hall↗

arXiv2021

Magnetodispersion of Two-Dimensional Plasmon Polaritons

We have investigated the spectrum of two-dimensional (2D) plasmon polaritons over the full range of magnetic fields. In our study, we investigate a disk-shaped two-dimensional electron system (2DES) with a metallic gate on the backside of the substrate. Importantly, we show that 2D plasmon polaritons hybridize with the TM$_0$ photonic mode of a dielectric waveguide formed by a sample substrate. We have developed a theory for plasmon-polaritons in an infinite 2DES. We find the experimental data to be in good agreement with the developed theory.

cond-mat.mes-hall↗

arXiv2020

Piezoplasmonics: strain-induced tunability of plasmon resonance in AlAs quantum wells

We demonstrate tuning of two-dimensional (2D) plasmon spectrum in modulation-doped AlAs quantum wells via the application of in-plane uniaxial strain. We show that dramatic change in the plasma spectrum is caused by strain-induced redistribution of charge carriers between anisotropic $X_x$ and $X_y$ valleys. Discovered piezoplasmonic effect provides a tool to study the band structure of 2D systems. We use piezoplasmonic effect to measure how the inter-valley energy splitting depends on the deformation. This dependency yields the AlAs deformation potential of $E_2 = (5.6 \pm 0.3)$~eV.

cond-mat.mes-hall↗

arXiv2020

A tunable plasmonic resonator using kinetic 2D inductance and patch capacitance

We have studied microwave response of a high-mobility two-dimensional electron system (2DES) contacted by two side electrodes. Using kinetic inductance of the 2DES and inter-electrode capacitance, we have constructed a subwavelength 2D plasmonic resonator. We have shown that the resonant frequency of this circuit can be controlled by 2D electron density, external magnetic field, or size of the electrodes. This opens up possibilities for using arrays of plasmonic circuits as tunable components in different frequency ranges.

cond-mat.mes-hall↗

arXiv2019

The Local Incompressibility of Fractional Quantum Hall States at a Filling Factor of 3/2

We studied neutral excitations in a two-dimensional electron system with an orbital momentum $ΔM = 1$ and spin projection over magnetic field axis $ΔS_z = 1$ in the vicinity of a filling factor of 3/2. It is shown that the 3/2 state is a singular point in the filling factor dependence of the spin ordering of the two-dimensional electron system. In the vicinity of $ν=3/2$, a significant increase in the relaxation time ($τ= 13$ $μ\text{s}$) for the excitations to the ground state is exhibited even though the number of vacancies in the lowest energy level is macroscopically large. The decrease of the relaxation rate is related to the spin texture transformation in the ground state induced by spin flips and electron density rearrangement. We claim the 3/2 state is a locally incompressible fractional quantum Hall state.

cond-mat.str-el↗

arXiv2019

Novel 2D Plasmon Induced by Metal Proximity

A new electromagnetic plasma mode has been discovered in the hybrid system formed by a highly conductive gate strip placed in proximity to the two-dimensional electron system. The new plasmon mode propagates along the gate strip with no potential nodes present in transverse direction. Its unique spectrum combines characteristic features of both gated and ungated 2D plasmons. The new plasma excitation has been found to exhibit anomalously strong interaction with light.

cond-mat.mes-hall↗

arXiv2019

Achieving Balance of Valley Occupancy in Narrow AlAs Quantum Wells

Terahertz photoconductivity of $100~μ$m and $20~μ$m Hall bars fabricated from narrow AlAs quantum wells (QWs) of different widths is investigated in this paper. The photoresponse is dominated by collective magnetoplasmon excitations within the body of the Hall structure. We observed a radical change of magnetoplasma spectrum measured precisely for AlAs QWs of width ranging from $4$~nm up to $15$~nm. We have shown that the observed behavior is a vivid manifestation of valley transition taking place in the two-dimensional electron system. Remarkably, we show that photoresponse for AlAs QWs of width $6$~nm features two resonances, indicating simultaneous occupation of strongly anisotropic $X_{x-y}$ valleys and isotropic $X_z$ valley in the QW plane. Our results pave the way to realizing valley-selective layered heterostructures, with potential application in valleytronics.

cond-mat.mes-hall↗

arXiv2018

The inherently absent 2-dimensional electron gas in ultra-pure GaN/AlGaN heterostructures

Gallium nitride (GaN) has emerged as an essential semiconductor material for energy-efficient lighting and electronic applications owing to its large direct bandgap of 3.4 eV. Present GaN/AlGaN heterostructures seemingly feature an inherently existing, highly-mobile 2-dimensional electron gas (2DEG), which results in normally-on transistor characteristics. Here we report on an ultra-pure GaN/AlGaN layer stack grown by molecular beam epitaxy, in which such a 2DEG is absent at 300 K in the dark, a property previously not demonstrated. Illumination with ultra-violet light however, generates a 2DEG at the GaN/AlGaN interface and the heterostructure becomes electrically conductive. At temperatures below 150 K this photo-conductivity is persistent with an insignificant dependence of the 2D channel density on the optical excitation power. Residual donor impurity concentrations below 10$^{17}$ cm$^{-3}$ in the GaN/AlGaN layer stack are one necessity for our observations. Fabricated transistors manifest that these characteristics enable a future generation of normally-off as well as light-sensitive GaN-based device concepts.

cond-mat.mes-hall↗

arXiv2018

Direct observation of $Γ- X$ energy spectrum transition in narrow AlAs quantum wells

Spectra of magnetoplasma excitations have been investigated in a two-dimensional electron systems in AlAs quantum wells (QWs) of different widths. The magnetoplasma spectrum have been found to change profoundly when the quantum well width became thinner than $5.5$~nm, indicating a drastic change in the conduction electron energy spectrum. The transformation can be interpreted in terms of transition from the in-plane strongly anisotropic $X_x - X_y$ valley occupation to the out-of-plane isotropic $X_z$ valley in the QW plane. Strong enhancement of the cyclotron effective mass over the band value in narrow AlAs QWs is reported.

cond-mat.mes-hall↗

arXiv2018

Drastic Reduction of Plasmon Damping in Two-Dimensional Electron Disks

The plasmon damping has been investigated using resonant microwave absorption of two-dimensional electrons in disks with different diameters. We have found an unexpected drastic reduction of the plasmon damping in the regime of strong retardation. This finding implies large delocalization of retarded plasmon field outside the plane of the two-dimensional electron system. A universal relation between the damping of plasmon polariton waves and retardation parameter is reported.

cond-mat.mes-hall↗

arXiv2018

Three-particle electron-hole complexes in two-dimensional electron systems

Three-particle complexes consisting of two holes in the completely filled zero electron Landau level and an excited electron in the unoccupied first Landau level are investigated in a quantum Hall insulator. The distinctive features of these three-particle complexes are an electron-hole mass symmetry and the small energy gap of the quantum Hall insulator itself. Theoretical calculations of the trion energy spectrum in a quantizing magnetic field predict that, besides the ground state, trions feature a hierarchy of excited bound states. In agreement with the theoretical simulations, we observe new photoluminescence lines related to the excited trion states. A relatively small energy gap allows the binding of three-particle complexes with magnetoplasma oscillations and formation of plasmarons. The plasmaron properties are investigated experimentally.

cond-mat.str-el↗