arXiv subjects

Dmitriy Yavorskiy

Publications and source records attributed to Dmitriy Yavorskiy.

5 recordsLinked to original sources

arXiv2026

Delayed Formation of Landau Polaritons in Phase-Resolved THz Spectroscopy

Strong light-matter coupling gives rise to polaritons through coherent and periodic energy exchange between electromagnetic cavity fields and material excitations. While this interaction is typically inferred from spectral mode splitting, its dynamics remain largely unexplored. Here, using phase-resolved terahertz time-domain spectroscopy, we observe Rabi oscillations of Landau polaritons formed by coupling the cyclotron resonance in a GaAs/Al$_{0.36}$Ga$_{0.64}$As two-dimensional electron gas with Fabry-Perot cavity modes. By employing cross-polarized spectroscopy and magnetic-field differential, we resolve the temporal beating of the cyclotron resonance oscillations. Remarkably, we find that the Rabi oscillations do not start immediately after excitation of the cyclotron resonance, but after a delay corresponding to one cavity round-trip time. This demonstrates that the strong-coupling regime sets up only after the formation of the cavity mode field. Our results provide direct insight into the dynamics of hybrid light-matter states in the THz regime.

cond-mat.mes-hall↗

arXiv2026

Deep Strong light-matter Coupling in 3D Kane Fermions

Deep strong light-matter coupling represents an extreme non-perturbative regime of quantum electrodynamics, in which the interaction strength exceeds the bare frequencies of the uncoupled systems. The ground state features strong quantum correlations between photons and matter excitations, and new cavity-driven phase transitions are expected to occur. Whether a superradiant quantum phase transition, marked by spontaneous dipole ordering and photon condensation, is possible has remained a long-standing and controversial question. Such phenomena have been proposed to arise in exotic electronic systems hosting Dirac and Kane fermions, owing to the formal absence of an $A^2$ term in their low-energy Hamiltonian. Here we exploit the ultralow effective mass of Kane fermions to realise Landau polaritons in a bulk mercury cadmium telluride layer coupled to a Fabry-Perot resonator. Using thermally tunable carrier density, we continuously tune the coupling from the weak to the deep-strong regime, achieving a record normalised coupling ratio exceeding 1.6 above room temperature. The measured polariton spectra are in excellent agreement with a rigorous, gauge-invariant microscopic theory. Despite the nonlinear Landau level structure of relativistic Kane fermions, we show that a diamagnetic $A^2$ term naturally emerges and precludes a superradiant phase transition. These results resolve the long-standing controversy surrounding cavity quantum electrodynamics of relativistic-like matter systems, extend deep-strong-coupling physics to Kane fermions, and open new opportunities for polaritonic semiconductor devices operating in extreme light-matter coupling regimes.

cond-mat.mes-hall↗

arXiv2025

Terahertz magnon-polaritons control using a tunable liquid crystal cavity

Strong coupling of light to a collective spin excitation in antiferromagnets gives rise to hybrid modes called magnon-polaritons. They are highly promising for data manipulation and transfer at terahertz rates, much faster than in the case of ferromagnetic magnon-polaritons, which operate at GHz frequencies. Yet, control of terahertz magnon-polaritons by the voltage, i.e. without ohmic dissipation losses, remains challenging. Here, we showcase the ability to remotely control antiferromagnetic magnon-polaritons at room temperature using an electric field by integrating a highly birefringent liquid crystal layer into a terahertz Fabry-Pérot cavity containing an antiferromagnetic crystal. Positioned several millimeters from the magnetic material, the liquid crystal allows for electrical manipulation of the cavity's photonic environment by control of its dielectric constant. This adjustment, in turn, influences the extent of magnon dressing by cavity photons, thereby controlling the vacuum Rabi oscillations of the magnon resonance coupled to a particular cavity mode. Our approach enables reversible tuning of magnon-photon hybridization that can be triggered without direct electrical contact or alteration of the magnetic medium. These findings pave the way for voltage-programmable terahertz magnonic devices and open new avenues for noninvasive control strategies in spin-based information processing technologies.

cond-mat.other↗

arXiv2025

Extreme Terahertz Nonlinearity of AlGaN/GaN-based Grating-Gate Plasmonic Crystals

We present a novel approach to enhance THz nonlinearity by the resonant excitation of two-dimensional plasmons in grating-gate plasmonic crystals. Using a high-electric-field THz pump-THz probe technique, we investigate the nonlinear interaction of spectrally narrow THz pulses with plasmon oscillations in a two-dimensional electron gas on an AlGaN/GaN interface integrated with metallic grating. Nonlinear effects are observed as ultrafast, pump-induced changes in THz transmission, with relative transparency strongly dependent on plasmonic mode excitation and saturating at pump fluences of about 200 nJ cm-2. The maximal relative transparency, reaching 45 % at 350 nJ cm -2, occurs under resonant excitation of a localized plasmon mode at the strong electrostatic modulation of 2DEG concentration. Transient dynamics reveal ultrafast relaxation times of 15-20 ps, while the effects can be observed at elevated temperatures of up to 150 K. A nonlinear model of plasmonic crystal, based on finite-difference time-domain electrodynamic simulations coupled with viscous hydrodynamic electron transport model, elucidates key nonlinear mechanisms, including near-field effects under metallic gratings, electron heating, plasmon resonance broadening, and redshift. These results demonstrate that even conventional semiconductors such as AlGaN/GaN can achieve nonlinear THz responses comparable to or exceeding those of graphene, showing strong potential for ultrafast THz modulation and nonlinear photonics applications.

physics.optics↗

arXiv2025

Optical bound states in the continuum in subwavelength gratings made of an epitaxial van der Waals material

High refractive index (4.4 at 1100 nm), negligibly small absorption in near-infrared spectral range, and ease of processing make MoSe$_2$ a perfect material for applications in near-infrared photonics. So far, implementation of MoSe$_2$-based photonic structures has been hindered by the lack of large surface MoSe$_2$ substrates. The use of molecular beam epitaxy allows the production of homogeneous layers of MoSe$_2$ with a few-inch surface and a thickness controlled at the sub-nm level. In the present work, we design by theoretical calculations and fabricate by a simple lithography process an ultrathin subwavelength grating out of 42-nm thick, epitaxially-grown MoSe$_2$ layer. Our polarization-resolved reflectivity measurements confirm that the gratings host a peculiar type of a confined optical mode that is a bound state in the continuum. Moreover, the fabricated structures enhance the efficiency of the third harmonic generation by over three orders of magnitude as compared to the unstructured MoSe$_2$ layer. The presented results are promising for the realization of flat, ultra-compact devices for lasing, wavefront control, and higher-order topological states of the light.

physics.optics↗