arXiv subjects

Marcin Białek

Publications and source records attributed to Marcin Białek.

3 recordsLinked to original sources

arXiv2026

Far-field terahertz spectroscopy across the charge-density-wave transition in 2H-NbSe$_2$

Charge-density-wave (CDW) formation in 2H-NbSe$_2$ modifies the low-energy electronic structure and gives rise to collective excitations coupled to the lattice. Here, we investigate bulk 2H-NbSe$_2$ single crystals using far-field terahertz time-domain spectroscopy (THz-TDS) in reflection geometry across the CDW transition at $T_{\mathrm{CDW}} \approx 33$~K. Below $T_{\mathrm{CDW}}$, the THz response shows a pronounced high-frequency feature near 1.5~THz together with longer-lived sub-THz oscillations. Both responses progressively weaken upon warming and are strongly suppressed across the CDW transition, supporting their association with the CDW state. Using time-dependent Ginzburg--Landau simulations, we reproduce the main features of the experimental THz response, associating the high-frequency response mainly with CDW amplitude dynamics and the sub-THz response with defect-pinned phase dynamics. The $\sim1.5$~THz feature lies close to the frequency range reported for the Raman CDW amplitude mode, while coupling to lattice degrees of freedom may also influence its spectral position. We also performed complementary angle-resolved photoemission spectroscopy measurements, which reveal momentum-selective redistribution of near-Fermi-level spectral weight across the transition. Together, these results show that far-field THz spectroscopy provides a sensitive probe of collective CDW dynamics in bulk 2H-NbSe$_2$.

cond-mat.mtrl-sci↗

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↗

arXiv2024

Hybridization of terahertz phonons and magnons in disparate and spatially-separated material specimens

The interaction between light and matter in condensed matter excitations and electromagnetic resonators serves as a rich playground for fundamental research and lies at the core of photonic and quantum technologies. Herein, we present comprehensive experimental and theoretical studies of the photon-mediated hybridization of magnons and phonons in the terahertz (THz) range. We demonstrate the intriguing concept of composite states formed by distinct electric and magnetic quasiparticles strongly coupled to the same optical cavity modes. Specifically, we explore magnons excited in a slab of an antiferromagnetic crystal and phonons excited in a distinct specimen of an insulating material. The crystal slabs form an optical cavity with Fabry-Pérot oscillations in the THz range. We demonstrate hybridized phonon-magnon polariton modes and their tunability by adjusting the distance between the slabs, showing that hybridization persists even at separations up to several millimeters. The experimental results are interpreted using both classical and quantum electrodynamical models. The quantum description allows us to quantify the degree of hybridization that is linked to a topological behavior of the electric field phasor, in agreement with the classical electrodynamics expectations. Importantly, the presented results refer to temperature conditions and cavities of millimeter size, paving the way for engineering realistic, frequency-tunable THz devices through the hybridization of electric (phononics) and magnetic (spintronics) elementary excitations of matter.

physics.optics↗