arXiv subjects

Dmitry Turchinovich

Publications and source records attributed to Dmitry Turchinovich.

18 recordsLinked to original sources

arXiv2026

Fundamental picture of the conduction mechanism in solid-state polymer electrolytes revealed by terahertz spectroscopy

Solid polymer electrolytes (SPEs) based on cross-linked poly(ethylene oxide) (PEO) encompassing lithium salts have gained significant attention as separators in solid-state lithium metal batteries. Here, we employ terahertz time-domain spectroscopy (THz-TDS), as a noninvasive contact-free technique, to investigate the conduction properties of these cross-linked SPEs and unravel their dependencies on the added lithium salt and the sample temperature. The obtained THz conductivity spectra are dominated by THz absorption bands, which we attribute to resonant vibrations within the polymer matrix of the electrolyte. By careful application of Lorentz model, the conductivity spectra have been analyzed, and the relevant polymer vibration modes have been quantitatively assessed. Calculations based on the density functional theory (DFT) were performed to elucidate the possible microscopic mechanisms of these resonant vibrations. This study sheds light on the relevance of polymer matrix vibrations validating the hopping transport of lithium ions in SPEs which ultimately leads to the technologically relevant ionic conduction in the solid-state polymer-based electrolytes.

cond-mat.soft↗

arXiv2026

Electrical tunability of terahertz nonlinearity in graphene

Graphene is conceivably the most nonlinear optoelectronic material. Its nonlinear optical coefficients in the terahertz (THz) frequency range surpass those of other materials by many orders of magnitude. This, in particular, allows one to use graphene for extremely efficient up-conversion of sub-THz electronic input signals into the THz frequency range at room temperature and under ambient conditions, thus paving the way for practical graphene-based ultrahigh-frequency electronic technology. Here, we show that the THz nonlinearity of graphene can be efficiently controlled using electrical gating, with gating voltages as low as a few volts. For example, optimal electrical gating enhances the power conversion efficiency in THz third-harmonic generation in graphene by about two orders of magnitude. This essentially converts graphene from an almost perfectly linear, inert electronic material to a material with the highest possible THz nonlinearity. We demonstrate gating control of THz nonlinearity of graphene for both ultrashort single-cycle and quasi-monochromatic multi-cycle input signals. Our experimental results are in quantitative agreement with a physical model of graphene nonlinearity, describing the time-dependent thermodynamic balance maintained within the electronic population of graphene during interaction with ultrafast electric fields. Our results can serve as a basis for straightforward and accurate design of devices and applications for efficient electronic signal processing in graphene at ultra-high frequencies.

cond-mat.mes-hall↗

arXiv2026

Efficient terahertz optical filtering with large-area all-metal and polymer-metal woven wire meshes

Many components for terahertz (THz) optical filtering are mechanically fragile and are hard to produce with large aperture, making them unsuitable for applications where larger THz beam diameter is required. In this work, the THz optical properties of industrial-grade, readily available and inexpensive woven wire meshes are studied using THz time-domain spectroscopy and numerical simulations. These meshes are meter-sized, free-standing sheet materials that are principally attractive for the use as robust, large-area THz components. Our results show that such meshes can act as efficient, tunable THz bandpass filters due to sharp plasmonic resonance supported by the interwoven metallic wires. Further, the meshes that combine metallic and polymer wires act as efficient THz linear polarizers with a polarization extinction ratio (field) above 60:1 for frequencies below 3 THz.

physics.optics↗

arXiv2026

Time-dependent terahertz dielectric function of ZnTe under two-photon optical excitation at 800 nm wavelength

ZnTe is arguably the most widely used nonlinear crystal for the generation and detection of THz radiation, used in conjunction with sub-bandgap optical excitation by femtosecond lasers operating near 800 nm. The THz dielectric function of ZnTe is the key parameter defining the efficiency and bandwidth of THz generation and detection. Here, we demonstrate that the THz dielectric function of ZnTe undergoes substantial transient modification at 800 nm sub-bandgap excitation under conditions typical for THz generation. These modifications arise from significant free-carrier generation via two-photon absorption of the 800 nm pump, accompanied by the pump-driven activation of the THz-active phonon modes. Using optical pump-THz probe spectroscopy, we characterized the THz dielectric function of ZnTe under 800 nm excitation as a function of pump fluence and pump-probe delay. Analysis of the experimental data within the Drude-Lorentz model provided the generated free carrier density and momentum scattering time, and oscillator strength of the pump activated THz phonon modes, revealing their transient evolution in dependence on the excitation conditions.

cond-mat.other↗

arXiv2025

Terahertz field effect in a two-dimensional semiconductor MoS2

Layered two-dimensional (2D) materials, with their atomic-scale thickness and tunable electronic, optical, and mechanical properties, open many promising pathways to significantly advance modern electronics. The field effect caused by a strong electric field, typically of MV/cm level, applied perpendicular to the material layers, is a highly effective method for controlling these properties. Field effect allows the regulation of the electron flow in transistor channels, improves the photodetector efficiency and spectral range, and facilitates the exploration of novel exotic quantum phenomena in 2D materials. However, existing approaches to induce the field effect in 2D materials utilize circuit-based electrical gating methods fundamentally limited to microwave response rates. Device-compatible ultrafast, sub-picosecond control needed for modern technology and basic science applications still remains a challenge. In this study, we demonstrate such an ultrafast field effect in atomically thin MoS2, an archetypal 2D semiconductor, embedded in a hybrid 3D-2D terahertz nanoantenna structure. This nanoantenna efficiently converts an incident terahertz electric field into the vertical ultrafast gating field in MoS2 while simultaneously enhancing it to the required MV/cm level. We observe the terahertz field effect optically as coherent terahertz-induced Stark shift of characteristic exciton resonances in MoS2. Our results enable novel developments in technology and the fundamental science of 2D materials, where the terahertz field effect is crucial.

cond-mat.mtrl-sci↗

arXiv2025

Enhanced THz emission from spintronic emitters with Pt-Al alloys

Platinum (Pt) is the element with the largest spin Hall conductivity and is known as the most efficient spin-to-charge conversion material in spintronic THz emitters. By alloying with aluminum (Al), its resistivity can be substantially increased, exceeding $100\,μΩ$cm. While the spin Hall conductivity is reduced by alloying, the relative resistivity increase surpasses the reduction of spin Hall conductivity and thereby enhances the spin Hall angle. We make use of this mechanism to improve the commonly used Pt-based spintronic THz emitter and demonstrate that an increase of 67% in the THz emission amplitude can be achieved between 20\% and 30\% Al in Pt. We show that the enhanced THz emission amplitude is driven by the enhanced multilayer impedance due to the larger resistivity.

cond-mat.mtrl-sci↗

arXiv2025

Emergent spin Hall conductivity in Tantalum-Rhenium alloys

We investigate the spin Hall conductivity (SHC) of a composition series of a Ta-Re bcc solid solution. At approximately 60 at.% Ta the Ta-Re alloy features an SHC similar to bcc-W, while both endpoints of the compositional series have rather moderate SHC. The intermediate stoichiometries exhibit a substantial enhancement due to Fermi level tuning through the same band structure feature which gives bcc-W and $β$-W its large SHC. We provide experimental evidence for the enhancement of the SHC in the alloy via THz emission upon ultrafast laser excitation of Ta-Re/CoFeB bilayers. We demonstrate that a rigid band model derived from bcc-W and Fermi level tuning describes the experimental data with a similar accuracy as coherent potential approximation alloy calculations of the SHC.

cond-mat.mtrl-sci↗

arXiv2024

Efficient Spintronic THz Emitters Without External Magnetic Field

We investigate the performance of state-of-the-art spintronic THz emitters (W or Ta)/CoFeB/Pt with non-magnetic underlayer deposited using oblique angle deposition. The THz emission amplitude in the presence or absence of an external magnetic field remains the same and remarkably stable over time. This stability is attributed to the enhanced uniaxial magnetic anisotropy in the ferromagnetic layer, achieved by oblique angle deposition of the underlying non-magnetic layer. Our findings could be used for the development of practical field-free emitters of linearly polarized THz radiation, potentially enabling novel applications in future THz technologies.

physics.app-ph↗

arXiv2023

Post-2000 Nonlinear Optical Materials and Measurements: Data Tables and Best Practices

In its 60 years of existence, the field of nonlinear optics has gained momentum especially over the past two decades thanks to major breakthroughs in material science and technology. In this article, we present a new set of data tables listing nonlinear-optical properties for different material categories as reported in the literature since 2000. The papers included in the data tables are representative experimental works on bulk materials, solvents, 0D-1D-2D materials, metamaterials, fiber waveguiding materials, on-chip waveguiding materials, hybrid waveguiding systems, and materials suitable for nonlinear optics at THz frequencies. In addition to the data tables, we also provide best practices for performing and reporting nonlinear-optical experiments. These best practices underpin the selection process that was used for including papers in the tables. While the tables indeed show strong advancements in the field over the past two decades, we encourage the nonlinear-optics community to implement the identified best practices in future works. This will allow a more adequate comparison, interpretation and use of the published parameters, and as such further stimulate the overall progress in nonlinear-optical science and applications.

physics.optics↗

arXiv2022

Disentangling complex current pathways in a metallic Ru/Co bilayer nanostructure using THz spectroscopy

Many modern spintronic technologies, such as spin valves, spin Hall applications, and spintronic THz emitters, are based on electrons crossing buried internal interfaces within metallic nanostructures. However, the complex current pathways within such nanostructures are difficult to disentangle using conventional experimental methods. Here, we measure the conductivity of a technologically relevant Ru/Co bilayer nanostructure in a contact-free fashion using THz time-domain spectroscopy. By applying an effective resistor network to the data, we resolve the complex current pathways within the nanostructure and determine the degree of electronic transparency of the internal interface between the Ru and Co nanolayers.

cond-mat.mes-hall↗

arXiv2021

Rigorous Signal Reconstruction in Terahertz Emission Spectroscopy

Terahertz (THz) emission spectroscopy is a powerful method that allows one to measure the ultrafast dynamics of polarization, current, or magnetization in a material based on THz emission from the material. However, the practical implementation of this method can be challenging, and can result in significant errors in the reconstruction of the quantity of interest. Here, we experimentally and theoretically demonstrate a rigorous method of signal reconstruction in THz emission spectroscopy, and describe the main experimental and theoretical sources of reconstruction error. We identify the linear line-of-sight geometry of the THz emission spectrometer as the optimal configuration for accurate, fully calibrated THz signal reconstruction. As an example, we apply our reconstruction method to ultrafast THz magnetometry experiment, where we recover the ultrafast magnetization dynamics in a photoexcited iron film, including both its temporal shape and absolute magnitude.

physics.optics↗

arXiv2021

Ultrastrong Magnon-Magnon Coupling Dominated by Antiresonant Interactions

Exotic quantum vacuum phenomena are predicted in cavity quantum electrodynamics (QED) systems with ultrastrong light-matter interactions. Their ground states are predicted to be vacuum squeezed states with suppressed quantum fluctuations. The source of such phenomena are antiresonant terms in the Hamiltonian, yet antiresonant interactions are typically negligible compared to resonant interactions in light-matter systems. We report an unusual coupled matter-matter system of magnons that can simulate a unique cavity QED Hamiltonian with coupling strengths that are easily tunable into the ultrastrong coupling regime and with dominant antiresonant terms. We found a novel regime where vacuum Bloch-Siegert shifts, the hallmark of antiresonant interactions, greatly exceed analogous frequency shifts from resonant interactions. Further, we theoretically explored the system's ground state and calculated up to 5.9 dB of quantum fluctuation suppression. These observations demonstrate that magnonic systems provide an ideal platform for simulating exotic quantum vacuum phenomena predicted in ultrastrongly coupled light-matter systems.

quant-ph↗

arXiv2020

Grating-graphene metamaterial as a platform for terahertz nonlinear photonics

Nonlinear optics is an increasingly important field for scientific and technological applications, owing to its relevance and potential for optical and optoelectronic technologies. Currently, there is an active search for suitable nonlinear material systems with efficient conversion and small material footprint. Ideally, the material system should allow for chip-integration and room-temperature operation. Two-dimensional materials are highly interesting in this regard. Particularly promising is graphene, which has demonstrated an exceptionally large nonlinearity in the terahertz regime. Yet, the light-matter interaction length in two-dimensional materials is inherently minimal, thus limiting the overall nonlinear-optical conversion efficiency. Here we overcome this challenge using a metamaterial platform that combines graphene with a photonic grating structure providing field enhancement. We measure terahertz third-harmonic generation in this metamaterial and obtain an effective third-order nonlinear susceptibility with a magnitude as large as 3$\cdot$10$^{-8}$m$^2$/V$^2$, or 21 esu, for a fundamental frequency of 0.7 THz. This nonlinearity is 50 times larger than what we obtain for graphene without grating. Such an enhancement corresponds to third-harmonic signal with an intensity that is three orders of magnitude larger due to the grating. Moreover, we demonstrate a field conversion efficiency for the third harmonic of up to $\sim$1% using a moderate field strength of $\sim$30 kV/cm. Finally we show that harmonics beyond the third are enhanced even more strongly, allowing us to observe signatures of up to the 9$^{\rm th}$ harmonic. Grating-graphene metamaterials thus constitute an outstanding platform for commercially viable, CMOS compatible, room temperature, chip-integrated, THz nonlinear conversion applications.

physics.optics↗

arXiv2019

Thickness-dependent electron momentum relaxation times in thin iron films

Terahertz time-domain conductivity measurements in 2 to 100 nm thick iron films resolve the femtosecond time delay between applied electric fields and resulting currents. This response time decreases for thinner metal films. The macroscopic response time depends on the mean and the variance of the distribution of microscopic momentum relaxation times of the conducting electrons. Comparing the recorded response times with DC-conductivities demonstrates increasing variance of the microscopic relaxation times with increasing film thickness. At least two electron species contribute to conduction in bulk with substantially differing relaxation times. The different electron species are affected differently by the confinement because they have different mean free paths.

cond-mat.mtrl-sci↗

arXiv2016

Probing the Charge Separation Process on In2S3/Pt-TiO2 Nanocomposites for Boosted Visible-light Photocatalytic Hydrogen Production

A simple refluxing wet-chemical approach is employed for fabricating In2S3/Pt-TiO2 heterogeneous catalysts for hydrogen generation under visible light irradiation. When the mass ratio between Pt-TiO2 and cubic-phased In2S3 (denoted as In2S3/Pt-TiO2) is two, the composite catalyst shows the highest hydrogen production, which exhibits an 82-fold enhancement over in-situ deposited Pt-In2S3. UV-vis diffuse reflectance and valence band X-ray photoelectron spectra elucidate that the conduction band of In2S3 is 0.3 eV more negative compared to that of TiO2, favoring charge separation in the nanocomposites. Photoelectrochemical transient photo-current measurements and optical pump - terahertz probe spectroscopic studies further corroborate the charge separation in In2S3/Pt-TiO2. The migration of photo-induced electrons from the In2S3 conduction band to the TiO2 conduction band and subsequently into the Pt nanoparticles is found to occur within 5 picoseconds. Based on the experimental evidence, a charge separation process is proposed which accounts for the enhanced activity exhibited by the In2S3/Pt-TiO2 composite catalysts.

physics.chem-ph↗

arXiv2014

Competing Ultrafast Energy Relaxation Pathways in Photoexcited Graphene

For most optoelectronic applications of graphene a thorough understanding of the processes that govern energy relaxation of photoexcited carriers is essential. The ultrafast energy relaxation in graphene occurs through two competing pathways: carrier-carrier scattering -- creating an elevated carrier temperature -- and optical phonon emission. At present, it is not clear what determines the dominating relaxation pathway. Here we reach a unifying picture of the ultrafast energy relaxation by investigating the terahertz photoconductivity, while varying the Fermi energy, photon energy, and fluence over a wide range. We find that sufficiently low fluence ($\lesssim$ 4 $μ$J/cm$^2$) in conjunction with sufficiently high Fermi energy ($\gtrsim$ 0.1 eV) gives rise to energy relaxation that is dominated by carrier-carrier scattering, which leads to efficient carrier heating. Upon increasing the fluence or decreasing the Fermi energy, the carrier heating efficiency decreases, presumably due to energy relaxation that becomes increasingly dominated by phonon emission. Carrier heating through carrier-carrier scattering accounts for the negative photoconductivity for doped graphene observed at terahertz frequencies. We present a simple model that reproduces the data for a wide range of Fermi levels and excitation energies, and allows us to qualitatively assess how the branching ratio between the two distinct relaxation pathways depends on excitation fluence and Fermi energy.

cond-mat.mes-hall↗

arXiv2012

Self-phase modulation of a single-cycle terahertz pulse by nonlinear free-carrier response in a semiconductor

We demonstrate the self-phase modulation (SPM) of a single-cycle THz pulse in a semiconductor, using bulk n-GaAs as a model system. The SPM arises from the heating of free electrons in the electric field of the THz pulse, leading to an ultrafast reduction of the plasma frequency, and hence to a strong modification of the THz-range dielectric function of the material. THz SPM is observed directly in the time domain. In the frequency domain it corresponds to a strong frequency-dependent refractive index nonlinearity of n-GaAs, found to be both positive and negative within the broad THz pulse spectrum, with the zero-crossing point defined by the electron momentum relaxation rate. We also observed the nonlinear spectral broadening and compression of the THz pulse.

cond-mat.mtrl-sci↗

arXiv2010

Semiconductor saturable absorbers for ultrafast THz signals

We demonstrate saturable absorber behavior of n-type semiconductors GaAs, GaP and Ge in THz frequency range at room temperature using nonlinear THz spectroscopy. The saturation mechanism is based on a decrease in electron conductivity of semiconductors at high electron momentum states, due to conduction band nonparabolicity and scattering into satellite valleys in strong THz fields. Saturable absorber parameters, such as linear and non-saturable transmission, and saturation fluence, are extracted by fits to a classic saturable absorber model. Further, we observe THz pulse shortening, and an increase of the group refractive index of the samples at higher THz pulse peak fields.

cond-mat.other↗