arXiv subjects

Yevhenii Vaskivskyi

Publications and source records attributed to Yevhenii Vaskivskyi.

9 recordsLinked to original sources

arXiv2026

Real-time imaging of quasiparticle dynamics at a topological defect in an electronic crystal

Defects formed during nonequilibrium self-assembly of quantum matter can dominate its emergent properties. Their macroscopic manifestations are typically characterised as noise, but their internal dynamics remain largely experimentally inaccessible. Making significant advances into the investigation of the microscopic degrees of freedom of such defects, we use fast scanning tunnelling microscopy to resolve, in real time, both internal and global dynamics of a mesoscopic Y-junction defect in an electronic crystal created through self-assembly after a local electromagnetic perturbation. We directly track individual electron rearrangements on millisecond timescales and map spatially localised telegraph noise characteristic of a two-level system. The phase and amplitude of these fluctuations are correlated with the observed charged particle trajectories, revealing a direct connection between collective order-parameter dynamics and microscopic charge motion. We model the dynamics as arising from the interplay of local Coulomb correlations, non-local configurational constraints and hybridised amplitude - phase collective modes bound to the junction. These constraints, together with the non-trivial broken symmetries of the defect, protect long-lived local quasiparticle configurations against external perturbations. Our results establish fast scanning tunnelling microscopy as a means of probing the internal dynamics of metastable quantum defects and reveal how microscopic correlations and collective modes are intertwined within topologically non-trivial structures in electronic crystals.

cond-mat.mes-hall↗

arXiv2025

Van der Waals devices for surface-sensitive experiments

In-operando characterization of van der Waals (vdW) devices using surface-sensitive methods provides critical insights into phase transitions and correlated electronic states. Yet, integrating vdW materials in functional devices while maintaining pristine surfaces is a key challenge for combined transport and surface-sensitive experiments. Conventional lithographic techniques introduce surface contamination, limiting the applicability of state-of-the-art spectroscopic probes. We present a stencil lithography-based approach for fabricating vdW devices, producing micron-scale electrical contacts, and exfoliation in ultra-high vacuum. The resist-free patterning method utilizes a shadow mask to define electrical contacts and yields thin flakes down to the single-layer regime via gold-assisted exfoliation. As a demonstration, we fabricate devices from 1$T-$TaS$_2$ flakes, achieving reliable contacts for application of electrical pulses and resistance measurements, as well as clean surfaces allowing for angle-resolved photoemission spectroscopy. The approach provides a platform for studying the electronic properties of vdW systems with surface-sensitive probes in well-defined device geometries.

cond-mat.mes-hall↗

arXiv2024

Non-equilibrium quantum domain reconfiguration dynamics in a two-dimensional electronic crystal: experiments and quantum simulations

Relaxation dynamics of complex many-body quantum systems brought out of equilibrium and subsequently trapped into metastable states is a very active field of research from both the theoretical and experimental point of view with implications in a wide array of topics from macroscopic quantum tunnelling and nucleosynthesis to non-equilibrium superconductivity and new energy-efficient memory devices. Understanding the dynamics of such systems is crucial for exploring fundamental aspects of many-body non-equilibrium quantum physics. In this work we investigate quantum domain reconfiguration dynamics in the electronic superlattice of a quantum material where classical dynamics is topologically constrained. The crossover from temperature to quantum fluctuation dominated dynamics in the context of environmental noise is investigated by directly observing charge reconfiguration with time-resolved scanning tunneling microscopy. The process is modelled using a programmable superconducting quantum simulator in which qubit interconnections correspond directly to the microscopic interactions between electrons in the quantum material. Crucially, the dynamics of both the experiment on the quantum material and the simulation is driven by spectrally similar pink noise. We find that the simulations reproduce the emergent time evolution and temperature dependence of the experimentally observed electronic domain dynamics remarkably well. The combined experiment and simulations lead to a better understanding of noise-driven quantum dynamics in open quantum systems. From a practical viewpoint, the results are important for understanding the origin of the retention time in non-volatile memory devices such as those based on 1T-TaS2.

quant-ph↗

arXiv2023

A high-efficiency programmable modulator for extreme ultraviolet light with nm feature size based on an electronic phase transition

The absence of efficient light modulators for extreme ultraviolet (EUV) and X-ray photons significantly limits their real-life application, particularly when even slight complexity of the beam patterns is required. Here we report on a novel approach to reversible imprinting of a holographic mask in an electronic Wigner crystal material with a sub-90 nm feature size. The structure is imprinted on a sub-picosecond time-scale using EUV laser pulses and acts as a high-efficiency diffraction grating that deflects EUV or soft X-ray light. The imprinted nanostructure is stable after the removal of the exciting beams at low temperatures but can be easily erased by a single heating beam. Modeling shows that the efficiency of the device can exceed 1%, approaching state-of-the-art etched gratings, but with the benefit of being programmable and tunable over a large range of wavelengths. The observed effect is based on the rapid change of lattice constant upon transition between metastable electronically-ordered phases in a layered transition metal dichalcogenide. The proposed approach is potentially useful for creating tunable light modulators in the EUV and soft X-ray spectral ranges.

physics.optics↗

arXiv2023

Unconventional photo-induced charge-density-wave dynamics in 2H-NbSe$_{2}$

We investigated temperature ($T$) dependent ultrafast near-infrared (NIR) transient reflectivity dynamics in coexisting superconducting (SC) and charge density wave (CDW) phases of two-dimensional 2H-NbSe$_{2}$ using NIR and visible excitations. With visible pump-photon excitation (400 nm) we find a slow high-energy quasiparticle relaxation channel which is present in all phases. In the CDW phase, we observe a distinctive transient response component, irrespective of the pump-photon energy. The component is marked by the absence of coherent amplitude mode oscillations and a relatively slow, picosecond rise time, which is different than in most of the typical CDW materials. In the SC phase, another tiny component emerges that is associated with optical suppression of the SC phase. The transient reflectivity relaxation in the CDW phase is dominated by phonon diffusive processes with an estimated low-$T$ heat diffusion constant anisotropy of $\sim30$. Strong excitation of the CDW phase reveals a weakly non-thermal CDW order parameter (OP) suppression. Unlike CDW systems with a larger gap, where the optical OP suppression involves only a small fraction of phonon degrees of freedom, the OP suppression in 2H-NbSe$_{2}$ is characterised by the excitation of a large amount of phonon degrees of freedom and significantly slower dynamics.

cond-mat.supr-con↗

arXiv2022

Ultra-Efficient Resistance Switching between Charge Ordered Phases in 1T-TaS$_2$ with a Single Picosecond Electrical Pulse

Progress in high-performance computing demands significant advances in memory technology. Among novel memory technologies that promise efficient device operation on a sub-ns timescale, resistance switching between charge ordered phases of the 1T-TaS$_2$ has shown to be potentially useful for the development of high-speed, energy efficient non-volatile memory device. While ultrafast switching was previously reported with optical pulses, determination of the intrinsic speed limits of actual devices that are triggered by electrical pulses is technically challenging and hitherto still largely unexplored. A new optoelectronic laboratory-on-a-chip, designed for measurements of ultrafast memory switching, enables an accurate measurement of the electrical switching parameters with 100 fs temporal resolution. A photoconductive response is used for ultrashort electrical pulse generation, while its propagation along a coplanar transmission line is detected using electro-optical sampling using a purpose-grown highly-resistive electro-optic (Cd,Mn)Te crystal substrate. By combining the transmission line and the 1T-TaS$_2$ device in a single optoelectronic circuit a non-volatile resistance switching with a single 1.9 ps electrical pulse is demonstrated, with an extremely small switching energy density per unit area E$_A$ = 9.4 fJ/$μ$m$^2$. The experiments demonstrate ultrafast, energy-efficient circuits utilizing switching between non-volatile charge-ordered states offers a new technological platform for cryogenic memory devices.

cond-mat.str-el↗

arXiv2021

Quantum billiards with correlated electrons confined in triangular transition metal dichalcogenide monolayer nanostructures created by laser quench

Forcing systems though fast non-equilibrium phase transitions offers the opportunity to study new states of quantum matter that self-assemble in their wake. Here we study the quantum interference effects of correlated electrons confined in monolayer quantum nanostructures, created by femtosecond laser-induced quench through a first-order polytype structural transition in a layered transition-metal dichalcogenide material. Scanning tunnelling microscopy of the electrons confined within equilateral triangles, whose dimensions are a few crystal unit cells on the side, reveals that the trajectories are strongly modified from free-electron states both by electronic correlations and confinement. Comparison of experiments with theoretical predictions of strongly correlated electron behaviour reveals that the confining geometry destabilizes the Wigner/Mott crystal ground state, resulting in mixed itinerant and correlation-localized states intertwined on a length scale of 1 nm. Occasionally, itinerant-electron states appear to follow quantum interferences which are suggestive of classical trajectories (quantum scars). The work opens the path toward understanding the quantum transport of electrons confined in atomic-scale monolayer structures based on correlated-electron-materials.

cond-mat.str-el↗

arXiv2020

A time-domain phase diagram of metastable states in a charge ordered quantum material

Metastable self-organized electronic states in quantum materials are of fundamental importance, displaying emergent dynamical properties that may be used in new generations of sensors and memory devices. Such states are typically formed through phase transitions under non-equilibrium conditions and the final state is reached through processes that span a large range of timescales. By using time-resolved optical techniques and femtosecond-pulse-excited scanning tunneling microscopy (STM), the evolution of the metastable states in the quasi-two-dimensional dichalcogenide 1T-TaS2 is mapped out on a temporal phase diagram using the photon density and temperature as control parameters on timescales ranging from 10^(-12) to 10^3 s. The introduction of a time-domain axis in the phase diagram enables us to follow the evolution of metastable emergent states created by different phase transition mechanisms on different timescales, thus enabling comparison with theoretical predictions of the phase diagram and opening the way to understanding of the complex ordering processes in metastable materials.

cond-mat.str-el↗

arXiv2016

Spectroscopic investigation of phase transitions in 1-nonanol and 1-decanol

FTIR spectra of monohydric alcohols 1-nonanol (C9H19OH) and 1-decanol (C10H21OH) were registered in the spectral region from 500 cm-1 to 4000 cm-1 at temperatures from -50 to + 25 °C for 1-nonanol and +100 °C for 1-decanol. Temperature-induced spectra changes were compared for these two alcohols. The authors link the observed changes with the transformations of cluster structure occurring during phase transitions.

physics.atm-clus↗