arXiv subjects

Vedran Jelic

Publications and source records attributed to Vedran Jelic.

4 recordsLinked to original sources

arXiv2026

Femtosecond tunneling spectroscopy of ultrafast band bending dynamics at the atomic limit

Atomic-scale disorder shapes the potential energy landscape traversed by photoexcited charge carriers, while the carriers themselves also dynamically reshape this landscape. However, resolving ultrafast photocarrier motion at atomic length scales has remained a central challenge in materials science. Here, we demonstrate that lightwave-driven terahertz scanning tunneling microscopy (THz-STM) provides access to these dynamics by probing the ultrafast evolution of local electronic structure following resonant interband excitation. Applying this approach to the photoexcited GaAs(110) surface, we image the resulting femtosecond carrier dynamics by tracking the transient photocurrents produced by ultrafast shifts in the energy alignment of surface and bulk electronic states near individual surface defects. Supported by modeling, we experimentally resolve the time-dependent band bending produced by photoinduced charge carriers across the atomic-scale landscape of the sample surface. Crucially, we employ terahertz time-domain spectroscopy in the tip near-field to disentangle the coherent sub-cycle dynamics induced by the terahertz driving field from the intrinsic sample response. We establish a new regime of ultrafast tunneling spectroscopy that captures transient electronic structure and dynamic band alignment with unprecedented spatio-temporal resolution, which has significant implications for understanding carrier transport, defect-mediated processes, and the development of optoelectronic technologies based on dynamically tunable materials.

cond-mat.mes-hall↗

arXiv2026

Phonon-driven decoherence of high-harmonic generation in the solid-state

High-harmonic generation in solids has emerged as a powerful probe of ultrafast electron dynamics and lattice motion, and recent theoretical work has suggested that thermally driven lattice fluctuations can act as an effective source of decoherence in the harmonic-generation process. However, a direct experimental link between high-harmonic emission and temperature-driven incoherent phonons has remained unclear. Here, we investigate the temperature dependence of high-harmonic generation in ultrapure silicon using reflection-geometry measurements over a wide temperature range. We observe that the harmonic yield increases significantly with decreasing temperature. To interpret these results, we introduce a one-dimensional atomic-chain model in which finite temperature is represented by random lattice displacements that mimic incoherent phonon fluctuations. The simulations reproduce the magnitude of temperature-dependent change of the harmonic signal and support a picture in which thermally induced lattice disorder enhances electron-hole decoherence, thereby reducing high-harmonic emission. Our results establish incoherent phonons as an important source of decoherence in solid-state high-harmonic generation.

cond-mat.mes-hall↗

arXiv2024

Terahertz control of surface topology probed with subatomic resolution

Light-induced phase transitions offer a method to dynamically modulate topological states in bulk complex materials. Yet, next-generation devices demand nanoscale architectures with contact resistances near the quantum limit and precise control over local electronic properties. The layered material WTe$_2$ has gained attention as a likely Weyl semimetal, with topologically protected linear electronic band crossings hosting massless chiral fermions. Here, we demonstrate a topological phase transition facilitated by light-induced shear motion of a single atomic layer at the surface of bulk WTe$_2$, thereby opening the door to nanoscale device concepts. Ultrafast terahertz fields enhanced at the apex of an atomically sharp tip resonantly couple to the key interlayer shear mode of WTe$_2$ via a ferroelectric dipole at the interface, inducing a structural phase transition at the surface to a metastable state. Subatomically resolved differential imaging, combined with hybrid-level density functional theory, reveals a shift of 7 $\pm$ 3 picometres in the top atomic plane. Tunnelling spectroscopy links electronic changes across the phase transition with the electron and hole pockets in the band structure, suggesting a reversible, light-induced annihilation of the topologically-protected Fermi arc surface states in the top atomic layer.

cond-mat.mtrl-sci↗

arXiv2023

Atomic-Scale Terahertz Near Fields for Ultrafast Tunnelling Spectroscopy

Lightwave-driven terahertz scanning tunnelling microscopy (THz-STM) is capable of exploring ultrafast dynamics across a wide range of materials with angstrom resolution. In contrast to scanning near-field optical microscopy, where photons scattered by the tip apex are analyzed to access the local dielectric function on the nanoscale, THz-STM uses a strong-field single-cycle terahertz pulse to drive an ultrafast current across a tunnel junction, thereby probing the local density of electronic states. Yet, the terahertz field in a THz-STM junction may also be spectrally modified by the electromagnetic response of the sample. Here, we demonstrate a reliable and self-consistent approach for terahertz near-field waveform acquisition in an atomic tunnel junction that can be generally applied to electrically conductive surfaces. By combining waveform sampling and tailoring with terahertz scanning tunnelling spectroscopy (THz-STS), we comprehensively characterize the tunnel junction and distinguish local sample properties from effects due to terahertz pulse coupling and field enhancement. Through modelling, we verify the presence of an isolated unipolar terahertz-induced current pulse, facilitating straightforward interpretation for differential THz-STS with high spectral resolution. Finally, we demonstrate the feasibility of atomic-scale terahertz time-domain spectroscopy via the extremely localized near-fields in the tunnel junction.

cond-mat.mes-hall↗