arXiv subjects

Á. Jiménez-Galán

Publications and source records attributed to Á. Jiménez-Galán.

7 recordsLinked to original sources

arXiv2025

Giant enhancement of attosecond tunnel ionization competes with disorder-driven decoherence in silicon

High-harmonic generation (HHG) is a strong-field phenomenon that is sensitive to the attosecond dynamics of tunnel ionization and coherent transport of electron-hole pairs in solids. While the foundations of solid HHG have been established, a deep understanding into the nature of decoherence on sub-cycle timescales remains elusive. Furthermore, there is a growing need for tools to control ionization at the nanoscale. Here, we study HHG in silicon along a crystalline-to-amorphous (c-Si to a-Si) structural phase transition and observe a dramatic reshaping of the spectrum, with enhanced lower-order harmonic yield accompanied by quenching of the higher-order harmonics. Modelling the real-space quantum dynamics links our observations to a giant enhancement (>250 times) of tunnel ionization yield in the amorphous phase and a disorder-induced decoherence that damps the electron-hole polarization over approximately six lattice sites. HHG spectroscopy also reveals remnant order that was not apparent with conventional probes. Finally, we observe a rapid and targeted non-resonant laser annealing of amorphous silicon islands. Our results offer a unique insight into attosecond decoherence in strong-field phenomena, establish HHG spectroscopy as a probe of structural disorder, and pave the way for new opportunities in lightwave nanoelectronics.

cond-mat.mtrl-sci↗

arXiv2023

Orbital perspective on high-harmonic generation from solids

High-harmonic generation in solids allows probing and controlling electron dynamics in crystals on few femtosecond timescales, paving the way to lightwave electronics. In the spatial domain, recent advances in the real-space interpretation of high-harmonic emission in solids allows imaging the field-free, static, potential of the valence electrons with picometer resolution. The combination of such extreme spatial and temporal resolutions to measure and control strong-field dynamics in solids at the atomic scale is poised to unlock a new frontier of lightwave electronics. Here, we report a strong intensity-dependent anisotropy in the high-harmonic generation from ReS$_2$ that we attribute to angle-dependent interference of currents from the different atoms in the unit cell. Furthermore, we demonstrate how the laser parameters control the relative contribution of these atoms to the high-harmonic emission. Our findings provide an unprecedented atomic perspective on strong-field dynamics in crystals and suggest that crystals with a large number of atoms in the unit cell are not necessarily more efficient harmonic emitters than those with fewer atoms.

physics.optics↗

arXiv2023

Reconstruction of attosecond beating by interference of two-photon interband transitions in solids

The reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) is one of the most widely used techniques for obtaining both the relative phases of harmonics forming an attosecond pulse train and the phase of atomic radiative transitions. If the latter is computed by theory, it allows to reconstruct the attosecond pulse train; if the former is known experimentally, it allows reconstruction of the electronic dynamics of photoionization in atomic and molecular systems with attosecond temporal resolution. As it relies on the interference of photo-electrons in vacuum, similar interference has never been contemplated inside crystals. Here we explore the applicability of this scheme to solid-state systems using a one-dimensional model and a DFT-calculated structure of 2D hexagonal boron nitride. We discuss the possibility of: (i) reconstructing the relative phases between harmonics with trivial influence of the 'atomic phase', (ii) retrieving the relative phases of two-photon transitions through different bands, which are generally challenging to obtain both experimentally and numerically. These phases are recorded in the beating of the population signal arising from interfering two-photon pathways, and can be read-out with angle-resolved photo-emission spectroscopy. Furthermore, the amplitude of the population beating decays as the pump and probe pulses are separated in time due to electron-hole decoherence, providing a simple interferometric method to extract dephasing times.

physics.optics↗

arXiv2021

High harmonic spectroscopy of disorder-induced Anderson localization

Exponential localization of wavefunctions in lattices, whether in real or synthetic dimensions, is a fundamental wave interference phenomenon. Localization of Bloch-type functions in space-periodic lattice, triggered by spatial disorder, is known as Anderson localization and arrests diffusion of classical particles in disordered potentials. In time-periodic Floquet lattices, exponential localization in a periodically driven quantum system similarly arrests diffusion of its classically chaotic counterpart in the action-angle space. Here we demonstrate that nonlinear optical response allows for clear detection of the disorder-induced phase transition between delocalized and localized states. The optical signature of the transition is the emergence of symmetry-forbidden even-order harmonics: these harmonics are enabled by Anderson-type localization and arise for sufficiently strong disorder even when the overall charge distribution in the field-free system spatially symmetric. The ratio of even to odd harmonic intensities as a function of disorder maps out the phase transition even when the associated changes in the band structure are negligibly small.

cond-mat.dis-nn↗

arXiv2020

Lightwave topology for strong-field valleytronics

Modern light generation technology offers extraordinary capabilities for sculpting light pulses, with full control over individual electric field oscillations within each laser cycle. These capabilities are at the core of lightwave electronics - the dream of ultrafast lightwave control over electron dynamics in solids, on a few-cycle to sub-cycle timescale, aiming at information processing at tera-Hertz to peta-Hertz rates. Here we show a robust and general approach to valley-selective electron excitations in two-dimensional solids, by controlling the sub-cycle structure of non-resonant driving fields at a few-femtosecond timescale. Bringing the frequency-domain concept of topological Floquet systems to the few-fsec time domain, we develop a transparent control mechanism in real space and an all-optical, non-element-specific method to coherently write, manipulate and read selective valley excitations using fields carried in a wide range of frequencies, on timescales that can be much shorter than the valley lifetime, crucial for implementation of valleytronic devices.

physics.optics↗

arXiv2018

Topological strong field physics on sub-laser cycle time scale

Sub-laser cycle time scale of electronic response to strong laser fields enables attosecond dynamical imaging in atoms, molecules and solids. Optical tunneling and high harmonic generation are the hallmarks of attosecond imaging in optical domain, including imaging of phase transitions in solids. Topological phase transition yields a state of matter intimately linked with electron dynamics, as manifested via the chiral edge currents in topological insulators. Does topological state of matter leave its mark on optical tunneling and sub-cycle electronic response? We identify distinct topological effects on the directionality and the attosecond timing of currents arising during electron injection into conduction bands. We show that electrons tunnel across the band gap differently in trivial and topological phases, for the same band structure, and identify the key role of the Berry curvature in this process. These effects map onto topologically-dependent attosecond delays in high harmonic emission and the helicities of the emitted harmonics, which can record the phase diagram of the system and its topological invariants. Thus, the topological state of the system controls its attosecond, highly non-equilibrium electronic response to strong low-frequency laser fields, in bulk. Our findings create new roadmaps in studies of topological systems, building on ubiquitous properties of sub-laser cycle strong field response - a unique mark of attosecond science.

physics.optics↗

arXiv2017

Time-frequency representations of autoionization dynamics in helium

Autoionization, which results from the interference between direct photoionization and photoexcitation to a discrete state decaying to the continuum by configuration interaction, is a well known example of the important role of electron correlation in light-matter interaction. Information on this process can be obtained by studying the spectral, or equivalently, temporal complex amplitude of the ionized electron wavepacket. Using an energy-resolved interferometric technique, we measure the spectral amplitude and phase of autoionized wavepackets emitted via the sp2+ and sp3+ resonances in helium. These measurements allow us to reconstruct the corresponding temporal profiles by Fourier transform. In addition, applying various time-frequency representations, we observe the build up of the wavepackets in the continuum, monitor the instantaneous frequencies emitted at any time and disentangle the dynamics of the direct and resonant ionization channels.

physics.atom-ph↗