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Dusan Lorenc

Publications and source records attributed to Dusan Lorenc.

10 recordsLinked to original sources
arXiv2026

Alignment-free ultra-broadband parametric frequency conversion in lead-halide perovskites

Lead-halide perovskites were demonstrated to exhibit some of the largest known optical nonlinearities, yet their potential for frequency conversion remains largely untapped. Here we demonstrate ultra-broadband four-wave mixing of near- and mid-infrared femtosecond pulses in thick single-crystal LHPs, generating bright, coherent, and highly collimated emission across an exceptionally wide continuous tuning range without phase-matching engineering, angular alignment, or dispersion optimization. Time resolved measurements reveal that the emission originates near the crystal surfaces, where phase-matching constraints are relaxed, while the unusually large intrinsic $\chi^{(3)}$ response preserves efficient and directional frequency conversion despite the strongly localized interaction volume. These results position LHPs as a powerful bulk platform for ultra-broadband nonlinear photonics, opening a pathway toward compact, alignment-free architectures for ultrafast frequency conversion.

cond-mat.mtrl-sci↗
arXiv2025

Spontaneous flexoelectricity in cubic lead-halide perovskite MAPbBr$_3$

Lead-halide perovskites exhibit remarkable efficiency in photovoltaics, driven by exceptionally long carrier diffusion lengths and recombination times. Paradoxically, this performance persists even in defect-rich, solution-grown samples. Here, we use a suite of optical and charge transport measurements to reveal that key optoelectronic properties of perovskites arise from localized flexoelectric polarization confined to the interfaces between domains of spontaneous strain, present even in nominally cubic single crystals. This insight provides a microscopic link between structural composition and charge transport in these materials, reconciling conflicting prior observations and offering new design principles for perovskite-based solar cells.

cond-mat.mtrl-sci↗
arXiv2024

Observation of Analogue Dynamic Schwinger Effect and Non-Perturbative Light Sensing in Lead Halide Perovskites

Dielectric breakdown of physical vacuum (Schwinger effect) is the textbook demonstration of compatibility of Relativity and Quantum theory. Although observing this effect is still practically unachievable, its analogue generalizations have been shown to be more readily attainable. This paper demonstrates that a gapped Dirac semiconductor, methylammonium lead-bromide perovskite (MAPbBr$_3$), exhibits analogue dynamical Schwinger effect. Tunneling ionization under deep sub-gap mid-infrared irradiation leads to intense photoluminescence in the visible range, in full agreement with quasi-adiabatic theory. In addition to revealing a gapped extended system suitable for studying the analogue Schwinger effect, this observation holds great potential for non-perturbative field sensing, i.e., sensing electric fields through non-perturbative light-matter interactions. First, this paper illustrates this by measuring the local deviation from the nominally cubic phase of a perovskite single crystal, which can be interpreted in terms of frozen-in fields. Next, it is shown that analogue dynamic Schwinger effect can be used for nonperturbative amplification of non-parametric upconversion process in perovskites driven simultaneously by multiple optical fields. This discovery demonstrates the potential for material response beyond perturbation theory in the Schwinger regime, offering extremely sensitive light detection and amplification across an ultrabroad spectral range not accessible by conventional devices.

cond-mat.mes-hall↗
arXiv2024

Resonantly enhanced terahertz four-wave mixing in fluorides

Converting a THz signal into the optical domain is of great interest for THz sensing and spectroscopy. Here intense broadband THz pulses with a central frequency of $\Omega$$_{THz}$ are mixed with an optical pump at $\omega$$_p$ and a signal is observed at a wavelength of $\omega$$_s$ = 2($\omega$$_p$ - $\Delta\omega$$_p$) - $\Omega_{THz}$ with the detuning $\omega$$_p$ - $\Delta\omega$$_p$ being due to pump pulse spectral broadening. The observed THz-FWM signal close to 400 nm is shown to result from a resonantly amplified four-wave mixing in CaF$_2$, BaF$_2$ and MgF$_2$.

physics.optics↗
arXiv2023

Interferometric determination of intrinsic nonlinear Kerr index in lead-halide perovskites

Lead halide perovskites have recently been reported to demonstrate an exceptionally high nonlinear (Kerr) refractive index n$_2$ of up to 10$^{-8}$ cm$^2$/W in CH$_3$NH$_3$PbBr$_3$. Other researchers however observe different, substantially more conservative numbers. In order to resolve this disagreement the nonlinear Kerr index of a bulk sample of lead halide perovskite was measured directly by means of an interferometer. This approach has many advantages as compared to the more standard z-scan technique. In particular this method allows studying the induced changes to the refractive index in a time-resolved manner, thus enabling to separate the different contributions to $n_2$. The extracted n$_2$ values for CsPbBr$_3$ and MAPbBr$_3$ at $\lambda \approx 1\mu m$ are $n_2=+2.1\times$ 10$^{-14}$ cm$^2$/W and $n_2=+6\times$ 10$^{-15}$ cm$^2$/W respectively hence substantially lower than what has been indicated in most of the previous reports implying the latter should be regarded with a great care.

physics.optics↗
arXiv2023

Bond polarizability as a probe of local crystal fields in hybrid lead-halide perovskites

A rotating organic cation and a dynamically disordered soft inorganic cage are the hallmark features of hybrid organic-inorganic lead-halide perovskites. Understanding the interplay between these two subsystems is a challenging problem but it is this coupling that is widely conjectured to be responsible for the unique behavior of photo-carriers in these materials. In this work, we use the fact that the polarizability of the organic cation strongly depends on the ambient electrostatic environment to put the molecule forward as a sensitive probe of local crystal fields inside the lattice cell. We measure the average polarizability of the C/N--H bond stretching mode by means of infrared spectroscopy, which allows us to deduce the character of the motion of the cation molecule, find the magnitude of the local crystal field and place an estimate on the strength of the hydrogen bond between the hydrogen and halide atoms. Our results pave the way for understanding electric fields in lead-halide perovskites using infrared bond spectroscopy.

cond-mat.mes-hall↗
arXiv2023

Dispersive effects in ultrafast non-linear phenomena

It is a basic principle that an effect cannot come before the cause. Dispersive relations that follow from this fundamental fact have proven to be an indispensable tool in physics and engineering. They are most powerful in the domain of linear response where they are known as Kramers-Kronig relations. However when it comes to nonlinear phenomena the implications of causality are much less explored, apart from several notable exceptions. Here in this work we demonstrate how to apply the dispersive formalism to analyse the ultrafast nonlinear response in the context of the paradigmatic nonlinear Kerr effect. We find that the requirement of causality introduces a noticeable effect even under assumption that Kerr effect is mediated by quasi-instantaneous off-resonant electronic hyperpolarizability. We confirm this by experimentally measuring the time resolved Kerr dynamics in GaAs by means of a hybrid pump-probe Mach-Zehnder interferometer and demonstrate the presence of an intrinsic lagging between amplitude and phase responses as predicted by dispersive analysis. Our results describe a general property of the time-resolved nonlinear processes thereby highlighting the importance of accounting for dispersive effects in the nonlinear optical processes involving ultrashort pulses.

physics.optics↗
arXiv2023

Mid-infrared Kerr index evaluation via cross-phase modulation with a near-infrared probe beam

We propose a simple method to measure nonlinear Kerr refractive index in mid-infrared frequency range that avoids using sophisticated infrared detectors. Our approach is based on using a near-infrared probe beam which interacts with a mid-IR beam via wavelength-non-degenerate cross-phase modulation (XPM). By carefully measuring XPM-induced spectral modifications in the probe beam and comparing the experimental data with simulation results we extract the value for the non-degenerate Kerr index. Finally, in order to obtain the value of degenerate mid-IR Kerr index we use the well-established two-band formalism of Sheik-Bahae et al., which is shown to become particularly simple in the limit of low frequencies. The proposed technique is complementary to the conventional techniques such as z-scan and has the advantage of not requiring any mid-infrared detectors.

physics.optics↗
arXiv2023

Effective model for studying optical properties of lead-halide perovskites

We use general symmetry-based arguments to construct an effective model suitable for studying optical properties of lead-halide perovskites. To build the model, we identify an atomic-level interaction between electromagnetic fields and the spin degree of freedom that should be added to a minimally-coupled $\mathbf{k\cdot p}$ Hamiltonian. As a first application, we study two basic optical characteristics of the material: the Verdet constant and the refractive index. Beyond these linear characteristics of the material the model is suitable for calculating non-linear effects such as the third-order optical susceptibility. Analysis of this quantity shows that the geometrical properties of the spin-electric term imply isotropic optical response of the system, and that optical anisotropy of lead-halide perovskites is a manifestation of hopping of charge carriers. To illustrate this, we discuss third-harmonic generation.

cond-mat.mes-hall↗
arXiv2023

Spin-Electric Coupling in Lead Halide Perovskites

Lead-halide perovskites enjoy a number of remarkable optoelectronic properties. To explain their origin, it is necessary to study how electromagnetic fields interact with these systems. We address this problem here by studying two classical quantities: Faraday rotation and the complex refractive index in a paradigmatic perovskite CH$_3$NH$_3$PbBr$_3$ in a broad wavelength range. We find that the minimal coupling of electromagnetic fields to the k$\cdot$p Hamiltonian is insufficient to describe the observed data even on the qualitative level. To amend this, we demonstrate that there exists a relevant atomic-level coupling between electromagnetic fields and the spin degree of freedom. This spin-electric coupling allows for quantitative description of a number of previous as well as present experimental data. In particular, we use it here to show that the Faraday effect in lead-halide perovskites is dominated by the Zeeman splitting of the energy levels, and has a substantial beyond-Becquerel contribution. Finally, we present general symmetry-based phenomenological arguments that in the low-energy limit our effective model includes all basis coupling terms to the electromagnetic field in the linear order.

cond-mat.other↗