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

TL;DR

This work demonstrates a solid-state analogue of the dynamical Schwinger effect in a gapped Dirac semiconductor, MAPbBr$_3$, by observing tunneling ionization under deep sub-gap mid-IR fields inferred from photoluminescence. The ionization dynamics are quantitatively described by quasi-adiabatic Landau–Dykhne theory, with a tunable Keldysh parameter around unity, and the PL–population model links tunneling rates to observable emission. The study also reveals frozen-in electric fields through polarization-dependent PL and introduces cooperative two-field (AC-biasing) pumping to non-perturbatively amplify upconversion, suggesting potential for ultra-sensitive, broadband electric-field sensing and non-perturbative light detection in perovskites. Overall, the results establish MAPbBr$_3$ as a practical platform for exploring non-perturbative light–matter interactions and for developing new sensing technologies that exploit analogue SE dynamics.

Abstract

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.

Figures (17)

• Figure 1: A) Schematic diagram of ionization across the energy gap $\Delta$ due to multiphoton process, and due to tunneling under the influence of different applied field amplitudes ($E_1$ and $E_1+ E_2$). It can be seen that the magnitude of $E$ determines the width of the forbidden range, thus affecting the net tunneling rate exponentially (see the text for details); B) MAPbBr$_3$ crystal with PL coming from the bulk of the sample; C) PL spectrum of MAPbBr$_3$ single crystal sample pumped by $\lambda=4\mu$m radiation; D) PL spectra of MAPbBr$_3$ single crystal sample under $\lambda=4\mu$m pumping, together with our theoretical prediction for weak and intermediate electric fields (see the main text and Methods for details); E) An illustration of several common channels of photo-carrier recombination with characteristic rate dependencies on the density of charge carriers, $n$.
• Figure 2: Sketch of tunneling under the influence of two slowly varying in time fields $E_1(t)$ and $E_2(t)$ (yellow and red curves at the top of the figure). Their sum $E_1(t)+E_2(t)$ is also presented (magenta). The tunneling rate (blue at the bottom of the figure) is exponentially enhanced at the maximum of the total field. Consequently the cumulatative number of transitions (green) is determined mainly by the value of this maximum.
• Figure 3: A) PL as a function of the applied electric field for two orthogonal polarization orientations aligned with the crystal axes of MAPbBr$_3$ (markers). The corresponding fits according to our theoretical model to the data are presented as solid curves. The inset shows a cartoon of MAPbBr$_3$ with hypothetical ferroelectric domains overlaid with a schematic representation of the irradiating laser spot whose diameter is $d\approx 200\mu$m ($1/e^2$); B) Polarization scan taken at a fixed value of the external electric field $E_{AC}\simeq 0.180 V/a$.
• Figure 4: A) Cumulative PL from a single-crystal sample MAPbBr$_3$ as a function of the time delay between 1$\mu$m and 4$\mu$m pulses with parallel- (blue circles) and orthogonal (yellow crosses) polarizations; solid red line is a Gaussian fit to the curve used as the guide to an eye; B) Differential PL from a single-crystal sample MAPbBr$_3$ as a function of mid-infrared intensity (4.5$\mu$m) biased with $1\mu$m at $I_{\mathrm{bias}}=5\times10^{13}$W/m$^2$ (mid- and near-infrared pulses overlap in time; red points) as compared to PL induced by the same mid-infrared beam in the absence of AC-biasing (mid- and near-infrared pulses do not overlap in time; black points). Panels C)-E) demonstrate spatial profiles of PL under AC-biasing in an abraded sample of MAPbBr$_3$. Namely, panel C) shows PL produced by the pulse $4.5\mu$m alone; panels D) and E) present spatial profiles of cumulative PL with $1\mu$m and $4.5\mu$m pulses not overlapped and overlapped in time, respectively. The red circle in C)-E) marks the position of the $4.5\mu$m light beam.
• Figure 5: Experimental Setup, BS - beamsplitter, WP - wiregrid polarizer, OC - optical chopper, PC - cube polarizers, HWP - half-wave plate, L - lens, S - sample.