Light-Assisted Resistance Collapse in a ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$-Based Mott-Insulator Device

Light-Assisted Resistance Collapse in a $V_{2} O_{3}$ -Based Mott-Insulator Device

A. Ronchi, P. Franceschini, P. Homm, M. Gandolfi, G. Ferrini, S. Pagliara, F. Banfi, M. Menghini, J-.P. Locquet, and C. Giannetti

Phys. Rev. Applied 15, 044023 – Published 13 April 2021

Abstract

The insulator-to-metal transition in Mott insulators is the key mechanism for most of the electronic devices belonging to the Mottronics family. Intense research efforts are currently devoted to the development of specific control protocols, usually based on the application of voltage, strain, pressure, and light excitation. The ultimate goal is to achieve the complete control of the electronic phase transformation, with dramatic impact on the performance, for example, of resistive-switching devices. Here, we investigate the simultaneous effect of external voltage and excitation by ultrashort light pulses on a single Mottronic device based on a $V_{2} O_{3}$ epitaxial thin film. The experiments are supported by both finite-element simulations of the thermal problem and a simpler lumped-element model. The thermal models are benchmarked against results obtained at very low applied voltage ( $Δ V = 5$ mV). When the voltage is significantly increased ( $Δ V = 0.5$ V), but still in the linear below-switching-threshold region, our results show that the light excitation drives a volatile resistivity drop, which goes beyond the combined effect of laser and Joule heating. Our results impact on the development of protocols for the nonthermal control of the resistive-switching transition in correlated materials.

Received 14 October 2020
Revised 15 January 2021
Accepted 19 March 2021

DOI:https://doi.org/10.1103/PhysRevApplied.15.044023

Physics Subject Headings (PhySH)

Heat transfer Metal-insulator transition Optoelectronics Photoinduced effect

Mott insulators Thin films Transition metal oxides

Femtosecond laser irradiation

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

A. Ronchi ^1,2,3,*, P. Franceschini^1,2,3, P. Homm¹, M. Gandolfi ^4,5, G. Ferrini ^2,3, S. Pagliara^2,3, F. Banfi ⁶, M. Menghini ^7,1, J-.P. Locquet¹, and C. Giannetti ^2,3,†

¹Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, Leuven 3001, Belgium
²Department of Mathematics and Physics, Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
³ILAMP (Interdisciplinary Laboratories for Advanced Materials Physics), Università Cattolica del Sacro Cuore, Brescia I-25121, Italy
⁴CNR-INO, Via Branze 45, Brescia 25123, Italy
⁵Department of Information Engineering, University of Brescia, Via Branze 38, Brescia 25123, Italy
⁶Université de Lyon, Institut Lumière Matiére (iLM), Université Lyon 1 and CNRS, 10 rue Ada Byron, Villeurbanne Cedex 69622, France
⁷IMDEA Nanociencia, Cantoblanco, Madrid 28049, Spain

^*andrea.ronchi@unicatt.it
^†claudio.giannetti@unicatt.it

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Vol. 15, Iss. 4 — April 2021

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Figure 1
Working principle of the experiment. (a) Left: sketch of the experimental setup. A finite train of laser pulses ( $ℏ ω = 1.55 eV$ , 50- $fs$ temporal width, $ν = 25 kHz$ ) is used to photoexcite the device. The change in the two-point resistance of the device is simultaneously measured before, during, and after the laser excitation by means of $Au$ / $Ti$ electrodes. The contact resistance can be neglected since is very small (approximately $5 Ω$ ) with respect to the $V_{2} O_{3}$ bridge resistance (approximately $15 k Ω$ ). Right: microscopic image of the device used during the experiment. (b) Equilibrium two-point resistance hysteresis measured as a function of the temperature. The red (blue) arrows indicate the heating (cooling) branch. Inset: two-point $I$ - $V$ curve showing volatile resistive switching at $T = 160$ K. The black thicker line highlights the below-threshold region in which the $I$ - $V$ curve is fully reversible. The measurement is performed through the 2- $μ m$ gap shown in (a). (c) Relative variation of resistance measured across the device as a function of the time delay at the base temperature $T_{0} = 161.6$ K. The time zero corresponds to the moment when the first pulse of the laser train arrives. (d) Result of the conversion of resistance drop measurements [see (c)] into effective local temperature (yellow solid line). The resistance versus temperature curve shown in Fig. 1 is inverted to obtain, for each value of resistance, the corresponding local temperature. As explained in the main text, the cooling down process takes place along a resistance-temperature curve, which differs from the equilibrium one reported in (b). The dashed line, corresponding to the cooling-down dynamics of the system, is the hypothetical local temperature obtained from the heating branch of the equilibrium resistance-temperature curve, but does not necessarily represent the actual local effective temperature of the system.
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Figure 2
Finite-element-method simulations. (a) The solid line represents the temperature increase due to the single-pulse excitation (black dashed area) as a function of the time (logarithmic scale). The black arrow indicates the instant ( $t = 40 μ s$ ) at which the following pulse arrives. Inset: sketch of the geometry used in the comsol simulations. The red dot indicates the point at which the temperature is evaluated ( $r = 50$ nm; $z = 33.5$ nm). (b) The temperature variation at saturation, induced by $2 \times 10^{5}$ laser pulses, is shown. The temperature is evaluated at half of the total thickness, i.e., $r = 50$ nm and $z = 33.5$ nm. The maximum temperature reached after the excitation with the pulse train is used as the input to build the curves reported in Fig. 3.
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Figure 3
Comparison between experimental and numerical results. (a) Maximum variation of the sample’s temperature induced by the laser pulses as a function of the total number of pulses (green circles). The applied voltage is $Δ V = 5$ mV. The solid black line represents the simulated data where the maximum temperature is extracted for each finite number of pulses. The gray area shows the error interval associated to the model assumptions and numerical approximations. The red solid line represents the exponential fit to the experimental data. (b) Maximum laser-induced drop of the device resistance when a constant voltage bias $Δ V = 0.5$ V is applied across the $Au$ / $Ti$ electrodes (green circles). The solid black line represents the outcome of numerical simulations, from which the expected resistance drop is retrieved from the local effective heating for each finite number of pulses. The dissipated power related to the Joule heating has been added to the power dissipated by the laser excitation. The gray areas show the error interval associated to the model assumptions and numerical approximations. The solid red line represents the exponential fit to the experimental data. In the inset we report the time-dependent relative resistance variation curves measured with $Δ V = 0.5$ V applied voltage for different numbers of excitation pulses (gray, $0.5 \times 10^{6}$ pulses; red, $5 \times 10^{6}$ pulses; blue, $10 \times 10^{6}$ pulses). The maximum resistance variation for each curve is reported as a single data point in the main panel.
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Physical Review Applied

Light-Assisted Resistance Collapse in a V2O3-Based Mott-Insulator Device

A. Ronchi, P. Franceschini, P. Homm, M. Gandolfi, G. Ferrini, S. Pagliara, F. Banfi, M. Menghini, J-.P. Locquet, and C. Giannetti

Phys. Rev. Applied 15, 044023 – Published 13 April 2021

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Light-Assisted Resistance Collapse in a $V_{2} O_{3}$ -Based Mott-Insulator Device