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Abstract: Phase transitions and competing orders in strongly correlated materials emerge from the delicate interplay of many interacting degrees of freedom (including charge, spin, and lattice). This intricate interplay makes these systems highly sensitive to external perturbations, making strongly correlated materials ideal for developing novel technologies and devices leveraging emergent phenomena. Their richness and technological potential, however, are counterbalanced by an inherent complexity originating from the strong intertwining of many degrees of freedom. In the first part of this thesis, we study non-equilibrium phases in prototypical Mott insulators (LaVO3 and V2O3) induced by means of ultrashort light pulses or application of current, with the aim of tackling open challenges in developing strategies for controlling quantum materials. When light excitations are employed, quantum coherence could be exploited to achieve enhanced functionalities and ultrafast and reversible manipulation of material properties. The light-induced excitonic population and decoherence dynamics is investigated in LaVO3, where long-range orders in the orbital and spin degrees of freedom strongly influence optical excitations and the evolution of excitonic states. By means of broadband pump-probe and two-dimensional electronic spectroscopy (2DES), we study how the interactions of the LaVO3 excitonic resonance with the ordered background influence the exciton spectral linewidth and decoherence time. When current is instead employed to control the phase of Mott materials, resistive switching - a sudden drop in resistance caused by a transition from an insulating to a metallic state - can take place. By combining transport measurements with Photo-Electron Emission Microscopy, we image the resistive switching process in V2O3 at the nanoscale. On this length scale, V2O3 displays spatial inhomogeneities resulting from the breaking of the crystal symmetry upon transitioning from the high-temperature metallic phase to the low-temperature insulating one. This experiment provides novel insights into the nature and mechanisms of resistive switching, as well as the role of the nanometric texture of the material, suggesting novel viable routes to control the current-induced insulator-metal transition. The second part of the thesis is dedicated to the quantum simulation of the physics of strongly correlated materials using artificial platforms. This approach aims to overcome the inherent complexity of quantum materials by employing systems where the phenomena typical of correlated systems can take place in a controlled way, with the relevant parameters that can be tuned on demand. We introduce synthetic lattices composed of lead halide perovskite nanocubes, which we propose as a suitable novel platform for quantum simulations. Pump-probe experiments on CsPbBr3 nanocube superlattices reveal the emergence of several phases relevant for strongly correlated materials (collective superradiant state, exciton gas and electron-hole liquid phases) that can be accessed upon controlling the excitation intensity, thus making the system a suitable platform for the investigation of long-range ordered phases in systems displaying insulator-metal Mott transitions. Nanocube superlattices of the hybrid organic-inorganic compound CH(NH2)2PbI3 are also investigated; 2DES is employed to trace the evolution of optical excitons in this artificial lattice, measure their decoherence time and address how the decoherence process is affected by the structural phase transition taking place in the system.

Open Access

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Abstract: Spin selective catalysis is an emerging approach for improving the thermodynamics and kinetics of reactions. The role of electron spins has been scarcely studied in catalytic reactions. One exception is the oxygen evolution reaction (OER) where strongly correlated metals and oxides are used as catalysts. In OER, spin alignment facilitates the transition of singlet state of the reactant to the triplet state of O2. However, the influence of strong correlations on spin exchange mechanism and spin selective thermodynamics of most catalytic reactions remain unclear. Here we decouple the strongly correlated catalyst from the electrolyte to study spin exchange in two-dimensional (2D) magnetic iron germanium telluride (FGT) heterostructure. We demonstrate that transmission of spin and electrochemical information between the catalyst and the reactant can occur through quantum exchange interaction despite the catalyst of FGT being completely encapsulated by graphene or hexagonal boron nitride (hBN). The strong correlations in FGT that lead to enhanced spin exchange in OER are observed in graphene or hBN layers with thicknesses of up to 6 nm. We demonstrate that spin alignment in FGT leads to a lowering of thermodynamic barrier for adsorption of hydroxide ion and electron transfer to the catalyst. This results in up to fivefold enhancement in OER performance and improved kinetics. Our results provide clear evidence that transmission of both quantum mechanical and electrochemical information through quantum spin exchange interaction in FGT leads to an enhancement in catalytic performance.

Open Access

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Abstract: Defects are inherent in transition metal dichalcogenides and significantly affect their chemical and physical properties. In this study, surface defect electrochemical nanopatterning is proposed as a promising method to tune in a controlled manner the electronic and functional properties of defective MoS₂ thin films. Using parallel electrochemical nanolithography, MoS₂ thin films are patterned, creating sulphur vacancy-rich active zones alternated with defect-free regions over a centimetre scale area, with sub-micrometre spatial resolution. The patterned films display tailored optical and electronic properties due to the formation of sulphur vacancy-rich areas. Moreover, the effectiveness of defect nanopatterning in tuning functional properties is demonstrated by studying the electrocatalytic activity for the hydrogen evolution reaction.

Open Access

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Abstract: Avalanche resistive switching is the fundamental process that triggers the sudden change of the electrical properties in solid-state devices under the action of intense electric fields. Despite its relevance for information processing, ultrafast electronics, neuromorphic devices, resistive memories and brain-inspired computation, the nature of the local stochastic fluctuations that drive the formation of metallic regions within the insulating state has remained hidden. Here, using operando X-ray nano-imaging, we have captured the origin of resistive switching in a V2O3-based device under working conditions. V2O3 is a paradigmatic Mott material, which undergoes a first-order metal-to-insulator phase transition together with a lattice transformation that breaks the threefold rotational symmetry of the rhombohedral metallic phase. We reveal a new class of volatile electronic switching triggered by nanoscale topological defects appearing in the shear-strain based order parameter that describes the insulating phase. Our results pave the way to the use of strain engineering approaches to manipulate such topological defects and achieve the full dynamical control of the electronic Mott switching. Topology-driven, reversible electronic transitions are relevant across a broad range of quantum materials, comprising transition metal oxides, chalcogenides and kagome metals.

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Abstract: The electron spin polarization on half-metallic double perovskites is usually conditioned to the ordered rock-salt arrangement of the transition-metal ions along the lattice. In this work, we investigate a polycrystalline sample of the Ca1.5⁢La0.5⁢MnRuO6 compound by employing x-ray powder diffraction, high-resolution transmission electron microscopy, x-ray absorption and magnetic circular dichroism at the Mn 𝐿2,3 and Ru 𝑀2,3 edges, magnetometry, electrical transport, and first-principles calculations in order to show that this is a fully disordered material exhibiting near-room-temperature ferrimagnetism and half-metallic conductivity, with significant intergrain tunneling magnetoresistance. These unprecedented results are compared to those of archetypical ordered double perovskites, and discussed in terms of the Mn and Ru valences and their orbital hybridization.