arXiv subjects

Gilles Versini

Publications and source records attributed to Gilles Versini.

6 recordsLinked to original sources

arXiv2026

Decoding Superconductivity in La$_3$Ni$_2$O$_{7-\delta}$ Thin Films via Ozone-Driven Structure and Oxidation Tuning

The discovery of superconductivity in bulk Ruddlesden-Popper La$_3$Ni$_2$O$_7$(LNO327) under high hydrostatic pressure has redefined the recent experimental consensus that nickelate superconductivity is restricted to systems with a $3d^9$ electronic configuration and square-planar coordination. However, the structural and electronic prerequisites for stabilizing superconductivity, whether under pressure or at ambient conditions in the case of thin films, remain poorly understood, largely due to the metastable nature of the LNO327 phase. Here, we present a detailed structural study of epitaxial La$_3$Ni$_2$O$_{7-\delta}$ thin films by using scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS). Grown via pulsed laser deposition onto SrLaAlO$_4$ substrates, those films exhibit distinct superconducting properties as a function of the different post-annealing conditions used. By correlating the rich landscape of stacking polymorphs with transport behavior, this work establishes a framework for understanding the metastable superconducting phase in bilayer nickelate thin films. Our findings underscore the critical role of homogeneity in oxygen stoichiometry, epitaxial strain and structural motif in stabilizing superconductivity, offering a clear pathway for designing ambient-pressure superconducting nickelates.

cond-mat.supr-con↗

arXiv2026

Strain-driven magnetic anisotropy and spin reorientation in epitaxial Co V 2 O 4 spinel oxide thin films

CoV___O___ (CVO) stands out among spinel vanadates for its ultra-short V-V distances, placing it at the brink of itinerant electron behaviour-an ideal playground for strain engineering. In this work, we exploit this sensitivity by growing high-quality epitaxial CVO thin films on SrTiO___ (001) and MgO (001), inducing compressive and tensile strain, respectively. Using pulsed laser deposition under ultra-low oxygen pressure, we achieve high crystalline quality and straincontrolled tetragonal distortions: c > a under compression (STO) and c < a under tension (MgO). Resonant elastic X-ray scattering confirms a normal spinel structure, with cobalt occupying tetrahedral sites and vanadium octahedral ones. Both strain types reduce charge transport, driving the system into a highly resistive state. Magnetic measurements reveal strain-driven anisotropy switching: STO films transition from out-of-plane to in-plane easy axis below 90 K, while MgO films flip from in-plane to out-of-plane below 45 K. These results highlight CVO's exceptional responsiveness to lattice strain, unlocking a path to finely tunable electronic and magnetic properties. With its strong spin-lattice coupling and potential in spin Hall magnetoresistance, strained CVO emerges as a compelling platform for next-generation lowpower spintronic devices.

cond-mat.mtrl-sci↗

arXiv2026

Technical design report of a complete and compact broadband high-harmonics femtosecond beamline based on a modular hollow waveguide for photons generation centered on the upper region of the extreme ultraviolet spectral range

We have successfully developed and implemented an entire and compact table-top high-order harmonics generation (HHG) setup from monochromatic and intense femtosecond ($10^{-15}$ s) laser pulses launched in a target composed of a high-purity monoatomic noble gas specie, which can be Argon or Helium, distinctively. Its frequency arrangement is distributed both in the full eXtreme UltraViolet (XUV, $22-124$ eV) spectral region and in the bottom part of the Soft-X Ray range (SXR, $124-132$ eV), at once. Specifically, the core of this coherent secondary light source is based solely on a homemade, modular, affordable, though sturdy, design. We take advantage of this opportunity to present our design guidance of the XUV generation from a hollow capillary waveguide apparatus, and our simple recipe regarding the alignment process of the latter, which is easily carried out thanks to our adjustable design. Then, a comprehensive description of our entire XUV beamline is described, and participate in adding essential contents to the existing literature. Concurrently, we conducted theoretical studies, in order to anticipate or explain our experimental results. Overall, we found very good consistency between the experimental and cost-effective time-consuming numerical results. Finally, our setup provides very good vacuum performance under high gas load pressures, to a few atmospheres. All of these attributes fulfill the requirements regarding ultrafast time-resolved pump-probe configuration in table-top element-sensitive spectroscopy of complex and integrated optoelectronic devices made of magnetic materials.

physics.optics↗

arXiv2022

Synthesis of infinite-layer nickelates and influence of the capping-layer on magnetotransport

The recent discovery of a zero-resistance state in nickel-based compounds has generated a re-excitement about the long-standing problem in condensed matter of high-critical-temperature superconductivity, in light of the analogies between infinite-layer nickelates and cuprates. However, despite some formal valence and crystal symmetry analogies, the electronic properties of infinite-layer nickelates are remarkably original accounting, among other properties, of a unique Nd5d-Ni3d hybridization. This designates infinite-layer nickelates as a new class of oxide superconductors which should be considered on their own. Here we report about Nd1-xSrxNiO2 (x = 0, 0.05 and 0.2) thin films synthesized with and without a SrTiO3 capping-layer, showing very smooth and step-terraced surface morphologies. Angle-dependent anisotropic magnetoresistance measurements performed with a magnetic field rotating in-plane or out-of-plane with respect to the sample surface, rendered important information about the magnetic properties of undoped SrTiO3-capped and uncapped samples. The results point at a key role of the capping-layer in controlling the magnitude and the anisotropy of the anisotropic magnetoresistance properties. We discuss this control in terms of a combined effect between the Nd-Ni hybridization and an intra-atomic exchange coupling between the Nd-4f and Nd-5d states, the latter essentially contributing to the (magneto)transport. Further studies foresee the influence of the capping layer on infinite-layer nickelates with no magnetic rare-earth.

cond-mat.mtrl-sci↗

arXiv2022

Quantum advantage in a molecular spintronic engine that harvests thermal fluctuation energy

Recent theory and experiments have showcased how to harness quantum mechanics to assemble heat/information engines with efficiencies that surpass the classical Carnot limit. So far, this has required atomic engines that are driven by cumbersome external electromagnetic sources. Here, using molecular spintronics, we propose an implementation that is both electronic and autonomous. Our spintronic quantum engine heuristically deploys several known quantum assets by having a chain of spin qubits formed by the paramagnetic Co centers of phthalocyanine (Pc) molecules electronically interact with electron-spin selecting Fe/C60 interfaces. Density functional calculations reveal that transport fluctuations across the interface can stabilize spin coherence on the Co paramagnetic centers, which host spin flip processes. Across vertical molecular nanodevices, we measure enduring dc current generation, output power above room temperature, two quantum thermodynamical signatures of the engine's processes, and a record 89% spin polarization of current across the Fe/C60 interface. It is crucially this electron spin selection that forces, through demonic feedback and control, charge current to flow against the built-in potential barrier. Further research into spintronic quantum engines, insight into the quantum information processes within spintronic technologies, and retooling the spintronic-based information technology chain, could help accelerate the transition to clean energy.

cond-mat.mes-hall↗

arXiv2022

Unveiling Unconventional Ferroelectric Switching in Multiferroic Ga0.6 Fe1.4O3 Thin Films Through Multiscale Electron Microscopy Investigations

Understanding the polarization switching mechanisms at play in ferroelectric materials is crucial for their exploitation in electronic devices. The conventional centrosymmetric reference structure-based mechanism which accounts for ferroelectricity in most of the usual displacive ferroelectric materials is too energy-demanding for some newly diagnosed ferroelectric materials such as the Ga2-xFexO3 (0.8 < x < 1.4) compounds. Some alternative theoretical propositions have been made and need experimental confirmation. A dual-scale electron microscopy study is performed on thin films of the Ga0.6Fe1.4O3 multiferroic compound. A wide scale precession-assisted electron diffraction tomography study first allows the determination of the structure the compound adopts in thin films, and even permits the refinement of the atomic positions within this structure. Cationic mobility is suggested for two of the atomic positions through the existence of extra electronic density. A local in situ high resolution scanning transmission electron microscopy study then allows confirming these mobilities by directly spotting the cationic displacements on successively acquired images. The whole study confirms an unconventional switching mechanism via local domain wall motion in this compound.

cond-mat.mtrl-sci↗