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P. Lecoeur

Publications and source records attributed to P. Lecoeur.

6 recordsLinked to original sources
arXiv2019

Conduction mechanism and switchable photovoltaic effect in (111) oriented BiFe$_{0.95}$Mn$_{0.05}$O$_{3}$ thin film

Epitaxial 200nm BiFe$_{0.95}$Mn$_{0.05}$O$_{3}$ (BFO) film was grown by pulsed laser deposition on (111) oriented SrTiO3 substrate buffered with a 50nm thick SrRuO$_{3}$ electrode. The BFO thin film shows a rhombohedral structure and a large remnant polarization of Pr = 104 $\mu$C/cm$^{2}$. By comparing I(V) characteristics with different conduction models we reveal the presence of both bulk limited Poole-Frenkel and Schottky interface mechanisms and each one dominates in a specific range of temperature. At room temperature and under 10mW laser illumination, the as grown BFO film presents short-circuit current density (Jsc) and open circuit voltage (Voc) of 2.25mA/cm$^{2}$ and -0.55V respectively. This PV effect can be switched by applying positive voltage pulses higher than the coercive field. For low temperatures a large Voc value of about -4.5V (-225kV/cm) is observed which suggests a bulk non-centrosymmetric origin of the PV response.

cond-mat.mtrl-sci↗
arXiv2018

Maximization of the thermoelectric cooling of graded Peltier by analytical heat equation resolution

Increasing the maximum cooling effect of a Peltier cooler can be achieved through materials and device design. The use of inhomogeneous, FGM (functionally graded materials) may be adopted in order to increase maximum cooling without improvement of the zT (figure of merit), however these systems are usually based on the assumption that the local optimization of the zT is the suitable criterion to increase thermoelectric performances. In the present paper, we solved the heat equation in a graded material and performed both analytic and numerical analysis of a graded Peltier cooler. We find a local criterion that we used to assess the possible improvement of graded materials for thermoelectric cooling. A fair improvement of cooling effect is predicted for semiconductor materials (up to $36\%$) and the best graded system for cooling is described. The influence of the equation of state of the electronic gas of the material is discussed, and the difference in term of entropy production between the graded and the classical system is also described.

physics.app-ph↗
arXiv2014

Orientational tuning of the Fermi sea of confined electrons at the SrTiO3 (110) and (111) surfaces

We report the existence of confined electronic states at the (110) and (111) surfaces of SrTiO3. Using angle-resolved photoemission spectroscopy, we find that the corresponding Fermi surfaces, subband masses, and orbital ordering are different from the ones at the (001) surface of SrTiO3. This occurs because the crystallographic symmetries of the surface and sub-surface planes, and the electron effective masses along the confinement direction, influence the symmetry of the electronic structure and the orbital ordering of the t2g manifold. Remarkably, our analysis of the data also reveals that the carrier concentration and thickness are similar for all three surface orientations, despite their different polarities. The orientational tuning of the microscopic properties of two-dimensional electron states at the surface of SrTiO3 echoes the tailoring of macroscopic (e.g. transport) properties reported recently in LaAlO3/SrTiO3 (110) and (111) interfaces, and is promising for searching new types of 2D electronic states in correlated-electron oxides.

cond-mat.mtrl-sci↗
arXiv2010

Tailoring strain in SrTiO3 compound by low energy He+ irradiation

The ability to generate a change of the lattice parameter in a near-surface layer of a controllable thickness by ion implantation of strontium titanate is reported here using low energy He+ ions. The induced strain follows a distribution within a typical near-surface layer of 200 nm as obtained from structural analysis. Due to clamping effect from the underlying layer, only perpendicular expansion is observed. Maximum distortions up to 5-7% are obtained with no evidence of amorphisation at fluences of 1E16 He+ ions/cm2 and ion energies in the range 10-30 keV.

cond-mat.mtrl-sci↗
arXiv2010

Unveiling a two-dimensional electron gas with universal subbands at the surface of SrTiO3

Similar to silicon that is the basis of conventional electronics, strontium titanate (SrTiO3) is the bedrock of the emerging field of oxide electronics. SrTiO3 is the preferred template to create exotic two-dimensional (2D) phases of electron matter at oxide interfaces, exhibiting metal-insulator transitions, superconductivity, or large negative magnetoresistance. However, the physical nature of the electronic structure underlying these 2D electron gases (2DEGs) remains elusive, although its determination is crucial to understand their remarkable properties. Here we show, using angle-resolved photoemission spectroscopy (ARPES), that there is a highly metallic universal 2DEG at the vacuum-cleaved surface of SrTiO3, independent of bulk carrier densities over more than seven decades, including the undoped insulating material. This 2DEG is confined within a region of ~5 unit cells with a sheet carrier density of ~0.35 electrons per a^2 (a is the cubic lattice parameter). We unveil a remarkable electronic structure consisting on multiple subbands of heavy and light electrons. The similarity of this 2DEG with those reported in SrTiO3-based heterostructures and field-effect transistors suggests that different forms of electron confinement at the surface of SrTiO3 lead to essentially the same 2DEG. Our discovery provides a model system for the study of the electronic structure of 2DEGs in SrTiO3-based devices, and a novel route to generate 2DEGs at surfaces of transition-metal oxides.

cond-mat.mtrl-sci↗