Controling And Manipulating ELEctronic Orders on the Nanoscale – CAMELEON

Manganites have been considered to be one of the most interesting systems in condensed matter physics in recent years. These materials crystallize into the ABO3 perovskite structure. Hole-doping is achieved by substituting divalent cations at the A-site which converts some of the Mn3+ ions (occupying the B-site) to the Mn4+ oxidation state. The general formula of a hole-doped manganite is RE1-xAExMnO3 (RE is a trivalent rare-earth ion such as La, Nd, Pr and AE is a divalent alkaline-earth ion such as Ca, Sr, Ba, Pb). Depending on the doping x, in manganites there are two dominant phases at low temperatures: a double-exchange ferromagnetic metal (FMM) and charge-ordered antiferromagnetic insulator (AFMI). These two phases are separated by a first order transition. At high temperatures there is a paramagnetic insulator phase (PMI) for all dopings. In the FMM these materials are found to be close to a perfect half metal (more than 90% spin polarized conduction electrons) ideal for spin injection and spin filter systems. It is hoped that this property will lead to important applications in spintronic devices. In addition to these potential applications, manganite systems have revealed exotic, new physics in the metal to insulator transition. In a single crystal, one expects a periodic array of atoms where each unit cell is identical to any other. In a certain number of manganite families this in not the case: electronic and magnetic orders coexist at different locations within the same sample. This multiphase coexistence arises because the free energy of the FMM and AFMI phases are very similar. This mesoscopic structure makes this material uniquely sensitive to external perturbations (such as magnetic fields, electric fields, light, hydrostatic pressure and biaxial strain). This particularity is often referred to as ‘electronic soft matter’. In this research proposal, we wish to study the consequences of these exotic electronic inhomogeneities on traditional macroscopic measurements. For this we will approach this issue from both sides: - firstly in a spontaneously phase separated material by mapping out the sample by electrostatic (EFM) and magnetic (MFM) force microscopies and measuring simultaneously the standard DC resistivity. Correlating these two types of probes will allow us to quantify how any microscopic domain transition shows up in macroscopic measurements. - secondly, by starting with a homogeneous manganite family and artificially nanostructuring it in a controlled fashion. This can be done by the combination of electronic lithography and ion bombardment. The optical spectra of such samples will be measured and analyzed using an effective medium approximation model. This will enable us to separate the contribution coming from the nanostructures and from the intrinsic physical properties of each domain. This multidisciplinary project will involve three permanent researchers at the ESPCI and two permanent researchers at the Chinese Academy of Sciences (CAS). The equipment needed to fulfill this project is divided equally between the different techniques involved: epitaxy and DC resistivity measurements of thin films at the CAS; local probe measurements EFM/MFM and optical spectroscopy at the ESPCI. Most importantly this project requires a great amount of time to complete all of these measurements. We are thus asking for a 3 year PhD fellowship, a one year post-doc fellowship and some reduction of teaching hours for the project manager.