Novel Electronic Materials

 
It is generally believed that the simple charge modulation employed in MOSFET electronics will not be sufficient for future electronic devices. Controlling and manipulating new degrees of freedom, like spin and orbits will play major role in the new generation of electronic materials like organic conductors, manganites, vanadates and cuprates. Therefore the understanding of the basic properties of such systems is primordial. Their engineering could have a significant impact on the electronics of the twenty first century and some of them are already present in new technologies.

It turns out that in most of these materials the electronic mean free path is very short, often even shorter than the lattice spacing. In other words, despite the metallic-like temperature dependence of the resistivity, strictly speaking they do not qualify for metals and they are very often called bad metals. Our goal is to investigate the bad metallicity by transport and magnetotransport studies in wide pressure (up to 20 GPa) and temperature (50 mK- 1000 K) ranges. The lattice compression can vary the electron-phonon coupling, the screening of the electron-electron interactions, alter the exchange interaction, suppress low-dimensional fluctuations, etc. We are confident that in some cases high pressures can tune the transition from a bad metal to a good metal (or from non-Fermi liquid to a Fermi liquid), thus contributing towards the understanding of this peculiar state. Our research in novel electronic materials is described in this general context.

Below we list  few families of low-dimensional metals, which are the subject of our investigations.

 
     1. Study of organic conductors

In the field of organic conductors there is enormous progress in the synthesis of new compounds with surprising properties, like conducting kagome, fumarates, zwitterions etc. We study their magnetic and transport properties. The provenance of these crystals is from P. Batail (Univ. Angers).

    

 2. Investigation of 2D dichalcogenides

Dichalogenides represent a family of 2D conductors, where charge density waves, Mott-transition, magnetism and superconductivity are present. These are excellent model system to study the competition and cooperation of different ground states.

    

 3. Pnictide superconductors

Iron-based pnictide superconductors represent the latest family of high temperature superconductors. We study the high pressure transport properties of several families.

    

 4. Low-dimensional Vanadium-based compounds

Vanadium-based compounds are expected to obey Mott physics: the relatively compact d-shells are associated with a comparable bandwidth and Coulomb interaction. They are strongly correlated d-metals, or Mott insulators with localized d-electrons, or show transition between such states at accessible temperatures and pressures.

 

    

 5. Graphene

Graphene represents a new exciting prospect in the field of organic compounds, mainly for the purpose of applications in novel electronic devices. We study graphene synthsized by different methods using Electron Spin Resonance measurements (image: courtesy T. Heinz).

 

      6. TiO2

Titanium dioxide is a compond which is present in many applications ranging from memristors to photovoltaics, mainly in the anatase form. To understand better its electronic properties we study its transport  coefficients of single crystalls of anatase. Surpisingly, the pristine crystal has a metallic-like resistivity.