Single Crystal Growth and Physical Characterization of Strongly Correlated Materials

Many materials studied within condensed matter physics are insensitive to the repulsive Coulombic interactions between electrons; simple metals and semiconductors possess this insensitivity. In such materials the kinetic energy of electrons dominate the electron-electron interaction, this is a consequence of the Pauli exclusion principle and the delocalized nature of the electron states. For these materials the electronic behavior can be theoretically studied with well developed perturbative techniques such as the (k P) expansion, the local density approximation and the Hartree-Fock approximation. In comparison, materials with open d and f electrons shells with electrons occupying narrow orbitals are greatly affected by the repulsive electron-electron interaction. This strong Coulombic repulsion leads to spatial confinement of the electrons within their orbital. This class of material are called strongly correlated materials. In strongly correlated materials, standard perturbative techniques are no longer applicable due to the electron-electron interactions invalidating the independent-electron approach whilst theoretical models for strongly correlated materials, such as dynamical mean field theory (DMFT), are still in their infancy. To further develop these theoretical models it is important that the fermiologies of strongly correlated materials are investigated and understood.

When a material transitions to the strongly correlated phase there is often a remarkable change in physical properties due to the difference in electronic and magnetic order between phases. Examples of the phenomena associated with electronic correlations are metal-insulator transitions, colossal magnetoresistance and superconductivity. These phenomena could lead to technological advancements whereby some small change in a controllable parameter e.g. temperature, pressure or field, can lead to a dramatic change in a physical property, such as a many orders-of-magnitude change in electrical conductivity in a metal-insulator transition. This is a quasiparticle study due to the metastable life times of the correlated electron properties following the phase transition; quasiparticles form an interesting field of study within condensed matter physics which has yet to be fully understood.

This PhD project shall study the single crystal growth and physical characterization of strongly correlated materials in order to investigate the fermiology of this class of material. X-ray diffraction will be used to study the structures and phases of materials produced. Electro- and magneto- transport properties will be studied to investigate the change in properties as samples transition into the strongly correlated regime. The Fermi surfaces will be constructed via the de Haas- van Alphen effect, along with anisotropic magnetoresistance and angular resolved photoemission spectroscopy to further understand the nature of the fermiology of the materials studied. Strongly correlated metal oxides and concentrated ferromagnetic semiconductors are the two classes of strongly correlated material to be studied in detail within this project although expansion into other classes of strongly correlated material is possible as the project progresses.