Strain Control of Fermiology and Many-Body Interactions in Two-Dimensional Ruthenates.

Here we demonstrate how the Fermi surface topology and quantum many-body interactions can be manipulated via epitaxial strain in the spin-triplet superconductor Sr_{2}RuO_{4} and its isoelectronic counterpart Ba_{2}RuO_{4} using oxide molecular beam epitaxy, in situ angle-resolved photoemission spectroscopy, and transport measurements. Near the topological transition of the γ Fermi surface sheet, we observe clear signatures of critical fluctuations, while the quasiparticle mass enhancement is found to increase rapidly and monotonically with increasing Ru-O bond distance. Our work demonstrates the possibilities for using epitaxial strain as a disorder-free means of manipulating emergent properties, many-body interactions, and potentially the superconductivity in correlated materials.

Quasiparticle mass enhancement and temperature dependence of the electronic structure of ferromagnetic SrRuO3 thin films.

We report high-resolution angle-resolved photoemission studies of epitaxial thin films of the correlated 4d transition metal oxide ferromagnet SrRuO(3). The Fermi surface in the ferromagnetic state consists of well-defined Landau quasiparticles exhibiting strong coupling to low-energy bosonic modes which contributes to the large effective masses observed by transport and thermodynamic measurements. Upon warming the material through its Curie temperature, we observe a substantial decrease in quasiparticle coherence but negligible changes in the ferromagnetic exchange splitting, suggesting that local moments play an important role in the ferromagnetism in SrRuO(3).

A tunable low-energy photon source for high-resolution angle-resolved photoemission spectroscopy.

We describe a tunable low-energy photon source consisting of a laser-driven xenon plasma lamp coupled to a Czerny-Turner monochromator. The combined tunability, brightness, and narrow spectral bandwidth make this light source useful in laboratory-based high-resolution photoemission spectroscopy experiments. The source supplies photons with energies up to ~7 eV, delivering under typical conditions >10(12) ph/s within a 10 meV spectral bandwidth, which is comparable to helium plasma lamps and many synchrotron beamlines.

Quantum many-body interactions in digital oxide superlattices.

Controlling the electronic properties of interfaces has enormous scientific and technological implications and has been recently extended from semiconductors to complex oxides that host emergent ground states not present in the parent materials. These oxide interfaces present a fundamentally new opportunity where, instead of conventional bandgap engineering, the electronic and magnetic properties can be optimized by engineering quantum many-body interactions. We use an integrated oxide molecular-beam epitaxy and angle-resolved photoemission spectroscopy system to synthesize and investigate the electronic structure of superlattices of the Mott insulator LaMnO(3) and the band insulator SrMnO(3).