The main topic of the research of A/Prof. Clemens Ulrich is optical spectroscopy, neutron scattering, and X-ray synchrotron scattering on systems with strongly correlated electrons, in particular transition metal oxides such as multiferroics or unconventional superconductors. Of special interest are effects of spin, charge, and orbital correlations in 3-dimensional perovskites with partly occupied 3d-electronic levels. The combination of the complementary techniques, in particular Raman light scattering and inelastic neutron scattering on the same samples opens new perspectives in the determination of the quantum mechanical processes which result in the fascinating phenomena arising from strong electronic correlations.
Among my current research projects is the investigation of novel multifunctional materials based on transition metal oxides, i.e. multiferroics (TbMnO3, RMn2O5 with R = Tb, Ho, Y, and BiFeO3). In addition to Raman light scattering, neutron diffraction as well as inelastic neutron scattering experiments are performed on single crystal and PLD grown thin film samples. For example, the influence of oxygen isotope substitution on the magnetic properties was investigated in order to shine light on the mechanism of the magnetoelectric coupling. This project was supported through the ARC (grant DP110105346, $420k). Co-funding of ANSTO allowed us to employ two postdoctoral research fellows.
Atomically precise thin film systems of transition metal oxides offer novel functionalities and the possibility to investigate fundamental effects such as the interplay between magnetism and superconductivity on artificially grown materials, which are not accessible in nature. For example, in a combined polarized neutron and X-ray synchrotron reflectometry approach we have investigated the magnetic and stoichiometric depth profile in BiFeO3/LaSrMnO3 heterostructures with Angstr¨om resolution [Phys. Rev. B. Rapid Com. 90, 041113(R) (2014)]. Neutron diffraction experiments on PLD grown SrCoO3 films did verify a theoretically predicted but hitherto unobserved strain induced magnetic phase transition (submitted to Phys. Rev B, Rapid Com.). Experiments on superconducting/ferromagnetic thin film and superlattices by polarized neutron reflection, diffraction, and Raman light scattering will continue our investigations of the interplay between magnetism and superconductivity (see [Nature Materials 11, 675 (2012)]).
In a further project organic superconductors based on -(BEDTTTF) are investigated by Raman light scattering. Of particular interest was the magnetic phase diagram above the superconducting dome. Here we were able to determine the energies of the pseudogaps directly and will, as next step, focus on the symmetry of the superconducting pair-breaking peak. This project is a collaboration with A/Prof. B. Powell from the University of Queensland.
Experimental Techniques Acessible in the Group of A/Prof. C. Ulrich
- Optical Spectroscopy (Raman Light Scattering, Photoluminescence, Absorption, Reflection)
- Time-Resolved Optical Spectroscopy
- Growth of large high quality single crystals
- Superconducting Quantum Interferrence Magnetometer (SQUID): MPMS3 (Quantum Design)
The purpose of the instruments is to measure the magnetization of samples with extremely weak magnetic signals, e.g.
1. single crystal or powder samples with small magnetic moments such as canted magnetic structures, frustrated spin systems, or molecular magnets, or
2. very small samples. In particular thin film with a film thickness of just a few atomic layers posse magnetic signals which cannot be detected with a standard magnetometer due to the limited sensitivity.
- Neutron Laue Diffraction (Instrument JOEY at ANSTO)
At the UNSW A/Prof. C. Ulrich has installed two state-of-the-art optical setups for Raman light scattering, photoluminescence, absorption, reflection and modulation spectroscopy. The successful ARC grant LE110100060 ($237.500) allowed for the installation of optical diamond anvil high pressure cells for a pressure range of up to 70 GPa and temperatures down to 1.4 K. Furthermore, ultrafast time-resolved optical spectroscopy will be established through our successful ARC research grant LE140100033 ”Ultrafast time-resolved optical spectroscopy for advanced multifunctional materials” ($317.5k).
Besides the optical laboratories A/Prof. C. Ulrich has established a laboratory for sample growth at the UNSW. The laboratory is equipped with two standard muffle furnaces and two tube furnaces for temperatures of up to 1700◦ C. The tube furnaces offer the possibility to apply ultraclean gas environments or vacuum for controlled post growth annealing of the samples. The successful ARC research grant LE140100033 ($317.5k) will allow for the installation of an optical four-mirror traveling solvent floating zone furnace.
At the new research reactor OPAL at ANSTO, A/Prof. C. Ulrich has building up the Neutron Laue Diffraction setup JOEY. The main purpose of this instrument is the test of sample quality and alignment of single crystals prior to an experiment on one of the high-flux instruments. The Neutron Laue Camera will be available for all neutron users at the Bragg Institute.