Correlated electron materials pose some of the most intriguing problems in modern condensed matter physics. These materials host a wide range of exotic properties, including high-Tc superconductivity, magnetism and tunable metal-insulator transitions. A fascinating consequence of strong electron correlations is the emergence of quasi-two-dimensional quantum phases at the interfaces between transition metal oxides. The canonical example is the LaAlO3/SrTiO3 system, which has attracted tremendous interest because the interface hosts a high-density 2DEG[1] with reports of coexisting superconductivity[2], magnetism[3] and large spin-orbit coupling[4], even though both constituent oxides are band insulators.
The intriguing properties of LAO/STO have stimulated recent work on other oxide interface systems with improved properties such as enhanced mobilities[5] or more controllable charge densities[6],[7]. We are interested in NdTiO3/SrTiO3[7], an MBE-grown interface system related to LaAlO3/SrTiO3, but which can be grown entirely by molecular beam epitaxy. We are currently exploring the electronic properties of the NdTiO3/SrTiO3 interface[8], with a focus on magnetism[9] and novel superconducting phases. In parallel to our work on oxide interfaces, we are also investigating superconductivity in doped STO thin films. The insulator-superconductor transition in STO was discovered in the 1960's[10], yet the details have remained elusive to this day, in part due to the dilute carrier concentrations at which superconductivity sets on and the possible multi-band nature of superconductivity in this exciting material.
A main theme of our current work on complex oxides is realizing locally-gated meso and nanoscale devices that will allow us to investigate quantum confinement in the presence of strong correations and to probe local inhomogeneities.
[1] Ohtomo, A. and Hwang, H. Y. Nature 427, 423 (2004).
[2] Reyren, N. et al. Science 317, 1196 (2007).
[3] Brinkman, A. et al. Nature Materials 6, 493 (2007).
[4] Caviglia, A. D. et al. Phys Rev Lett 104, 126803 (2010).
[5] Chen, Y. Z. et al. Nature Materials 14, 801 (2015).
[6] Moetakef, P. et al. Applied Physics Letters 98, 112110 (2011).
[7] Xu, P. et al. Advanced Materials Interfaces 3, 1500432 (2016).
[8] Xu, P. et al. Phys. Rev. Lett. 117, 106803 (2016).
[9] Ayino, Y. et al. Phys. Rev. Materials (2018) (in print), arXiv:1704.08828.
