Creating Emergent Phases in Transition Metal Oxides

Transition Metal Oxides (TMOs) exhibit unique and multifunctional physical phenomena directly related to the spin and orbital degrees of freedom of metal d-states and their interplay with the lattice. Importantly, the iso-structure of TMOs permits realization of hetero-structures generating at their surfaces and interfaces new physical matters that radically differ from those of the constituent bulk materials.
Through two examples, novel and fascinating properties emerged in TMO based hetero-structures and routes to control them will be presented:

1. Altering orbital ordering and band filling of the 2DEG at titanates surfaces. Employing Angle-Resolved Photoemission Spectroscopy (ARPES) we found ways to manipulate the 2DEG and, consequently, to tune electronic properties of titanates surfaces (SrTiO3, TiO2-anatase and CaTiO3).

2. Tuning electronic phases in ultra-thin NdNiO3 (NNO) films via the strain and the proximity to a magnetic layer. Our study reveals that substrate-induced strain tunes the crystal field splitting, consequently changing the Fermi surface, nesting conditions and spin-fluctuation strength. All of them thereby effect and control the Metal Insulator Transition (MIT). In addition, we found that the ferromagnetic metallic (FM-M) state can be induced while MIT is quenched in ultra-thin NNO via the proximity to the magnetically ordered manganite buffer layer.

Overall our studies establish different approaches to manipulate the properties of the two-dimensional electron gas and electronic phases in NNO signifying perspectives of TMO for novel applications.