dr. Debakanta Samal: Exploration of novel structural, electronic and magnetic phenomena in ultrathin cuprates
|When:||We 03-09-2014 15:00 - 16:00|
Atomic engineering of complex oxide thin films/hetrostructures is now reaching a new paradigm: the possibility to control the cation coordination by oxygen anions that can dramatically change the structure-property affair . Different symmetry constraints and electrostatic boundary conditions can be used to design novel oxide thin film structures with exciting properties that have no bulk analogue. The last decade has witnessed explosive growth of research on atomic-scale synthesis of oxide heterostructures that provides a fertile ground to create exotic phases at their interface. In this talk, I will present two examples of stabilization of novel structural phases and their electronic and magnetic properties by manipulating the oxygen sub-lattices in complex Cu-based oxide thin films.
In the first half, I will discuss about the infinite-layer SrCuO2, which in the bulk-form, has each Cu2+ ion coordinated by four planar O2- ions. However, for ultrathin layers, we show a transformation from bulk-planar to chain-type structure having apical oxygen via atomic re-arrangement [1,2]. This phenomena turns out to be a direct consequence of electrostatic instability associated with the polar nature of SrCuO2. We illustrate that the geometry of CuO4 plaquette can precisely be controlled from in-plane to out-of-plane upon reducing the film thickness at the sub-unit cell level and this opens possibilities to design structures that have specific functions, e.g. current-carrying layers, charge reservoirs and scaffolding layers. From magnetic point of view, the plane and chain-type SrCuO2 layers exhibit sharply distinct behavior in terms of their magnetic excitations. In the second half, I will discuss about CuO, which unlike other 3d transition metal monoxides is found in a low symmetry distorted monoclinic structure. We demonstrate direct evidence of strain-induced structural transformation to an elongated rocksalt-like phase in ultrathin-limit, pointing to metastable six-fold coordinated Cu with the hole occupied in the 3dx 2 -y 2 orbital. The experimental confirmation of the high symmetry structure of CuO opens up new avenues to explore its electronic and magnetic properties and its relevance as a proxy structure in the context of high-Tc superconductivity. In essence, both our findings testify unique stabilization processes through atomic re-arrangement and provide new insight for the experimental realization of novel cuprate-hybrids to look for exciting electronic properties.