Complex Oxide Interfaces: A Path to Design New Materials
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Complex Oxide Interfaces: A Path to Design New Materials Hanns-Ulrich Habermeier Max-Planck Institute for Solid State Research Heisenbergstr 1 D 70569 Germany ABSTRACT Heterostructures composed of transition metal oxides with strong electron correlation offer a unique opportunity to design new artificial materials whose electrical, magnetic and optical properties can be manipulated by tailoring the occupation of the d-orbitals of the transition metal in the compound. This possibility is an implication of symmetry constraints at interfaces with the consequence of a reconstruction of the coupled charge-, spin-, and orbital states of the constituents and their interactions. Novel architectures can be constructed showing functions well beyond charge density manipulations determining the functionality of conventional semiconductor heterostructures. Success in this endeavor requires the mastering of technological prerequisites such as structurally as well as chemically controlled interface preparation down to atomic scales. Additionally, a fundamental understanding of the modifications of the electronic structure at the interface imposed by structural boundary conditions and consequently by the constituent’s orbital occupation is required. A path towards a new generation of electronic devices with multiple functionalities can thus be opened by exploiting the correlation driven interface phenomena. In this paper, the technological challenges and experimental realizations along this concept are described with an emphasis of growth techniques based on the pulsed laser deposition method. As a case study, results of investigations of YBa2Cu3O7/La2/3Ca1/3MnO3 superlattices are compiled and the conclusions regarding the orbital manipulation at the interface are used to pave the way for orbital engineering of oxides with electronic structures similar to the cuprates in order to find novel ordered quantum states at the interfaces including magnetism and superconductivity. INTRODUCTION Artificial superlattices (SL’s) represent a well established research topic in condensed matter physics and modern device technology. Semiconductor heterostructures and SL’s have proven to form the basis for unexpected advances in science and device physics over the past decades. A prominent example is the formation of a 2-dimensional electron gas in III-V-compound semiconductor heterostructures or in silicon metal-oxide-semiconductor field-effect transistors with the subsequent discovery of the quantum Hall effect by von Klitzing et al. [1]. Similarly, metallic SL’s consisting of paramagnetic and ferromagnetic layers give rise to a giant magnetoresistance [2] and serve now as sensing elements in reading heads of hard disk drives. The attempt to replicate such SL’s using transition metal oxides (TMO’s) with strong electron correlation –i.e. motion of a charge carriers depends crucially on the motion of the others - will pave the way for an even more exciting research area. This is due to the delicate interplay of spin-, charge-, orbital and lattice i
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