Artificial design of correlated electron systems with atomic precision

Speaker: 
Roman Engel - Herbert, Penn State University
Event Date and Time: 
Mon, 2016-02-29 11:00 - 12:30
Location: 
Hennings 318
Local Contact: 
Leanne Ebbs / Andrea Damascelli
Molecular beam epitaxy has played a key role in the recent progress to explore and understand fundamental concepts in condensed matter physics of materials exhibiting nanoscale features. Synthesizing high quality semiconductor heterostructures with unparalleled precision and atomically abrupt interfaces, while maintaining an excellent control over the stoichiometry of the individual layers has opened the door to the discovery of new states of matter and fascinating transport phenomena. Devices stemming from the heterostructural designs are forming the backbone of today’s high speed wireless and optical communication. Utilizing molecular beam epitaxy to design artificial crystals in which spin, charge, lattice and orbital degrees of freedom are strongly coupled seems a promising strategy to study the intriguing phenomena emerging in these materials, such as frustration among the competing order mechanisms at play, and to explore the phase transition in these complex systems. However, the unfavorable growth kinetics of many complex oxide thin film materials result in high defect concentrations that can mask and intrinsic properties, posing a serious roadblock towards ‘electronic grade’ complex oxide thin films. In this talk I will discuss the application of an epitaxial thin film synthesis technique, dubbed hybrid molecular beam epitaxy, for the growth of transition metal oxide films in general and titanate and vanadate compounds in particular. This combinatorial approach of conventional MBE and chemical beam epitaxy (CBE) has been applied to the growth of SrTiO3 and CaTiO3, both quantum paraelectric materials, and SrVO3, a correlated metal. Intrinsic material quality and its dependence on growth conditions will be discussed and compared to single crystal bulk standards. It will be shown that functional oxide thin films of ‘electronic grade’ quality is possible using this technique, and that control over stoichiometry is a mandatory requirement to enable new ground states in complex oxide thin films stabilized by epitaxial strain. The specific example of SrVO3 a transparent conductor is given to illustrate how correlated electron systems offer new material design strategies beyond conventional semiconductors with band structures dominated by s and p-orbitals.
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