Understanding Interfaces as a Route to Control the Orbital Degree of Freedom in Cuprates

Functional oxides based on the transition metal series display a wide spectrum of remarkable electronic properties including magnetism, superconductivity and metal-insulator transitions, which offer potential important properties for practical applications including colossal responses to external fields, switchable conductivity, and efficient energy conversion.These novel properties arise from the interaction between the charge, orbital, spin, and lattice degrees of freedom. By using epitaxial growth to stabilize novel oxide crystal structures, thin film synthesis offers uniqueroute to control oxide structure in ways not attainable in the bulk counterparts. Interfaces in particular offer an opportunity to break the symmetry present in the bulk and alter the local environment [1]. This allows one to access new regions of phase to explore emergent states not present in bulk form. In the bulk of materials such as superconducting YBa2Cu3O7 the electrons reside in very specific electronic orbitals. However, when atomically abrupt interfaces between YBa2Cu3O7 and the ferromagnetic oxide (LaCaMnO3) are created, this order is drastically altered inways never seen in the bulk [2-5]. Here, I will discuss our recent results in the ultra-thin regime, which allow us to directly tune the degree of orbital polarization directly via superlattice structure.
Work at Argonne is supported by the U.S. Department of Energy, Office of Science, under Contract No.  DE-AC02-06CH11357.

[1] S.J. May, J.M. Rondinelli, and J.W. Freeland, MRS Bulletin 37, 261 (2012)
[2] Te-Yu Chien et al. Nature Communications 4, 2336 (2013)
[3] J. Chakhalian, J.W. Freeland et. al. Nature Physics 2, 244 (2006). 
[4] J.W. Freeland, et al. Appl. Phys. Lett. 90, 242502 (2007).
[5] J. Chakhalian, J.W. Freeland et al. Science 318, 1114 (2007).