Recent theoretical topics of strongly-correlated heterostructures

 

Satoshi Okamoto

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831

 

The fabrication and characterization of artificial heterostructures involving transition-metal oxides is one of the main topics of current materials science [1]. Among various oxides, of particular interest are correlated-electron systems which exhibit a variety of phenomena such as high-Tc superconductivity in cuprates. Correlated heterostructures are expected to become fundamental building blocks of future oxide electronics utilizing the novel properties of the oxides. Understanding of the correlated electron behaviors at surfaces and interfaces is, therefore, of crucial importance. In this talk, I will present the recent theoretical developments on the strongly correlated heterostructures. In particular, I would like to discuss the following three topics.

1. Mott-insulator/metal interface [2] and transport of two-terminal metal/Mott-insulator/metal junctions [3] It is shown that the spectral function in the interacting region is modified by the coupling with metallic regions. Such sensitivity creates rather non-linear transport behavior.

2. Surface magnetic behavior of double-exchange ferromagnet [4] We find about three unit-cell wide surface layers in which the magnetic moment decreases more rapidly than in the bulk with increasing temperature. We discuss the implication to the tunneling magnetoresistance effect using manganites and possible improvement near the bulk Curie temperature.

3. Superlattices of high-Tc cuprates [5] Both experimental and theoretical studies show strong pairing scale in the underdoped (UD) region of cuprates and strong coherency in the overdoped (OD) region. These observations may suggest higher-Tc superconductivity in artificial heterostructures in which UD and OD cuprates are connected. We apply some extensions of the dynamical-mean-field theory to such heterostructures and examine the possibility of higher-Tc superconductivity.

 

Work in ORNL is supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy.

 

[1] For example, A. Ohtomo et al., Nature (London) 419, 378 (2002).

[2] S. Okamoto (unpublished).

[3] S. Okamoto, PRL 101, 116807 (2008).

[4] S. Okamoto (unpublished).

[5] S. Okamoto and T. A. Maier, PRL 101, 156401 (2008).