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Science Alliance Annual Report

2008–2009

UT-ORNL Distinguished Scientists

UTK physics and astronomy; ORNL materials science and technology

Elbio Dagotto
Nanoscale dimensions and correlated electronic behavior

Scientists have speculated in earnest about the behavior and properties of materials with nanoscale dimensions, at least since Richard Feynman’s famous 1959 talk suggesting that devices and materials could someday be fabricated to atomic specifications. Even earlier in the century, 1932 Nobel Laureate Irving Langmuir and Katharine Blodgett introduced the concept of one-molecule-thick films and the two-dimensional physics to describe such a surface.

A nano-length object behaves differently from its larger-scaled counterpart. For one thing, more surface area in relation to volume creates a different dynamic inside the material. Atoms and molecules in one-dimensional materials are next to each other in a line; in two dimensions, they form a one-atom/molecule-thick plane. Electronic and atomic movement is confined (restrained) to the interior of the nanoscale object—a fact that changes the material’s mechanical, thermal, and catalytic characteristics. At nanoscales the movement of every atom and electron is influenced by its neighbors—hence physicists use the phrase “strongly correlated electronic behavior” to describe what happens with these materials.

Theoretical physicist Elbio Dagotto develops computational techniques and models to predict how strongly correlated electronic materials respond in the presence or absence of an electronic or magnetic field. His group studies a family of materials called transition metal oxides, which have enormous promise for improving memory devices and energy saving electronics. Taking advantage of new scientific ability to prepare multilayered materials with atomically perfect interfaces between alternating layers of oxides, they use their models to explore how differences in chemical composition might be exploited to transfer charge from one material layer to another.

Recently Dagotto’s group also successfully implemented and applied a technique called the Time-Dependent Density Matrix Renormalization Group. This technique allows the study of dynamical properties of electrons, as opposed to studies that calculate averages over time. The calculation of time-dependent quantities allows studies of non-equilibrium situations, which are often found in real materials.