Andrew J. Millis

Dynamic Jahn-Teller Effect and Colossal Magnetoresistance in La 1 − x Sr x MnO 3

A model for

Lattice effects in magnetoresistive manganese perovskites

La_{1-x}Sr_xMnO_3

Quantifying strain dependence in “colossal” magnetoresistance manganites

which incorporates the physics of dynamic Jahn-Teller and double-exchange effects is presented and solved via a dynamical mean field approximation. In an intermediate coupling regime the interplay of these two effects is found to reproduce the behavior of the resistivity and magnetic transition temperature observed in

Co-occurrence of Superparamagnetism and Anomalous Hall Effect in Highly Reduced Cobalt-Doped Rutile TiO~2~-~d~e~l~t~a Films

La_{1-x} Sr_x MnO_3

Electronic reconstruction at an interface between a Mott insulator and a band insulator

.

Continuous-Time Solver for Quantum Impurity Models

The discovery of spectacularly large magnetoresistive responses in a class of metallic manganese oxides has raised hopes that these compounds might be of practical utility. But regardless of whether this promise is realized, these materials provide an ideal system in which to elucidate the properties of metals in which electron–lattice interactions play a key role.

Ba2YCu3O7-δ: electrodynamics of crystals with high reflectivity

Experimental, phenomenological, and theoretical analyses are given of the dependence on strain of the ferromagnetic Tc of the colossal magnetoresistance (CMR) rare earth manganese perovskites. It is found that Tc is extremely sensitive to biaxial strain; by implication other physical properties are also. The results indicate that biaxial strain is an important variable which must be considered in the design of devices based on thin films and provide evidence in favor of the relevance of the Jahn–Teller electron-phonon coupling to the CMR phenomenon.

Electroresistance and Electronic Phase Separation in Mixed-Valent Manganites

We report a detailed magnetic and structural analysis of highly reduced Co doped rutile TiO(2-delta) films displaying an anomalous Hall effect (AHE). The temperature and field dependence of magnetization, and transmission electron microscopy, clearly establish the presence of nanosized superparamagnetic cobalt clusters of approximately 8-10 nm size in the films at the interface. The co-occurrence of superparamagnetism and AHE raises questions regarding the use of the AHE as a test of the intrinsic nature of ferromagnetism in diluted magnetic semiconductors.

Phonon effects in molecular transistors: Quantal and classical treatment

Surface science is an important and well-established branch of materials science involving the study of changes in material properties near a surface or interface. A fundamental issue has been atomic reconstruction: how the surface lattice symmetry differs from the bulk. ‘Correlated-electron compounds’ are materials in which strong electron–electron and electron–lattice interactions produce new electronic phases, including interaction-induced (Mott) insulators, many forms of spin, charge and orbital ordering, and (presumably) high-transition-temperature superconductivity. Here we propose that the fundamental issue for the new field of correlated-electron surface/interface science is ‘electronic reconstruction’: how does the surface/interface electronic phase differ from that in the bulk? As a step towards a general understanding of such phenomena, we present a theoretical study of an interface between a strongly correlated Mott insulator and a band insulator. We find dramatic interface-induced electronic reconstructions: in wide parameter ranges, the near-interface region is metallic and ferromagnetic, whereas the bulk phase on either side is insulating and antiferromagnetic. Extending the analysis to a wider range of interfaces and surfaces is a fundamental scientific challenge and may lead to new applications for correlated electron materials.

FERMI-LIQUID-TO-POLARON CROSSOVER. II. DOUBLE EXCHANGE AND THE PHYSICS OF COLOSSAL MAGNETORESISTANCE

We present a new continuous-time solver for quantum impurity models such as those relevant to dynamical mean field theory. It is based on a stochastic sampling of a perturbation expansion in the impurity-bath hybridization parameter. Comparisons with Monte Carlo and exact diagonalization calculations confirm the accuracy of the new approach, which allows very efficient simulations even at low temperatures and for strong interactions. As examples of the power of the method we present results for the temperature dependence of the kinetic energy and the free energy, enabling an accurate location of the temperature-driven metal-insulator transition.