Quantum Materials

Ramamoorthy Ramesh, Program Leader

Systems in which the quantum-mechanical correlations of electrons play a dominant role possess a rich and diverse spectrum of physical phenomena.  Interacting charge, spin, orbital, and lattice degrees of freedom create a multi-dimensional phase space that make possible novel phases of matter and new functionalities.  This program seeks a fundamental understanding of the novel phases and elementary excitations of bulk crystalline transition metal oxides so as to guide our development of new functionality in oxide heterointerfaces and other artificially prepared nanostructures.

CURRENT PROJECTS

R. Ramesh
The Ramesh group is synthesizing epitaxial interfaces between perovskite TMO’s with different A-site constituents using laser-MBE, and then measuring conductivity at the buried interface using rapid time-scan time-domain terahertz spectroscopy.  They study the dynamics of correlated multifunctional oxide nanostructures, specifically measuring the rate of magnetization reversal in spinel nanorods in a perovskite matrix induced by electric field poling.

Electrical control of local ferromagnetism. PEEM images of ferromagnetic domain structure of a CoFe feature taken in the as-grown state (a), after the first electrical switch (b), and after the second electrical switch (c). d-f, Schematic descriptions of the observed magnetic contrast (gray, black, and white) in the corresponding PEEM images reveals that the net magnetization of the CoFe feature rotations by 90° upon application of an electric field.

R. Birgeneau
This project entails the setup of a crystal growth facility, and the growth of single crystals of the parent compound La2CuO4, to then be electrically intercalated with oxygen.  Studies will use stage-4 La2CuO4.12 in the phase in which the intercalant oxygen ions are ordered as model system.   Data is to be collected particularly at high energies and at optimal doping and near the upper and lower boundaries of the superconducting “dome”.
The project will continue elucidating the microscopic magnetism and its interplay with superconductivity in various high-Tc materials. Emerging crystal growth studies include multiferroic oxides (BiFeO3) and related systems.

A. Lanzara
Lanzara studies the role of the lattice and spin degrees of freedom and its interplay with charge ordering and high temperature superconductivity.   The study will be extended to a broader class of materials, from high temperature superconductors to manganites and nickelates using angle resolved photoemission spectroscopy (ARPES) and Spin-ARPES, and to a broader class of oxides. The state of solid will be engineered and modified by using a coherent laser source.

D.-H. Lee
The theory arm of this program seeks to understand the nature of the observed density wave order and its relation with the pseudogap, as well as gaining understanding of the relation between the stripe order manifested by the Birgeneau neutron studies and the checkerboard density wave order seen in STM.
Lee et al will study unconventional materials such as x-(BEDT-TTF)2Cu2(CN)3 to understand whether it is a true spin liquid or an inhomogeneous Mott insulator near its first order Mott transition and will investigate Mott insulator interfaces.

J. Orenstein
This project involves the measurement of spin propagation in GaAs quantum wells and related systems using a combination of time-resolved magneto-optic Kerr effect (TR-MOKE) and the transient spin grating technique.
Thin films of SrRuO3 will be studied, ultimately to measure the spin transport coefficients as a function of T in the CaxSr1-xRuO3 system.   The quantum critical point at or near optimal doping of cuprate superconductors is also under investigation.

A. Vishwanath
Using a complementary set of theoretical techniques, this project studies continuous quantum phase transitions in a variety of lattice quantum systems, and in the strongly correlated systems studied experimentally by others in this program.  Vishwanath studies the physics of Mott insulators in heterostructures, applying methods for doping band insulators and adjusting them to Mott insulators, as well as the physics of transition metal oxide spinels.