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.
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