Professor of Physics
Department of Physics
qiu@socrates.berkeley.edu
(510) 642-2959

Research Expertise and Interest

physics, novel behavior of the quantum magnetism in magnetic nanostructures, oscillatory interlayer coupling, the giant magnetoresistance, condensed matter experiment, technology applications, molecular beam epitaxy, artificial structures

Description

The overall objective of our research is to develop a fundamental understanding of the novel behavior of the quantum magnetism in magnetic nanostructures. As a magnetic structure is reduced to the nanometer size, quantum confinement of the electrons will generate fascinating properties such as the oscillatory interlayer coupling and the giant magnetoresistance. Investigation on these new phenomena will generate a great interest in the fundamental science and a great potential in the technology applications.

Molecular Beam Epitaxy (MBE) is used to fabricate the magnetic nanostructures with the film thickness controlled on the atomic scale. Using this "atomic engineering" technique, artificial structures will be synthesized and investigated in situ using the High Energy Electron Diffraction (HEED), Low Energy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES), Scanning Tunneling Microscope (STM), and the Surface Magneto-Optic Kerr Effect (SMOKE).

Current Projects

Quantum Well Coupling: As the layer thickness is reduced to the nanometer range, electron confinement due to the potential barriers at the interfaces will result in the formation of Quantum Well (QW) states which play a very important role in the oscillatory interlayer coupling in the giant magnetoresistance multilayers. Our current investigation on this project involved two parts. First, we want to understand the relation between the interlayer coupling and the QW states in the momentum space. Second, we plan to engineer the QW wavefunction to generate new magnetic properties in these nanostructures. The magnetic coupling is measured by SMOKE, and the QW states are investigated by photoemission technique at the Advanced Light Source (ALS) of Lawrence Ber keley National Laboratory (LBNL).

Quasi 1D magnetism: Research from the last decade has demonstrated that fascinating phenomena can be created by converting 3D bulk materials into 2D layered films. The next generation research is expected to be dominated by going from 2D films into quasi 1D systems. This is a challenging area with great potentials. Unlike semiconductor research whereas sub-micron size is already small enough to produce quantum effect, a magnetic heterostructure has to be controlled on the nanometer range to generate extraordinary phenomena. We use nanometer-sized atomic steps to realize the lateral modulation. Our preliminary results have demonstrated a great promising of this research direction.

Metastable Phases of Materials: The epitaxial growth of thin films makes it possible to stabilize some new phases of materials which do not exist in 3D bulk materials. This opens a new opportunity to investigate some fundamental physics from artificial materials created in the laboratory. For example, the fcc structure of Fe exists only above 910oC, making it impossible to study its magnetic phase. Using the MBE technique, we can stabilize the fcc Fe at room temperature so that to study its rich magnetic phases under various conditions.

Collaborative Researches: We are currently collaborating with the ALS at LBNL, the Argonne National Laboratory, and the Los Alamos National Laboratory, to investigate various properties of the magnetic nanostructures. These include the element specific measurement by X-ray Magnetic Circular Dichroism (XMCD), symmetry-breaking-induced magnetic anisotropy, and the colossal magnetoresistance junctions, etc.

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