Condensed Matter Physics Seminar
2 p.m., Thursday, January 29, 2004
Room 1201, Physics Building
Coherent Spin Memory and Transfer in Chemically
Synthesized Semiconductor Quantum Dots
Min Ouyang
(California NanoSystems Institute and
Department of Physics, UC Santa Barbara)
Abstract: Semiconductor quantum dots (QDs)
are attractive candidates for scalable solid state implementations of quantum
information processing based on electron spin states, where the crucial
requirement of practical devices is to have efficient and tunable spin coupling
between them. I will first discuss the general spin dynamic behavior of isolated
colloidal quantum dots. Then I will focus on recent femtosecond time-resolved
Faraday rotation studies of self-assembled multilayer spintronic devices of
colloidal quantum dots bridged by conjugated molecules. The data reveal the
instantaneous transfer of spin coherence through conjugated molecular bridges
spanning quantum dots of different size over a broad range of temperature. The
room temperature spin transfer efficiency exceeds 20%, which approximately
doubles the value measured at T=4.5K. A molecular π -orbital mediated spin
coherence transfer mechanism is proposed to provide a qualitative insight into
the experimental observations, further suggesting the correlation between
stereochemistry of molecules and spin coherence transfer process. These findings
show that conjugated molecules can be used not only as physical links for the
assembly of functional networks but also as efficient channels for shuttling
quantum information. The results suggest that this class of structures may be
useful as room temperature two-spin quantum devices and offer a rational pathway
for bottom-up hierarchical assembly of QDs into well defined functional
nanometer-scale spintronic systems that can connect the nanometer through
micrometer regimes.
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Host: Williams
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