Onset of Spin Entanglement in Doped Carbon Nanotubes Studied by EPR
arxiv(2024)
摘要
Nanoscale semiconductors with isolated spin impurities have been touted as
promising materials for their potential use at the intersection of quantum,
spin, and information technologies. Electron paramagnetic resonance (EPR)
studies of spins in semiconducting carbon nanotubes have overwhelmingly focused
on spins more strongly localized by sp^3-type lattice defects. However,
the creation of such impurities is irreversible and requires specific reactions
to generate them. Shallow charge impurities, on the other hand, are more
readily and widely produced by simple redox chemistry, but have not yet been
investigated for their spin properties. Here we use EPR to study p-doped (6,5)
semiconducting single-wall carbon nanotubes (s-SWNTs) and elucidate the role of
impurity-impurity interactions in conjunction with exchange and correlation
effects for the spin behavior of this material. A quantitative comparison of
the EPR signals with phenomenological modeling combined with configuration
interaction electronic structure calculations of impurity pairs shows that
orbital overlap, combined with exchange and correlation effects, causes the EPR
signal to disappear due to spin entanglement for doping levels corresponding to
impurity spacings of 14 nm (at 30 K). This transition is predicted to
shift to higher doping levels with increasing temperature and to lower levels
with increasing screening, providing an opportunity for improved spin control
in doped s-SWNTs.
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