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Our
investigations into sample topology effects on nano electronic
materials have lead to two distinct methods to attain these unique
samples. One method
utilizes the latest in e-beam lithography technology, allowing us to
fabricate samples of practically
any geometry, limited by our beam
size
and complexity of the geometry.
The other method of obtaining these is to utilize more
“table top” methods for fabricating nanoscale materials, be
these quantum dots, single-crystal nanowires, or nanoscale
cylinders. For
example,
to
prepare a
nano cylinders we first
draw
a quartz filament
by rapidly separating two pieces of quartz melted at the tips
creating a filament with a
size
controlled by the student. The
perfection of
this method
makes
it possible to fabricate
filaments down to 100 nm in diameter, using only a blowtorch and
skill. Evaporating
metal around the filament then completes fabrication of the
cylinder. The
preparation of doubly connected cylindrical samples
allows
us to investigate the sample topology effects in
quasi one dimensional materials.
Our
earlier efforts lead to important discoveries on the effects of
sample topology in superconductors.
We discovered an h/4e rather than the conventional h/2e
resistance oscillation [1], and double resistance anomalies [2] in
lithographically prepared rings.
Our most important
work in this area is the confirmation of de Gennes' prediction that
superconductivity would be destroyed around the half-flux quanta in
doubly connected superconductors with a diameter smaller than the zero-temperature
superconducting coherence length. We
carried out measurements on doubly connected ultrathin
cylinders of Al and Au0.7In0.3 and found that
superconductivity was indeed suppressed completely near half-flux
quantum [3]. In
contrast, single-crystal Sn and Pb wires [4] with a diameter as
small as 20 nm prepared by electrochemical deposition, much thinner
than the nanocylinders of Al and Au0.7In0.3, showed no sign of the
destructive regime, highlighting the importance of sample topology
in nanoscopic superconductors. This work has provided us an
experimental system to address a set of important issues on
nanoscopic superconductivity.
It
is interesting to ask what role the sample topology plays in other
effective dimensions (such as zero-dimension quantum dots), and/or
in other physical processes. We are exploring these issues through
the synthesis and characterization of nano materials with innovative
sample geometries, and electrical, magneto, and optical
measurements.
Contacts:
Neal Staley, nes151 @ psu.edu
Selected Publications:
[1] Yu.
Zadorozhny and Y. Liu, “Fractional-Flux Little-Parks Resistance
Oscillations in Superconducting Au0.71n0.3 Cylinders,” Europhys.
Lett. 55, 712 (2001).
[2] H. Wang,
M.M. Rosario, and Y. Liu, “Observation of h/2e resistance
oscillation, double resistance anomalies, and excessive resistance
in mesoscopic Au0.7In0.3 rings,” submitted to Phys. Rev. B (2004).
[3] Y. Liu, Yu.
Zadorozhny, M. M. Rosario, B. Y. Rock, P. T. Carrigan, and H. Wang,
“Destruction of the Global Phase Coherence in Ultrathin, Doubly
Connected Superconducting Cylinders,” Science 294, 2332 (2001).
[4] Mingliang
Tian, Jingguo Wang, Joseph Snyder, James Kurtz, Ying Liu, Peter
Schiffer, Thomas E. Mallouk, and M. H. W. Chan, “Synthesis and
characterization of superconducting single-crystal Sn wire,” App.
Phys. Lett. 83, 1620 (2003).
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AFM image of an e-beam lithography patterned nano ring.
Data taken on superconducting cylinders showing
the zero temperature "destructive regime" at half-flux
quanta.
Single crystal 40nm tin
nanorods.
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