Electrostatically Switching Between Ground States of Ultrathin Films A. M. Goldman, University of Minnesota, DMR-0138209/0455121

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Electrostatically Switching Between Ground States
of Ultrathin Films A. M. Goldman, University of
Minnesota, DMR-0138209/0455121
There are many physical systems which can be
tuned from one electronic phase to another by
changing the systems properties, such as
applying a magnetic field, changing chemical
doping, or altering the level of disorder. An
alternative to these methods is capacitive
charging in a field effect geometry. In this
method, the film is used as one electrode of a
parallel plate capacitor and an insulating
substrate (SrTiO3) separates the film from the
other electrode, which is a thick metal layer
called the gate. As a voltage is applied to the
gate, electrons are added to the film. We have
increased the density of electrons in a 10Å thick
film of bismuth by approximately 3 x 1013 cm-2,
which switches the low temperature state from
insulating to superconducting. We are using this
technique to study the insulator-superconductor
transition, which is a quantum phase transition.
Bismuth Film
Source
Drain
Gate
SrTiO3 substrate
Cartoon of parallel plate capacitor geometry,
with insulating substrate separating a bismuth
film from the gate electrode. The thickness of
the film is about 10 Å, the source and drain are
about 100 Å, and the thickness of the substrate
between the gate and the film is approximately 45
?m.
Graph of the film resistance versus temperature
at multiple gate voltages between 0 V (top
curve) and 42.5 V (bottom curve). The films
state at the lowest temperatures switches between
insulating and superconducting upon application
of gate voltage.
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Electrostatically Switching Between Ground States
of Ultrathin Films A. M. Goldman, University of
Minnesota, DMR-0138209/0455121
Education This research is being performed by
two graduate students, Kevin Parendo and Sarwa
Tan. Kevin Parendo is a Graduate Dissertation
Fellow. Previous work on strontium titanate
substrates was done by a graduate student,
Melissa Eblen-Zayas, a postdoctoral associate,
Dr. Anand Bhattacharya, and an undergraduate,
Neal Staley. Ms. Eblen-Zayas was an NSF
pre-doctoral fellow and University of Minnesota
Graduate Dissertation Fellow. She is now on the
Carleton College faculty. Dr. Bhattacharya is
now at Argonne National Laboratory, and Mr.
Staley is now a graduate student in physics at
Penn State University.
Societal Impact This tuning between two vastly
different electronic ground states (one with a
large resistance, the other with zero resistance)
can in principle be used as a switching device
and employed in manipulating data in a manner
similar to the application of the silicon field
effect transistor. It is possible that this work
will serve as a baseline for investigations
involving high-temperature superconductors and
thus could impact technology if it lead to a high
temperature superconduc-ting field effect
transistor.