Electrostatic Tuning of the Superconductivity of Yttrium Barium Copper Oxide

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15 Νοε 2013 (πριν από 3 χρόνια και 4 μήνες)

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Electrostatic Tuning of the Superconductivity

of Yttrium Barium Copper Oxide


Allen M. Goldman

School of Physics and Astronoomy

University of Minnesota


Ultrathin YBa
2
Cu
3
O
7−x

(YBCO)
films were grown on SrTiO
3
(

(STO)
substrates in a
high
-
pressure oxygen
sputtering system
. The films

were used

in a field effect
transistor configuration

to study the control of superconductivity by electrostatic
charging. While
devices

using

STO

as the gate dielectric induced only small T
c
shifts,
a clear transition betwee
n superconducting and insulating behavior was realized
using the ionic liquid DEME
-
TFSI

to deplete holes
. Employing a finite size scaling
analysis, curves of resistance versus temperature, R(T), over the temperature range
from 6K to 22K were found to col
lapse onto a single function, which suggests the
presence of a quantum critical point. However the scaling failed at the lowest
temperatures indicating the possible presence of an additional phase between the
superconducting and insulat
ing regimes.
Further

depletion of holes
appears to
result in the accumulation of

electrons
with the recovery of superconductivity.

By
changing the polarity of the gate voltage, an underdoped film was tuned into the
overdoped regi
me. An unexpected two
-
step mechanism for elect
rostatic doping
was revealed. Transport measurements exhibited
anomalous features
which
suggest that there is an electronic phase transition
near optimal doping
.


* Supported in part by the NSF under grants

NSF/DMR
-
0709584 and 0854752

and
performed in collaboration with Xiang Leng

and

Javier Garcia
-
Barriocanal.