Mailing Address:
Department of Physics
The Pennsylvania State University
104 Davey Lab
University Park, PA 16802
USA
Last Updated:2-12-2009
Superconductivity
and emergent phenomena at atomically sharp interfaces
The
eutectic phase
of Ru-Sr2RuO4
consists of
mesoscopic
islands of pure Ru metal embedded in bulk single crystal
of Sr2RuO4.
In order to synthesize superconducting Sr2RuO4
single crystals, excess RuO2is
added to the feed
rod
to compensate the Ru loss as Ru is very refractory.
As a
result, mesoscopic Ru islands are formed in Sr2RuO4
crystals close to the center of the crystal rod. Surprisingly,
superconductivity with a Tc as high as
3 K was found in crystals
containing
these
Ru
islands. Thus the eutectic system is referred to as the 3-K phase of Sr2RuO4.
Optical and AFM images of
polished crystal surface of Ru
embedded in Sr2RuO4.
(Polished down to 0.1 mm
in roughness
)The typical size of the Ru island is about 1mm
x 5mm.
The
anisotropy of the 3-K phase suggested that the enhancement of superconductivity
occurs on the Sr2RuO4
side of the RuSr2RuO4
interface. Furthermore, the 3-K phase regions can form a fully
superconducting network even above the bulk Tc of Sr2RuO4
[1]. Previous
work
[2] using break junctions (see
below, right panel) provided the first experimental evidence for the
existence of the Andreev bound states (manifested as a zero-biased
conductance peak, see below, right panel) in the 3-K phase, which in
turn suggested that the 3 K phase is also unconventional.
Normalized
resistance RJ(T) for SRO/Ru/SRO and SRO/SRO
junctions. Inset: (a) RJ(T) of the SRO/Ru/SRO
junction under fields, from top to bottom, B=4.0, 0.6, 0.2 and
0 T, and rc(T)
of the bulk Ru-containing Sr2RuO4
crystals. (b) Schematic of the SRO/Ru/SRO
junction.
Tunneling
spectra dI/dV for the SRO/Ru/SRO junction at various
temperatures.
Currently,
we are measuring superconducting energy gap induced by proximity
effect using plane tunnel junctions prepared on individual Ru islands.
We found strong evidence that the proximity induced energy gap is
strongly suppressed in the interior of a Ru island despite of the
very sharp, clean interface between Ru and Sr2RuO4. We
are also exploring the physical origin of the unexpected suppression
of the proximity effect, focusing on possible reconstruction of the
electronic states, or magnetic effects at the interface.
Contacts:
Yiqun Alex Ying, yzy116 @ psu.edu
Neal Staley, nes151 @ psu.edu
Ronald Justin
Myers, rjm31 @ psu.edu
Publications:
1) J.
Hooper, Z. Q. Mao, K. D. Nelson, Y. Liu, M. Wada, and Y. Maeno,
“Anomalous Josephson network in the Ru-Sr2RuO4
eutectic system,” Phys. Rev. B 70, 014510 (2004).
2)
Z.Q. Mao, K.D. Nelson, R.
Jin, Y. Liu, and Y. Maeno, “Observation of Andreev Surface Bound
State in the 3-K Phase Region of Sr2RuO4,”
Phys. Rev. Lett. 87, 037003 (2001).
