Mott Transition, i.e., the interactiondriven metaltoinsulator transition MIT, is a fundamental issue

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CAREER New Phases at the Surfaces/Interfaces of
Transition-Metal OxidesJiandi Zhang, Florida
International University, DMR-0346826
Mott Transition, i.e., the interaction-driven
metal-to-insulator transition (MIT), is a
fundamental issue in the physics of strongly
correlated electron systems. Conversely,
searching for new a playground bestowing a truly
archetypical Mott MIT to test our understanding
of it seems to be and incessant effort in the
condensed matter physics community. Here we
present a broken-symmetry manifested Mott MIT at
the surface of a prototype Mott system
Ca1.9Sr0.1RuO4. In the bulk crystal of
Ca1.9Sr0.1RuO4, a first-order MIT with an abrupt
structural transition occurs at TC 154 K on
cooling. In contrast, both scanning tunneling
spectroscopy (STS) and electron energy loss
spectroscopy (EELS) show that a surface MIT
without simultaneous structural transition is
found at a temperature of TC,S 130 K,
remarkably lower than that in the bulk crystal.
Furthermore, a surface phonon anomaly is observed
at TC,S indicating a strong electron-phonon
coupling. Our structural study by using low
energy electron diffraction (LEED) I-V refinement
and also first principle calculations finally
discovered that the broken symmetry at the
surface simply restrains the structure from the
lattice distortion which is intimately involved
in the bulk MIT, thus persisting the metallic
phase at surface to lower temperature and
preventing any structural transition across the
surface MIT. Our results clearly show that this
unique surface provides a unique opportunity to
gain insight into the precise nature of Mott
transition with no participation of structural
transition.
(top) The T-dependence of STS and EELS spectra of
Ca1.9Sr0.1RuO4 showing the surface MIT associated
with a phonon anomaly at 130 K. (bottom) An LEED
image and schematic view of the surface lattice
relaxation of Ca1.9Sr0.1RuO4 which does not
change across the observed surface MIT.
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CAREER New Phases at the Surfaces/Interfaces of
Transition-Metal OxidesJiandi Zhang, Florida
International University, DMR-0346826
EDUCATION Four graduate students (Anne Cai,
Fernanda Foetter who is now at Univ. of Florida,
Yanxin Liu, and Rajendra Joshi), two
undergraduates (Sarah Bryan and Dalgis Mesa), and
a postdoctoral fellow (Lei Cai) are involved in
this research program. This program also provided
the independent studies of few undergraduate
students in Physics Department. This project is
also a partnership between Florida International
University, University of Tennessee, and Oak
Ridge National Lab. The collaborations being set
up will lead a unique opportunity for the
materials research and education, especially the
training of minority students for their careers
in this technology-driven world. Several
education outreach activities have been
accomplished through this funded program. These
included the open house and lectures to local
public. Shown on the right is the picture taken
during a visiting of local high school students
and teachers.
Societal Impact The technological impact by the
studies of new phenomena at the proximity of
surfaces interfaces of correlated electron
materials like doped transition-metal oxides
could eventually be enormous, because most of the
devices one conceives of making from these novel
materials involve surfaces and interfaces, such
as spin valves, spin transistors, hard disk
read/write heads, many types of sensors, memory
devices, etc. If these materials are going to
find their way into the marketplace it is obvious
that the properties of the surface and interfaces
must be understood and controlled at a level that
is now commonplace for devices made of more
conventional materials.