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Scientific Report 2007-2009
Condensed matter physics and biophysics
C4. Phase separation and spectroscopy of inhomogeneous and
correlated functional materials
Development of new materials with functional properties
require knowledge of the physical parameters that
control the structure-function relationship in the quantum
matter. The first step is to identify these fundamental
parameters, optimize them by controlling atomic
and electronic properties exploiting advanced physical
methods. An effective experimental approach is based on
manipulation and control of phase separation in lamellar
materials for developing new systems with desired application
oriented quantum function. The approach is to
bring the physical system in a fragile metastabile state,
that could be characterized by an electronic topological
transition of the Fermi surface, and manipulate the
phase separation and self-organization at a nano-scale,
determining the physical parameters and optimize them
through changing external conditions, as the chemical
pressure, charge density, magnetic field and temperature.
The approach, combined with scattering and spectroscopic
tools, provides key features on the structuralfunction
relation, taking a step forward in designing new
systems with desired functions for the future technology.
and lattice heterogeneities. Among these are the materials
showing high T c superconductivity, colossal magneto
resistance (CMR), metal insulator transition and ferroelectricity.
In addition to the TMOs, the highly correlated
4f systems also have been focus of spectroscopic
studies to understand the underlying physics. Since the
discovery of the Fe-based superconducting materials, the
group has looked into their atomic scale structure, addressing
the similarities with the copper oxide superconductors,
not only from structural topology point of view
but also for the mesoscopic inhomogeneties, in which
the chemical pressure and the atomic scale disorder are
found to be key ingredients. The group has routine excess
to the most advanced international synchrotron radiation
facilities for the characterization by scattering
and spectroscopic methods. The in-house UHV facility
permits to use photoemission method, in addition to
permitting an epitaxial growth. The non-contact complex
conductivity measurements down to He3 and an
AFM/STM system further adds to the key facilities.
In the field, the group has organized a series of conferences
with the specific topic, Stripes and High T c Superconductivity.
The group has also been part of recently
concluded FP6-STREP EU project on the Controlling
Mesoscopic Phase Separation.
Figure 1: Structure of Fe-based superconductors with electronically
active layers and the spacer blocks.
Mesoscopic phase separation and self-organization are
common to the functional materials. The superstripes
group on the functional materials is active in the field
of heterogeneous materials with competing electronic
degerees of freedom that control the basic functional
properties. The complexity due to competing phases
at the atomic scale drives the system to get electronically
self-organized in textured states. A particular
kind of self-organization in the superconducting systems
is the so-called superstripes. This materials architecture
show high T c superconductivity in which the chemical
potential is tuned near an ETT where the Fermi
surface topology undergoes dimensionality change. In
these conditions, the physical system is in an electronically/atomically
fragile and one can manipulate its physical
parameters by changing external conditions as the
pressure, temperature and magnetic field, in addition
to the chemical pressure and atomic disorder. Consequently,
it is possible to optimize them to obtain new
materials with possibly better superconducting function.
We have widely investigated the highly correlated
transition metal oxides (TMOs) with nanoscale charge
Figure 2: UHV system with MBE and photoemission spectroscopy
chambers.
References
1. M. Filippi, et al., J. Appl. Phys. 106, 104116 (2009).
2. S. Sanna, et al., EPL 86, 67007 (2009).
3. B. Joseph, et al., J. Phys: Cond.Mat B 21, 432201 (2009).
4. A. Iadecola, et al., EPL 87, 26005 (2009).
Authors
A. Bianconi, N.L. Saini, A. Iadecola, B. Joseph, M. Fratini
http://superstripes.com/
Sapienza Università di Roma 57 Dipartimento di Fisica