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