RICERCA ITALIANA     

Superconductivity and coherence phenomena in unconventional and strongly correlated materials

Università degli Studi di Roma "La Sapienza"

Abstract

After 20 years from the discovery,
the phenomenon of the high critical temperature
superconductivity (HTSC) represents still one of the
most investigated and challenging open issues
in the whole landscape of Physics.
The analysis of the complex properties, not only
of cuprates but also of other superconductors
as the fullerenes, magnesium diboride MgB2 etc.,
Has led to a global rexamination of many basilar
concepts of the solid state physics,
as the metallic properties in regimes of strong
electronic correlation and strong electron-lattice coupling.
Besides the issues more related to the HTSC's,
the technological progress has made now possible
to investigate physical systems in extreme
regimes (low dimensionality, low charge carrier
density, strong coupling, low disorder/impurity
concentrations) previously not achievable.
These topics have led to a strong hybridization
between the study of the high-Tc phenomenon
and other related issues in the condensed matter.

In this framework the present research project
involves a group of researchers who represent
an acknowledged pool at the international level.
Motivated by the open issues prompted by
the phenomenology of the high-Tc superconductors
different but complementary research lines
have been developed in this field:
the >>>

Principal Investigator

Luciano Pietronero Università degli Studi di ROMA "La Sapienza"

Research Objectives

Overall aim of the present project
is to study the different factors which
affect the quantum coherence in the
several sistems of high theoretical and
applicative interest, as the
high Tc superconductors, other novel
materials and many electronic systems.
Object of investigation will be the physical origin
of these processes, their properties
and the physical consequences of such quantum coherence.
Particular care will be devoted to the integration
and coordination of the expertises of the different
involved researchers in oder to favour the transfer of
scientific skills and knowledges among the different research
activities and among the different researchers.

More in details, we identify below the specific aims
of the project grouped for research activity
in order to show in the most clear way the structure
and organization of the project.

1 - ANOMALOUS BEHAVIORS OF THE NORMAL AND SUPERCONDUCTING
STATE IN STRONGLY CORRELATED ELECTRON SYSTEMS

Understanding of the
mechanisms of violation of standard paradigms of the
metallic [Landau Fermi-Liquid theory] and superconducting
[BCS theory] states
More specifically, we intend to study:
- the quantum criticality as a possible source of
anomalies of the metallic and superconducting states,
in the priximity of >>>

First Results

During the two years of the project we intend to achieve
the objectives above described and to obtain the following
results:

1 - ANOMALOUS BEHAVIORS OF THE NORMAL AND SUPERCONDUCTING
STATE IN STRONGLY CORRELATED ELECTRON SYSTEMS

- Concerning the study of general properties of quantum criticality
we will identify the effect of disorder in fermionic systems coupled
with critical modes close to the antiferromagnetic transition in two
dimensions (2D). The presence of singular vertices in the effective
field theory makes this analysis delicate, but at the same time relevant
for many strongly correlated systems. In the specific case of HTSC cuprates,
we aim to completely characterize some effects due to the presence of a
charge-ordering quantum critical point proposed by Unit II. Namely,
we will address the effects of charge critical modes on transport and
on various spectroscopy and the role of disorder in Raman and optical
spectroscopy. Regarding photoemission we plan to explain recently uncovered
effects like Fermi surface anomalies in HTSC.
- The study of charge inhomogeneities in correlated systems is naturally
connected to the analysis of point 1), but it has also a general character
and it will be focused on coarse-grained models for the formation of
inhomogeneous phases and on the study of the evolution between
>>>

Timescale

24 months

National and international background

Quantum coherent processes are at the basis of large part
of the most important features of the Condensed Matter Physics.
Superconductivity, superfluidity and the Bose condensation
represent for example just few of the most known phenomena
where the quantum coherence is established on a macroscopic level.
Also correlation and many-body effects due to interactions involving
electronic and the lattice/spin degrees of freedom
can be important,
specifically in the normal state.
They give rise to
the exchange-correlation processes which characterize
metallic Fermi liquid properties, and in the other interesting
cases they are able to establish a new Non Fermi liquid state,
as for instance in the presence of a quantum critical point
or in the case where a Resonant Valence Bond state occurs.
In the presence of interactions
quantum coherence effects between different degrees of freedom
can be relevant also on a microscopic scale.
They are related, for instance, to the possible formation
of electron-lattice bound states (lattice polaron)
or electron-spin states (magnetic polaron).
Short range correlation is also fundamental to understand
the dissociation and metallization processes
of molecular crystal as the hydrogen at high pressure.
In addition, it should be reminded that in this context
dimensionality plays >>>