[LA-SiGMA] LASiGMA Seminar - Dr. Rafael Fernandes, 3:30pm at Louisiana State University

[shelley lee]

Dear All,

 

Dr. Rafael Fernandes of the University of Minnesota will be giving a seminar
Wednesday, October 16th at 3:30 pm in 1008B in the Digital Media Center at
the Louisiana State University. The title of his talk is "What role does
nematicity play in the high-temperature superconductivity of the iron
pnictides? "

 

Abstract:

Five years after their discovery, much of the interest in the iron pnictides
remains in understanding not only their high-temperature superconducting
phase, but also the nature of their normal state. In this context, recent
experiments have provided strong evidence for the existence of an unusual
correlated state in the phase diagram of these materials, dubbed electronic
nematic. Below the nematic transition temperature, the tetragonal symmetry
of the system is broken down to orthorhombic not by lattice vibrations, but
by electronic degrees of freedom. However, two questions remain open: What
is the origin of this nematic state? What is its relationship to the
superconducting state? In this talk we will explore these two issues via a
microscopic theoretical model in which the nematic instability is caused by
magnetic fluctuations arising from a degenerate ground state. A key
consequence of this model is that lattice fluctuations and magnetic
fluctuations are not independent. Instead, they follow a simple scaling
relation, which we will show to be satisfied by elastic modulus and NMR
experimental data. We will also demonstrate that, in general, nematic order
competes with the unconventional sign-changing s+- superconducting state.
However, when the s+- instability is in close competition with a d-wave
instability - as it has been suggested in several iron pnictides - we find
that nematic and superconducting degrees of freedom are strongly coupled. As
a result, not only Tc can be significantly enhanced by nematic order, but
also nematicity itself can be used as a diagnostic tool to search for novel
unconventional superconducting states.

 

Biography:

Rafael Fernandes received his Bachelor degree (2003) and my PhD in Physics
(2008) from the State University of Campinas, in Brazil. Before joining the
University of Minnesota, he was a postdoc in Ames Laboratory and a joint
postdoc in Columbia University/Los Alamos National Lab.

 

His current research activities are in theoretical condensed matter physics,
particularly in strongly correlated electronic many-body systems. Dr.
Fernandes is interested in clean and disordered systems in which the
collective behavior of the electrons give rise to ordered states that break
different symmetries of the system, such as superconductivity, magnetism,
nematic ordering, and orbital ordering. His aim is to understand not only
the impact of these individual phases on the electronic structure and
macroscopic properties of the system, but also how they interact with each
other. To achieve this goal, he relies not only on the theoretical methods
from quantum statistical mechanics and many-body theory, but also on the
invaluable empirical information obtained from a variety of experimental
techniques, such as x-ray diffraction, neutron scattering, optical
spectroscopy, thermodynamic measurements, and angle-resolved photo-emission
spectroscopy.

 

Please note, due to technical difficulties this seminar will ONLY be
available via abobe connect. Please click on the link provided:
<http://connect.lsu.edu/la-sigma/> http://connect.lsu.edu/la-sigma/

 

UNO - Liberal Arts Building 234

LATech - PML 1015, Center for Instructional Technology, at the Wyly Tower

 

Please see attached flyer and let me know if you have any questions.

 

Regards,

Shelley Lee

Project Coordinator

225-578-0465

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