University of Minnesota
Nine years after their discovery, much of the interest in the iron-based materials remains in understanding not only their high-temperature superconducting phase, but also the nature of their normal state. Besides magnetic order, an unusual correlated state is observed 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. It has been proposed that this electronic nematic phase is a composite order resulting from the partial melting of the stripe-type magnetic order. In this talk, I will present a theoretical microscopic model for the formation of this emergent composite order, and discuss its experimental manifestations. The same model also predicts two additional magnetic ground states that, in contrast to the stripe one, preserve tetragonal symmetry. I will present evidence that these states have been recently observed in hole-doped pnictides. Finally, I will discuss the unusual composite orders that emerge from these tetragonal magnetic states, manifested as charge order and chiral order. This model provides an interesting framework connecting magnetic degeneracy and emergent electronic orders.
Dr. Rafael Fernandes is an Associate Professor at the School of Physics and Astronomy of the University of Minnesota. After completing his PhD in 2008 at the State University of Campinas, Brazil, he was a postdoc at Ames Laboratory and Columbia University/Los Alamos National Laboratory before joining the faculty at the University of Minnesota in 2012. He is a theoretical condensed matter physicist working on a variety of strongly correlated electronic systems, with emphasis on unconventional superconductors. Among the prizes he has received in his career are the DOE Early Career Award (2014), the McKnight Land-Grant Professorship (2015), the Cottrell Research Scholar Award (2016), the George Taylor Award (2017), and the McKnight Presidential Fellowship (2017).
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