Interplay between magnetic, electronic and elastic degrees of freedom in the iron pnictides

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Date/Time:Thursday, 05 Nov 2009 from 4:10 pm to 5:00 pm
Location:Physics 5
Channel:Condensed Matter Physics
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Rafael Fernandes (Ames Laboratory)

The new iron arsenide superconductors present a very rich phase diagram with superconducting, magnetic and structural order. In this talk, I present a theoretical model that describes the interplay between these distinct phases.

First, I investigate the possibility of coexistence between magnetism and superconductivity. Particularly, I focus on how distinct regimes of competition between these two phases are related to different symmetries of the Cooper pair wave-function. Assuming that superconductivity and itinerant antiferromagnetism are caused by electrons sharing the same bands, I show that while the so-called s ++ state is generally incompatible to the antiferromagnetic phase, the unconventional s +- state can coexist with magnetism depending on the Fermi surface topology.

The coupling between magnetic and elastic degrees of freedom is also investigated. I show that nematic fluctuations associated to the frustrated nature of the spin lattice couple to the shear modes, leading to a significant softening of the lattice in the paramagnetic phase. Supported by Resonant Ultrasound Spectroscopy measurements, I demonstrate that these nematic fluctuations are low-energy collective excitations that can be efficiently probed by the shear modulus of the system.