Berlin 2012 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 33: Superconductivity, Measuring Devices, Matter at Low Temperature: Poster Session
TT 33.15: Poster
Wednesday, March 28, 2012, 15:00–19:00, Poster B
Preemptive Nematic Order, Pseudogap, and Orbital Order in the Iron Pnictides — •Johannes Knolle1, Ilya Eremin2, Rafael M. Fernandes3, Andrey V. Chubukov4, and Jorg Schmalian5 — 1Max-Planck-Institut für Physik komplexer Systeme, D-01187 Dresden, Germany — 2Institut für Theoretische Physik III, Ruhr-Universität Bochum, D-44801 Bochum, Germany — 3Department of Physics, Columbia University, New York, New York 10027, USA — 4Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA — 5Karlsruher Institut für Technologie, D-76131 Karlsruhe, Germany
Starting from a microscopic itinerant model, we derive and analyze the effective low-energy model for collective magnetic excitations in the iron pnictides. We show that the stripe magnetic order is generally preempted by an Ising-nematic order which breaks C4 lattice symmetry but preserves O(3) spin-rotational symmetry. This leads to a rich phase diagram as function of doping, pressure, and elastic moduli, displaying split magnetic and nematic tri-critical points. The nematic transition may instantly bring the system to the verge of a magnetic transition, or it may occur first, being followed by a magnetic transition at a lower temperature. In the latter case, the preemptive nematic transition is accompanied by either a jump or a rapid increase of the magnetic correlation length, triggering a pseudogap behavior associated with magnetic precursors. Furthermore, due to the distinct orbital character of each Fermi pocket, the nematic transition also induces orbital order. We compare our results to various experiments.