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PRODID:UW-Madison-Physics-Events
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UID:UW-Physics-Event-2331
DTSTART:20120306T160000Z
DURATION:PT1H0M0S
DTSTAMP:20260420T062535Z
LAST-MODIFIED:20120201T181318Z
LOCATION:5310 Chamberlin
SUMMARY:Magnetic interactions and anisotropies in iron superconductors
 \, R. G. Herb Condensed Matter Seminar\, Leni Bascones\, Instituto de 
 Ciencia de Materiales de Madrid (ICMM-CSIC)
DESCRIPTION:A major breakthrough took place in 2008 with the discovery
  of high temperature superconductivity in iron pnictides. The basic st
 ructure of these materials are FeAs layers.  In these materials superc
 onductivity emerges when doping or applying pressure to an antiferroma
 gnetic compound. Most iron pnictides order with (pi\,0) momentum\, ant
 iferromagnetic in the x direction and ferromagnetic in the y direction
 . The magnetic state of iron pnictides is metallic and presents unusua
 l magnetic moment and resistivity anisotropy [1].<br>
\n<br>
\nThe ori
 gin of magnetism in iron superconductors is still unsettled. At the he
 art of the debate are the itinerant (weak coupling) versus localized (
 strong coupling) nature of magnetism\, the role played by the orbital 
 degree of freedom and Hund's coupling and a possible nematic phase. Th
 e itinerant picture relies on the metallicity of the magnetic state an
 d an approximate (pi\,0) nesting of the Fermi surface. In the strong c
 oupling picture localized moments interact with AF exchange constants 
 J1 and J2 with their first and second nearest neighbors respectively. 
 (pi\,0) state can be stabilized with J1< 2 J2\, but little is known on
  the actual value of these constants. Orbital ordering has been propos
 ed as a leading instability and to explain the anisotropic properties.
 <br>
\n<br>
\nIn this talk I will present our recent calculations whic
 h try to make connection between the itinerant and localized picture. 
 We have analyzed the magnetic interactions of iron superconductors on 
 the basis of a five orbital model treated both within Hartree-Fock and
  Heisenberg approximations [2].  We show that the exchange constants d
 epend on charge and orbital filling and on Hund's coupling with unexpe
 cted consequences on the phase diagram [2]. We have also studied the d
 c and optical conductivities and separated the effect of magnetism and
  of orbital ordering on the anisotropic properties [3].<br>
\n<br>
\n<
 br>
\n[1] For a review see\, J. Paglione and R.L. Greene\, Nature Phys
 . 6\, 645 (2010).<br>
\n[2] M.J. Calderon\, G. Leon\, B. Valenzuela an
 d E. Bascones\, arXiv:1107.2279. E. Bascones\, M.J. Calderon\, B. Vale
 nzuela\, PRL 104\, 227201 (2010)<br>
\n[3] B. Valenzuela\, E. Bascones
 \, M.J. Calderon\, PRL 105\, 207202 (2010)<br>
\n
URL:https://www.physics.wisc.edu/events/?id=2331
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