Iron Superconductivity !! Superconducting Gap in FeAs from PCAR “Minimal” Mode

Iron Superconductivity !! Superconducting Gap in FeAs from PCAR “Minimal” Mode www.phwiki.com

Iron Superconductivity !! Superconducting Gap in FeAs from PCAR “Minimal” Mode

Powell, Chuck, Morning On-Air Personality has reference to this Academic Journal, PHwiki organized this Journal Iron Superconductivity !! Superconducting Gap in FeAs from PCAR “Minimal” Model of FeAs planes – Different from CuO2!! Multib in addition to Magnetism in addition to Superconductivity Zlatko Tesanovic, Johns Hopkins University E-mail: zbt@pha.jhu.edu Web: http://www.pha.jhu.edu/~zbt V. Cvetkovic in addition to ZT, arXiv/0804.4678 T. Y. Chen et al., Nature 453, 1224 (2008) Coastline of the Fermi Sea New REOFeAs SC Tc 55K What can tell us about superconducting state St in addition to ard BCS theory works well in materials like Nb, Sn or Hg. In Pb in addition to more complex systems (Va3Sn) one needs “strong coupling” theory (2/Tc 4-6 )

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What can tell us about superconducting state Our results as long as FeAs are inconsistent with either of these features Andreev Spectroscopy Gap value from Andreev peaks 2 13.4 meV 2/kBTC = 3.68 (BCS) Extra features beyond gap (contact specific) Slanted background [Always G(-V) > G(V)] Experimental setup Gold tip in contact with FeAs SC in FeAs superconductors I T. Y. Chen et al., Nature 453, 1224 (2008) Conclusions: Nodeless superconducting gap in addition to no pseudogap behavior. Very different from high temperature cuprate superconductors !!

At 4.52 K BCS-like gap from BTK analysis 2D/kBTC = 3.68 closer to 3.53 (BCS s-wave) than 4.28 (BCS d-wave) 2D = 13.34 ± 0.3 meV TC = 42 K in FeAs superconductors II Conclusions: Conventional phonon-mechanism is unlikely but so is Mott limit-induced repulsion of the cuprate d-wave kind. We have something new !! V. Cvetkovic in addition to ZT, arXiv/0804.4678 Emerge systematically ZBA obscures gap ZBA due to SC H field has small effect at 4.5K Emergence of Zero Bias Anomaly (ZBA) Contact size Small contact Large contact

P. Xiong, G. Xiao, R. B. Laibowitz, Phys. Rev. Lett. 71, 1907 (1993) ZBA in s-wave Nb Nb tip on Cu thin film (Chen et al) Nb tip on Cu thin film (Chen et al)

V. Cvetkovic in addition to ZT, arXiv/0804.4678 “Minimal” Model of FeAs layers I “Puckering” of FeAs planes is essential: All d-orbitals are near EF Large overlap with As p-orbitals below EF enhanced itinerancy of d electrons defeats Hund’s rule in addition to large local moment V. Cvetkovic in addition to ZT, arXiv/0804.4678 Hund’s Rule Defeated “Puckering” of FeAs planes is essential: All d-orbitals are near EF Large overlap with As p-orbitals below EF enhanced itinerancy of d electrons defeats Hund’s rule in addition to large local moment Hund’s rule rules as long as Mn2+ : all five d-electrons line up to minimize Coulomb repulsion S = 5/2 V. Cvetkovic in addition to ZT, arXiv/0804.4678 “Minimal” Model of FeAs layers II Important: Near EF e in addition to h b in addition to s contain significant admixture of all five Wannier d-orbitals, dxz in addition to dyz of odd parity in FeAs plane) in addition to the remaining three d-orbitals of even parity in FeAs plane

V. Cvetkovic in addition to ZT, arXiv/0804.4678 “Minimal” Model of FeAs layers III FeAs are different from CuO2 Charge carriers are more itinerant in addition to less localized on atomic sites. Multib in addition to description is necessary, unlike an effective single b in addition to model of cuprates Interactions in FeAs I V. Cvetkovic in addition to ZT, arXiv/0804.4678 Interactions in FeAs II Typically, we find Vs is dominant Valley density-wave(s) (VDW) in FeAs V. Cvetkovic in addition to ZT, arXiv/0804.4678 h1 h2 e1

Valley Density-Wave (VDW) in addition to SC in FeAs Outcome: CDW (structural) in addition to SDW (AF) orders at q = M V. Cvetkovic in addition to ZT, arXiv/0804.4678

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Powell, Chuck Morning On-Air Personality

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