Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P3: Fe-based Superconductors: Correlation Effects |
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Sponsoring Units: DCMP Chair: Steve Kivelson, Stanford University Room: 301/302 |
Wednesday, March 18, 2009 8:00AM - 8:36AM |
P3.00001: ARPES studies of the electronic structure of Fe-based superconductors Invited Speaker: The recent discovery of superconductivity in Fe-based layered compounds has created renewed interest in high temperature superconductivity. With a superconducting transition temperature as high as 55 K, this discovery provides a new direction to understand the essential ingredients for achieving a high superconducting transition temperature. In this talk, I will present our recent angle-resolved photoemission spectroscopy (ARPES) studies on LaOFeP and (Ba,K)Fe$_{2}$As$_{2}$ systems, with special emphasis on the basic electronic structure of the parent compounds. For LaOFeP, quantitative agreement can be found between our ARPES data and the LDA band structure calculations, suggesting that a weak coupling approach based on an itinerant ground state may be more appropriate for understanding this new superconducting compound [1]. On the other hand, the picture for (Ba,K)Fe$_{2}$As$_{2}$ system is more complicated. I will discuss two important issues in these FeAs compounds: 1) the unexpected Fermi surface topology in both undoped and doped compounds; 2) the peculiar signature of the SDW transition in ARPES spectra for the parent compound. \\[4pt] [1] D. H. Lu, M. Yi, S.-K. Mo, A. S. Erickson, J. Analytis, J.-H. Chu, D. J. Singh, Z. Hussain, T. H. Geballe, I. R. Fisher {\&} Z.-X. Shen, Nature 455, 81 (2008). [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 9:12AM |
P3.00002: Charge dynamics in the normal state of the iron oxypnictide superconductor LaFePO Invited Speaker: Many-body interactions in materials govern diverse and complex phenomena like high-$T_c$ superconductivity, density wave instabilities and metal-insulator transitions. Infrared spectroscopy is an ideal tool for identifying the fingerprints of the various interactions in a material. We present infrared and optical properties in the normal state of $ab$-plane oriented single crystals of the iron oxypnictide superconductor LaFePO. Prominent Drude peaks and low scattering rates indicate the presence of coherent quasiparticles. We find that this metal has a relatively low carrier density compared to MgB$_2$, for example. An important result is that the Drude spectral weight i.e. the kinetic energy of itinerant quasiparticles is reduced by correlation effects to 50\% of the band theory value. Even though LaFePO is among the most conducting of the iron-pnictides, we find that electronic correlations cannot be ignored in any realistic physical description of this material. We classify LaFePO as a moderately correlated metal. [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:48AM |
P3.00003: Electronic Correlations and Magnetic Frustration in the Iron Pnictides Invited Speaker: An important question about the high Tc iron pnictides is the extent to which they are strongly correlated. Based on the fact that they are ``bad metals,'' we propose that these materials are in proximity to a Mott insulator [1,2]. In other words, the degree of the electronic correlations here is closer to that of intermediately-coupled metallic systems like V2O3, which lies near the Mott transition, rather than that of simple antiferromagnetic metals such as Cr. Consequently, we model the incoherent electronic excitations in terms of localized moments, whose superexchange interactions contain the competing nearest-neighbor (J1) and next-nearest-neighbor (J2) components [1]. The magnetic frustration of the J1-J2 model in the relevant parameter range leads to a (pi,0) antiferromagnet and a reduced ordered moment. The model also features an Ising transition that naturally yields a structural phase transition. All these are consistent with the neutron scattering results. With the coupling of the local moments to the coherent electronic excitations, the strength of the antiferromagnetic order is tuned, leading to a magnetic quantum critical point [2]. The ordered moment should therefore vary across the undoped iron arsenides. In addition, the magnetic quantum criticality can be probed by P doping for As in the parent iron pnictides, where the disruption to the quantum criticality caused by superconductivity is likely to be less compared to the electron or hole doped cases. Finally, the implications of the electronic correlations and magnetic frustration on the multi-band superconductivity will be briefly discussed. \\[4pt] [1] Q. Si and E. Abrahams, PRL 101, 076401 (2008); \\[0pt] [2] J. Dai, Q. Si, J-X Zhu and E. Abrahams, arXiv:0808.0305. [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:24AM |
P3.00004: Pairing symmetry and Antiferromagnetic Exchange Coupling in Fe-Based Superconductors Invited Speaker: I discuss the existence of strikingly identical paradigms applicable to both cuprates and iron-based superconductors in understanding magnetism, superconductivity and the interplay between the two. The magnetic states and transitions in iron- based superconductors are well described by a $J_1-J_2-J_z$ magnetic exchange model where $J_1$, $J_2$ and $J_z$ are nearest neighbour, next nearest neighbour and inter-layer couplings respectively. Differing from the t-J model for cuprates where d-wave pairing symmetry is favored, the magnetic exchange in the iron based supercondunctors predicts an unconventional s-wave $cosk_x cosk_y$ pairing. I will show that the predicted pairing symmetry is supported by many experimental results, and also discuss new predictions associated with the pairing symmetry. \\[4pt] References: \\[0pt] [1]: Chen Fang, Hong Yao, Wei-Feng Tai, Jiangping Hu and S. Kivelson ``Theory of Electron Nematic Order in LaOFeAs''; Phys. Rev. B 77 224509 (2008).\\[0pt] [2]: Kangjun Seo, A. B. Bernevig and JiangPing Hu, ``Pairing Symmetry in a Two-Orbital Exchange Coupling Model of Oxypnictides''; PRL 101, 206404 (2008) ArXiv: 0805.2958.\\[0pt] [3]: Meera M. Parish, Jiangping Hu and B. Andrei Bernevig ``Experimental Consequences of the S-wave cos(kx)cos (ky) Superconductivity in the Iron-Pnictides'', Phys. Rev. B 78, 144514 (2008) ArXiv:0807.4572.\\[0pt] [4]: Chen Fang, B. Andrei Bernevig, Jiangping Hu,``Theory of Magnetic Order in $ Fe_{1+y}Te_{1-x}Se_x$'', arXiv:0811.1294 (2008). [Preview Abstract] |
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