### Session P3: Invited Session: Alkaline Iron Selenides vs Iron Pnictides: Properties and Their Implications

8:00 AM–11:00 AM, Wednesday, February 29, 2012
Room: 205AB

Chair: Qimiao Si, Rice University

Abstract ID: BAPS.2012.MAR.P3.2

### Abstract: P3.00002 : Distinct Fermi Surface Topology and nearly Isotropic Superconducting Gap in A$_{x}$Fe$_{2-y}$ Se$_{2}$ (A=K, Tl, Rb) Superconductors

8:36 AM–9:12 AM

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#### Author:

Xingjiang Zhou
(Institute of Physics, Chinese Academy of Sciences, Beijing 100190)

High resolution angle-resolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the newly discovered A$_{x}$Fe$_{2-y}$Se$_{2}$ [A=K, (Tl,K) and (Tl,Rb)] superconductors[1,2,3] 1. Distinct Fermi surface topology, consisting of two electron-like Fermi surface sheets around the $\Gamma$(0,0) point and an electron-like Fermi surface sheet near the M($\pi$,$\pi )$ point, was revealed in all these samples. This is in strong contrast to the Fermi surface topology of other Fe-based superconductors where hole-like Fermi surface sheets are present near the $\Gamma$(0,0) point. 2. Both the electron-like Fermi surface sheet near M point and the large electron-like Fermi surface sheet near $\Gamma$ point show nearly isotropic superconducting gap without nodes 3. The doping evolution of the electronic structure from insulating samples to the superconducting samples is consistent with a phase separation picture. The information on the Fermi surface topology and superconducting gap of this new A$_{x}$Fe$_{2-y}$Se$_{2}$ superconductor will provide key insights and constraints to understand the superconductivity mechanism in iron-based superconductors. \\[4pt] [1]. D. X. Mou, X. J. Zhou et. al, Phys. Rev. Lett. \textbf{106}, 107001 (2011). \\[0pt] [2]. L. Zhao, X. J. Zhou et. al, Phys. Rev. B \textbf{83}, 140508(R) (2011). \\[0pt] [3]. L. Yu, X. J. Zhou et al., unpublished.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.P3.2