### Session W13: Focus Session: Iron Pnictides and Other Novel Superconductors XIV: ARPES

11:15 AM–2:03 PM, Thursday, March 19, 2009
Room: 309

Chair: Norman Mannella, University of Tennessee, Knoxville

Abstract ID: BAPS.2009.MAR.W13.6

### Abstract: W13.00006 : Momentum dependence of superconducting gap, strong-coupling dispersion kink, and tightly bound Cooper pairs in the high-Tc (Sr,Ba)1-x(K,Na)xFe2As2 superconductors

12:15 PM–12:27 PM

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#### Authors:

Lewis Wray
(Princeton University)

Dong Qian
(Princeton University)

David Hsieh
(Princeton University)

Yuqi Xia
(Princeton University)

Ali Yazdani
(Princeton University)

N. Phuan Ong
(Princeton University)

Nanlin Wang
(Beijing National Laboratory for Condensed Matter Physics)

M. Zahid Hasan
(Princeton University)

We present a systematic angle-resolved photoemission spectroscopic study of the high-T$c$ superconductor class (Sr/Ba)$_{1-x}$(K/Na)$_x$Fe$_2$As$_2$. By utilizing a photon-energy-modulation contrast and scattering geometry we report the Fermi surface and the momentum dependence of the superconducting gap, $\Delta(\overrightarrow{k})$. A prominent quasiparticle dispersion kink reflecting strong scattering processes is observed in a binding-energy range of 25-55 meV in the superconducting state, and the coherence length or the extent of the Cooper pair wave function is found to be about 20 $\AA$, which is uncharacteristic of a superconducting phase realized by the BCS-phonon-retardation mechanism. The observed 40$\pm$15 meV kink likely reflects contributions from the frustrated spin excitations in a J$_1$-J$_2$ magnetic background and scattering from the soft phonons. Results taken collectively provide direct clues to the nature of the pairing potential including an internal phase-shift factor in the superconducting order parameter which leads to a Brillouin zone node in a strong-coupling setting.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.MAR.W13.6