Surface Structure of Stripe ordered 1x2 phase on (Ba, Ca)(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$

ORAL

Abstract

Low energy electron diffraction (LEED) and scanning tunneling microscopy/spectroscopy (STM/S) have been utilized to investigate the geometric structure of the stripe 1$\times $2 surface phase of (Ba, Ca)(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ iron pnictides. STM images show that the surface consists of competing ordered and disordered regions. The 1$\times $2 phase appears on the surface of all compounds but coexist with ($\surd $2 $\times \surd $2)R45$^{\circ}$ phase on the surface of Ba122. Quantitative structural analysis of LEED-I(V) using the fractional spots of the 1$\times $2 phase on both parent compounds as well as Ca(Fe$_{0.925}$Co$_{0.075})_{2}$As$_{2}$ gives a similar surface structure with a termination layer of 50{\%} Ca/Ba atoms. The surface Ca/Ba layer has a large inward relaxation $\sim $ 0.5 {\AA} and the underneath As-Fe-As layer displays a buckling distortion. The Pendry Rp factor ($\sim $ 0.24) obtained in the structural refinement is excellent for all three systems.

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Authors

  • Guorong Li

    Louisiana State University, Louisiana State University, Baton Rouge, LA 70803, USA

  • Von Braun Nascimento

    Louisiana State University, Louisiana State University, Baton Rouge, LA 70803, USA

  • Xiaobo He

    Louisiana State University, Baton Rouge, LA 70803, USA, Louisiana State University

  • Amar B. Karki

    Louisiana State University

  • Rongying Jin

    Louisiana State University, Louisiana State University, Baton Rouge, LA 70803, USA, Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, Dept. of Physics, Louisiana State University, Baton Rouge, LA 70802

  • Jiandi Zhang

    Louisiana State University, Louisiana State University, Baton Rouge, LA 70803, USA, Dept. of Physics, Louisiana State University, Baton Rouge, LA 70802

  • E.W. Plummer

    Louisiana State University, Louisiana State University, Baton Rouge, LA 70803, USA, Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, Dept. of Physics, Louisiana State University, Baton Rouge, LA 70802