Distinct Fermi Surface Topology and Nodeless Superconducting Gap in a $({\mathrm{Tl}}_{0.58}{\mathrm{Rb}}_{0.42}){\mathrm{Fe}}_{1.72}{\mathrm{Se}}_{2}$ Superconductor

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Distinct Fermi Surface Topology and Nodeless Superconducting Gap in a $({Tl}_{0.58} {Rb}_{0.42}) {Fe}_{1.72} {Se}_{2}$ Superconductor

Daixiang Mou, Shanyu Liu, Xiaowen Jia, Junfeng He, Yingying Peng, Lin Zhao, Li Yu, Guodong Liu, Shaolong He, Xiaoli Dong, Jun Zhang, Hangdong Wang, Chiheng Dong, Minghu Fang, Xiaoyang Wang, Qinjun Peng, Zhimin Wang, Shenjin Zhang, Feng Yang, Zuyan Xu, Chuangtian Chen, and X. J. Zhou

Phys. Rev. Lett. 106, 107001 – Published 8 March 2011

Abstract

High resolution angle-resolved photoemission measurements have been carried out to study the electronic structure and superconducting gap of the $({Tl}_{0.58} {Rb}_{0.42}) {Fe}_{1.72} {Se}_{2}$ superconductor with a $T_{c} = 32 K$ . The Fermi surface topology consists of two electronlike Fermi surface sheets around the $Γ$ point which is distinct from that in all other iron-based superconductors reported so far. The Fermi surface around the $M$ point shows a nearly isotropic superconducting gap of $\sim 12 meV$ . The large Fermi surface near the $Γ$ point also shows a nearly isotropic superconducting gap of $\sim 15 meV$ , while no superconducting gap opening is clearly observed for the inner tiny Fermi surface. Our observed new Fermi surface topology and its associated superconducting gap will provide key insights and constraints into the understanding of the superconductivity mechanism in iron-based superconductors.

Received 24 January 2011

DOI:https://doi.org/10.1103/PhysRevLett.106.107001

Authors & Affiliations

Daixiang Mou¹, Shanyu Liu¹, Xiaowen Jia¹, Junfeng He¹, Yingying Peng¹, Lin Zhao¹, Li Yu¹, Guodong Liu¹, Shaolong He¹, Xiaoli Dong¹, Jun Zhang¹, Hangdong Wang², Chiheng Dong², Minghu Fang², Xiaoyang Wang³, Qinjun Peng³, Zhimin Wang³, Shenjin Zhang³, Feng Yang³, Zuyan Xu³, Chuangtian Chen³, and X. J. Zhou^1,*

¹Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
²Department of Physics, Zhejiang University, Hangzhou 310027, China
³Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China

^*Corresponding author. XJZhou@aphy.iphy.ac.cn

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Vol. 106, Iss. 10 — 11 March 2011

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Figure 1
Fermi surface of $({Tl}_{0.58} {Rb}_{0.42}) {Fe}_{1.72} {Se}_{2}$ superconductor ( $T_{c} = 32 K$ ). (a) Spectral weight distribution integrated within [ $- 20 meV$ ,10 meV] energy window near the Fermi level as a function of $k_{x}$ and $k_{y}$ measured using $h ν = 21.2 eV$ light source. Two Fermi surface sheets are observed around the $Γ$ point which are marked as $α$ for the inner small sheet and $β$ for the outer large one. Near the $M (π, π)$ point, one Fermi surface sheet is clearly observed which is marked as $γ$ . (b) Fermi surface mapping measured using the $h ν = 40.8 eV$ light source. Although the signal is relatively weak, one can see traces of two Fermi surface sheets around $Γ$ and one around $M$ .Reuse & Permissions
Figure 2
Band structure and photoemission spectra of $({Tl}_{0.58} {Rb}_{0.42}) {Fe}_{1.72} {Se}_{2}$ measured along two high symmetry cuts. (a) Band structure along cut 1 crossing the $Γ$ point; the location of the cut is shown on the top of (a). The $α$ band and two Fermi crossings of the $β$ band ( $β_{L}$ and $β_{R}$ ) are marked. (b) Corresponding EDC second derivative image of (a). (c) Band structure along cut 2 crossing the $M$ point; the location of the cut is shown on the top of (c). The two Fermi crossings of the $γ$ band ( $γ_{L}$ and $γ_{R}$ ) are marked. (d) Corresponding EDC second derivative image of (c). (e) EDCs corresponding to (a) for cut 1. (f) EDCs corresponding to Fig. 2c for cut 2.Reuse & Permissions
Figure 3
Temperature dependence of energy bands and superconducting gap near $Γ$ and $M$ points. (a) Photoemission images along cut B (bottom-right inset). (b) Photoemission spectra at the Fermi crossing of $γ$ Fermi surface and their corresponding symmetrized spectra (c) measured at different temperatures. (d) Temperature dependence of the superconducting gap. The dashed line is a BCS gap form. (e) Photoemission images along cut A (bottom-right inset) at different temperatures. The original EDCs at the $Γ$ point and at the Fermi crossing of $β$ Fermi surface measured at different temperatures are shown in (f) and their corresponding symmetrized EDCs are shown in (g).Reuse & Permissions
Figure 4
Momentum-dependent superconducting gap along the $γ$ and the $β$ Fermi surface sheets measured at $T = 15 K$ . Fermi surface mapping near $M$ (a) and near $Γ$ (b) and the corresponding Fermi crossings marked by red circles. (c) EDCs along the $γ$ Fermi surface and their corresponding symmetrized EDCs (d). (e) EDCs along the $β$ Fermi surface and their corresponding symmetrized EDCs (f). (g) Momentum dependence of the superconducting gap, obtained by fitting the symmetrized EDCs, along the $γ$ Fermi surface sheet (red circles) and along the $β$ Fermi surface sheet (blue circles).Reuse & Permissions

Physical Review Letters

Distinct Fermi Surface Topology and Nodeless Superconducting Gap in a (Tl0.58Rb0.42)Fe1.72Se2 Superconductor

Daixiang Mou, Shanyu Liu, Xiaowen Jia, Junfeng He, Yingying Peng, Lin Zhao, Li Yu, Guodong Liu, Shaolong He, Xiaoli Dong, Jun Zhang, Hangdong Wang, Chiheng Dong, Minghu Fang, Xiaoyang Wang, Qinjun Peng, Zhimin Wang, Shenjin Zhang, Feng Yang, Zuyan Xu, Chuangtian Chen, and X. J. Zhou

Phys. Rev. Lett. 106, 107001 – Published 8 March 2011

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Distinct Fermi Surface Topology and Nodeless Superconducting Gap in a $({Tl}_{0.58} {Rb}_{0.42}) {Fe}_{1.72} {Se}_{2}$ Superconductor