Characteristic two-dimensional Fermi surface topology of high-Tc iron-based superconductors

Masanori Sunagawa,Kanta Ono,Masashi Arita,Hiroshi Kumigashira,Yuji Muraoka,Koji Tsubota,Takayoshi Yokoya,Junki Sonoyama,Toshihiko Ishiga,Hirofumi Namatame,Kazutaka Kudo,Taihei Jabuchi,Takanori Wakita,Minoru Nohara,Kenya Shimada,Keita Iba,Tomohiro Matsushita,Masaki Taniguchi

doi:10.1038/srep04381

Abstract

Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors. Such pairing may be enhanced by quasi-nesting of two-dimensional electron and hole-like Fermi surfaces (FS), which is considered an important ingredient for superconductivity at high critical temperatures (high-Tc). However, the dimensionality of the FS varies for hole and electron-doped systems, so the precise importance of this feature for high-Tc materials remains unclear. Here we demonstrate a phase of electron-doped CaFe2As2 (La and P co-doped CaFe2As2) with Tc = 45 K, which is the highest Tc found for the AEFe2As2 bulk superconductors (122-type; AE = Alkaline Earth), possesses only cylindrical hole- and electron-like FSs. This result indicates that FS topology consisting only of two-dimensional sheets is characteristic of both hole- and electron-doped 122-type high-Tc superconductors.

Highlights

Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors
In order to clarify the relevance of the Fermi surface to the mechanism of superconductivity in iron-based superconductors from an experimental perspective, numerous angle-resolved photoemission spectroscopy (ARPES) measurements, which are a direct measurement of the Fermi surface, have been conducted on ironbased superconductors[8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]
In ARPES data for circular-polarized (c-pole) light (Fig. 2a, S2a–d), we found that the hole-like band (a2) approaches and crosses EF, as evident from multiple structures in the momentum distribution curve (MDC) at EF (Fig. S2c) and the parabolic dispersion in the energy distribution curve (EDC) (Fig. S2d)

Summary

Introduction

Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors Such pairing may be enhanced by quasi-nesting of two-dimensional electron and hole-like Fermi surfaces (FS), which is considered an important ingredient for superconductivity at high critical temperatures (high-Tc). Spin fluctuation-mediated superconductivity, as proposed for cuprate and heavy fermion systems, and orbital fluctuation-mediated superconductivity have been proposed as mechanisms for superconductivity[4,5,6,7] Such fluctuations are believed to be derived from the quasinesting between the hole- and electron-like Fermi surfaces (FSs) (Fig. 1a).

Methods

Results

Conclusion