Possible Phase-Sensitive Tests of Pairing Symmetry in Pnictide Superconductors

The discovery of the new class of pnictide superconductors has engendered a controversy about their pairing symmetry, with proposals ranging from an extended $s$ wave or “$s_{\pm }$” symmetry to nodal or nodeless $d$-wave symmetry to still more exotic order parameters such as $p$ wave. In this Letter, building on the earlier, similar work performed for the cuprates, we propose several phase-sensitive Josephson interferometry experiments, each of which may allow resolution of the issue.

Figure 1

A view of the calculated Fermi surface geometry in a superconducting pnictide ${\mathrm{LaFeAsO}}_{0.9}{\mathrm{F}}_{0.1}$, with hole ($\Gamma$) and electron pockets ($\pi$, $\pi$) indicated. For a thick barrier the black circles represent the Fermi surface states which dominate the (100) current, while the green circles represent the states which dominate the (110) current. A possible intermediate angle, where the electron surface may dominate the current, is shown by the arrow. Greek characters represent standard BZ points, while Roman characters refer to the adjacent circles whose wave function character is given in Table .

Figure 2

A schematic view of tunneling geometry for two possible experiments: left, a (100) -near-(110) orientation, right, an $ac$ orientation with specular and thick barriers as indicated.

Figure 3

A schematic view of the tunneling geometry for the proposed bicrystal experiments. Left: an $ab$-plane orientation with two possible lead orientations; right: a $c$-axis orientation.

Figure 4

A first-principles calculation of the $ab$-plane projected three dimensional Fermi surfaces of ${\mathrm{Ba}}_{0.6}{\mathrm{K}}_{0.4}{\mathrm{Fe}}_2{\mathrm{As}}_2$ (green/gray) and ${\mathrm{BaFe}}_{1.6}{\mathrm{Co}}_{0.4}{\mathrm{As}}_2$ (red/black).