Figure 2
From: Neutron Scattering Studies of spin excitations in hole-doped Ba0.67K0.33Fe2As2 superconductor
Wave-vector and temperature dependence of the scattering at excitation energies below the neutron spin resonance energy in Ba0.67K0.33Fe2As2.
(a), (b) Q-scans at E = 5 meV along the (H,0,0) and (H,0,1) directions above and below Tc . While the scattering centered at (1,0,0) clearly vanishes below Tc , at (1,0,1) it persists and sharpens. (d) Q-scans at E = 1.5 meV along the (H,0,1) direction at 2 K and 45 K. The normal state peak at 45 K clearly survives superconductivity at 2 K. (c) Similar scans at E = 0.75 meV, where the normal state peak clearly disappears at 2 K, indicating the presence of a 0.75 meV spin gap. (e) Temperature dependence of the E = 3 meV scattering at the signal [Q = (1,0,0)] and background [Q = (1.3,0,0)] positions. The signal shows a clear suppression below Tc , while the background scattering goes smoothly across Tc . At low temperature, the signal merges into the background scattering, thus confirming the vanishing magnetic scattering. (f) Similar data at QAFM = (1,0,1) and Q = (1.4,0,1). While the signal also responds to Tc , the background scattering does not merge into the signal at low-temperature, thus indicating the continued presence of magnetic scattering. (g) Overall scattering in the (H,0,L) plane at E = 5 meV and 2 K. The data show a clear sinusoidal modulation along the L-direction. Data in (a,b,d) are from SPINS, (c) from MACS, (e) from BT-7, (f) from HB-3 and (g) from MACS. The horizontal bars indicate instrumental resolutions. The slight off-centering in peak positions for different experiments from the expected QAFM = (1,0,1) position is due to small sample mis-alignment problems. The scattering at (0.6,0,L) with L = 0,2.5 is of phonon or spurious origin.
