Abstract
We report a combined study of the spin resonances and superconducting gaps for underdoped (Tc=19 K), optimally doped (Tc=25 K), and overdoped (Tc=19 K) Ba(Fe1-xCox)2As2 single crystals with inelastic neutron scattering and angle resolved photoemission spectroscopy. We find a quasi-two-dimensional spin resonance whose energy scales with the superconducting gap in all three compounds. In addition, anisotropic low energy spin excitation enhancements in the superconducting state have been deduced and characterized for the under and optimally doped compounds. Our data suggest that the quasi-two-dimensional spin resonance is a spin exciton that corresponds to the spin singlet-triplet excitations of the itinerant electrons. However, the intensity enhancements of the anisotropic spin excitations are dominated by the out-of-plane spin excitations of the ordered moments due to the suppression of damping in the superconducting state. Hence we offer an interpretation of the double energy scales differing from previous interpretations based on anisotropic superconducting energy gaps and systematically explain the doping-dependent trend across the phase diagram.
| Original language | English |
|---|---|
| Article number | 205149 |
| Journal | Physical Review B |
| Volume | 93 |
| Issue number | 20 |
| DOIs | |
| State | Published - May 26 2016 |
Funding
This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the US Department of Energy under Contract No. DE-AC02-05-CH11231 with the Quantum Materials Program (KC2202) and the Office of Basic Energy Sciences U.S. DOE Grant No. DE-AC03-76SF008.