We present a systematic investigation of the electrical, structural, and antiferromagnetic properties for the series of Ba(Fe1-x-yCoxRhy)2As2 compounds with fixed x≈0.027 and 0≤y≤0.035. We compare our results for the Co-Rh doped Ba(Fe1-x-yCoxRhy)2As2 compounds with the Co doped Ba(Fe1-xCox)2As2 compounds. We demonstrate that the electrical, structural, antiferromagnetic, and superconducting properties of the Co-Rh doped compounds are similar to the properties of the Co doped compounds. We find that the overall behaviors of Ba(Fe1-x-yCoxRhy)2As2 and Ba(Fe1-xCox)2As2 compounds are very similar when the total number of extra electrons per Fe/TM (TM=transition metal) site is considered, which is consistent with the rigid band model. Despite the similarity, we find that the details of the transitions, for example, the temperature difference between the structural and antiferromagnetic transition temperatures and the incommensurability of the antiferromangetic peaks, are different between Ba(Fe1-x-yCoxRhy)2As2 and Ba(Fe1-xCox)2As2 compounds.

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.

We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba(Fe0.957Cu0.043)2As2, a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe2As2 and superconducting Ba(Fe1-xNix)2As2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba(Fe0.957Cu0.043)2As2, which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouples the interaction between quasiparticles and the spin fluctuations. We also show that the spin-spin correlation length ξ(T) increases rapidly as the temperature is lowered and find ω/T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.

We have developed a near-infrared spectrometer designed to measure the absolute intensity of the solar 854.2 nm Ca II Fraunhofer line, scattered by interplanetary dust, in the zodiacal light (ZL) spectrum. Based on the known equivalent line width in the solar spectrum, this measurement can derive the zodiacal brightness, testing models of the ZL based on morphology that are used to determine the extragalactic background light in absolute photometry measurements. The spectrometer is based on a simple high-resolution tipped filter placed in front of a compact camera with wide-field refractive optics to provide the large optical throughput and high sensitivity required for rocket-borne observations. We discuss the instrument requirements for an accurate measurement of the absolute ZL brightness, the measured laboratory characterization, and the instrument performance in flight. © 2013. The American Astronomical Society. All rights reserved.

Absolute spectrophotometric measurements of diffuse radiation at 1 μm to 2 μm are crucial to our understanding of the radiative content of the universe from nucleosynthesis since the epoch of reionization, the composition and structure of the zodiacal dust cloud in our solar system, and the diffuse galactic light arising from starlight scattered by interstellar dust. The Low Resolution Spectrometer (LRS) on the rocket-borne Cosmic Infrared Background Experiment is a λ/Δλ ∼ 15-30 absolute spectrophotometer designed to make precision measurements of the absolute near-infrared sky brightness between 0.75 μm <λ < 2.1 μm. This paper presents the optical, mechanical, and electronic design of the LRS, as well as the ground testing, characterization, and calibration measurements undertaken before flight to verify its performance. The LRS is shown to work to specifications, achieving the necessary optical and sensitivity performance. We describe our understanding and control of sources of systematic error for absolute photometry of the near-infrared extragalactic background light. © 2013. The American Astronomical Society. All rights reserved.