Spin excitations in hole-overdoped iron-based superconductors

Abstract

Understanding the overall features of magnetic excitation is essential for clarifying the mechanism of Cooper pair formation in iron-based superconductors. In particular, clarifying the relationship between magnetism and superconductivity is a central challenge because magnetism may play a key role in their exotic superconductivity. BaFe2As2 is one of ideal systems for such investigation because its superconductivity can be induced in several ways, allowing a comparative examination. Here we report a study on the spin fluctuations of the hole-overdoped iron-based superconductors Ba1-xKxFe2As2 (x = 0.5 and 1.0; Tc = 36 K and 3.4 K, respectively) over the entire Brillouin zone using inelastic neutron scattering. We find that their spin spectra consist of spin wave and chimney-like dispersions. The chimney-like dispersion can be attributed to the itinerant character of magnetism. The band width of the spin wave-like dispersion is almost constant from the non-doped to optimum-doped region, which is followed by a large reduction in the overdoped region. This suggests that the superconductivity is suppressed by the reduction of magnetic exchange couplings, indicating a strong relationship between magnetism and superconductivity in iron-based superconductors.

Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex II: Neutron Scattering Instruments

“…A study of the magnetic structure of the honeycomb antiferromagnet Co 4 Nb 2 O 9 using the single-crystal diffractometer SENJU revealed that the magnetic structure is different from that proposed previously, but it better explains the magnetic properties as well as the magnetoelectric response of this compound [153]. In the following, we show in greater detail a recent inelastic scattering study on magnetic fluctuations in iron-based superconductors performed using the 4SEASONS spectrometer [48].…”

“…These features of the instrument were originally designed for studies of high-critical-temperature (high-T c ) oxide superconductors. Indeed, copper and iron-based superconductors are still major research targets at 4SEASONS [44][45][46][47][48][49]. Including these materials, strongly correlated electron systems and magnetism dominate 80% of the experimental proposals.…”

“…Recently, Horigane et al performed an inelastic neutron scattering study on the spin fluctuations in hole-overdoped Ba 1−x K x Fe 2 As 2 with x = 0.5 and x = 1.0 by using the 4SEASONS spectrometer [48]. They measured the inelastic scattering spectra of single crystals of x = 0.5 (superconducting transition temperature T c = 36 K) and x = 1.0 (T c = 3.4 K) at 6 K. Taking advantage of a large quantity of crystals (~5 g) and the high neutron flux at J-PARC, they successfully observed the magnetic excitations in these crystals over entire Brillouin zones.…”

“…Figure 32. Excitation spectra of Ba0.5K0.5Fe2As2 and KFe2As2 at 6 K observed using 4SEASONS [48]. in (b,c) show the boundaries of the magnetic zone.…”

Instrumental resolution of the chopper spectrometer 4SEASONS evaluated by Monte Carlo simulation

“…The [001] axis is parallel to the incident beam, and the [100] axis is on the horizontal plane and perpendicular to the incident beam. This configuration is similar to those often employed in measurements of 2D systems [10][11][12][13]. The incident energy (E i ) is 71 meV, and the rotating frequency of the Fermi chopper ( f ) is 250 Hz.…”