Abstract
Magnetic excitations and magnetic structure of EuRbFe4As4 were investigated by inelastic neutron scattering (INS), neutron diffraction, and random phase approximation (RPA) calculations. Below the superconducting transition temperature Tc=36.5 K, the INS spectra exhibit the neutron spin resonances at Qres=1.27(2) and 1.79(3)Å-1. They correspond to the Q=(0.5,0.5,1) and (0.5,0.5,3) nesting wave vectors, showing three-dimensional nature of the band structure. The characteristic energy of the neutron spin resonance is Eres=17.7(3) meV corresponding to 5.7(1)kBTc. Observation of the neutron spin resonance mode and our RPA calculations in conjunction with the recent optical conductivity measurements are indicative of the s± superconducting pairing symmetry in EuRbFe4As4. In addition to the neutron spin resonance mode, upon decreasing temperature below the magnetic transition temperature TN=15 K, the spin wave excitation originating in the long-range magnetic order of the Eu sublattice was observed in the low-energy inelastic channel. Single-crystal neutron diffraction measurements demonstrate that the magnetic propagation vector of the Eu sublattice is k=(0,0,0.25), representing the three-dimensional antiferromagnetic order. Linear spin wave calculations assuming the obtained magnetic structure with the intra- and interplane nearest neighbor exchange couplings of J1/kB=-1.31 K and Jc/kB=0.08 K can reproduce quantitatively the observed spin wave excitation. Our results show that superconductivity and long-range magnetic order of Eu coexist in EuRbFe4As4, whereas the coupling between them is rather weak.
| Original language | English |
|---|---|
| Article number | 014506 |
| Journal | Physical Review B |
| Volume | 100 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jul 8 2019 |
Funding
We thank Ryoichi Kajimoto for helpful discussion. Magnetic susceptibility measurements were performed at the CROSS user laboratories. This research at SNS was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Travel expenses for the ARCS experiment were provided by the General User Program for Neutron Scattering Experiments, Institute for Solid State Physics, The University of Tokyo (GPTAS:16913), at JRR-3, Japan Atomic Energy Agency (JAEA), Tokai, Japan. The experiments at 4SEASONS and SENJU in J-PARC were conducted under the user program with the Proposals No. 2017A0005 and No. 2018B0008, respectively. The calculations were performed by the supercomputing systems SGI ICE X at JAEA. The present work was partially supported by JSPS KAKENHI Grants No. JP15K17712, No. JP17K14349, and No. JP18K03552, and the Cooperative Research Program of \u201CNetwork Joint Research Center for Materials and Devices\u201D (20181072). A.D.C. was partiality supported by the U.S. DOE, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. D.K. and M.E. were supported by the Austrian Science Fund (FWF) I2814-N36.