PC9-1-INV

Spin resonance and long-range magnetic order of Eu coexisted in EuRbFe4As4

Dec.3 15:45-16:15 (Tokyo Time)

*Kazuki Iida1

Comprehensive Research Organization for Science and Society (CROSS), Japan1

Eu-containing iron-based superconductors are outstanding materials because the system shows both superconductivity in the FeAs layers and local-moment long-range magnetic order in the Eu sublattice. EuRbFe4As4 [K. Kawashima et al., J. Phys. Soc. Jpn. 85, 064710 (2016).] is such a compound in the absence of chemical disorder. In EuRbFe4As4, the neutron spin resonance which gives the crucial information on the microscopic mechanism underlying the superconductivity as well as the magnetic structure and the spin Hamiltonian of the Eu sublattice have never been reported yet by means of the microscopic techniques. To investigate the neutron spin resonance and the magnetic structure, we performed inelastic neutron scattering (INS) and neutron diffraction measurements [K. Iida et al., Phys. Rev. B 100, 014506 (2019).].

Below the superconducting transition temperature Tc = 35 K, the INS spectra exhibit the neutron spin resonance at Qres = 1.27(2) and 1.79(3) Å-1, which correspond to the (0.5, 0.5, 1) and (0.5, 0.5, 3) nesting wave vectors [Fig. 1(a)]. The characteristic energy of the spin resonance is Eres = 17.7(3) meV corresponding to 5.7(1)kBTc. Observation of the spin resonance and our random phase approximation calculations suggest the superconducting order parameter in EuRbFe4As4 is the s+/- pairing symmetry. In addition to the neutron spin resonance, 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 [Fig. 1(b)]. Linear spin wave calculations can reproduce quantitatively the observed spin wave excitation. Single-crystal neutron diffraction measurements demonstrate that the magnetic propagation vector of the Eu sublattice is k = (0, 0, 0.25) [Fig. 1(c)], indicating the three-dimensional antiferromagnetic order. Our results show that superconductivity and long-range magnetic order coexist in EuRbFe4As4 whereas the coupling between them is rather weak.

In my talk, I will also review for recent results on EuRbFe4As4.

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