Single to Multiquasiparticle Excitations in the Itinerant Helical MagnetCeRhIn5

Abstract

CeRhIn5 is an itinerant magnet where the Ce 3+ spins order in a simple helical phase. We investigate the spin excitations and observe sharp spin-waves parameterized by a nearest neighbor exchange JRKKY =0.88 ± 0.05 meV. At higher energies, the spin fluctuations are heavily damped where single quasiparticle excitations are replaced by a momentum and energy broadened continuum constrained by kinematics of energy and momentum conservation. The delicate energy balance between localized and itinerant characters results in the breakdown of the single quasiparticle picture in CeRhIn5.The noninteracting quasiparticle description of excitations is fundamental to condensed matter physics and the understanding of low energy fluctuations. However, interacting quasiparticle states have recently been recognized as important for the understanding of anomalous phases. For example, composite states including resonating valence bond states [1], Zhang-Rice singlets [2] or spinon-holons in the pseudogap, [3] have been suggested to be fundamental to superconductivity, frustrated magnetism, and even quantum criticality. [4][5][6] We use neutron scattering to measure the breakdown of the single quasiparticle description of the spin excitations in a helical itinerant heavy fermion magnet.CeRhIn 5 is a heavy fermion metal, part of the CeT In 5 (T =Rh, Ir, and Co) series displaying an interplay between localized antiferromagnetism and superconductivity. [7][8][9][10] The presence of two-dimensional layers of Ce 3+ ions connects the physics of these systems with other unconventional superconductors as in the cuprates [11][12][13][14][15] CeRhIn 5 is isostructural with CeCoIn 5 , which is superconducting at ambient pressures with a T c =2.3 K. [14] The order parameter of the superconducting phase has a d-wave symmetry with nodes in the ab plane. [27,28] Magnetism and superconductivity are strongly coupled as evidenced by neutron scattering measurements reporting a doublet spin-resonance peak connected with superconductivity and indicating an order parameter that changes sign, consistent with d-wave symmetry. conductivity and the localized magnetism. [32,33] Neutron measurements were performed at NIST (Gaithersburg, USA) using MACS [34] and at the ILL (Grenoble, France) using the IN12 spectrometer and the D23 and D3 diffractometers. The HHL aligned sample was prepared using self-flux method. [14] To correct for the large neutron absorption, [35,36] a finite element analysis has been done. Further details are provided in the supplementary information.arXiv:1511.09003v1 [cond-mat.str-el]

Low temperature magnetic structure of CeRhIn5by neutron diffraction on absorption-optimized samples

“…[22]. This narrows the range of previously reported moments to 0.34-0.8 + [19][20][21][22][23] (cf. table 1).…”

Robust upward dispersion of the neutron spin resonance in the heavy fermion superconductor Ce1−xYbxCoIn5

“…( i ) Calculated intensity for the spin-exciton along the [ H , H ] direction. ( j ) Comparison of dispersions of the resonance in Ce 0.95 Yb 0.05 CoIn 5 (solid cyan line) and spin waves in CeRhIn 5 (dashed purple and orange lines) 38 39 . ( k ) Calculated intensity of the resonance along the [0.5, K ] direction assuming it is a magnon-like excitation.…”

“…We thus conclude that the upward-dispersing resonance mode in Ce 0.95 Yb 0.05 CoIn 5 cannot be interpreted as a spin-exciton arising from the feedback of unconventional d -wave superconductivity 12 27 28 . On the other hand, the similarity of the resonance's dispersion along the [ H , H , 0.5] direction with the spin-wave dispersion in AF-ordered nonsuperconducting CeRhIn 5 along the same direction 38 39 ( Fig. 1j ) suggests that the upward-dispersing resonance may be magnon-like.…”

“…If the resonance in CeCoIn 5 is a spin-exciton, it should be dramatically affected by the Yb-doping-induced changes in Fermi surface topology and superconducting gap. On the other hand, if the resonance is a magnon-like excitation, it should be much less sensitive to Yb-doping across x =0.2 and display a upward dispersion similar to spin waves in antiferromagnetically ordered nonsuperconducting CeRhIn 5 characteristic of a robust effective nearest-neighbour exchange coupling, regardless of its itinerant electron or local moment origin 7 38 39 .…”

Imitation of spin density wave order in Cu3Nb2O8

“…This allows a much greater level of accuracy and affords the ability to distinguish between structures which would appear similar in an unpolarized study [26][27][28]. This was shown in the case of FeAs [29] (and also using polarized x-ray scattering) [30] and CeRhIn 5 [31,32] where the structures were found to be the spin density wave and helical arrangement, respectively. Furthermore, it is also for this reason that SNP can determine complex magnetic structures as shown in the cases of CaBa(Co 3 Fe)O 7 [33] and Mn 2 GeO 4 [34].…”