Superconductivity in layered copper oxide compounds emerges when charge carriers are added to antiferromagnetically ordered CuO(2) layers. The carriers destroy the antiferromagnetic order, but strong spin fluctuations persist throughout the superconducting phase and are intimately linked to superconductivity. Neutron scattering measurements of spin fluctuations in hole-doped copper oxides have revealed an unusual 'hour-glass' feature in the momentum-resolved magnetic spectrum that is present in a wide range of superconducting and non-superconducting materials. There is no widely accepted explanation for this feature. One possibility is that it derives from a pattern of alternating spin and charge stripes, and this idea is supported by measurements on stripe-ordered La(1.875)Ba(0.125)CuO(4) (ref. 15). Many copper oxides without stripe order, however, also exhibit an hour-glass spectrum. Here we report the observation of an hour-glass magnetic spectrum in a hole-doped antiferromagnet from outside the family of superconducting copper oxides. Our system has stripe correlations and is an insulator, which means that its magnetic dynamics can conclusively be ascribed to stripes. The results provide compelling evidence that the hour-glass spectrum in the copper oxide superconductors arises from fluctuating stripes.
We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba 3 ZnIr 2 O 9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba 3 ZnIr 2 O 9 with Ir 5þ (5d 4 ) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J ¼ 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir 2 O 9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK. DOI: 10.1103/PhysRevLett.116.097205 5d transition metal compounds often exhibit unusual electronic and magnetic properties due to the presence of strong spin-orbit coupling (SOC), comparable to their onsite Coulomb (U) and crystal field (Δ CFE ) interactions [1,2]. In the strong spin-orbit coupling regime, M J ( P m j ) becomes the only valid quantum number instead of m l (orbital) and m s (spin), and the multiplets and their degeneracies are solely determined by the total angular momentum J. The electronic and magnetic responses of a system in such limits are not yet well understood and have generated significant curiosity in recent times. For example, the curious insulating state of the layered tetravalent iridates (Ir 4þ ; 5d 5 ) has recently been explained within single particle theories assuming splitting of t 2g bands into a set of fully filled quartet bands separated from another set of half-filled narrow doublet bands due to finite SOC. The half-filled doublet bands further split into fully occupied lower and empty upper Hubbard bands in the presence of relatively small Hubbard U [3-5].The pentavalent Iridates (Ir 5þ ; 5d 4 ) are more intriguing, where in the strong SOC limit all the spin-orbit entangled electrons will be confined to singlet J ¼ 0 (M J ¼ 0) ground state, with no net moment. The evolution of ground and excited states of a low spin 5d t 4 2g Ir 5þ ion as a function of SOC parameter λ 0 is illustrated in Fig. 1(a) and a J ¼ 0 ground state is realized in the strong SOC limit [6]. A possibility of excitonic magnetism has been predicted for these systems where the energy scale of the singlet-triplet splitting determined by SOC is comparable to superexchange interaction promoted by hopping [10]. The breakdown of the J ¼ 0 nonmagnetic state in d 4 systems can also be realized within a single electron picture primarily driven by band-structure effect that allows the hybridization between the quartet and the doublet redistributed orbitals (eigenstates of the spin-orbit coupled Hamiltonian). Overall, d 4 Ir compounds in the strong SOC limit may host weak magnetic moment unless the λ 0 becomes so large that any excitonic or hopping-assisted magnetism become...
We have observed a diffuse component to the low-energy magnetic excitation spectrum of stripeordered La 5/3 Sr 1/3 NiO4 probed by neutron inelastic scattering. The diffuse scattering forms a square pattern with sides parallel and perpendicular to the stripe directions. The signal is dispersive, with a maximum energy of ∼ 10 meV. Probed at 2 meV the scattering decreases in strength with increasing temperature, and is barely visible at 100 K. We argue that the signal originates from dynamic, quasione-dimensional, antiferromagnetic correlations among the stripe electrons.PACS numbers: 75.40. Gb, 71.45.Lr, 75.30.Et, 75.30.Fv The occurence of stripe correlations in superconducting cuprates and other doped antiferromagnets is well established from extensive experimental studies [1] following earlier theoretical work [2]. The stripe phase is characterized by a segregation of charge carriers into narrow channels that act as antiphase domain walls separating antiferromagnetic regions of the host spins. Several theoretical scenarios have been presented in which a spin gap and pairing instabilities appear among the stripe electrons, opening the door to superconductivity [3]. These findings suggest that stripes could play an important role in the physics of high-T c superconductivity.Given the characteristic spin and charge correlations associated with local stripe order it is natural to search the spin excitation spectrum for clues to the relationship between stripes and superconductivity. Neutron inelastic scattering has revealed a number of interesting features in the spin dynamics of the cuprate superconductors, some of which, e.g. excitations at incommensurate wavevectors [4], have been interpreted as evidence for dynamic stripe correlations [5]. At the same time, the characteristic spin excitation spectrum of ideal stripes has been probed in studies of non-superconducting compounds with well defined stripe order, especially La 2−x Sr x NiO 4+δ [6,7]. In none of these previous studies, however, has any evidence been found for spin correlations among the stripe electrons themselves.In this paper we report neutron inelastic scattering measurements on La 5/3 Sr 1/3 NiO 4 which reveal a pattern of inelastic diffuse scattering consistent with the existence of quasi-one-dimensional (1D) antiferromagnetic (AF) correlations parallel to the stripe direction. The correlations are found to be dynamic, with a maximum energy ∼ 10 meV. The results provide the first evidence for spin correlations among the charge carriers in a stripe phase.The experiments were performed on single crystals of La 5/3 Sr 1/3 NiO 4 grown by the floating-zone method [8]. Neutron inelastic scattering data were collected on the triple-axis spectrometers IN8, IN20 and IN22 at the Institut Laue-Langevin, and RITA-II at the Paul Scherrer Institut. Most of the data reported here were obtained with a fixed scattered neutron energy E f = 14.7 meV and with a graphite filter installed after the sample to suppress higher orders. The exception is the inelastic sca...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.