Half-metallic magnetization plateaux

Hao, Zhihao; Starykh, Oleg A.

doi:10.1103/physrevb.87.161109

Cited by 7 publications

(7 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Remarkably, the measured dynamic structure factor shows hardly any momentum dependence along several high-symmetry directions. By contrast, all mean-field models with spinons [6][7][8][9][10][11], whether gapless or gapped, give rise to sharp dispersing features in the dynamic structure factor [12,13] which have not been observed. In particular, theory predicts a vanishing structure factor below the onset of the two spinon continuum, which is at a finite energy even for gapless spin liquids, apart from the small set of crystal momenta where the spinon gap closes.…”

Section: Introductionmentioning

confidence: 99%

Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice

2014

View full text Add to dashboard Cite

Recent neutron scattering experiments on the spin-1/2 kagome lattice antiferromagnet ZnCu 3 (OH) 6 Cl 2 (Herbertsmithite) provide the first evidence of fractionalized excitations in a quantum spin liquid state in two spatial dimensions 1 . In contrast to existing theoretical models of both gapped and gapless spin liquids 2-8 , which give rise to sharp dispersing features in the dynamic structure factor 9,10 , the measured dynamic structure factor reveals an excitation continuum that is remarkably flat as a function of frequency. Here we show that many experimentally observed features can be explained by the presence of topological vison excitations in a Z 2 spin liquid 11 . These visons form flat bands on the kagome lattice, and thus act as a momentum sink for spin-carrying excitations that are probed by neutron scattering. We compute the dynamic structure factor for two di erent Z 2 spin liquids 2 and find that our results for one of them are in qualitative agreement with the neutron scattering experiments above a very low energy cuto , below which the structure factor is probably dominated by impurities.Herbertsmithite, a layered spin-1/2 kagome lattice antiferromagnet 12 , is one of the strongest contenders for an experimental realization of a spin liquid state 13 . Indeed, no sign of magnetic ordering is observed down to temperatures around 50 mK, whereas the natural energy scale set by the magnetic exchange coupling J ∼ 200 K is four orders of magnitude larger 14 . Neutron scattering experiments 1 on single crystals of this material are consistent with a continuum of fractionalized spinon excitations as expected in a quantum spin liquid state. However, mean-field theories predict a vanishing structure factor below the onset of the two-spinon continuum, which is at a finite energy even for gapless spin liquids, apart from the small set of crystal momenta where the spinon gap closes. This is in stark contrast to experiments, where the measured structure factor is finite and almost constant as a function of frequency down to energies of the order of ∼ J /10 (ref. 1).Here we propose an explanation for the lack of a momentumdependent spinon continuum threshold via the interaction of spinons with another set of excitations which form a (nearly) flat band. Such localized excitations act as a momentum sink for the spinons, thereby flattening the dynamic structure factor. So far, the only theoretical model for a spin liquid state on the kagome lattice which naturally gives rise to a flat excitation band at low energies consists of the Z 2 spin liquids 2-4 . Besides spinons, these states exhibit gapped vortex excitations 15,16 of an emergent Z 2 gauge field 17,18 , socalled visons 11 , which indeed have a lowest energy band that is nearly flat 19,20 . Because the visons carry neither charge nor spin, they do not couple directly to neutrons. They interact with spinons, however, and we show that this coupling is responsible for flattening the dynamic structure factor and removing the sharp onset at the twospinon contin...

show abstract

Section: Introductionmentioning

confidence: 99%

Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice

2014

View full text Add to dashboard Cite

show abstract

“…A different point of view on the magnetization plateau was presented recently in [131]. The authors asked if the plateau is possible in an itinerant system of weakly-interacting electrons.…”

Section: Magnetization Plateaus In Itinerant Electron Systemsmentioning

confidence: 99%

Unusual ordered phases of highly frustrated magnets: a review

2015

View full text Add to dashboard Cite

We review ground states and excitations of a quantum antiferromagnet on triangular and other frustrated lattices. We pay special attention to the combined effects of magnetic field h, spatial anisotropy R, and spin magnitude S. The focus of the review is on the novel collinear spin density wave and spin nematic states, which are characterized by fully gapped transverse spin excitations with S z = ±1. We discuss extensively R − h phase diagram of the antiferromagnet, both in the large-S semiclassical limit and the quantum S = 1/2 limit. When possible, we point out connections with experimental findings.[This is the originally submitted version of the invited review, to be published in Reports on Progress in Physics in 2015. The link, via DOI, to the accepted and published version of the manuscript, which is updated according to the referees comments, will be provided upon its actual publication.]

show abstract

“…Unfortunately, our convergence breaks down around this temperature. Thus, more theoretical studies, perhaps based on Z 2 quantum spin-liquids [19,35], are needed to see if such a behavior is real or an artifact of these computational methods. We note that such a peak is not seen in the experimental data.…”

Section: Discussionmentioning

confidence: 99%

Nuclear relaxation rates in the herbertsmithite kagome antiferromagnets ZnCu3(OH)6Cl2

2016

View full text Add to dashboard Cite

Local spectral functions and Nuclear Magnetic Relaxation (NMR) rates, 1/T1, for the spin-half Heisenberg antiferromagnet on the Kagome Lattice are calculated using Moriyas Gaussian approximation, as well as through an extrapolation of multiple frequency moments. The temperature dependence of the calculated rates is compared with the oxygen 1/T1 NMR data in Herbertsmithite. We find that the Gaussian approximation for 1/T1 shows behavior qualitatively similar to experiments with a sharp drop in rates at low temperatures, consistent with a spin-gapped behavior. However, this approximation significantly underestimates the magnitude of 1/T1 even at room temperature. Rates obtained from extrapolation of multiple frequency moments give very good agreement with the room temperature NMR data with J = 195 ± 20K and hyperfine couplings determined independently from other measurements. The use of multiple frequency moments also leads to additional low frequency weight in the local structure factors. The convergence of our calculations with higher frequency moments breaks down at low temperatures suggesting the existence of longer range dynamic correlations in the system despite the very short-range static correlations.

show abstract

Half-metallic magnetization plateaux

Cited by 7 publications

References 38 publications

Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice

Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice

Unusual ordered phases of highly frustrated magnets: a review

Nuclear relaxation rates in the herbertsmithite kagome antiferromagnets ZnCu3(OH)6Cl2

Contact Info

Product

Resources

About