Neutron scattering studies of spin ices and spin liquids

Abstract

Abstract. In frustrated magnets, competition between interactions, usually due to incompatible lattice and exchange geometries, produces an extensively degenerate manifold of groundstates. Exploration of these states results in a highly correlated and strongly fluctuating cooperative paramagnet, a broad classification which includes phases such as spin liquids and spin ices. Generally, there is no long range order and associated broken symmetry, so quantities typically measured by neutron scattering such as magnetic Bragg peaks and magnon dispersions are absent. Instead, spin correlations characterized by emergent gauge structure and exotic fractional quasiparticles may emerge. Neutron scattering is still an excellent tool for the investigation these phenomena, and this review outlines examples of frustrated magnets on the pyrochlore and kagome lattices with reference to experiments and quantities of interest for neutron scattering. PREAMBLEIn physics, a frustrated system is one in which all interactions cannot be simultaneously minimized, which is also to say that there is competition amongst the interactions. Frustration is most commonly associated with spin systems [1], where its consequences can be particularly well identified, but is by no means limited to magnetism. Frustrated interactions are also relevant in certain structural problems [2][3][4][5][6] Interest in frustrated spin systems stems from the idea that conventional order will be suppressed by the frustration, and an unconventional state will appear in its place. For example, Anderson proposed that in high temperature superconductors, antiferromagnetic Néel ordering would be replaced by a resonating valence bond state (RVB) [17], which would host the superconductivity on doping. If the RVB state could be promoted by enhancing frustration, a route to high(er)-T c materials might appear. This has never been realized, and understanding the character of the "unconventional" states, particularly the quantum spin liquid, which emerge in frustrated magnets is usually the objective of current studies.Extensive reviews of topics in frustrated magnetism can be found in the books edited by Lacroix, Mendels and Mila [1], and by Diep [18]. Topics recently reviewed in the literature include quantum spin liquids [19,20]; various aspects of spin ice [21][22][23]; rare earth pyrochlores [24], spinels [25]; and spin ices and kagome spin liquids have their own chapters in Ref. [1]. In the following, I present a brief This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Quantum spin liquid at finite temperature: Proximate dynamics and persistent typicality

“…Well-known examples are the low-lying singlets seen in the kagome antiferromagnet [111,112] and their interpretation in terms of nearest-neighbour valence bond states, [5,[113][114][115][116] or the two-in/two-out states in pyrochlore spin ice. [117][118][119][120] Finally, adapting a less methodological viewpoint, it is perhaps also interesting to try to extend the phenomena observed here beyond highly frustrated magnets, by viewing these phenomena more generally from the perspective of confinement of fractional quasiparticles. For instance, this could be a useful analogy for the confinement of spinons in quasi-1D spin chain materials, like SrCo 2 V 2 O 8 , [63] at very low T .…”

Competing magnetic orders and spin liquids in two- and three-dimensional kagome systems: Pseudofermion functional renormalization group perspective

“…14 X-points, respectively), commonly associated with Coulomb phase physics [83]. Such Coulomb phases arise for frustrated magnets which have local constraints that can be mapped to a divergence-free "flux" [83] -such as pyrochlore antiferromagnets [84,85], spin-ice systems [86][87][88], dimer models [89][90][91] or classical Kitaev models [92,93] -and reflect the characteristic power-law decay (1/r d in d spatial dimensions) of the real-space correlations. Here, we do not observe sharp bow-tie features, in accordance with the exponential decay of real-space correlations, which leaves room for multiple interpretations.…”

Structural and magnetic properties of the quantum magnet BaCuTe2O6

“…Famous examples are the kagome [two-dimensional (2D) network of corner-sharing triangles] and pyrochlore [three-dimensional (3D) network of corner-sharing tetrahedra] lattices [11,12]. In the case of extreme magnetic frustration a quantum spin liquid state may be realized where there is total suppression of static magnetism and the spins are moving coherently even at zero temperature [12][13][14].…”