Some experimental schemes to identify quantum spin liquids

Despite the apparent ubiquity and variety of quantum spin liquids in theory,experimental confirmation of spin liquids remains to be a huge challenge.Motivated by the recent surge of evidences for spin liquids in a series of candidate materials,we highlight the experimental schemes,involving the thermal Hall transport and spectrum measurements,that can result in smoking-gun signatures of spin liquids beyond the usual ones.For clarity,we investigate the square lattice spin liquids and theoretically predict the possible phenomena that may emerge in the corresponding spin liquids candidates.The mechanisms for these signatures can be traced back to either the intrinsic characters of spin liquids or the external field-driven behaviors.Our conclusion does not depend on the geometry of lattices and can broadly apply to other relevant spin liquids.

Field distribution of the Z_(2)topological edge state revealed by cathodoluminescence nanoscopy

Photonic topological insulators with robust boundary states can enable great applications for optical communication and quantum emission,such as unidirectional waveguide and single-mode laser.However,because of the diffraction limit of light,the physical insight of topological resonance remains unexplored in detail,like the dark line that exists with the crys-talline symmetry-protected topological edge state.Here,we experimentally observe the dark line of the Z_(2)photonic topo-logical insulator in the visible range by photoluminescence and specify its location by cathodoluminescence characteriza-tion,and elucidate its mechanism with the p-d orbital electromagnetic field distribution which calculated by numerical sim-ulation.Our investigation provides a deeper understanding of Z_(2)topological edge states and may have great signific-ance to the design of future on-chip topological devices.

Quantum superposition demonstrated higher-order topological bound states in the continuum

Higher-order topological insulators,as newly found non-trivial materials and structures,possess topological phases beyond the conventional bulk-boundary correspondence.In previous studies,in-gap boundary states such as the corner states were regarded as conclusive evidence for the emergence of higher-order topological insulators.Here,we present an experimental observation of a photonic higher-order topological insulator with corner states embedded into the bulk spectrum,denoted as the higher-order topological bound states in the continuum.Especially,we propose and experimentally demonstrate a new way to identify topological corner states by exciting them separately from the bulk states with photonic quantum superposition states.Our results extend the topological bound states in the continuum into higher-order cases,providing an unprecedented mechanism to achieve robust and localized states in a bulk spectrum.More importantly,our experiments exhibit the advantage of using the time evolution of quantum superposition states to identify topological corner modes,which may shed light on future exploration between quantum dynamics and higher-order topological photonics.

三角格子伊辛磁体中量子效应的外场调控

文章结合中子散射和热力学测量研究了三角格子量子伊辛磁体TmMgGaO_(4)的磁关联行为在外加纵向磁场下的演变.实验发现,在中等强度的磁场下系统出现了一个量子涨落诱导的准平台相.该相的磁有序和自旋能隙表现出非单调的磁场和温度依赖关系,随着磁场的增大先变大后变小.在更高的外磁场下,量子涨落被大部分抑制后系统进入了一个无序相,自旋激发强度同时变弱.结合细致的半经典计算,该研究可以定量地理解量子涨落和阻挫伊辛相互作用之间的竞争作用所导致的上述新奇物理现象.

Generic spiral spin liquids

Spiral spin liquids are unique classical spin liquids that occur in many frustrated spin systems,but do not comprise a new phase of matter.Owing to extensive classical ground-state degeneracy,the spins in a spiral spin liquid thermally fluctuate cooperatively from a collection of spiral configurations at low temperatures.These spiral propagation wavevectors form a continuous manifold in reciprocal space,i.e.,a spiral contour or a spiral surface,that strongly governs the low-temperature thermal fluctuations and magnetic physics.In this paper,the relevant spin models conveying the spiral spin liquid physics are systematically explored and the geometric origin of the spiral manifold is clarified in the model construction.The spiral spin liquids based on the dimension and the codimension of the spiral manifold are further clarified.For each class,the physical properties are studied both generally and for specific examples.The results are relevant to a wide range of frustrated magnets.A survey of materials is given and future experiments are suggested.

Spin-1 pyrochlore antiferromagnets:Theory,model,and materials'survey

Pyrochlore magnets can be a unique platformn to demonstrate numerous important concepts and appli-cations of frustrated magnetic physics in modern condensed matter physics.Most works on pyrochlore magnets deal with the interacting spin-1/2 local moments,while much less works have studied the spin-1 systems.We here review the physics with interacting spin-1 local moments on the pyrochlore lattice to ilustrate the potentially interesting physics associated with spin-1 magnets.The generic pyrochlore spin-1 model includes the antiferromagnetic Heisenberg interaction,the Dzyaloshinski-Moriya interaction and the single ion spin anisotropy.The global phase diagram of this generic spin model is reviewed,and the relation between different quantum phases in the phase diagram is clari-fied.The critical properties of the transition from the parent quantum paramagnet to the proximate orders are discussed.The presence of quantum order by disorder in the parts of the ordered phases is analyzed.The elementary excitations with respect to the ground states are further reviewed,and the topological natures of these excitations are carefully addressed.The materials'relevance of the spin-1 pyrochlore magnets are finally reviewed.This review may provide insights about the interesting spin-1 local moments on frustrated systems.