Quantum spin fluctuations in the spin-liquid state of Tb₂Ti₂O₇

Low-temperature behaviors of the dipolar magnet Dy3Sb3Zn2O14with a strongly site-mixing disordered kagome lattice

Interesting behaviors may emerge in the magnetic frustrated materials with significant site-mixing disorder. We present the results of the structural, magnetic susceptibility, and specific heat measurements of Dy3Sb3Zn2O14with ∼20%Dy/Zn site-mixing disorder, which results in either a diluted 2D triangular lattice, or an intermediate structure between the kagome and pyrochlore lattice. In addition to the sharp anomaly of the temperature dependence of specific heat atT∼0.35 K, which was attributed to the emergent charge order state for the sample with less disorder, a broad peak atT∼1.5 K, and a small hump belowT∼0.1 K are observed. The measured temperature dependence of specific heat and the Monte Carlo simulation suggest that the magnetic frustration persists despite of a strong site-mixing disorder.

Chemistry of Quantum Spin Liquids

Quantum spin liquids are an exciting playground for exotic physical phenomena and emergent many-body quantum states. The realization and discovery of quantum spin liquid candidate materials and associated phenomena lie at the intersection of solid-state chemistry, condensed matter physics, and materials science and engineering. In this review, we provide the current status of the crystal chemistry, synthetic techniques, physical properties, and research methods in the field of quantum spin liquids. We highlight a number of specific quantum spin liquid candidate materials and their structure-property relationships, elucidating their fascinating behavior and connecting it to the intricacies of their structures. Furthermore, we share our thoughts on defects and their inevitable presence in materials, of which quantum spin liquids are no exception, which can complicate the interpretation of characterization of these materials, and urge the community to extend their attention to materials preparation and data analysis, cognizant of the impact of defects. This review was written with the intention of providing guidance on improving the materials design and growth of quantum spin liquids, and to paint a picture of the beauty of the underlying chemistry of this exciting class of materials.

Sensitivity of magnetic properties to chemical pressure in lanthanide garnets Ln 3 A 2 X 3O12, Ln = Gd, Tb, Dy, Ho, A = Ga, Sc, In, Te, X = Ga, Al, Li

A systematic study of the structural and magnetic properties of three-dimensionally frustrated lanthanide garnets Ln ₃ A ₂ X ₃O₁₂, Ln  =  Gd, Tb, Dy, Ho, A  =  Ga, Sc, In, Te, X  =  Ga, Al, Li is presented. Garnets with Ln  =  Gd show magnetic behaviour consistent with isotropic Gd³⁺ spins; no magnetic ordering is observed for T  ⩾  0.4 K. Magnetic ordering features are seen for garnets with Ln  =  Tb, Dy, Ho in the temperature range 0.4  <  T  <  2.5 K, however the nature of the magnetic ordering varies for the different Ln as well as for different combinations of A and X. The magnetic behaviour can be explained by tuning of the magnetic interactions and changes in the single-ion anisotropy. The change in magnetic entropy is evaluated from isothermal magnetisation measurements to characterise the magnetocaloric effect in these materials. Among the Gd garnets, the maximum change in magnetic entropy per mole (15.45 J K^-1 [Formula: see text]) is observed for Gd₃Sc₂Ga₃O₁₂ at 2 K, in a field of 9 T. The performance of Dy₃Ga₅O₁₂ as a magnetocaloric material surpasses the other garnets with Ln  =  Tb, Dy, Ho.

Quantum spin liquids: a review

Quantum spin liquids may be considered 'quantum disordered' ground states of spin systems, in which zero-point fluctuations are so strong that they prevent conventional magnetic long-range order. More interestingly, quantum spin liquids are prototypical examples of ground states with massive many-body entanglement, which is of a degree sufficient to render these states distinct phases of matter. Their highly entangled nature imbues quantum spin liquids with unique physical aspects, such as non-local excitations, topological properties, and more. In this review, we discuss the nature of such phases and their properties based on paradigmatic models and general arguments, and introduce theoretical technology such as gauge theory and partons, which are conveniently used in the study of quantum spin liquids. An overview is given of the different types of quantum spin liquids and the models and theories used to describe them. We also provide a guide to the current status of experiments in relation to study quantum spin liquids, and to the diverse probes used therein.

Order by disorder spin wave gap in the XY pyrochlore magnet Er2Ti2O7

The recent determination of a robust spin Hamiltonian for the antiferromagnetic XY pyrochlore Er2Ti2O7 reveals a most convincing case of the "Order-by-Quantum-Disorder" mechanism for ground state selection. This mechanism relies on quantum fluctuations to remove an accidental symmetry of the magnetic ground state, and selects a particular ordered spin structure below TN=1.2 K. The removal of the continuous degeneracy results in an energy gap in the spectrum of spin wave excitations, long wavelength pseudo-Goldstone modes. We have measured the Order-by-Quantum-Disorder spin wave gap at a zone center in Er2Ti2O7, using low incident energy neutrons and the time-of-flight inelastic scattering method. We report a gap of Δ=0.053±0.006  meV, which is consistent with upper bounds placed on it from heat capacity measurements and roughly consistent with the theoretical estimate of ∼0.02  meV, further validating the spin Hamiltonian that led to that prediction. The gap is observed to vary with the square of the order parameter, and goes to zero for T∼TN.

Anisotropic propagating excitations and quadrupolar effects in Tb2Ti2O7

The dynamical magnetic correlations in Tb2Ti2O7 have been investigated using polarized inelastic neutron scattering. Dispersive excitations are observed, emerging from pinch points in reciprocal space and characterized by an anisotropic spectral weight. Anomalies in the crystal field and phonon excitation spectrum at Brillouin zone centers are also reported. These findings suggest that Coulomb phases, although they present a disordered ground state with dipolar correlations, allow the propagation of collective excitations. They also point out a strong spin-lattice coupling, which likely drives effective interactions between the 4f quadrupolar moments.

Low-temperature low-field phases of the pyrochlore quantum magnet Tb2Ti2O7

By means of ac magnetic-susceptibility measurements, we find evidence for a new magnetic phase of Tb2Ti2O7 below about 140 mK in zero magnetic field. In magnetic fields parallel to [111], this phase is characterized by frequency- and amplitude-dependent susceptibility and extremely slow spin dynamics. In the zero-temperature limit, it extends to about 67 mT (the internal field H(int)≃52  mT), at which it makes transition to another phase. The field dependence of the susceptibility of this second phase, which extends to about 0.60 T (H(int)≃0.54  T) in the zero-temperature limit, indicates the presence of a weak magnetization plateau below about 50 mK, as has been predicted by a single-tetrahedron four-spin model, suggesting that the second phase is a quantum kagome ice.

Power-law spin correlations in the pyrochlore antiferromagnet Tb(2)Ti(2)O(7)

We investigate the low-temperature state of the rare-earth pyrochlore Tb(2)Ti(2)O(7) using polarized neutron scattering. Tb(2)Ti(2)O(7) is often described as an antiferromagnetic spin liquid with spin correlations extending over lengths comparable to individual tetrahedra of the pyrochlore lattice. We confirm this picture at 20 K but find that at 0.05 K the data contain evidence of pinch-point scattering, suggesting that the low temperature state of Tb(2)Ti(2)O(7) has power-law spin correlations.