A search for neutrinoless double-β decay (0νββ) in 136 Xe is performed with the full EXO-200 dataset using a deep neural network to discriminate between 0νββ and background events. Relative to previous Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP 3 .

Neutron scattering measurements on the pyrochlore magnet Ce2Zr2O7 reveal an unusual crystal field splitting of its lowest J = 5/2 multiplet, such that its ground state doublet is composed of mJ = ± 3/2, giving these doublets a dipole -octupole (DO) character with local Ising anisotropy. Its magnetic susceptibility shows weak antiferromagnetic correlations with θCW = -0.4(2) K, leading to a naive expectation of an All-In, All-Out ordered state at low temperatures. Instead our low energy inelastic neutron scattering measurements show a dynamic quantum spin ice state, with suppressed scattering near |Q| = 0, and no long range order at low temperatures. This is consistent with recent theory predicting symmetry enriched U(1) quantum spin liquids for such DO doublets decorating the pyrochlore lattice. Finally, we show that disorder, especially oxidation of powder samples, is important in Ce2Zr2O7 and could play an important role in the low temperature behaviour of this material.The rare-earth pyrochlore oxides R 2 B 2 O 7 , where R 3+ and B 4+ consist generally of rare earth and transitionmetal ions respectively, display a wealth of both exotic and conventional magnetic ground states. Their R 3+ ions decorate a network of corner-sharing tetrahedra, one of the archetypes for geometrical frustration in three dimensions. Due to strong crystal electric field (CEF) effects, the nature of the magnetic interactions in such materials are strongly influenced by their single-ion physics [1][2][3]. A naive theoretical description of the magnetic interactions in rare-earth pyrochlores is generally performed by introducing an ad hoc effective single-ion term in addition to Heisenberg exchange interactions. For example, Heisenberg antiferromagnetism with an effective Ising anisotropy leads to non-frustrated All-In, All-Out (AIAO) magnetic order, as seen in several heavy rare earth iridate pyrochlores [4,5] and illustrated in the insert to Fig.1(a). Heisenberg ferromagnetism and an effective Ising anisotropy give rise to a classical spin ice ground state [6], as seen in (Ho,Dy) 2 Ti 2 O 7 [7, 8] and illustrated as the 2I2O local structure in the inset to Fig.1(a). However, to capture all the physics that can arise at low temperatures, the magnetic interactions should be projected into pseudo-spin operators acting solely on the low energy CEF states [3,[9][10][11][12][13]. This procedure has been applied for example in the Yb 3+ [11,14,15] and Er 3+ [12, 16-18] XY pyrochlores where CEF effects give rise to effective S = 1/2 quantum degrees of freedom that interact via anisotropic exchange interactions.More recently, it has been realized that the precise composition of the ground state crystal field doublets in rare-earth pyrochlores is crucial in determining the form of the microscopic Hamiltonian, and in itself, diversifies the possibility of quantum magnetic states [3,19]. This has been appreciated for some time in the case of non-Kramers doublets, based on magnetic ions with an even number of electrons such as the 4f 2 configuratio...

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Rare earth garnets are an exciting playground for studying the exotic magnetic properties of the frustrated hyperkagome lattice. Here we present a comprehensive study of the single ion and collective magnetic properties of the garnet Er3Ga5O12. Using inelastic neutron scattering, we find a crystal field ground state doublet for Er 3+ with strong Ising anisotropy along local [100] axes. Magnetic susceptibility and heat capacity measurements provide evidence for long-range magnetic ordering with TN = 0.8 K, and no evidence for residual entropy is found when cooling through the ordering transition. Neutron powder diffraction reveals that the ground state spin configuration corresponds to the six-sublattice, Ising antiferromagnetic state (Γ3) common to many of the rare earth garnets. Our results indicate that Er3Ga5O12 is an excellent model system for studying the complex metamagnetism expected for a multi-axis antiferromagnet.

The quantum dimer magnet (QDM) is the canonical example of quantum magnetism. The QDM state consists of entangled nearest-neighbor spin dimers and often exhibits a field-induced triplon Bose-Einstein condensate (BEC) phase. We report on a new QDM in the strongly spin-orbit coupled, distorted honeycomb-lattice material Yb2Si2O7. Our single crystal neutron scattering, specific heat, and ultrasound velocity measurements reveal a gapped singlet ground state at zero field with sharp, dispersive excitations. We find a field-induced magnetically ordered phase reminiscent of a BEC phase, with exceptionally low critical fields of Hc1 ∼ 0.4 T and Hc2 ∼ 1.4 T. Using inelastic neutron scattering in an applied magnetic field we observe a Goldstone mode (gapless to within δE = 0.037 meV) that persists throughout the entire field-induced magnetically ordered phase, suggestive of the spontaneous breaking of U(1) symmetry expected for a triplon BEC. However, in contrast to other well-known cases of this phase, the high-field (µ0H ≥ 1.2T) part of the phase diagram in Yb2Si2O7 is interrupted by an unusual regime signaled by a change in the field dependence of the ultrasound velocity and magnetization, as well as the disappearance of a sharp anomaly in the specific heat. These measurements raise the question of how anisotropy in strongly spin-orbit coupled materials modifies the field induced phases of QDMs.Quantum dimer magnets (QDMs) represent the simplest cases of quantum magnetism, where entanglement is a required ingredient for even a qualitative understanding of the phase. In a QDM, entangled pairs of spins form S tot = 0 dimers and result in a non-magnetic ground state. The excited states of these entangled spins can be treated as bosons, called triplons, which can undergo Bose-Einstein condensation (BEC) as their density is tuned by an applied magnetic field. This BEC state is a magnetic field-induced long range ordered phase, which occupies a symmetric "dome" in the field vs. temperature phase diagram with two temperature-dependent critical fields, H c1 (T ) and H c2 (T ). The vast majority of the previously studied QDMs are based on 3d transition metal ions with "bare" (spin-only) S = 1/2 or S = 1 angular momentum, resulting in simple Heisenberg or XXZ spin interaction Hamiltonians, and high critical fields set by the relatively high energy scale of exchange interactions [1-6].Lanthanide-based magnetic materials with spin-orbit coupled pseudo-spin 1/2 (S eff = 1/2) angular momenta can also exhibit quantum phases, and these are often directly analogous to their traditional 3d transition metal ion counterparts. However, entirely new phases are possible due to the anisotropic exchange in these materials [7][8][9][10][11][12]. In the lanthanide series, Yb 3+ has been of particular interest as it can generically host interactions leading to quantum fluctuations irrespective of the Crystal Electric Field (CEF) ground state doublet composition [13]. Indeed, various quantum phases have been discovered in Yb-based systems [14][15][...

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