Quantum spin liquids (QSLs) are exotic phases of matter exhibiting long-range entanglement and supporting emergent gauge fields. A vigorous search for experimental realizations of these states has identified several materials with properties hinting at QSL physics. A key issue in understanding these QSL candidates is often the interplay of weak disorder of the crystal structure with the spin liquid state. It has recently been pointed out that in at least one important class of candidate QSLs-pyrochlore magnets based on non-Kramers ions such as Pr^{3+} or Tb^{3+}-structural disorder can actually promote a U(1) QSL ground state. Here we set this proposal on a quantitative footing by analyzing the stability of the QSL state in the minimal model for these systems: a random transverse field Ising model. We consider two kinds of instability, which are relevant in different limits of the phase diagram: condensation of spinons and confinement of the U(1) gauge fields. Having obtained stability bounds on the QSL state, we apply our results directly to the disordered candidate QSL Pr_{2}Zr_{2}O_{7}. We find that the available data for currently studied samples of Pr_{2}Zr_{2}O_{7} are most consistent with it a ground state outside the spin liquid regime, in a paramagnetic phase with quadrupole moments near saturation due to the influence of structural disorder.
We study the uniform
U(1) quantum spin liquid (QSL) with low-energy fermionic quasiparticles for pyrochlore magnets with dipolar-octupolar symmetry, employing a fermionic parton mean-field theory approach. Self-consistent calculations stabilize 12 fully symmetric uniform
U(1) QSLs, of which four mean-field states are ``monopole-flux'' states. Several of these mean-field states show a linear temperature dependence of specific heat at low temperatures, the other phases show a power-law temperature dependence of specific heat $C\ensuremath{\sim}{T}^{\ensuremath{\alpha}}$. The linear temperature dependence of specific heat at low temperatures is reminiscent of the observations in
Nd2ScNbO7. We further compute the dynamic spin structure factors and discuss the possible signature of these fermionic spinons in neutron-scattering experiments.
Simplified models for quantum spin-ice materials, such as the XXZ model on the pyrochlore lattice, may host interesting new spin-liquid ground states. In this work, the authors provide a complete classification of nearest-neighbor chiral
Z2 spin-liquid states on the pyrochlore lattice using a projective symmetry group analysis. Moreover, the newly classified states are applied to the XXZ model within a self-consistent mean-field scheme. Observable signatures in neutron scattering experiments are discussed.
Here, the authors report the discovery of novel types of U(1) and \ensuremath{\mathbb{Z}}
2 quantum spin liquids on the pyrochlore lattice through a projective symmetry group classification. The classification highlights a special type of U(1) spin liquid, possessing an unusual symmetry-protected gapless multi-nodal-line structure in the spinon bands. The effect of gauge fluctuations for such a nodal structure is discussed. The leading contributions to the low-temperature specific heat are calculated, providing a clear experimental diagnostic of this U(1) spin liquid.
We study the
S=1/2 Heisenberg antiferromagnet on the pyrochlore lattice in the limit of strong easy-axis exchange anisotropy. We find, using only standard techniques of degenerate perturbation theory, that the model has a
U(1) gauge symmetry generated by certain local rotations about the z axis in spin space. Upon addition of an extra local interaction in this and a related model with spins on a three-dimensional network of corner-sharing octahedra, we can write down the exact ground-state wave function with no further approximations. Using the properties of the soluble point we show that these models enter the
U(1) spin liquid phase, a fractionalized spin liquid with an emergent
U(1) gauge structure. This phase supports gapped
Sz=1/2 spinons carrying the
U(1) ``electric'' gauge charge, a gapped topological point defect or ``magnetic'' monopole, and a gapless ``photon,'' which in spin language is a gapless, linearly dispersing
Sz=0 collective mode. There are power-law spin correlations with a nontrivial angular dependence, as well as
U(1) topological order. This state is stable to all zero-temperature perturbations and exists over a finite extent of the phase diagram. Using a convenient lattice version of electric-magnetic duality, we develop the effective description of the
U(1) spin liquid and the adjacent soluble point in terms of Gaussian quantum electrodynamics and calculate a few of the universal properties. The resulting picture is confirmed by our numerical analysis of the soluble point wave function. Finally, we briefly discuss the prospects for understanding this physics in a wider range of models and for making contact with experiments.
Quantum spin liquids (QSLs) have generated considerable excitement as phases of matter with emergent gauge structures and fractionalized excitations. In this context, phase transitions out of QSLs have been widely discussed as Higgs transitions from deconfined to confined phases of a lattice gauge theory. However, the possibility of a wider range of novel phases, occurring between these two limits, has yet to be systematically explored. In this Research Letter, we develop a formalism which allows for interactions between fractionalized quasiparticles coming from the constraint on the physical Hilbert space and can be used to search for exotic, hidden phases. Taking pyrochlore spin ice as a starting point, we show how a U(1) QSL can give birth to abundant daughter phases, without the need for fine-tuning of parameters. These include a (charged)
Z2 QSL and a supersolid. We discuss implications for experiment, and numerical results which support our analysis. These results are of broad relevance to QSLs subject to a parton description and offer a useful perspective in the search for exotic hidden phases in quantum magnets.