Unusual Liquid State of Hard-Core Bosons on the Pyrochlore Lattice

Banerjee, Agnid; Isakov, Sergei V.; Damle, Kedar; Kim, Yong Baek

doi:10.1103/physrevlett.100.047208

Cited by 150 publications

(239 citation statements)

References 30 publications

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“…The effects of certain types of quantum fluctuations on the spin ice state have been investigated theoretically 12 and numerically 13,14 , where they have been demonstrated to lift the classical degeneracy and promote a three-dimensional (3D) QSL phase with low-energy gapless excitations that behave like photons 12,13 [15][16][17] . In an attempt to elucidate the microscopic underpinnings of these and related materials, recent theoretical studies have produced a general low-energy effective spin-1/2 model for magnetism in rare earth pyrochlores [18][19][20] .…”

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confidence: 99%

A two-dimensional spin liquid in quantum kagome ice

2015

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Actively sought since the turn of the century, two-dimensional quantum spin liquids (QSLs) are exotic phases of matter where magnetic moments remain disordered even at zero temperature. Despite ongoing searches, QSLs remain elusive, due to a lack of concrete knowledge of the microscopic mechanisms that inhibit magnetic order in materials. Here we study a model for a broad class of frustrated magnetic rare-earth pyrochlore materials called quantum spin ices. When subject to an external magnetic field along the [111] crystallographic direction, the resulting interactions contain a mix of geometric frustration and quantum fluctuations in decoupled two-dimensional kagome planes. Using quantum Monte Carlo simulations, we identify a set of interactions sufficient to promote a groundstate with no magnetic long-range order, and a gap to excitations, consistent with a Z 2 spin liquid phase. This suggests an experimental procedure to search for two-dimensional QSLs within a class of pyrochlore quantum spin ice materials.

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A two-dimensional spin liquid in quantum kagome ice

2015

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“…In the low T limit, GB0.17 meV is similar to the spin flip energy 2J ff ¼ D w B1.6 K inferred from AC-w(T). The observation of a broad spectrum rather than a sharp spin flip mode indicates monopole quantum dynamics 12,14,15 . A possible low-energy regime of photons predicted for a U(1) spin liquid 12,14,15 , however, cannot be resolved in the present neutron scattering experiment.…”

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“…The classical nature of Ising spins precludes attainment of thermal equilibrium at temperatures (T) below the effective nearest neighbor energy scale J ff . Quantum fluctuations enhance dynamics and might allow coherent propagation of magnetic charge 12,13,14,15 , much as spinons in one-dimensional quantum magnets 16 .…”

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Quantum fluctuations in spin-ice-like Pr2Zr2O7

et al. 2013

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Spin ice is a magnetic analog of H 2 O ice that harbors dense static disorder. Dipolar interactions between classical spins yield a frozen frustrated state with residual configurational Pauling entropy and emergent magnetic monopolar quasiparticles. Introducing quantum fluctuations is of great interest as this could melt spin ice and allow coherent propagation of monopoles. Here, we report experimental evidence for quantum dynamics of magnetic monopolar quasiparticles in a new class of spin ice based on exchange interactions, Pr 2 Zr 2 O 7 . Narrow pinch point features in otherwise diffuse elastic neutron scattering reflects adherence to a divergence-free constraint for disordered spins on long time scales. Magnetic susceptibility and specific heat data correspondingly show exponentially activated behaviors. In sharp contrast to conventional ice, however, 490% of the neutron scattering is inelastic and devoid of pinch points furnishing evidence for magnetic monopolar quantum fluctuations.

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“…Recent numerical studies have found evidence that QED-like phenomena may be at play in some minimal quantum spin ice (QSI) lattice models [13] -but does the QSI picture apply to real materials? Also, should a QSI state be solely defined by whether or not a QSL state is realized?…”

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Vindication ofYb2Ti2O7as a Model Exchange Quantum Spin Ice

et al. 2012

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We use numerical linked cluster (NLC) expansions to compute the specific heat, C(T ), and entropy, S(T ), of a quantum spin ice model of Yb2Ti2O7 using anisotropic exchange interactions recently determined from inelastic neutron scattering measurements and find good agreement with experimental calorimetric data. In the perturbative weak quantum regime, this model has a ferrimagnetic ordered ground state, with two peaks in C(T ): a Schottky anomaly signalling the paramagnetic to spin ice crossover followed at lower temperature by a sharp peak accompanying a first order phase transition to the ferrimagnetic state. We suggest that the two C(T ) features observed in Yb2Ti2O7 are associated with the same physics. Spin excitations in this regime consist of weakly confined spinon-antispinon pairs. We suggest that conventional ground state with exotic quantum dynamics will prove a prevalent characteristic of many real quantum spin ice materials.PACS numbers: 75.10.Jm,75.40.Gb,75.30.Ds The experimental search for quantum spin liquids (QSLs), magnetic systems disordered by large quantum fluctuations, has remained unabated for over twenty years [1]. One direction that is rapidly gathering momentum is the search for QSLs among materials that are close relatives to spin ice systems [2], but with additional quantum fluctuations, or quantum spin ice [3,4].Spin ices are found among insulating pyrochlore oxides, such as R 2 M 2 O 7 (R=Ho, Dy; M=Ti, Sn) [5]. In these compounds, the magnetic R rare earth ions sit on a lattice of corner-sharing tetrahedra, experiencing a large singleion anisotropy forcing the magnetic moment to point strictly "in" or "out" of the two tetrahedra it joins (see. Fig. 1a). Consequently, the direction of a moment can be described by a classical Ising spin [2]. In these materials, the combination of nearest-neighbor exchange and longrange magnetostatic dipolar interactions lead to an exponentially large number of low-energy states characterized by two spins pointing in and two spins pointing out on each tetrahedron (see Fig. 1a). This energetic constraint is equivalent to the Bernal-Fowler ice rule which gives water ice a residual entropy S P ∼ k B ( 1 2 ) ln(3/2) per proton, estimated by Pauling [6] and in good agreement with experiments on water ice [7]. Since they share the same "ice-rule", the (Ho,Dy) 2 (Ti,Sn) 2 O 7 pyrochlores also possess a residual low-temperature Pauling entropy S P [8], hence the name spin ice. The spin ice state is not thermodynamically distinct from the paramagnetic phase. Yet, because of the ice-rules, it is a strongly correlated state of matter -a classical spin liquid of sorts [1,2].For infinite Ising anisotropy, quantum effects are absent [2]. However, these can be restored when considering the realistic situation of finite anisotropy. In two closely related papers, Hermele et al. [9] and Castro-Neto et al. [10] considered effective spins one-half on a py- rochlore lattice where the highly degenerate classical spin ice state is promoted via quantum fluctuations to a QS...

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Unusual Liquid State of Hard-Core Bosons on the Pyrochlore Lattice

Cited by 150 publications

References 30 publications

A two-dimensional spin liquid in quantum kagome ice

A two-dimensional spin liquid in quantum kagome ice

Quantum fluctuations in spin-ice-like Pr2Zr2O7

Vindication ofYb2Ti2O7as a Model Exchange Quantum Spin Ice

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