Possible observation of highly itinerant quantum magnetic monopoles in the frustrated pyrochlore Yb2Ti2O7

Tokiwa, Y.; Yamashita, Takuya; Udagawa, Masafumi; Kittaka, Shunichiro; Sakakibara, Toshiro; Terazawa, Daiki; Shimoyama, Yusuke; Terashima, T.; Yasui, Yukihiko; Shibauchi, T.; Matsuda, Yuji

doi:10.1038/ncomms10807

Cited by 64 publications

(83 citation statements)

References 43 publications

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“…Possible monopole dynamics at temperatures ∼1.5 K was recently reported [40,41]. Furthermore, the broad anomaly in heat capacity, which we associate here with the inelastic continuum developing at low temperatures, seems to configure an important turning point in the magnetic dynamics of the compound without any obvious consequences in the elastic scattering.…”

Section: Figmentioning

confidence: 83%

Magnetic excitations in the ground state of Yb2Ti2O7

Peçanha-Antonio

Feng

et al. 2017

Phys. Rev. B

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We report an extensive study on the zero field ground state of a powder sample of the pyrochlore Yb 2 Ti 2 O 7 . A sharp heat capacity anomaly that labels a low temperature phase transition in this material is observed at 280 mK. Neutron diffraction shows that a quasicollinear ferromagnetic order develops below T c with a magnetic moment of 0.87(2)μ B . High resolution inelastic neutron scattering measurements show, below the phase transition temperature, sharp gapped low-lying magnetic excitations coexisting with a remnant quasielastic contribution likely associated with persistent spin fluctuations. Moreover, a broad inelastic continuum of excitations at ∼0.6 meV is observed from the lowest measured temperature up to at least 2.5 K. At 10 K, the continuum has vanished and a broad quasielastic conventional paramagnetic scattering takes place at the observed energy range. Finally, we show that the exchange parameters obtained within the framework of linear spin-wave theory do not accurately describe the observed zero field inelastic neutron scattering data.

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Section: Figmentioning

confidence: 83%

Magnetic excitations in the ground state of Yb2Ti2O7

Peçanha-Antonio

Feng

et al. 2017

Phys. Rev. B

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“…Currently, much of the interest in this field concentrates on a handful of materials that seem to fall outside a semiclassical understanding of these systems. The pyrochlore Yb 2 Ti 2 O 7 [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25], where Kramers Yb 3+ ions behave as effective spin 1/2 moments, is quite unique in its behavior: in high applied magnetic fields dispersive magnons were observed [12], which are apparently replaced by a broad continuum of scattering at zero field [16] despite the presence of ferromagnetic order. This exotic behavior is not yet understood.…”

mentioning

confidence: 99%

Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum PyrochloreYb2Ti2O7
Thompson
¹
,
McClarty
²
,
Prabhakaran
³

et al. 2017
Phys. Rev. Lett.
106
16
181
0
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The frustrated pyrochlore magnet Yb2Ti2O7 has the remarkable property that it orders magnetically, but has no propagating magnons over wide regions of the Brillouin zone. Here we use inelastic neutron scattering to follow how the spectrum evolves in cubic-axis magnetic fields. At high fields we observe in addition to dispersive magnons also a two-magnon continuum, which grows in intensity upon reducing the field and overlaps with the one-magnon states at intermediate fields leading to strong renormalization of the dispersion relations, and magnon decays. Using heat capacity measurements we find that the low and high field regions are smoothly connected with no sharp phase transition, with the spin gap increasing monotonically in field. Through fits to an extensive data set we re-evaluate the spin Hamiltonian finding dominant quantum exchange terms, which we propose are responsible for the anomalously strong fluctuations and quasiparticle breakdown effects observed at low fields. The lattice of corner-shared tetrahedra realized in cubic A 2 B 2 O 7 pyrochlores and AB 2 O 4 spinels, is a canonical lattice to explore correlated magnetism in the presence of strong geometric frustration effects. In the strongly spin-orbit coupled rare earth pyrochlores, experiment has uncovered materials offering a tremendously rich spectrum of magnetic behavior. Notable examples include classical spin ice physics as in the rare-earth titanates (Ho/Dy) 2 Ti 2 O 7 where Ising antiferromagnetism leads to an emergent classical electrostatics at low temperatures [1] and "order-by-disorder" in XY antiferromagnets where thermal and quantum fluctuations lift a large frustration-induced degeneracy resulting in unconventional magnetic order as in Er 2 Ti 2 O 7 [2-5]. Currently, much of the interest in this field concentrates on a handful of materials that seem to fall outside a semiclassical understanding of these systems. The pyrochlore Yb 2 Ti 2 O 7 [6-25], where Kramers Yb 3+ ions behave as effective spin 1/2 moments, is quite unique in its behavior: in high applied magnetic fields dispersive magnons were observed [12], which are apparently replaced by a broad continuum of scattering at zero field [16] despite the presence of ferromagnetic order. This exotic behavior is not yet understood. To make progress one would like to know i) how the broad scattering continuum in zero field originates from quantum fluctuations, whether those fluctuations are also present at high field and, if so, how they manifest themselves, ii) how the sharp magnons "disappear" over a wide range of the Brillouin zone as the field is lowered. Here we experimentally answer those questions by studying the behavior in a magnetic field applied along the cubic [001] direction, which has not been explored in detail before and which, we will show, allows for a transparent interpretation of the phase diagram and evolution of the spectrum in a magnetic field. The experiment also allows us to re-visit the parametrization of the magnetic exchange, which is a critical ingredien...

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“…The properties of such mobile monopoles are currently subject to both experimental [15][16][17] and theoretical work [18].…”

Section: Introductionmentioning

confidence: 99%

Single-ion anisotropy and magnetic field response in the spin-ice materialsHo2Ti2O7andDy2Ti
Tomasello
¹
,
Castelnovo
²
,
Moessner
³

et al. 2015
Phys. Rev. B
45
3
48
0
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Motivated by its role as a central pillar of current theories of the dynamics of spin ice in and out of equilibrium, we study the single-ion dynamics of the magnetic rare-earth ions in their local environments, subject to the effective fields set up by the magnetic moments with which they interact. This effective field has a transverse component with respect to the local easy axis of the crystal electric field, which can induce quantum tunneling. We go beyond the projective spin-1/2 picture and use instead the full crystal-field Hamiltonian. We find that the Kramers versus non-Kramers nature, as well as the symmetries of the crystal-field Hamiltonian, result in different perturbative behavior at small fields ( 1 T), with transverse field effects being more pronounced in Ho 2 Ti 2 O 7 than in Dy 2 Ti 2 O 7 . Remarkably, the energy splitting range we find is consistent with time scales extracted from experiments. We also present a study of the static magnetic response, which highlights the anisotropy of the system in the form of an off-diagonal g tensor, and we investigate the effects of thermal fluctuations in the temperature regime of relevance to experiments. We show that there is a narrow but accessible window of experimental parameters where the anisotropic response can be observed.

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Possible observation of highly itinerant quantum magnetic monopoles in the frustrated pyrochlore Yb2Ti2O7

Cited by 64 publications

References 43 publications

Magnetic excitations in the ground state of Yb2Ti2O7

Magnetic excitations in the ground state of Yb2Ti2O7

Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum PyrochloreYb2Ti2O7
Thompson
¹
,
McClarty
²
,
Prabhakaran
³

et al. 2017
Phys. Rev. Lett.
106
16
181
0
View full text Add to dashboard Cite

Single-ion anisotropy and magnetic field response in the spin-ice materialsHo2Ti2O7andDy2Ti
Tomasello
¹
,
Castelnovo
²
,
Moessner
³

et al. 2015
Phys. Rev. B
45
3
48
0
View full text Add to dashboard Cite

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Possible observation of highly itinerant quantum magnetic monopoles in the frustrated pyrochlore Yb2Ti2O7

Cited by 64 publications

References 43 publications

Magnetic excitations in the ground state of Yb2Ti2O7

Magnetic excitations in the ground state of Yb2Ti2O7

Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum PyrochloreYb2Ti2O7Thompson1, McClarty2, Prabhakaran3 et al. 2017Phys. Rev. Lett.106161810View full textAdd to dashboardCite

Single-ion anisotropy and magnetic field response in the spin-ice materialsHo2Ti2O7andDy2TiTomasello1, Castelnovo2, Moessner3 et al. 2015Phys. Rev. B453480View full textAdd to dashboardCite

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Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum PyrochloreYb2Ti2O7
Thompson
¹
,
McClarty
²
,
Prabhakaran
³

et al. 2017
Phys. Rev. Lett.
106
16
181
0
View full text Add to dashboard Cite

Single-ion anisotropy and magnetic field response in the spin-ice materialsHo2Ti2O7andDy2Ti
Tomasello
¹
,
Castelnovo
²
,
Moessner
³

et al. 2015
Phys. Rev. B
45
3
48
0
View full text Add to dashboard Cite