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Intrinsic disorder in the candidate quantum spin ice Pr$_2$Zr$_2$O$_7$
Authors:
T. J. Hicken,
P. Meadows,
D. Prabhakaran,
A. Szabó,
S. E. Dutton,
C. Castelnovo,
K. Moovendaran,
T. S. Northam de la Fuente,
L. Mangin-Thro,
G. B. G. Stenning,
M. J. Gutmann,
G. Sala,
M. B. Stone,
P. F. Henry,
D. J. Voneshen,
J. P. Goff
Abstract:
Quantum spin liquids with long-range entanglement are of great interest for applications in quantum technology. The quantum spin ice Pr$_2$Zr$_2$O$_7$ is a promising example, where it is believed that structural disorder plays a key role in enhancing quantum mechanical effects by introducing strains that split the ground state doublet akin to the effect of a local disordered transverse field. Howe…
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Quantum spin liquids with long-range entanglement are of great interest for applications in quantum technology. The quantum spin ice Pr$_2$Zr$_2$O$_7$ is a promising example, where it is believed that structural disorder plays a key role in enhancing quantum mechanical effects by introducing strains that split the ground state doublet akin to the effect of a local disordered transverse field. However, the precise defect structure responsible for this behaviour is unknown. Here we have determined the intrinsic defect structure of Pr$_2$Zr$_2$O$_7$ using neutron and x-ray scattering techniques supported by density functional theory. We find the main defect is the stuffing of Zr$^{4+}$ sites by Pr$^{3+}$ ions, accompanied by charge compensating O$^{2-}$ vacancies, and the relaxation of a neighbouring O$^{2-}$ ion to an interstitial site. Our results explain the single-ion magnetism by considering the non-magnetic singlets that arise on neighbouring sites as a result of the defect structure. These singlets account for additional features in the crystal electric field excitations. The effects caused by this low level of structural disorder are magnified since several neighbouring Pr sites are affected. This makes a significant contribution towards the observed broadening of pinch points in the magnetic diffuse scattering, which was previously attributed purely to quantum effects.
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Submitted 12 September, 2025;
originally announced September 2025.
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Magnetotransport of single crystal Sm$_2$Ir$_2$O$_7$ across the pressure-induced quantum-critical phase boundary
Authors:
M. J. Coak,
K. Götze,
T. Northam De La Fuente,
C. Castelnovo,
J. P. Tidey,
J. Singleton,
A. T. Boothroyd,
D. Prabhakaran,
P. A. Goddard
Abstract:
Rare-earth pyrochlore iridates host two interlocking magnetic sublattices of corner-sharing tetrahedra and can harbour a unique combination of frustrated moments, exotic excitations and highly correlated electrons. They are also the first systems predicted to display both topological Weyl semimetal and axion insulator phases. We have measured the transport and magnetotransport properties of single…
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Rare-earth pyrochlore iridates host two interlocking magnetic sublattices of corner-sharing tetrahedra and can harbour a unique combination of frustrated moments, exotic excitations and highly correlated electrons. They are also the first systems predicted to display both topological Weyl semimetal and axion insulator phases. We have measured the transport and magnetotransport properties of single-crystal Sm$_2$Ir$_2$O$_7$ up to and beyond the pressure-induced quantum critical point for all-in-all-out (AIAO) Ir order at $p_{\rm c}$ = 63 kbar previously identified by resonant X-ray scattering and close to which Weyl semimetallic behavior has been previously predicted. Our findings overturn the accepted expectation that the suppression of AIAO order should lead to metallic conduction persisting down to zero temperature. Instead, the resistivity-minimum temperature, which tracks the decrease in the AIAO ordering temperature for pressures up to 30~kbar, begins to increase under further application of pressure, pointing to the presence of a second as-yet unidentified mechanism leading to non-metallic behavior. The magnetotransport does track the suppression of Ir magnetism, however, with a strong hysteresis observed only within the AIAO phase boundary, similar to that found for Ho$_2$Ir$_2$O$_7$ and attributed to plastic deformation of Ir domains. Around $p_{\rm c}$ we find the emergence of a new type of electronic phase, characterized by a negative magnetoresistance with small hysteresis at the lowest temperatures, and hysteresis-free positive magnetoresistance above approximately 5 K. The temperature dependence of our low-temperature transport data are found to be best described by a model consistent with a Weyl semimetal across the entire pressure range.
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Submitted 8 February, 2024; v1 submitted 11 October, 2022;
originally announced October 2022.
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Quantifying the non-equilibrium activity of an active colloid
Authors:
Sarah Eldeen,
Ryan Muoio,
Paris Blaisdell-Pijuan,
Ngoc La,
Mauricio Gomez,
Alex Vidal,
Wylie Ahmed
Abstract:
Active matter systems exhibit rich emergent behavior due to constant injection and dissipation of energy at the level of individual agents. Since these systems are far from equilibrium, their dynamics and energetics cannot be understood using the framework of equilibrium statistical mechanics. Recent developments in stochastic thermodynamics extend classical concepts of work, heat, and energy diss…
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Active matter systems exhibit rich emergent behavior due to constant injection and dissipation of energy at the level of individual agents. Since these systems are far from equilibrium, their dynamics and energetics cannot be understood using the framework of equilibrium statistical mechanics. Recent developments in stochastic thermodynamics extend classical concepts of work, heat, and energy dissipation to fluctuating non-equilibrium systems. We use recent advances in experiment and theory to study the non-thermal dissipation of individual light-activated self-propelled colloidal particles. We focus on characterizing the transition from thermal to non-thermal fluctuations and show that energy dissipation rates on the order of $\sim k_BT/$s are measurable from finite time series data.
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Submitted 9 April, 2020;
originally announced April 2020.