The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
S T Bramwell - One of the best experts on this subject based on the ideXlab platform.
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Nuclear spin assisted quantum tunnelling of magnetic Monopoles in spin ice
Nature Communications, 2019Co-Authors: Carley Paulsen, S. R. Giblin, Keisuke Matsuhira, Elsa Lhotel, Ganesh Balakrishnan, Dorairaj Prabhakaran, S T BramwellAbstract:Spin ice compounds have localised excitations that behave as magnetic Monopoles which move by hopping from site to site, creating a chain of spins. Here the authors show that the hyperfine coupling between electron and nuclear spins is an important part of the mechanism underlying Monopole motion.AbstractExtensive work on single molecule magnets has identified a fundamental mode of relaxation arising from the nuclear-spin assisted quantum tunnelling of nearly independent and quasi-classical magnetic dipoles. Here we show that nuclear-spin assisted quantum tunnelling can also control the dynamics of purely emergent excitations: magnetic Monopoles in spin ice. Our low temperature experiments were conducted on canonical spin ice materials with a broad range of nuclear spin values. By measuring the magnetic relaxation, or Monopole current, we demonstrate strong evidence that dynamical coupling with the hyperfine fields bring the electronic spins associated with magnetic Monopoles to resonance, allowing the Monopoles to hop and transport magnetic charge. Our result shows how the coupling of electronic spins with nuclear spins may be used to control the Monopole current. It broadens the relevance of the assisted quantum tunnelling mechanism from single molecular spins to emergent excitations in a strongly correlated system.
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Generalized longitudinal susceptibility for magnetic Monopoles in spin ice
Philosophical Transactions of the Royal Society A, 2012Co-Authors: S T BramwellAbstract:The generalized longitudinal susceptibility χ(q,ω) affords a sensitive measure of the spatial and temporal correlations of magnetic Monopoles in spin ice. Starting with the Monopole model, a mean field expression for χ(q,ω) is derived as well as expressions for the mean square longitudinal field and induction at a point. Monopole motion is shown to be strongly correlated, and both spatial and temporal correlations are controlled by the dimensionless Monopole density x which defines the ratio of the magnetization relaxation rate and the Monopole hop rate. Thermal effects and spin-lattice relaxation are also considered. The derived equations are applicable in the temperature range where the Wien effect for magnetic Monopoles is negligible. They are discussed in the context of existing theories of spin ice and the following experimental techniques: DC and AC magnetization, neutron scattering, neutron spin echo and longitudinal and transverse field μSR. The Monopole theory is found to unify diverse experimental results, but several discrepancies between theory and experiment are identified. One of these, concerning the neutron scattering line shape, is explained by means of a phenomenological modification to the theory.
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Generalised Longitudinal Susceptibility for Magnetic Monopoles in Spin Ice
Philosophical transactions. Series A Mathematical physical and engineering sciences, 2012Co-Authors: S T BramwellAbstract:The generalised longitudinal susceptibility $\chi({\bf q}, \omega)$ affords a sensitive measure of the spatial and temporal correlations of magnetic Monopoles in spin ice. Starting with the Monopole model, a mean field expression for $\chi({\bf q}, \omega)$ is derived as well as expressions for the mean square longitudinal field and induction at a point. Monopole motion is shown to be strongly correlated, and both spatial and temporal correlations are controlled by the dimensionless Monopole density $x$ which defines the ratio of the magnetization relaxation rate and the Monopole hop rate. Thermal effects and spin lattice relaxation are also considered. The derived equations are applicable in the temperature range where the Wien effect for magnetic Monopoles is negligible. They are discussed in the context of existing theories of spin ice and the following experimental techniques: dc and ac-magnetization, neutron scattering, neutron spin echo, and longitudinal and transverse field $\mu$SR. The Monopole theory is found to unify diverse experimental results, but several discrepancies between theory and experiment are identified. One of these, concerning the neutron scattering line shape, is explained by means of a phenomenological modification to the theory.
M Nourizonoz - One of the best experts on this subject based on the ideXlab platform.
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classical Monopoles newton nut space gravomagnetic lensing and atomic spectra
Reviews of Modern Physics, 1998Co-Authors: D Lyndenbell, M NourizonozAbstract:Stimulated by a scholium in Newton's Principia we find some beautiful results in classical mechanics which can be interpreted in terms of the orbits in the field of a mass endowed with a gravomagnetic Monopole. All the orbits lie on cones! When the cones are slit open and flattened the orbits are exactly the ellipses and hyperbolae that one would have obtained without the gravomagnetic Monopole. The beauty and simplicity of these results has led us to explore the similar problems in Atomic Physics when the nuclei have an added Dirac magnetic Monopole. These problems have been explored by others and we sketch the derivations and give details of the predicted spectrum of monopolar hydrogen. Finally we return to gravomagnetic Monopoles in general relativity. We explain why NUT space has a non-spherical metric although NUT space itself is the spherical space-time of a mass with a gravomagnetic Monopole. We demonstrate that all geodesics in NUT space lie on cones and use this result to study the gravitational lensing by bodies with gravomagnetic Monopoles. We remark that just as electromagnetism would have to be extended beyond Maxwell's equations to allow for magnetic Monopoles and their currents so general relativity would have to be extended to allow torsion for general distributions of gravomagnetic Monopoles and their currents. Of course if Monopoles were never discovered then it would be a triumph for both Maxwellian Electromagnetism and General Relativity as they stand!
Mohammad Nouri-zonoz - One of the best experts on this subject based on the ideXlab platform.
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Classical Monopoles: Newton, NUT space, gravomagnetic lensing, and atomic spectra
Reviews of Modern Physics, 1998Co-Authors: Donald Lynden-bell, Mohammad Nouri-zonozAbstract:Stimulated by a scholium in Newton's Principia we find some beautiful results in classical mechanics which can be interpreted in terms of the orbits in the field of a mass endowed with a gravomagnetic Monopole. All the orbits lie on cones! When the cones are slit open and flattened the orbits are exactly the ellipses and hyperbolae that one would have obtained without the gravomagnetic Monopole. The beauty and simplicity of these results has led us to explore the similar problems in Atomic Physics when the nuclei have an added Dirac magnetic Monopole. These problems have been explored by others and we sketch the derivations and give details of the predicted spectrum of monopolar hydrogen. Finally we return to gravomagnetic Monopoles in general relativity. We explain why NUT space has a non-spherical metric although NUT space itself is the spherical space-time of a mass with a gravomagnetic Monopole. We demonstrate that all geodesics in NUT space lie on cones and use this result to study the gravitational lensing by bodies with gravomagnetic Monopoles. We remark that just as electromagnetism would have to be extended beyond Maxwell's equations to allow for magnetic Monopoles and their currents so general relativity would have to be extended to allow torsion for general distributions of gravomagnetic Monopoles and their currents. Of course if Monopoles were never discovered then it would be a triumph for both Maxwellian Electromagnetism and General Relativity as they stand!Comment: 39 pages, 9 figures and 2 tables available on request from the author
D Lyndenbell - One of the best experts on this subject based on the ideXlab platform.
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classical Monopoles newton nut space gravomagnetic lensing and atomic spectra
Reviews of Modern Physics, 1998Co-Authors: D Lyndenbell, M NourizonozAbstract:Stimulated by a scholium in Newton's Principia we find some beautiful results in classical mechanics which can be interpreted in terms of the orbits in the field of a mass endowed with a gravomagnetic Monopole. All the orbits lie on cones! When the cones are slit open and flattened the orbits are exactly the ellipses and hyperbolae that one would have obtained without the gravomagnetic Monopole. The beauty and simplicity of these results has led us to explore the similar problems in Atomic Physics when the nuclei have an added Dirac magnetic Monopole. These problems have been explored by others and we sketch the derivations and give details of the predicted spectrum of monopolar hydrogen. Finally we return to gravomagnetic Monopoles in general relativity. We explain why NUT space has a non-spherical metric although NUT space itself is the spherical space-time of a mass with a gravomagnetic Monopole. We demonstrate that all geodesics in NUT space lie on cones and use this result to study the gravitational lensing by bodies with gravomagnetic Monopoles. We remark that just as electromagnetism would have to be extended beyond Maxwell's equations to allow for magnetic Monopoles and their currents so general relativity would have to be extended to allow torsion for general distributions of gravomagnetic Monopoles and their currents. Of course if Monopoles were never discovered then it would be a triumph for both Maxwellian Electromagnetism and General Relativity as they stand!
Donald Lynden-bell - One of the best experts on this subject based on the ideXlab platform.
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Classical Monopoles: Newton, NUT space, gravomagnetic lensing, and atomic spectra
Reviews of Modern Physics, 1998Co-Authors: Donald Lynden-bell, Mohammad Nouri-zonozAbstract:Stimulated by a scholium in Newton's Principia we find some beautiful results in classical mechanics which can be interpreted in terms of the orbits in the field of a mass endowed with a gravomagnetic Monopole. All the orbits lie on cones! When the cones are slit open and flattened the orbits are exactly the ellipses and hyperbolae that one would have obtained without the gravomagnetic Monopole. The beauty and simplicity of these results has led us to explore the similar problems in Atomic Physics when the nuclei have an added Dirac magnetic Monopole. These problems have been explored by others and we sketch the derivations and give details of the predicted spectrum of monopolar hydrogen. Finally we return to gravomagnetic Monopoles in general relativity. We explain why NUT space has a non-spherical metric although NUT space itself is the spherical space-time of a mass with a gravomagnetic Monopole. We demonstrate that all geodesics in NUT space lie on cones and use this result to study the gravitational lensing by bodies with gravomagnetic Monopoles. We remark that just as electromagnetism would have to be extended beyond Maxwell's equations to allow for magnetic Monopoles and their currents so general relativity would have to be extended to allow torsion for general distributions of gravomagnetic Monopoles and their currents. Of course if Monopoles were never discovered then it would be a triumph for both Maxwellian Electromagnetism and General Relativity as they stand!Comment: 39 pages, 9 figures and 2 tables available on request from the author
