Ludovic Jaubert - Academia.edu (original) (raw)
Uploads
Papers by Ludovic Jaubert
Since its discovery approximately 10 years ago [1], spin ice has proved to be an abounding source... more Since its discovery approximately 10 years ago [1], spin ice has proved to be an abounding source of exotic collective phenomena, in particular long-range dipolar correlations and unconventional phase transitions. But its most impressive property is undoubtedly the occurrence of 3d fractionalisation through excitations out of its topological ground state, behaving like effective magnetic monopoles [2]. I shall present an
Journal of Statistical Mechanics-theory and Experiment, 2007
We study numerically spatio-temporal fluctuations during the out-of-equilibrium relaxation of the... more We study numerically spatio-temporal fluctuations during the out-of-equilibrium relaxation of the three-dimensional Edwards–Anderson model. We focus on two issues. (1) The evolution of a growing dynamical length scale in the glassy phase of the model, and the consequent collapse of the distribution of local coarse-grained correlations measured at different pairs of times on a single function using two scaling parameters,
Physical Review Letters, 2010
We study the low-temperature behaviour of spin ice when uniaxial pressure induces a tetragonal di... more We study the low-temperature behaviour of spin ice when uniaxial pressure induces a tetragonal distortion. There is a phase transition between a Coulomb liquid and a fully magnetised phase. Unusually, it combines features of discontinuous and continuous transitions: the order parameter exhibits a jump, but this is accompanied by a divergent susceptibility and vanishing domain wall tension. All these aspects can be understood as a consequence of an emergent SU(2) symmetry at the critical point. We map out a possible experimental realisation. PACS numbers: 05.50.+q 05.70.Jk 75.10.Hk 75.40.Cx 75.40.Mg
Physical Review Letters, 2011
The Coulomb phase of spin ice, and indeed the I(c) phase of water ice, naturally realize a fully ... more The Coulomb phase of spin ice, and indeed the I(c) phase of water ice, naturally realize a fully packed two-color loop model in 3D. We present a detailed analysis of the statistics of these loops: we find loops spanning the system multiple times hosting a finite fraction of all sites while the average loop length remains finite. We contrast the behavior with an analogous 2D model. We connect this body of results to properties of polymers, percolation and insights from Schramm-Loewner evolution processes. We also study another extended degree of freedom, called worms, which appear as "Dirac strings" in spin ice. We discuss implications of these results for the efficiency of numerical cluster algorithms, and address implications for the ordering properties of a broader class of magnetic systems, e.g., with Heisenberg spins, such as CsNiCrF(6) or ZnCr(2)O(4).
Physica Scripta, 2007
Semiclassical approximations for tunneling processes usually involve complex trajectories or comp... more Semiclassical approximations for tunneling processes usually involve complex trajectories or complex times. In this paper we use a previously derived approximation involving only real trajectories propagating in real time to describe the scattering of a Gaussian wavepacket by a finite square potential barrier. We show that the approximation describes both tunneling and interferences very accurately in the limit of small Planck's constant. We use these results to estimate the tunneling time of the wavepacket and find that, for high energies, the barrier slows down the wavepacket but that it speeds it up at energies comparable to the barrier height.
Journal of Statistical Mechanics: Theory and Experiment, 2007
We study numerically spatio-temporal fluctuations during the out-ofequilibrium relaxation of the ... more We study numerically spatio-temporal fluctuations during the out-ofequilibrium relaxation of the three-dimensional Edwards-Anderson model. We focus on two issues. (1) The evolution of a growing dynamical length scale in the glassy phase of the model, and the consequent collapse of the distribution of local coarse-grained correlations measured at different pairs of times on a single function using two scaling parameters, the value of the global correlation at the measuring times and the ratio of the coarse graining length to the dynamical length scale (in the thermodynamic limit).
Nature Physics, 2009
Magnetic monopoles have eluded experimental detection since their prediction nearly a century ago... more Magnetic monopoles have eluded experimental detection since their prediction nearly a century ago by Dirac. Recently it has been shown that classical analogues of these enigmatic particles occur as excitations out of the topological ground state of a model magnetic system, dipolar spin ice. These quasi-particle excitations do not require a modification of Maxwell's equations, but they do interact via
Journal of Physics: Condensed Matter, 2011
One of the most remarkable examples of emergent quasi-particles, is that of the "fractionalizatio... more One of the most remarkable examples of emergent quasi-particles, is that of the "fractionalization" of magnetic dipoles in the low energy configurations of materials known as "spin ice", into free and unconfined magnetic monopoles interacting via Coulomb's 1/r law [Castelnovo et. al., Nature, 451, 42-45 (2008)]. Recent experiments have shown that a Coulomb gas of magnetic charges really does exist at low temperature in these materials and this discovery provides a new perspective on otherwise largely inaccessible phenomenology. In this paper, after a review of the different spin ice models, we present detailed results describing the diffusive dynamics of monopole particles starting both from the dipolar spin ice model and directly from a Coulomb gas within the grand canonical ensemble. The diffusive quasi-particle dynamics of real spin ice materials within "quantum tunneling" regime is modeled with Metropolis dynamics, with the particles constrained to move along an underlying network of oriented paths, which are classical analogues of the Dirac strings connecting pairs of Dirac monopoles.
Journal of Physics A: Mathematical and General, 2005
We consider a semiclassical approximation, first derived by Heller and coworkers, for the time ev... more We consider a semiclassical approximation, first derived by Heller and coworkers, for the time evolution of an originally gaussian wave packet in terms of complex trajectories.
![Research paper thumbnail of Three-Dimensional Kasteleyn Transition: Spin Ice in a [100] Field](https://attachments.academia-assets.com/38363017/thumbnails/1.jpg)
](Physical Review Letters - PHYS REV LETT, 2008
We examine the statistical mechanics of spin-ice materials with a [100] magnetic field. We show t... more We examine the statistical mechanics of spin-ice materials with a [100] magnetic field. We show that the approach to saturated magnetisation is, in the low-temperature limit, an example of a 3D Kasteleyn transition, which is topological in the sense that magnetisation is changed only by excitations that span the entire system. We study the transition analytically and using a Monte Carlo cluster algorithm, and compare our results with recent data from experiments on Dy2Ti2O7.
![Research paper thumbnail of The Kasteleyn transition in three dimensions: Spin ice in a [100] field](https://attachments.academia-assets.com/38363014/thumbnails/1.jpg)
](Journal of Physics: Conference Series, 2009
We discuss the nearest neighbour spin ice model in the presence of a magnetic field placed along ... more We discuss the nearest neighbour spin ice model in the presence of a magnetic field placed along the cubic [100] direction. As recently shown in Phys. Rev. Lett. 100, 067207, 2008, the symmetry sustaining ordering transition observed at low temperature is a three dimensional Kasteleyn transition. We confirm this with numerical data using a non-local algorithm that conserves the topological
Physical Review X 3, 011014 (2013), 2013
At low temperatures, a spin ice enters a Coulomb phase-a state with algebraic correlations and to... more At low temperatures, a spin ice enters a Coulomb phase-a state with algebraic correlations and topologically constrained spin configurations. We show how analytical and numerical approaches for model spin-ice systems reveal a crossover between two Curie laws. One of these laws characterizes the hightemperature paramagnetic regime, while the other, which we call the ''spin-liquid Curie law,'' characterizes the low-temperature Coulomb-phase regime, which provides implicit evidence that the topological sector fluctuates. We compare our theory with experiment for Ho 2 Ti 2 O 7 , where this process leads to a nonstandard temperature evolution of the bulk susceptibility and the wave-vector-dependent magnetic susceptibility, as measured by neutron scattering. Theory and experiment agree for bulk quantities and at large scattering wave vectors, but differences at small wave vectors indicate that the classical spin-ice states are not equally populated at low temperatures. More generally, the crossover appears to be a generic property of the emergent gauge field for a classical spin liquid, and it sheds light on the experimental difficulty of measuring a precise Curie-Weiss temperature in frustrated materials. The susceptibility at finite wave vectors is shown to be a local probe of fluctuations among topological sectors on varying length scales.
Since its discovery approximately 10 years ago [1], spin ice has proved to be an abounding source... more Since its discovery approximately 10 years ago [1], spin ice has proved to be an abounding source of exotic collective phenomena, in particular long-range dipolar correlations and unconventional phase transitions. But its most impressive property is undoubtedly the occurrence of 3d fractionalisation through excitations out of its topological ground state, behaving like effective magnetic monopoles [2]. I shall present an
Journal of Statistical Mechanics-theory and Experiment, 2007
We study numerically spatio-temporal fluctuations during the out-of-equilibrium relaxation of the... more We study numerically spatio-temporal fluctuations during the out-of-equilibrium relaxation of the three-dimensional Edwards–Anderson model. We focus on two issues. (1) The evolution of a growing dynamical length scale in the glassy phase of the model, and the consequent collapse of the distribution of local coarse-grained correlations measured at different pairs of times on a single function using two scaling parameters,
Physical Review Letters, 2010
We study the low-temperature behaviour of spin ice when uniaxial pressure induces a tetragonal di... more We study the low-temperature behaviour of spin ice when uniaxial pressure induces a tetragonal distortion. There is a phase transition between a Coulomb liquid and a fully magnetised phase. Unusually, it combines features of discontinuous and continuous transitions: the order parameter exhibits a jump, but this is accompanied by a divergent susceptibility and vanishing domain wall tension. All these aspects can be understood as a consequence of an emergent SU(2) symmetry at the critical point. We map out a possible experimental realisation. PACS numbers: 05.50.+q 05.70.Jk 75.10.Hk 75.40.Cx 75.40.Mg
Physical Review Letters, 2011
The Coulomb phase of spin ice, and indeed the I(c) phase of water ice, naturally realize a fully ... more The Coulomb phase of spin ice, and indeed the I(c) phase of water ice, naturally realize a fully packed two-color loop model in 3D. We present a detailed analysis of the statistics of these loops: we find loops spanning the system multiple times hosting a finite fraction of all sites while the average loop length remains finite. We contrast the behavior with an analogous 2D model. We connect this body of results to properties of polymers, percolation and insights from Schramm-Loewner evolution processes. We also study another extended degree of freedom, called worms, which appear as "Dirac strings" in spin ice. We discuss implications of these results for the efficiency of numerical cluster algorithms, and address implications for the ordering properties of a broader class of magnetic systems, e.g., with Heisenberg spins, such as CsNiCrF(6) or ZnCr(2)O(4).
Physica Scripta, 2007
Semiclassical approximations for tunneling processes usually involve complex trajectories or comp... more Semiclassical approximations for tunneling processes usually involve complex trajectories or complex times. In this paper we use a previously derived approximation involving only real trajectories propagating in real time to describe the scattering of a Gaussian wavepacket by a finite square potential barrier. We show that the approximation describes both tunneling and interferences very accurately in the limit of small Planck's constant. We use these results to estimate the tunneling time of the wavepacket and find that, for high energies, the barrier slows down the wavepacket but that it speeds it up at energies comparable to the barrier height.
Journal of Statistical Mechanics: Theory and Experiment, 2007
We study numerically spatio-temporal fluctuations during the out-ofequilibrium relaxation of the ... more We study numerically spatio-temporal fluctuations during the out-ofequilibrium relaxation of the three-dimensional Edwards-Anderson model. We focus on two issues. (1) The evolution of a growing dynamical length scale in the glassy phase of the model, and the consequent collapse of the distribution of local coarse-grained correlations measured at different pairs of times on a single function using two scaling parameters, the value of the global correlation at the measuring times and the ratio of the coarse graining length to the dynamical length scale (in the thermodynamic limit).
Nature Physics, 2009
Magnetic monopoles have eluded experimental detection since their prediction nearly a century ago... more Magnetic monopoles have eluded experimental detection since their prediction nearly a century ago by Dirac. Recently it has been shown that classical analogues of these enigmatic particles occur as excitations out of the topological ground state of a model magnetic system, dipolar spin ice. These quasi-particle excitations do not require a modification of Maxwell's equations, but they do interact via
Journal of Physics: Condensed Matter, 2011
One of the most remarkable examples of emergent quasi-particles, is that of the "fractionalizatio... more One of the most remarkable examples of emergent quasi-particles, is that of the "fractionalization" of magnetic dipoles in the low energy configurations of materials known as "spin ice", into free and unconfined magnetic monopoles interacting via Coulomb's 1/r law [Castelnovo et. al., Nature, 451, 42-45 (2008)]. Recent experiments have shown that a Coulomb gas of magnetic charges really does exist at low temperature in these materials and this discovery provides a new perspective on otherwise largely inaccessible phenomenology. In this paper, after a review of the different spin ice models, we present detailed results describing the diffusive dynamics of monopole particles starting both from the dipolar spin ice model and directly from a Coulomb gas within the grand canonical ensemble. The diffusive quasi-particle dynamics of real spin ice materials within "quantum tunneling" regime is modeled with Metropolis dynamics, with the particles constrained to move along an underlying network of oriented paths, which are classical analogues of the Dirac strings connecting pairs of Dirac monopoles.
Journal of Physics A: Mathematical and General, 2005
We consider a semiclassical approximation, first derived by Heller and coworkers, for the time ev... more We consider a semiclassical approximation, first derived by Heller and coworkers, for the time evolution of an originally gaussian wave packet in terms of complex trajectories.
Physical Review Letters - PHYS REV LETT, 2008
We examine the statistical mechanics of spin-ice materials with a [100] magnetic field. We show t... more We examine the statistical mechanics of spin-ice materials with a [100] magnetic field. We show that the approach to saturated magnetisation is, in the low-temperature limit, an example of a 3D Kasteleyn transition, which is topological in the sense that magnetisation is changed only by excitations that span the entire system. We study the transition analytically and using a Monte Carlo cluster algorithm, and compare our results with recent data from experiments on Dy2Ti2O7.
Journal of Physics: Conference Series, 2009
We discuss the nearest neighbour spin ice model in the presence of a magnetic field placed along ... more We discuss the nearest neighbour spin ice model in the presence of a magnetic field placed along the cubic [100] direction. As recently shown in Phys. Rev. Lett. 100, 067207, 2008, the symmetry sustaining ordering transition observed at low temperature is a three dimensional Kasteleyn transition. We confirm this with numerical data using a non-local algorithm that conserves the topological
Physical Review X 3, 011014 (2013), 2013
At low temperatures, a spin ice enters a Coulomb phase-a state with algebraic correlations and to... more At low temperatures, a spin ice enters a Coulomb phase-a state with algebraic correlations and topologically constrained spin configurations. We show how analytical and numerical approaches for model spin-ice systems reveal a crossover between two Curie laws. One of these laws characterizes the hightemperature paramagnetic regime, while the other, which we call the ''spin-liquid Curie law,'' characterizes the low-temperature Coulomb-phase regime, which provides implicit evidence that the topological sector fluctuates. We compare our theory with experiment for Ho 2 Ti 2 O 7 , where this process leads to a nonstandard temperature evolution of the bulk susceptibility and the wave-vector-dependent magnetic susceptibility, as measured by neutron scattering. Theory and experiment agree for bulk quantities and at large scattering wave vectors, but differences at small wave vectors indicate that the classical spin-ice states are not equally populated at low temperatures. More generally, the crossover appears to be a generic property of the emergent gauge field for a classical spin liquid, and it sheds light on the experimental difficulty of measuring a precise Curie-Weiss temperature in frustrated materials. The susceptibility at finite wave vectors is shown to be a local probe of fluctuations among topological sectors on varying length scales.