Format results
Spinon Walk in Quantum Spin Ice
Yuan Wan Chinese Academy of Sciences
Universal Dynamic Magnetism in the Ytterbium Pyrochlores
Alannah Hallas McMaster University
Spin Slush in an Extended Spin Ice Model
Jeff Rau University of Waterloo
Stochastic Resonance Magnetic Force Microscopy: A Technique for Nanoscale Imaging of Vortex Dynamics
Raffi Budakian Institute for Quantum Computing (IQC)
Dynamics of Superrotations in 2+1 Dimensions
Steve Carlip University of California, Davis
From Wires to Cosmology
Mustafa Amin Massachusetts Institute of Technology (MIT)
Honeycomb lattice quantum magnets with strong spin-orbit coupling
Young-June Kim University of Toronto
CMB spectral distortions within LCDM
Jens Chluba University of Manchester
Superconductivity and Charge Density Waves in the Clean 2D Limit
Adam Tsen Institute for Quantum Computing (IQC)
Growth dynamics and scaling laws across levels of biological organization.
Ian Hatton McGill University
Recent findings on quantitative growth patterns have revealed striking generalities across the tree of life, and recurring over distinct levels of organization. Growth-mass relationships in 1) individual growth to maturity, 2) population reproduction, 3) insect colony enlargement and 4) community production across wholeecosystems of very different types, often follow highly robust near ¾ scaling laws. These patterns represent some of the most general relations in biology, but the reasons they are so strangely similar across levels of organization remains a mystery. The dynamics of these distinct levels are connected, yet their scaling can be shown to arise independently, and free of system-specific properties. Numerous experiments in prebiotic chemistry have shown that minimal self-replicating systems that undergo template-directed synthesis, typically show reaction orders (ie. growth-mass exponents) between ½ and 1. I will outline how modifications to these simplified reaction schemes can yield growth-mass exponents near ¾, which may offer insight into dynamical connections across hierarchical systems.
Spinon Walk in Quantum Spin Ice
Yuan Wan Chinese Academy of Sciences
Quantum spin ice is a frustrated magnet that displays rich emergent phenomena. For example, the magnetic moments carried by the spins may separate into mobile magnetic charges, producing quantum fractional excitations known as spinons. The spinon moves in a background of disordered spins, and its motion is strongly coupled to the spin background. In this talk, I will demonstrate that the spinon dynamics can be described as a quantum walk with entropy-induced memory. Our numerical simulation shows that the dynamics of spinon exhibits a remarkable renormalization phenomenon: the spinon behaves as a massive free particle at low energy despite its strong coupling at the lattice scale.Universal Dynamic Magnetism in the Ytterbium Pyrochlores
Alannah Hallas McMaster University
The ytterbium pyrochlores, Yb2B2O7, are a family of materials with a remarkable diversity in their low-temperature physics. At the heart of their interesting physics is the proximity of their ground states to numerous competing phases. These proximate phases make the Yb pyrochlores very sensitive to perturbations such as pressure and off-stoichiometry. I will present a study of the effects of chemical pressure on the ytterbium pyrochlores, in which substitution of a non-magnetic constituent alters the lattice size and consequently inflicts an internal pressure on the system. We find that although each of Yb2B2O7 (B = Ge, Ti, Sn) exhibits a distinct dipole ordered state, there is a ubiquitous nature to their spin excitations. Furthermore, these spin excitations are highly unconventional in their own right and may hint at a hidden order parameter.Spin Slush in an Extended Spin Ice Model
Jeff Rau University of Waterloo
We introduce a new classical spin liquid on the pyrochlore lattice by extending spin ice with further neighbour interactions. This disorder-free spin model exhibits a form of dynamical heterogeneity with extremely slow relaxation for some spins while others fluctuate quickly down to zero temperature. We thus call this state "spin slush", in analogy to the heterogeneous mixture of solid and liquid water. This behaviour is driven by the structure of the ground state manifold that extends the two-in/two-out ice states to include branching structures built from three-in/one-out, three-out/one-in and all-in/all-out defects. Distinctive liquid-like patterns in the spin correlations serve as a signature of this intermediate range order. Finally, we discuss possible applications to materials as well the effects of quantum tunneling.Stochastic Resonance Magnetic Force Microscopy: A Technique for Nanoscale Imaging of Vortex Dynamics
Raffi Budakian Institute for Quantum Computing (IQC)
In this talk, I will describe a new technique—stochastic resonance magnetic force microscopy (SRMFM)—developed in my group for imaging the vortex dynamics in multiply connected superconducting devices. Unlike existing techniques, which directly image vortices, our technique relies on the mechanism of stochastic resonance to image the fluctuations between different vortex configurations. I will present data, taken using Josephson junction arrays and ring structures, that reveal striking geometric patterns which emerge when the energy of different vortex configurations become degenerate at well-defined positions of a magnetic tip that is scanned above the surface of the device. By analyzing the fluctuation rate as a function of temperature or external field, we obtain detailed information regarding the energy barriers connecting different vortex configurations, as well as energy scales associated with vortex-vortex interactions. The technique also provides a convenient means to manipulate vortices in multiply connected superconducting structures, which may prove useful in certain topological quantum-computing applications.Dynamics of Superrotations in 2+1 Dimensions
Steve Carlip University of California, Davis
General relativity is invariant under diffeomorphisms, and
excitations of the metric corresponding to diffeomorphisms
are nonphysical. In the presence of a boundary, though --
including a boundary at infinity -- the Einstein-Hilbert
action with suitable boundary terms is no longer fully
invariant, and certain diffeomorphisms are promoted to
physical degrees of freedom. After briefly describing how
this happens in (2+1)-dimensional AdS gravity, I will
report on work in progress on the asymptotically flat case,
for which the newly dynamical diffeomorphisms are the
superrotations, and the boundary action is related to
coadjoint orbits of the Virasoro group and Hill's equation.
Evidence for a Gapped Spin Liquid Ground State in Herbertsmithite Kagome Heisenberg Antiferromagnet
Takashi Imai McMaster University
The kagome lattice in a mineral compound "Herbertsmithite" represents structurally the most ideal kagome Heisenberg antiferromagnet known to date. Herbertsmithite does not undergo a magnetic long-range order or spin freezing at least down to ~J/2000. We will present 17-Oxygen and 2-Deuterium single crystal NMR study of Herbertsmithite. We will demonstrate that the ground state of the kagome plane has a spin gap ~ 0.05J [1], and ~5% excess Cu2+ ions occupying the out-of-plane Zn2+ sites are the only defects [2]. [1] M. Fu et al., Science 350, 655 (2015). [2] T. Imai et al., Phys. Rev. B 84, 020411 (2011).Organic materials: all-in-one systems for Mott physics - Quantum criticality, preformed pairs and spin liquids
Kazushi Kanoda University of Tokyo
A many-body quantum system on the verge of instability between competing ground states exhibits emergent phenomena. Interacting electrons on triangular lattices are likely subjected to multiple instabilities in the charge and spin degrees of freedom, affording diverse phenomena related to the Mott physics. The molecular conductors are superior model systems for studying the Mott physics because of the designability and controllability of material parameters such as lattice geometry and bandwidth by chemical substitution and/or pressure. In this symposium, I first introduce the fundamentals of organic materials and then present various quantum manifestations that interacting electrons in triangular-lattice organics show under variable correlation on the verge of the Mott metal-insulator transition. The topics include i) the quantum criticality of the Mott transition revealed by the resistivity that obeys quantum-critical scaling, ii) the pseudo-gap-like behavior of the metallic state, which is found to originate from preformed Cooper pairs that persist up to twice as high as Tc, and iii) the spin liquid state that emerges in the Mott insulating state, depending on the lattice geometry. I may touch the recent finding on a doped triangular lattice that exhibits a possible BEC-to-BCS crossover in superconductivity. The work presented here was performed in collaboration with T. Furukawa, H. Oike, J. Ibuka, M. Urai, Y. Suzuki, K. Miyagawa (UTokyo), Y. Shimizu (Nagoya Univ.), M. Ito, H. Taniguchi (Saitama Univ.) and R. Kato (RIKEN)From Wires to Cosmology
Mustafa Amin Massachusetts Institute of Technology (MIT)
Current observations provide precise but limited information about inflation and reheating. Theoretical considerations, however, suggest that the early universe might be filled with a large number of interacting fields with unknown interactions. How can we quantitatively understand the dynamics of perturbations during inflation and reheating in such scenarios and when only limited
constraints are available from observations? Based on a precise
mapping between particle production in cosmology to resistivity in disordered, quasi one-dimensional wires, I will provide a statistical framework to resolve such seemingly intractable calculations. A number of phenomenon in disordered wires find an analogue in particle production. For example, Anderson localization in quasi one-dimensional wires can be directly mapped to exponential particle production in the early universe. The talk will be focussed on the general framework and some toy examples, though in the end I will discuss possible (future) applications to calculating observables.
Honeycomb lattice quantum magnets with strong spin-orbit coupling
Young-June Kim University of Toronto
In recent years, there has been much interest in honeycomb lattice quantum magnets described by Kitaev-Heisenberg Hamiltonian. For example, honeycomb lattice iridates, such as Na2IrO3 and Li2IrO3 have been intensely scrutinized. Recently, we proposed that a 4d honeycomb magnet α-RuCl3 is a promising candidate material in which Kitaev physics could be studied. I will give an overview of the physics of alpha-RuCl3, and talk about recent experimental and theoretical advances.CMB spectral distortions within LCDM
Jens Chluba University of Manchester
Spectral distortions of the CMB provide a powerful new probe of early Universe processes. Even if so far no average spectral distortion has been seen, LCDM does predict several signals that are within reach of current technology. In this talk, I will give a broad brush overview of our most recent understanding of the formation and evolution of distortions in the early Universe, highlighting guaranteed LCDM signals and what we hope to learn from them about the Universe we live in.
Superconductivity and Charge Density Waves in the Clean 2D Limit
Adam Tsen Institute for Quantum Computing (IQC)
We have recently demonstrated an experimental platform to isolate 2D materials that are unstable in the ambient environment. I will discuss our recent studies of the charge density wave compound 1T-TaS2 and superconducting 2H-NbSe¬ in the atomically thin limit, made possible using this technique. In TaS2, we uncover a new surface charge density wave transition that is distinct from that in the bulk layers, as well as demonstrate continuous electrical control over this phase transition. In NbSe2, a small perpendicular magnetic field induces a transition to a quantum metallic phase, the resistivity of which obeys a unique field-scaling consistent with that predicted for a Bose metal. These methods and experiments open new doors for the study of other correlated 2D systems in the immediate future.