Inelastic Neutron Scattering Signal from Deconfined Spinons in a Fractionalized Antiferromagnet

We calculate the contribution of deconfined spinons to inelastic neutron scattering (INS) in the fractionalized antiferromagnet (AF*), introduced elsewhere. We find that the presence of free spin-1/2 charge-less excitations leads to a continuum INS signal above the Néel gap. This signal is found above and in addition to the usual spin-1 magnon signal, which to lowest order is the same as in the more conventional confined antiferromagnet. We calculate the relative weights of these two signals and find that the spinons contribute to the longitudinal response, where the magnon signal is absent to lowest order. Possible higher-order effects of interactions between magnons and spinons in the AF* phase are also discussed

Critical Dynamics of Superconductors in the Charged Regime

The charged regime of the superconductor-metal transition was analyzed by applying a finite temperature critical dynamics. A transverse gage field coupling was applied to the superconducting order parameter. A new dynamic universality class characeterized by a finite fixed point ratio between the transport coefficients associated with the order parameter and gage fields was found by assuming relaxational dynamics for both the order parameter and gage fields within a renormalization group scheme. It was found that various features of the dynamic universality class of the charged superconductor appeared in measurable quantities

Quasiparticle density of states in dirty high-T_c superconductors

We study the density of quasiparticle states of dirty d-wave superconductors. We show the existence of singular corrections to the density of states due to quantum interference effects. We then argue that the density of states actually vanishes in the localized phase as $|E|$ or $E^2$ depending on whether time reversal is a good symmetry or not. We verify this result for systems without time reversal symmetry in one dimension using supersymmetry techniques. This simple, instructive calculation also provides the exact universal scaling function for the density of states for the crossover from ballistic to localized behaviour in one dimension. Above two dimensions, we argue that in contrast to the conventional Anderson localization transition, the density of states has critical singularities which we calculate in a $2+\epsilon$ expansion. We discuss consequences of our results for various experiments on dirty high-$T_c$ materials

Integrating mission, logistics, and task planning for skills-based robot control in industrial kitting applications

This paper presents an integrated cognitive robotics systemfor industrial kitting operations in a modern factory setting.The robot system combines low-level robot control and execution monitoring with automated mission and task planning,and a logistics planner which communicates with the factory’smanufacturing execution system. The system has been implemented and tested on a series of automotive kitting problems,where collections of parts are picked from a warehouse anddelivered to the production line. The system has been empirically evaluated and the complete framework shown to besuccessful at assembling kits in a small factory environment

Interplay between lattice-scale physics and the quantum Hall effect in graphene

Graphene's honeycomb lattice structure underlies much of the remarkable physics inherent in this material, most strikingly through the formation of two ``flavors'' of Dirac cones for each spin. In the quantum Hall regime, the resulting flavor degree of freedom leads to an interesting problem when a Landau level is partially occupied. Namely, while Zeeman splitting clearly favors polarizing spins along the field, precisely how the states for each flavor are occupied can become quite delicate. Here we focus on clean graphene sheets in the regime of quantum Hall ferromagnetism, and discuss how subtler lattice-scale physics, arising either from interactions or disorder, resolves this ambiguity to measurable consequence. Interestingly, such lattice-scale physics favors microscopic symmetry-breaking order coexisting with the usual liquid-like quantum Hall physics emerging on long length scales. The current experimental situation is briefly reviewed in light of our discussion.Comment: 6 pages, 2 figures; short revie

Advanced technologies for future ground-based, laser-interferometric gravitational wave detectors

We present a review of modern optical techniques being used and developed for the field of gravitational wave detection. We describe the current state-of-the-art of gravitational waves detector technologies with regard to optical layouts, suspensions and test masses. We discuss the dominant sources and noise in each of these subsystems and the developments that will help mitigate them for future generations of detectors. We very briefly summarise some of the novel astrophysics that will be possible with these upgraded detectors

Detecting fractions of electrons in the high-TcT_c cuprates

We propose several tests of the idea that the electron is fractionalized in the underdoped and undoped cuprates. These include the ac Josephson effect, and tunneling into small superconducting grains in the Coulomb blockade regime. In both cases, we argue that the results are qualitatively modified from the conventional ones if the insulating tunnel barrier is fractionalized. These experiments directly detect the possible existence of the chargon - a charge $e$ spinless boson - in the insulator. The effects described in this paper provide a means to probing whether the undoped cuprate (despite it's magnetism) is fractionalized. Thus, the experiments discussed here are complementary to the flux-trapping experiment we proposed in our earlier work(cond-mat/0006481).Comment: 7 pages, 5 figure

Fractionalization, topological order, and cuprate superconductivity

This paper is concerned with the idea that the electron is fractionalized in the cuprate high-$T_c$ materials. We show how the notion of topological order may be used to develop a precise theoretical characterization of a fractionalized phase in spatial dimension higher than one. Apart from the fractional particles into which the electron breaks apart, there are non-trivial gapped topological excitations - dubbed "visons". A cylindrical sample that is fractionalized exhibits two disconnected topological sectors depending on whether a vison is trapped in the "hole" or not. Indeed, "vison expulsion" is to fractionalization what the Meissner effect ("flux expulsion") is to superconductivity. This understanding enables us to address a number of conceptual issues that need to be confronted by any theory of the cuprates based on fractionalization ideas. We argue that whether or not the electron fractionalizes in the cuprates is a sharp and well-posed question with a definite answer. We elaborate on our recent proposal for an experiment to unambiguously settle this issue.Comment: 18 pages, 7 figure

Ring exchange, the Bose metal, and bosonization in two dimensions

Motivated by the high-T_c cuprates, we consider a model of bosonic Cooper pairs moving on a square lattice via ring exchange. We show that this model offers a natural middle ground between a conventional antiferromagnetic Mott insulator and the fully deconfined fractionalized phase which underlies the spin-charge separation scenario for high-T_c superconductivity. We show that such ring models sustain a stable critical phase in two dimensions, the *Bose metal*. The Bose metal is a compressible state, with gapless but uncondensed boson and ``vortex'' excitations, power-law superconducting and charge-ordering correlations, and broad spectral functions. We characterize the Bose metal with the aid of an exact plaquette duality transformation, which motivates a universal low energy description of the Bose metal. This description is in terms of a pair of dual bosonic phase fields, and is a direct analog of the well-known one-dimensional bosonization approach. We verify the validity of the low energy description by numerical simulations of the ring model in its exact dual form. The relevance to the high-T_c superconductors and a variety of extensions to other systems are discussed, including the bosonization of a two dimensional fermionic ring model