arXiv subjects

Alan R. Bishop

Publications and source records attributed to Alan R. Bishop.

30 records · Page 2Linked to original sources

arXiv2007

Terahertz and Infrared Uncooled Detector Based on a Microcantilever as a Radiation Pressure Sensor

We consider a far infrared (terahertz), room-temperature detector based on a microcantilever sensor of the radiation pressure. This system has a significantly higher sensitivity than existing uncooled detectors in the far infrared (terahertz) spectral region. The significant enhancement of sensitivity is due the combination non-absorption detection method and high quality optical microcavity. Our theoretical analysis of the detector sensitivity and numerical simulations demonstrate that the narrowband heterodyne detector with the band width 30 MHz has a minimal measurable intensity by three orders of magnitude less than conventional uncooled detectors. In the case of the broadband detector, the noise equivalent temperature difference (NETD) is 7.6 mK, which is significantly smaller than for conventional uncooled thermal detectors.

physics.ins-det↗

arXiv2007

Suppression of Intensity Fluctuations in Free Space High-Speed Optical Communication Based on Spectral Encoding of a Partially Coherent Beam

A new concept of a free-space, high-speed (Gbps) optical communication system based on spectral encoding of radiation from a broadband pulsed laser is developed. It is shown that, in combination with the use of partially coherent laser beams and a relatively slow photosensor, scintillations can be suppressed by orders of magnitude for distances of more than 10 km. We also consider the spectral encoding of radiation from a LED as a gigabit rate solution of the "last mile" problem and rapid-deployment systems for disaster recovery.

physics.optics↗

arXiv2006

Phase diagram of the spin-Peierls chain with local coupling

We explore the ground-state phase diagram of a Heisenberg spin chain coupled locally to optical phonons (bond coupling), using large-scale density matrix renormalization group calculations and an extended perturbative analysis. For the quantum phase transition from the spin liquid to the dimerized phase, we find deviations from previous quantum Monte Carlo and flow equation results.

cond-mat.str-el↗

arXiv2005

Local edge modes in doped cuprates with checkerboard polaronic heterogeneity

We study a periodic polaronic system, which exhibits a nanoscale superlattice structure, as a model for hole-doped cuprates with checkerboard-like heterogeneity, as has been observed recently by scanning tunneling microscopy (STM). Within this model, the electronic and phononic excitations are investigated by applying an unrestricted Hartree-Fock and a random phase approximation (RPA) to a multiband Peierls-Hubbard Hamiltonian in two dimensions.

cond-mat.str-el↗

arXiv2004

Super-roughening as a disorder-dominated flat phase

We study the phenomenon of super-roughening found on surfaces growing on disordered substrates. We consider a one-dimensional version of the problem for which the pure, ordered model exhibits a roughening phase transition. Extensive numerical simulations combined with analytical approximations indicate that super-roughening is a regime of asymptotically flat surfaces with non-trivial, rough short-scale features arising from the competition between surface tension and disorder. Based on this evidence and on previous simulations of the two-dimensional Random sine-Gordon model [Sanchez et al., Phys. Rev. E 62, 3219 (2000)], we argue that this scenario is general and explains equally well the hitherto poorly understood two-dimensional case.

cond-mat.stat-mech↗

arXiv2002

Enhancements of the superconducting transition temperature within the two-band model

The two-band model as introduced by Suhl, Matthias and Walker [Phys. Rev. Lett. 3, 551 (1959)] accounts for multiple energy bands in the vicinity of the Fermi energy which could contribute to electron pairing in superconducting systems. Here, extensions of this model are investigated wherein the effects of coupled superconducting order parameters with different symmetries and the presence of strong electron-lattice coupling on the superconducting transition temperature Tc are studied. Substantial enhancements of Tc are obtained from both effects.

cond-mat.supr-con↗

arXiv2002

Glassy behavior in systems with Kac-type step-function interaction

We study a system with a weak, long-range repulsive Kac-type step-function interaction within the framework of a replicated effective $ϕ^4$-theory. The occurrence of extensive configurational entropy, or an exponentially large number of metastable minima in the free energy (characteristic of a glassy state), is demonstrated. The underlying mechanism of mesoscopic patterning and defect organizations is discussed.

cond-mat.soft↗

arXiv2001

Effects of Transport Memory and Nonlinear Damping in a Generalized Fisher's Equation

Memory effects in transport require, for their incorporation into reaction diffusion investigations, a generalization of traditional equations. The well-known Fisher's equation, which combines diffusion with a logistic nonlinearity, is generalized to include memory effects and traveling wave solutions of the equation are found. Comparison is made with alternate generalization procedures.

nlin.PS↗

arXiv2001

The Phase Diagram of High-Tc Superconductors in the Presence of Dynamic Stripes

The phase diagram of superconducting copper oxides is calculated as a function of doping based on a theory of dynamic stripe induced superconductivity. The two major conclusions from the theory and the numerical analysis are that T* (the pseudogap onset) and Tc (superconductivity onset) are correlated through the pseudogap, which induces a gap in the single particle energies that persists into the superconducting state. By decreasing the doping the pseudogap Delta* increases and T* increases, but when Delta* exceeds a certain critical value the superconducting transition temperature Tc is suppressed. A mixed s- and d-wave pairing symmetry is also examined as function of doping.

cond-mat.supr-con↗

arXiv2000

Theory of Dynamic Stripe Induced Superconductivity

Since the recently reported giant isotope effect on T* [1] could be consistently explained within an anharmonic spin-charge-phonon interaction model, we consider here the role played by stripe formation on the superconducting properties within the same model. This is a two-component scenario and we recast its basic elements into a BCS effective Hamiltonian. We find that the stripe formation is vital to high-Tc superconductivity since it provides the glue between the two components to enhance Tc to the unexpectedly large values observed experimentally.

cond-mat.supr-con↗

arXiv1999

Intrinsic localized modes in the charge-transfer solid PtCl

We report a theoretical analysis of intrinsic localized modes in a quasi-one-dimensional charge-transfer-solid $[Pt(en)_2][Pt(en)_2 Cl_2](ClO_4)_4$(PtCl). We discuss strongly nonlinear features of resonant Raman overtone scattering measurements on PtCl, arising from quantum intrinsic localized (multiphonon) modes (ILMs) and ILM-plus-phonon states. We show, that Raman scattering data displays clear signs of a non-thermalization of lattice degrees-of-freedom, manifested in a nonequilibrium density of intrinsic localized modes.

cond-mat↗

arXiv1997

Theory of colossal magnetoresistance

The history and recent developments in studying (colossal) magnetoresistance in perovskite manganese oxides is reviewed. We emphasize the growing evidence for strongly coupled spin, charge and lattice degrees of freedom. Together with disorder, these provide the microscopic driving forces for local and inhomogeneous textures. The modeling and experimental probes for localized charge-spin-lattice (polaron) structures, and their multiscale ordering, is discussed in terms of a growing synergy of solid state physics and materials science perspectives.

cond-mat↗