Quantum oscillations in electron doped high temperature superconductors

Quantum oscillations in hole doped high temperature superconductors are difficult to understand within the prevailing views. An emerging idea is that of a putative normal ground state, which appears to be a Fermi liquid with a reconstructed Fermi surface. The oscillations are due to formation of Landau levels. Recently the same oscillations were found in the electron doped cuprate, $\mathrm{Nd_{2-x}Ce_{x}CuO_{4}}$, in the optimal to overdoped regime. Although these electron doped non-stoichiometric materials are naturally more disordered, they strikingly complement the hole doped cuprates. Here we provide an explanation of these observations from the perspective of density waves using a powerful transfer matrix method to compute the conductance as a function of the magnetic field.Comment: An expanded version, accepted in Phys. Rev. B

The sound of concepts: The link between auditory and conceptual brain systems

Concepts in long-term memory are important building blocks of human cognition and are the basis for object recognition, language and thought. While it is well accepted that concepts are comprised of features related to sensory object attributes, it is still unclear how these features are represented in the brain. Of central interest is whether concepts are essentially grounded in perception. This would imply a common neuroanatomical substrate for perceptual and conceptual processing. Here we show using functional magnetic resonance imaging and recordings of event-related potentials that acoustic conceptual features rapidly recruit auditory areas even when implicitly presented through visual words. Recognizing words denoting objects for which acoustic features are highly relevant (e.g. "telephone") suffices to ignite cell assemblies in the posterior superior and middle temporal gyrus (pSTG/MTG) that were also activated by listening to real sounds. Activity in pSTG/MTG had an onset of 150 ms and increased parametrically as a function of acoustic feature relevance. Both findings suggest a conceptual origin of this effect rather than post-conceptual strategies such as imagery. The presently demonstrated link between auditory and conceptual brain systems parallels observations in other memory systems suggesting that modality-specificity represents a general organizational principle in cortical memory representation. The understanding of concepts as a partial reinstatement of brain activity during perception stresses the necessity of rich sensory experiences for concept acquisition. The modality-specific nature of concepts could also explain the difficulties in achieving a consensus about overall definitions of abstract concepts such as freedom or justice unless embedded in a concrete, experienced situation

Cooper pair tunneling in junctions of singlet quantum Hall states and superconductors

We propose tunnel junctions of a Hall bar and a superconducting lead, for observing Cooper-pair tunneling into singlet fractional quantum Hall edge states. These tunnel junctions provide a natural means of extracting precise information of the spin polarization and the filling factor of the state. The low energy regime of one of the set-ups is governed by a novel quantum entangled fixed point.Comment: 4 pages, 1 figure (3 subfigures); new title and abstract; new discussion of the quantum entangled fixed point; final manuscript as publishe

Signatures of unconventional pairing in near-vortex electronic structure of LiFeAs

A major question in Fe-based superconductors remains the structure of the pairing, in particular whether it is of unconventional nature. The electronic structure near vortices can serve as a platform for phase-sensitive measurements to answer this question. By solving Bogoliubov-de Gennes equations for LiFeAs, we calculate the energy-dependent local electronic structure near a vortex for different nodeless gap-structure possibilities. At low energies, the local density of states (LDOS) around a vortex is determined by the normal-state electronic structure. However, at energies closer to the gap value, the LDOS can distinguish an anisotropic from a conventional isotropic s-wave gap. We show within our self-consistent calculation that in addition, the local gap profile differs between a conventional and an unconventional pairing. We explain this through admixing of a secondary order parameter within Ginzburg-Landau theory. In-field scanning tunneling spectroscopy near vortices can therefore be used as a real-space probe of the gap structure

A Fractional Fokker-Planck Model for Anomalous Diffusion

In this paper we present a study of anomalous diffusion using a Fokker-Planck description with fractional velocity derivatives. The distribution functions are found using numerical means for varying degree of fractionality observing the transition from a Gaussian distribution to a L\'evy distribution. The statistical properties of the distribution functions are assessed by a generalized expectation measure and entropy in terms of Tsallis statistical mechanics. We find that the ratio of the generalized entropy and expectation is increasing with decreasing fractionality towards the well known so-called sub-diffusive domain, indicating a self-organising behavior.Comment: 22 pages, 14 figure

Sub-monolayer nucleation and growth of complex oxide heterostructures at high supersaturation and rapid flux modulation

We report on the non-trivial nanoscale kinetics of the deposition of novel complex oxide heterostructures composed of a unit-cell thick correlated metal LaNiO3 and dielectric LaAlO3. The multilayers demonstrate exceptionally good crystallinity and surface morphology maintained over the large number of layers, as confirmed by AFM, RHEED, and synchrotron X-ray diffraction. To elucidate the physics behind the growth, the temperature of the substrate and the deposition rate were varied over a wide range and the results were treated in the framework of a two-layer model. These results are of fundamental importance for synthesis of new phases of complex oxide heterostructures.Comment: 13 pages, 6 figure

Interspecific competition underlying mutualistic networks

The architecture of bipartite networks linking two classes of constituents is affected by the interactions within each class. For the bipartite networks representing the mutualistic relationship between pollinating animals and plants, it has been known that their degree distributions are broad but often deviate from power-law form, more significantly for plants than animals. Here we consider a model for the evolution of the mutualistic networks and find that their topology is strongly dependent on the asymmetry and non-linearity of the preferential selection of mutualistic partners. Real-world mutualistic networks analyzed in the framework of the model show that a new animal species determines its partners not only by their attractiveness but also as a result of the competition with pre-existing animals, which leads to the stretched-exponential degree distributions of plant species.Comment: 5 pages, 3 figures, accepted version in PR

A microfabricated steel and glass radiation detector with inherent wireless signaling

This paper describes an investigation of the performance compromises imposed by a manufacturing approach that utilizes lithographic micromachining processes to fabricate a wireless beta/gamma radiation detector. The device uses in-package assembly of stainless steel electrodes and glass spacers. These elements are micromachined using photochemical etching and powder blasting, respectively. The detector utilizes a commercial, TO-5 package that is hermetically sealed at 760 Torr with an Ar fill-gas. Gas microdischarges between the electrodes, which are initiated by the radiation, transmit wideband wireless signals. The detector diameter and height are 9 and 9.6 mm, respectively, and it weighs 0.97 g. The device performance has been characterized using various sealed, radioisotope sources, e.g., 30–99 µCi from 137 Cs (which is a beta and gamma emitter) and 0.1 µCi from 90 Sr (which is a pure beta emitter). It has a measured output of >15.5 counts s _1 when in close proximity to 99 µCi from 137 Cs. The wireless signaling spans 1.25 GHz at receiving antenna-to-detector distances >89 cm, when in close proximity to a 0.1 µCi 90 Sr source. The estimated intrinsic detection efficiency (i.e. with the background rate subtracted) is 3.34% as measured with the biasing arrangement described in the paper.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90792/1/0960-1317_21_1_015003.pd