The New York Stock Market in the 1920s and 1930s: Did Stock Prices Move Together Too Much?

In this paper, we re-examine the stock market of the 1920s and 1930s for evidence of a bubble, a 'fad' or 'herding' behavior by studying individual stock returns. One story often advanced for the boom of 1928 and 1929 is that it was driven by the entry into the market of largely uninformed investors, who followed the fortunes of and invested in 'favorite' stocks. The recent theoretical literature on how 'noise traders' perturb financial markets is consistent with this description. The result of this behavior would be a tendency for the favorite stocks' prices to move together more than would be predicted by their shared fundamentals. Our results suggest that there was excess comovement in returns even before the boom began, but comovement increased significantly during the boom and was a signal characteristic of the tumultuous market of the early 1930s. These results are thus consistent with the possibility that a fad or crowd psychology played a role in the rise of the market, its crash and subsequent volatility.

Was there a bubble in the 1929 Stock Market?

Standard tests find that no bubbles are present in the stock price data for the last one hundred years. In contrast., historical accounts, focusing on briefer periods, point to the stock market of 1928-1929 as a classic example of a bubble. While previous studies have restricted their attention to the joint behavior of stock prices and dividends over the course of a century, this paper uses the behavior of the premia demanded on loans collateralized by the purchase of stocks to evaluate the claim that the boom and crash of 1929 represented a bubble. We develop a model that permits us to extract an estimate of the path of the bubble and its probability of bursting in any period and demonstrate that the premium behaves as would be expected in the presence of a bubble in stock prices. We also find that our estimate of the bubble's path has explanatory power when added to the standard cointegrating regressions of stock prices and dividends, in spite of the fact that our stock price and dividend series are cointegrated.

The effect of the Abrikosov vortex phase on spin and charge states in magnetic semiconductor-superconductor hybrids

We explore the possibility of using the inhomogeneous magnetic field carried by an Abrikosov vortex in a type-II superconductor to localize spin-polarized textures in a nearby magnetic semiconductor quantum well. We show how Zeeman-induced localization induced by a single vortex is indeed possible, and use these results to investigate the effect of a periodic vortex array on the transport properties of the magnetic semiconductor. In particular, we find an unconventional Integer Quantum Hall regime, and predict directly testable experimental consequences due to the presence of the periodic spin polarized structure induced by the superconducting vortex lattice in the magnetic semiconductor.Comment: 12 pages, 15 figure

Understanding the electromagnetic response of Graphene/Metallic nanostructures hybrids of different dimensionality

Plasmonic excitations, such as surface-plasmonpolaritons (SPPs) and graphene-plasmons (GPs), carry large momenta and are thus able to confine electromagnetic fields to small dimensions. This property makes them ideal platforms for subwavelength optical control and manipulation at the nanoscale. The momenta of these plasmons are even further increased if a scheme of metal-insulator-metal and graphene-insulator-metal are used for SPPs and GPs, respectively. However, with such large momenta, their far-field excitation becomes challenging. In this work, we consider hybrids of graphene and metallic nanostructures and study the physical mechanisms behind the interaction of far-field light with the supported high momenta plasmon modes. While there are some similarities in the properties of GPs and SPPs, since both are of the plasmon-polariton type, their physical properties are also distinctly different. For GPs we find two different physical mechanism related to either GPs confined to isolated cavities or large area collective grating couplers. Strikingly, we find that, although the two systems are conceptually different, under specific conditions, they can behave similarly. By applying the same study to SPPs, we find a different physical behavior, which fundamentally stems from the different dispersion relations of SPPs as compared to GPs. Furthermore, these hybrids produce large field enhancements that can also be electrically tuned and modulated making them the ideal candidates for a variety of plasmonic devices.N.M.R. P. and F. H.L.K. acknowledge support from the European Commission through the Project "Graphene-Driven Revolutions in ICT and Beyond" (Ref. No. 881603, CORE 3). N. M.R. P. and T.G.R. acknowledge COMPETE 2020, PORTUGAL 2020, FEDER and the Portuguese Foundation for Science and Technology (FCT) through Project POCI-01-0145-FEDER-028114. F.H.L.K. acknowledges financial support from the Government of Catalonia through the SGR Grant, and from the Spanish Ministry of Economy and Competitiveness through the "Severo Ochoa" Programme for Centres of Excellence in RD (SEV-2015-0522); support by Fundacio Cellex Barcelona, Generalitat de Catalunya through the CERCA Program, and the Mineco Grants Ramo ' n y Cajal (RYC-2012-12281, Plan Nacional (FIS2013-47161-P and FIS2014-59639-JIN) and the Agency for Management of University and Research Grants (AGAUR) 2017 SGR 1656. This work was supported by the ERC TOPONANOP under Grant Agreement No. 726001 and the MINECO Plan Nacional Grant 2D-NANOTOP under Reference No. FIS2016-81044-P

Topological Graphene plasmons in a plasmonic realization of the Su-Schrieffer-Heeger Model

Graphene hybrids, made of thin insulators, graphene, and metals can support propagating acoustic plasmons (AGPs). The metal screening modifies the dispersion relation of usual graphene plasmons leading to slowly propagating plasmons, with record confinement of electromagnetic radiation. Here, we show that a graphene monolayer, covered by a thin dielectric material and an array of metallic nanorods, can be used as a robust platform to emulate the Su-Schrieffer-Heeger model. We calculate the Zak's phase of the different plasmonic bands to characterize their topology. The system shows bulk-edge correspondence: strongly localized interface states are generated in the domain walls separating arrays in different topological phases. We find signatures of the nontrivial phase which can directly be probed by far-field mid-IR radiation, hence allowing a direct experimental confirmation of graphene topological plasmons. The robust field enhancement, highly localized nature of the interface states, and their gate-tuned frequencies expand the capabilities of AGP-based devices.T.G.R. acknowledges funding from Fundacao para a Ciência e a Tecnologia and Instituto de Telecomunicacoes. grant number UID/50008/2020.in the framework of the project Sym-Break and Mario G. Silveirinha for useful discussions. Y.V.B., N.M.R.P. and F.H.L.K. acknowledge support from the European Commission through the project "Graphene-Driven Revolutions in ICT and Beyond" (ref. no. 881603, CORE 3). Y.V.B. and N.M.R.P. acknowledge COMPETE 2020, PORTUGAL 2020, FEDER, and the Portuguese Foundation for Science and Technology (FCT) through project POCI-010145-FEDER-028114. F.H.L.K. acknowledges financial support from the Government of Catalonia through the SGR grant, the Spanish Ministry of Economy and Competitiveness, through the "Severo Ochoa" Programme for Centres of Excellence in RD (SEV-2015-0522), Fundacio Cellex Barcelona, Generalitat de Catalunya through the CERCA program, the Mineco grants Ramon y Cajal (RYC-201212281), Plan Nacional (FIS2013-47161-P and FIS2014-59639JIN), and the Agency for Management of University and Research Grants (AGAUR) 2017 SGR 1656. This work was supported by the ERC TOPONANOP under grant agreement n 726001 and the MINECO Plan Nacional Grant 2DNANOTOP under reference no FIS2016-81044-P

Cloaking resonant scatterers and tuning electron flow in graphene

We consider resonant scatterers with large scattering cross-sections in graphene that are produced by a gated disk or a vacancy, and show that a gated ring can be engineered to produce an efficient electron cloak. We also demonstrate that this same scheme can be applied to tune the direction of electron flow. Our analysis is based on a partial-wave expansion of the electronic wave-functions in the continuum approximation, described by the Dirac equation. Using a symmetrized version of the massless Dirac equation, we derive a general condition for the cloaking of a scatterer by a potential with radial symmetry. We also perform tight-binding calculations to show that our findings are robust against the presence of disorder in the gate potential.NMRP acknowledges support from EC under Graphene Flagship (Contract No. CNECT-ICT604391), the hospitality of the Instituto de Física of the UFRJ, and stimulating discussions with Bruno Amorim on the Lippamnn-Schwinger equation for Dirac electrons. TGR thanks the Brazilian agencies CNPq and FAPERJ and Brazil Science without Borders program for nancial support. FAP acknowledges CAPES (Grant No. BEX 1497/14-6) and CNPq (Grant No. 303286/2013-0) for financial suppor

Topological photonic Tamm states and the Su-Schrieffer-Heeger model

In this paper we study the formation of topological Tamm states at the interface between a semi-infinite one-dimensional (1D) photonic crystal and a metal. We show that when the system is topologically nontrivial there is a single Tamm state in each of the band gaps, whereas if it is topologically trivial the band gaps host no Tamm states. We connect the disappearance of the Tamm states with a topological transition from a topologically nontrivial system to a topologically trivial one. This topological transition is driven by the modification of the dielectric functions in the unit cell. Our interpretation is further supported by an exact mapping between the solutions of Maxwell's equations and the existence of a tight-binding representation of those solutions. We show that the tight-binding representation of the 1D photonic crystal, based on Maxwell's equations, corresponds to a Su-Schrieffer-Heeger-type model (SSH model) for each set of pairs of bands. By expanding this representation near the band edge we show that the system can be described by a Dirac-like Hamiltonian. It allows one to characterize the topology associated with the solution of Maxwell's equations via the winding number. In addition, for the infinite system, we provide an analytical expression for the photonic bands from which the band gaps can be computed.N.M.R.P., M.I.V., and Y.V.B. acknowledge support from the European Commission through the project GrapheneDriven Revolutions in ICT and Beyond (Ref. No. 785219) and the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Financing UID/FIS/04650/2019. N.M.R.P., T.G.R., and Y.V.B. acknowledge COMPETE2020, PORTUGAL2020, FEDER, and the Portuguese Foundation for Science and Technology (FCT) through Project No. POCI-01-0145-FEDER-028114. The authors acknowledge Andre Chaves for suggesting the starting point of the analytical approach to the photonic bands. N.M.R.P. acknowledges stimulating discussions with Joaquin Fernandez-Rossier on the topic of the paper. J.C.G.H. acknowledges the hospitality of the physics department of SDU, Denmark, where this work was completed. The authors are thankful to Asger Mortensen and Mario Silveirinha for their careful and critical reading of the manuscript

PANDORA: analysis of protein and peptide sets through the hierarchical integration of annotations

Derivation of biological meaning from large sets of proteins or genes is a frequent task in genomic and proteomic studies. Such sets often arise from experimental methods including large-scale gene expression experiments and mass spectrometry (MS) proteomics. Large sets of genes or proteins are also the outcome of computational methods such as BLAST search and homology-based classifications. We have developed the PANDORA web server, which functions as a platform for the advanced biological analysis of sets of genes, proteins, or proteolytic peptides. First, the input set is mapped to a set of corresponding proteins. Then, an analysis of the protein set produces a graph-based hierarchy which highlights intrinsic relations amongst biological subsets, in light of their different annotations from multiple annotation resources. PANDORA integrates a large collection of annotation sources (GO, UniProt Keywords, InterPro, Enzyme, SCOP, CATH, Gene-3D, NCBI taxonomy and more) that comprise ∼200 000 different annotation terms associated with ∼3.2 million sequences from UniProtKB. Statistical enrichment based on a binomial approximation of the hypergeometric distribution and corrected for multiple hypothesis tests is calculated using several background sets, including major gene-expression DNA-chip platforms. Users can also visualize either standard or user-defined binary and quantitative properties alongside the proteins. PANDORA 4.2 is available at http://www.pandora.cs.huji.ac.il

Entanglement in the One-dimensional Kondo Necklace Model

We discuss the thermal and magnetic entanglement in the one-dimensional Kondo necklace model. Firstly, we show how the entanglement naturally present at zero temperature is distributed among pairs of spins according to the strength of the two couplings of the chain, namely, the Kondo exchange interaction and the hopping energy. The effect of the temperature and the presence of an external magnetic field is then investigated, being discussed the adjustment of these variables in order to control the entanglement available in the system. In particular, it is indicated the existence of a critical magnetic field above which the entanglement undergoes a sharp variation, leading the ground state to a completely unentangled phase.Comment: 8 pages, 13 EPS figures. v2: four references adde