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  • 1
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    Evidence for Majorana bound states in an iron-based superconductor (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-10-19
    Description: The search for Majorana bound states (MBSs) has been fueled by the prospect of using their non-Abelian statistics for robust quantum computation. Two-dimensional superconducting topological materials have been predicted to host MBSs as zero-energy modes in vortex cores. By using scanning tunneling spectroscopy on the superconducting Dirac surface state of the iron-based superconductor FeTe 0.55 Se 0.45 , we observed a sharp zero-bias peak inside a vortex core that does not split when moving away from the vortex center. The evolution of the peak under varying magnetic field, temperature, and tunneling barrier is consistent with the tunneling to a nearly pure MBS, separated from nontopological bound states. This observation offers a potential platform for realizing and manipulating MBSs at a relatively high temperature.
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Probing the ultimate plasmon confinement limits with a van der Waals heterostructure (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-04-20
    Description: The ability to confine light into tiny spatial dimensions is important for applications such as microscopy, sensing, and nanoscale lasers. Although plasmons offer an appealing avenue to confine light, Landau damping in metals imposes a trade-off between optical field confinement and losses. We show that a graphene-insulator-metal heterostructure can overcome that trade-off, and demonstrate plasmon confinement down to the ultimate limit of the length scale of one atom. This is achieved through far-field excitation of plasmon modes squeezed into an atomically thin hexagonal boron nitride dielectric spacer between graphene and metal rods. A theoretical model that takes into account the nonlocal optical response of both graphene and metal is used to describe the results. These ultraconfined plasmonic modes, addressed with far-field light excitation, enable a route to new regimes of ultrastrong light-matter interactions.
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Percolation on networks with weak and heterogeneous dependency (2017)
    American Physical Society (APS)
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    Publication Date: 2017-03-02
    Description: Author(s): Ling-Wei Kong, Ming Li, Run-Ran Liu, and Bing-Hong Wang In real networks, the dependency between nodes is ubiquitous; however, the dependency is not always complete and homogeneous. In this paper, we propose a percolation model with weak and heterogeneous dependency; i.e., dependency strengths could be different between different nodes. We find that the … [Phys. Rev. E 95, 032301] Published Wed Mar 01, 2017
    Keywords: Networks and Complex Systems
    Print ISSN: 1539-3755
    Electronic ISSN: 1550-2376
    Topics: Physics
    Published by American Physical Society (APS)
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  • 4
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    Extortion provides alternative routes to the evolution of cooperation in structured populations (2017)
    American Physical Society (APS)
    Details
    Publication Date: 2017-05-03
    Description: Author(s): Xiongrui Xu, Zhihai Rong, Zhi-Xi Wu, Tao Zhou, and Chi Kong Tse In this paper, we study the evolution of cooperation in structured populations (individuals are located on either a regular lattice or a scale-free network) in the context of repeated games by involving three types of strategies, namely, unconditional cooperation, unconditional defection, and extort… [Phys. Rev. E 95, 052302] Published Mon May 01, 2017
    Keywords: Networks and Complex Systems
    Print ISSN: 1539-3755
    Electronic ISSN: 1550-2376
    Topics: Physics
    Published by American Physical Society (APS)
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  • 5
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    iPTF Discovery of the Rapid "Turn-On" of a Luminous Quasar (2017)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present a radio-quiet quasar at z = 0.237 discovered ''turning on'' by the intermediate Palomar Transient Factory (iPTF). The transient, iPTF 16bco, was detected by iPTF in the nucleus of a galaxy with an archival Sloan Digital Sky Survey spectrum with weak narrow-line emission characteristic of a low-ionization nuclear emission-line region (LINER). Our follow-up spectra show the dramatic appearance of broad Balmer lines and a power-law continuum characteristic of a luminous (L(sub bol) approx. equal 10(exp 45) erg/s) type 1 quasar 12 yr. later. Our photometric monitoring with PTF from 2009-2012 and serendipitous X-ray observations from the XMM-Newton Slew Survey in 2011 and 2015 constrain the change of state to have occurred less than 500 days before the iPTF detection. An enhanced broad H(alpha)/[O III] (lambda)5007 line ratio in the type 1 state relative to other changing-look quasars also is suggestive of the most rapid change of state yet observed in a quasar. We argue that the greater than 10 increase in Eddington ratio inferred from the brightening in UV and X-ray continuum flux is more likely due to an intrinsic change in the accretion rate of a preexisting accretion disk than an external mechanism such as variable obscuration, microlensing, or the tidal disruption of a star. However, further monitoring will be helpful in better constraining the mechanism driving this change of state. The rapid ''turn-on'' of the quasar is much shorter than the viscous infall timescale of an accretion disk and requires a disk instability that can develop around a approx. equal 10(exp 8)solar mass black hole on timescales less than 1 yr.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN51264 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 835; 2; 144
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  • 6
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    Sifting for Sapphires: Systematic Selection of Tidal Disruption Events in iPTF (2018)
    In:  CASI
    Details
    Publication Date: 2019-11-16
    Description: We present results from a systematic selection of tidal disruption events (TDEs) in a wide-area (4800 deg (exp 2)), g + R band, Intermediate Palomar Transient Factory (iPTF) experiment. Our selection targets typical optically-selected TDEs: bright (〉60% flux increase) and blue transients residing in the center of red galaxies. Using photometric selection criteria to down-select from a total of 493 nuclear transients to a sample of 26 sources, we then use follow-up UV imaging with the Neil Gehrels Swift Telescope, ground-based optical spectroscopy, and light curve fitting to classify them as 14 Type Ia supernovae (SNe Ia), 9 highly variable active galactic nuclei (AGNs), 2 confirmed TDEs, and 1 potential core-collapse supernova. We find it possible to filter AGNs by employing a more stringent transient color cut (g - r 〈 -0.2 mag); further, UV imaging is the best discriminator for filtering SNe, since SNe Ia can appear as blue, optically, as TDEs in their early phases. However, when UV- optical color is unavailable, higher precision astrometry can also effectively reduce SNe contamination in the optical. Our most stringent optical photometric selection criteria yields a 4.5:1 contamination rate, allowing for a manageable number of TDE candidates for complete spectroscopic follow-up and real-time classification in the ZTF era. We measure a TDE per galaxy rate of 1.7(sup +2:9) (sub -1:3) X 10(exp -4) gal(exp -1) yr(exp -1) (90% CL in Poisson statistics). This does not account for TDEs outside our selection criteria, thus may not reflect the total TDE population, which is yet to be fully mapped.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN67017 , Astrophysical Journal Supplement (ISSN 0067-0049) (e-ISSN 1538-4365); 238; 2; 15
    Format: application/pdf
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