56 research outputs found
Evaluation of conduction eigenchannels of an adatom probed by an STM tip
Ballistic conductance through a single atom adsorbed on a metallic surface
and probed by a scanning tunneling microscope (STM) tip can be decomposed into
eigenchannel contributions, which can be potentially obtained from shot noise
measurements. Our density functional theory calculations provide evidence that
transmission probabilities of these eigenchannels encode information on the
modifications of the adatom's local density of states caused by its interaction
with the STM tip. In the case of open shell atoms, this can be revealed in
nonmonotonic behavior of the eigenchannel's transmissions as a function of the
tip-adatom separation.Comment: 4.5 pages, 5 figures, REVTe
Electron-Phonon Coupling in Highly-Screened Graphene
Photoemission studies of graphene have resulted in a long-standing
controversy concerning the strength of the experimental electron-phonon
interaction in comparison with theoretical calculations. Using high-resolution
angle-resolved photoemission spectroscopy we study graphene grown on a copper
substrate, where the metallic screening of the substrate substantially reduces
the electron-electron interaction, simplifying the comparison of the
electron-phonon interaction between theory and experiment. By taking the
nonlinear bare bandstructure into account, we are able to show that the
strength of the electron-phonon interaction does indeed agree with theoretical
calculations. In addition, we observe a significant bandgap at the Dirac point
of graphene.Comment: Submitted to Phys. Rev. Lett. on July 20, 201
Electron dynamics in topological insulator based semiconductor-metal interfaces (topological p-n interface based on Bi2Se3 class)
Single-Dirac-cone topological insulators (TI) are the first experimentally
discovered class of three dimensional topologically ordered electronic systems,
and feature robust, massless spin-helical conducting surface states that appear
at any interface between a topological insulator and normal matter that lacks
the topological insulator ordering. This topologically defined surface
environment has been theoretically identified as a promising platform for
observing a wide range of new physical phenomena, and possesses ideal
properties for advanced electronics such as spin-polarized conductivity and
suppressed scattering. A key missing step in enabling these applications is to
understand how topologically ordered electrons respond to the interfaces and
surface structures that constitute a device. Here we explore this question by
using the surface deposition of cathode (Cu/In/Fe) and anode materials (NO)
and control of bulk doping in BiSe from P-type to N-type charge
transport regimes to generate a range of topological insulator interface
scenarios that are fundamental to device development. The interplay of
conventional semiconductor junction physics and three dimensional topological
electronic order is observed to generate novel junction behaviors that go
beyond the doped-insulator paradigm of conventional semiconductor devices and
greatly alter the known spin-orbit interface phenomenon of Rashba splitting.
Our measurements for the first time reveal new classes of diode-like
configurations that can create a gap in the interface electron density near a
topological Dirac point and systematically modify the topological surface state
Dirac velocity, allowing far reaching control of spin-textured helical Dirac
electrons inside the interface and creating advantages for TI superconductors
as a Majorana fermion platform over spin-orbit semiconductors.Comment: 14 pages, 4 Figure
Weak antilocalization in quasi-two-dimensional electronic states of epitaxial LuSb thin films
Observation of large non-saturating magnetoresistance in rare-earth
monopnictides has raised enormous interest in understanding the role of its
electronic structure. Here, by a combination of molecular-beam epitaxy,
low-temperature transport, angle-resolved photoemssion spectroscopy, and hybrid
density functional theory we have unveiled the bandstructure of LuSb, where
electron-hole compensation is identified as a mechanism responsible for large
magnetoresistance in this topologically trivial compound. In contrast to bulk
single crystal analogues, quasi-two-dimensional behavior is observed in our
thin films for both electron and holelike carriers, indicative of dimensional
confinement of the electronic states. Introduction of defects through growth
parameter tuning results in the appearance of quantum interference effects at
low temperatures, which has allowed us to identify the dominant inelastic
scattering processes and elucidate the role of spin-orbit coupling. Our
findings open up new possibilities of band structure engineering and control of
transport properties in rare-earth monopnictides via epitaxial synthesis.Comment: 20 pages, 12 figures; includes supplementary informatio
Why Virtue Ethics?
Contemporary virtue ethics, an agent-centred ethical theory, has been presented as a response to inadequacies in more traditional act-centred theories. In this paper, I argue that such a response is insufοcient: contemporary virtue ethics fails to avoid the inadequacies that it purports to avoid, and brings with it problems of its own. This paper is divided into 5 sections, in the οrst of which I introduce contemporary virtue ethics as an agent-centred and pluralistic ethical theory. In section 2, I present inadequacies that virtue ethics claims to avoid: being too reductive, too algorithmic, too abstract, self-effacing, and self-other asymmetric. In section 3, I consider and analyse virtue ethics’ account of right action and of motives in order to argue in section 4 that, if these inadequacies are indeed problems affecting traditional ethical theories, virtue ethics does not avoid these problems either— particularly because of its basis in the concept of virtues and its heavy reliance on phronesis. I show that another ethical theory, limited moral pluralism, has the same advantages of not being overly reductive, algorithmic, or abstract, and being self-other symmetric, and that virtue ethics does not avoid self-effacement as it claims to. I also question here whether self-effacement and self-other asymmetry should be considered problems when evaluating moral theories. Finally, I suggest in section 5 that virtue ethics is open to further criticisms of indeterminacy and lack of explanatory power
Growth and characterization of -Sn thin films on In- and Sb-rich reconstructions of InSb(001)
-Sn thin films can exhibit a variety of topologically non-trivial
phases. Both studying the transitions between these phases and making use of
these phases in eventual applications requires good control over the electronic
and structural quality of -Sn thin films. -Sn growth on InSb
often results in out-diffusion of indium, a p-type dopant. By growing
-Sn via molecular beam epitaxy on the Sb-rich c(44) surface
reconstruction of InSb(001) rather than the In-rich c(82), we
demonstrate a route to substantially decrease and minimize this indium
incorporation. The reduction in indium concentration allows for the study of
the surface and bulk Dirac nodes in -Sn via angle-resolved
photoelectron spectroscopy without the common approaches of bulk doping or
surface dosing, simplifying topological phase identification. The lack of
indium incorporation is verified in angle-resolved and -integrated ultraviolet
photoelectron spectroscopy as well as in clear changes in the Hall response
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