999 research outputs found
Structure and correlation effects in semiconducting SrTiOâ
We have investigated the effects of structure change and electron correlation on SrTiOâ single crystals using angle-resolved photoemission spectroscopy. We show that the cubic to tetragonal phase transition at 105 K is manifested by a charge transfer from in-plane (dyz and dzx) bands to out-of-plane (dxy) band, which is opposite to the theoretical predictions. Along this second-order phase transition, we find a smooth evolution of the quasiparticle strength and effective masses. The in-plane band exhibits a peak-dip-hump lineshape, indicating a high degree of correlation on a relatively large (170 meV) energy scale, which is attributed to the polaron formation
Morphology of graphene thin film growth on SiC(0001)
Epitaxial films of graphene on SiC(0001) are interesting from a basic physics
as well as applications-oriented point of view. Here we study the emerging
morphology of in-vacuo prepared graphene films using low energy electron
microscopy (LEEM) and angle-resolved photoemission (ARPES). We obtain an
identification of single and bilayer of graphene film by comparing the
characteristic features in electron reflectivity spectra in LEEM to the PI-band
structure as revealed by ARPES. We demonstrate that LEEM serves as a tool to
accurately determine the local extent of graphene layers as well as the layer
thickness
On the zeros of a minimal realization
AbstractIn an earlier work, the authors have introduced a coordinate-free, module-theoretic definition of zeros for the transfer function G(s) of a linear multivariable system (A,B,C). The first contribution of this paper is the construction of an explicit k[z]-module isomorphism from that zero module, Z(G), to Vâ/Râ, where Vâ is the supremal (A,B)-invariant subspace contained in kerC and Râ is the supremal (A,B)-controllable subspace contained in kerC, and where (A,B,C) constitutes a minimal realization of G(s). The isomorphism is developed from an exact commutative diagram of k-vector spaces. The second contribution is the introduction of a zero-signal generator and the establishment of a relation between this generator and the classic notion of blocked signal transmissions
AntipsychoticâInduced Hyperprolactinemia
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90238/1/phco.29.1.64.pd
Three Papers in Applied Microeconomics and Econometrics
This dissertation is comprised of three distinct papers covering topics in appliedmicroeconomics and applied econometrics. The first paper addresses a common problem faced by empirical researchers wishing to estimate Markov regime-switching models. For these models, testing for the possible presence of more than one regime requires the use of a non-standard test statistic. The analytic steps needed to implement the test of Markov regime-switching proposed by Cho & White (2007) are derived in detail in Carter & Steigerwald (2013). We summarize those implementation steps and address the computational issues that arise. A new Stata command to compute the regime-switching critical values, rscv, is introduced and presented in the context of empirical economic research. This paper is joint work with Douglas Steigerwald, and has previously appeared in the Stata Journal (Bostwick and Steigerwald, 2014).In the second paper, I address a question in the field of economics of education: that is,whether college students use their choice of major as a signal of unobserved productivityin the labor market. I propose a model of postsecondary education in which major fieldof study can be used by individuals to signal productivity to employers. Under thissignaling model, I show that geographic areas with high access to elite universities resultin fewer science, technology, engineering, and mathematics (STEM) majors among lower ability students at non-elite colleges. Using data from the National Center for Education Statistics' Baccalaureate and Beyond survey, I find evidence that is consistent with the signaling model prediction, specifically a 2.3-3.7 percentage point (or 16-25%) decrease in the probability of choosing a STEM major among lower ability students in areas with greater access to elite colleges. This paper has previously appeared in Economic Inquiry (Bostwick, 2016).In the third paper, I analyze an unexpected consequence of a highly debated educationpolicy. Many school districts are now considering delaying high school start times toaccommodate the sleep schedules of teens. This paper explores whether such policychanges can have an impact on teen car accident rates. This impact could functionboth through a direct effect on teen sleep deprivation and indirectly through changes tothe driving environment, i.e. shifting teen commute times into the high volume, "rushhour" of the morning. I find that, during the morning commute hours, any potentialeffect stemming from avoided sleep deprivation is offset by the effect of shifting teendriving into rush hour, so that a 15 minute delay in high school start times leads to a21% increase in morning teen accidents. However, by focusing on late-night accidents, Ialso find evidence of a persistent sleep effect. By decreasing teen sleep deprivation, a 15 minute delay in school start times leads to a 26% decrease in late-night teen accidents
Anderson Transition in Disordered Graphene
We use the regularized kernel polynomial method (RKPM) to numerically study
the effect disorder on a single layer of graphene. This accurate numerical
method enables us to study very large lattices with millions of sites, and
hence is almost free of finite size errors. Within this approach, both weak and
strong disorder regimes are handled on the same footing. We study the
tight-binding model with on-site disorder, on the honeycomb lattice. We find
that in the weak disorder regime, the Dirac fermions remain extended and their
velocities decrease as the disorder strength is increased. However, if the
disorder is strong enough, there will be a {\em mobility edge} separating {\em
localized states around the Fermi point}, from the remaining extended states.
This is in contrast to the scaling theory of localization which predicts that
all states are localized in two-dimensions (2D).Comment: 4 page
Controlling the Electronic Structure of Bilayer Graphene
We describe the synthesis of bilayer graphene thin films deposited on insulating silicon carbide and report the characterization of their electronic band structure using angle-resolved photoemission. By selectively adjusting the carrier concentration in each layer, changes in the Coulomb potential led to control of the gap between valence and conduction bands. This control over the band structure suggests the potential application of bilayer graphene to switching functions in atomic-scale electronic devices
Quasiparticle dynamics in graphene
The effectively massless, relativistic behaviour of graphene's charge carriersâknown as Dirac fermionsâis a result of its unique electronic structure, characterized by conical valence and conduction bands that meet at a single point in momentum space (at the Dirac crossing energy). The study of many-body interactions amongst the charge carriers in graphene and related systems such as carbon nanotubes, fullerenes and graphite is of interest owing to their contribution to superconductivity and other exotic ground states in these systems. Here we show, using angle-resolved photoemission spectroscopy, that electronâplasmon coupling plays an unusually strong role in renormalizing the bands around the Dirac crossing energyâanalogous to mass renormalization by electronâboson coupling in ordinary metals. Our results show that electronâelectron, electronâplasmon and electronâphonon coupling must be considered on an equal footing in attempts to understand the dynamics of quasiparticles in graphene and related systems
Experimental Determination of the Spectral Function of Graphene
A number of interesting properties of graphene and graphite are postulated to
derive from the peculiar bandstructure of graphene. This bandstructure consists
of conical electron and hole pockets that meet at a single point in momentum
(k) space--the Dirac crossing, at energy . Direct
investigations of the accuracy of this bandstructure, the validity of the
quasiparticle picture, and the influence of many-body interactions on the
electronic structure have not been addressed for pure graphene by experiment to
date. Using angle resolved photoelectron spectroscopy (ARPES), we find that the
expected conical bands are distorted by strong electron-electron,
electron-phonon, and electron-plasmon coupling effects. The band velocity at
and the Dirac crossing energy are both renormalized by these
many-body interactions, in analogy with mass renormalization by electron-boson
coupling in ordinary metals. These results are of importance not only for
graphene but also graphite and carbon nanotubes which have similar
bandstructures.Comment: pdf file, 10 pages, 4 figure
The formation of an energy gap in graphene on ruthenium by controlling the interface
In this work, we have investigated the spectral function of graphene on a monolayer of intercalated gold on Ru(0001) using angle-resolved photoemission spectroscopy (ARPES). The intercalation leads to a decoupling of the graphene film, as documented by emergence of the characteristic linear Ï-bands near the Fermi level. However, a band gap at the band crossing is observed. We relate this gap opening to the broken symmetry of the two carbon sublattices, induced by the special lattice mismatch of the graphene and the intercalated gold monolayer
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