Stanford Institute for Materials and Energy Science

Menlo Park, CA, United States

Stanford Institute for Materials and Energy Science

Menlo Park, CA, United States
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Mishchenko A.S.,RIKEN | Mishchenko A.S.,RAS Research Center Kurchatov Institute | Nagaosa N.,RIKEN | Nagaosa N.,University of Tokyo | And 6 more authors.
EPL | Year: 2011

We present a combined study of the angle-resolved-photoemission spectroscopy (ARPES) and quantum Monte Carlo simulations to propose a novel polaronic metallic state in underdoped cuprates. An approximation scheme is proposed to represent underdoped cuprates away from 1/2 filling, replacing the many-body Hamiltonian by that of a single polaron with effective electron-phonon interaction (EPI), that successfully explains many puzzles such as a large momentum-dependent dichotomy between nodal and antinodal directions, and an unconventional doping dependence of ARPES in the underdoped region. © 2011 EPLA.

Guizar-Sicairos M.,University of Rochester | Zhu D.,Stanford University | Zhu D.,Stanford Institute for Materials and Energy Science | Fienup J.R.,University of Rochester | And 5 more authors.
Optics Letters | Year: 2010

We introduce a noniterative image-reconstruction technique for coherent diffractive imaging. Through the application of differential and integral operators, an extended reference can be used to recover the complex-valued transmissivity of an object, in closed form, from a measurement of its far-field (Fraunhofer) diffraction intensity. We demonstrate the feasibility of this approach, using a reference of a pair of crossed wires and slits, through numerical simulations and a soft x-ray coherent diffractive imaging experiment. © 2010 Optical Society of America.

Thareja V.,Stanford University | Kang J.-H.,Stanford University | Kang J.-H.,Stanford Institute for Materials and Energy science | Yuan H.,Stanford University | And 9 more authors.
Nano Letters | Year: 2015

We demonstrate electrical control over coherent optical absorption in a graphene-based Salisbury screen consisting of a single layer of graphene placed in close proximity to a gold back reflector. The screen was designed to enhance light absorption at a target wavelength of 3.2 m by using a 600 nm-thick, nonabsorbing silica spacer layer. An ionic gel layer placed on top of the screen was used to electrically gate the charge density in the graphene layer. Spectroscopic reflectance measurements were performed in situ as a function of gate bias. The changes in the reflectance spectra were analyzed using a Fresnel based transfer matrix model in which graphene was treated as an infinitesimally thin sheet with a conductivity given by the Kubo formula. The analysis reveals that a careful choice of the ionic gel layer thickness can lead to optical absorption enhancements of up to 5.5 times for the Salisbury screen compared to a suspended sheet of graphene. In addition to these absorption enhancements, we demonstrate very large electrically induced changes in the optical absorption of graphene of ∼3.3% per volt, the highest attained so far in a device that features an atomically thick active layer. This is attributable in part to the more effective gating achieved with the ion gel over the conventional dielectric back gates and partially by achieving a desirable coherent absorption effect linked to the presence of the thin ion gel that boosts the absorption by 40%. © 2015 American Chemical Society.

Wehling T.O.,University of Hamburg | Dahal H.P.,Los Alamos National Laboratory | Lichtenstein A.I.,University of Hamburg | Katsnelson M.I.,Radboud University Nijmegen | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We theoretically investigate Fano factors arising in local spectroscopy of impurity resonances in graphene. It is demonstrated that Fano line shapes can strongly differ from the antiresonances usually found on metal surfaces. Graphene's highly symmetric Fermi points make this effect particularly sensitive to the detailed atomistic structure and orbital symmetries of the impurity. After a model discussion based on an Anderson impurity coupled to an electron bath with linearly vanishing density of states, we present first-principles calculations of Co adatoms on graphene. For Co above the center of a graphene hexagon, we find that the two-dimensional E1 representation made of dxz, dyz orbitals is likely responsible for the hybridization and ultimately Kondo screening for cobalt on graphene. Anomalously large Fano q factors depending strongly on the orbitals involved are obtained. For a resonant s -wave impurity, a similarly strong adsorption site dependence of the q factor is demonstrated. These anomalies are striking examples of quantum-mechanical interference related to the Berry phase inherent to the graphene band structure. © 2010 The American Physical Society.

PubMed | Stanford Institute for Materials and Energy Science
Type: Journal Article | Journal: Physical review letters | Year: 2011

The results of model calculations using exact diagonalization reveal the orbital character of states associated with different Raman loss peaks in Cu K-edge resonant inelastic x-ray scattering (RIXS) from LaCuO. The model includes electronic orbitals necessary to highlight the nonlocal Zhang-Rice singlet, charge transfer, and d-d excitations, as well as states with apical oxygen 2p(z) character. The dispersion of these excitations is discussed with prospects for resonant final state wave-function mapping. A good agreement with experiments emphasizes the substantial multiorbital character of RIXS profiles in the energy transfer range 1-6 eV.

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