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Search Publications by: Mark Keller (Fed)

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Displaying 1 - 25 of 50

Symmetry-dependent ultrafast manipulation of nanoscale magnetic domains

December 23, 2022
Author(s)
Nanna Hagstrom, Rahul Jangid, F. N. U. Meera, Diego Turenne, Jeffrey Brock, Erik Lamb, Boyan Stoychev, Justine Schlappa, Natalia Gerasimova, Benjamin Van Kuiken, Rafael Gort, Laurent Mercadier, Loic Le Guyader, Andrey Samartsev, Andreas Scherz, Giuseppe Mercurio, Hermann Durr, Alexander Reid, Monika Arora, Hans Nembach, Justin Shaw, Emmanuelle Jal, Eric Fullerton, Mark Keller, Roopali Kukreja, Stefano Bonetti, Thomas J. Silva, Ezio Iacocca
Symmetry is a powerful concept in physics, but its applicability to far-from-equilibrium states is still being understood. Recent attention has focused on how far-from-equilibrium states lead to spontaneous symmetry breaking. Conversely, ultrafast optical

Megahertz-rate Ultrafast X-ray Scattering and Holographic Imaging at the European XFEL

August 23, 2022
Author(s)
Thomas J. Silva, Hans Nembach, Mark Keller, Justin Shaw, Nanna Hagstrom, michael schneider, Nico Kerber, Alexander Yaroslavtsev, Erick Parra, Eric Fullerton, Oleg Shpyrko, Christian Gutt, Hermann Durr, Ezio Iacocca, Roopali Kukreja, stefano Bonetti, Emmanuelle Jal
The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence, and pulse duration

Near-Unity Spin Hall Ratio in Ni$_x$Cu$_{1-x}$ Alloys

June 7, 2019
Author(s)
Mark W. Keller, Katy Gerace, Monika Arora, Justin M. Shaw, Thomas J. Silva
We report a large spin Hall effect in the 3$d$ transition metal alloy Ni$_x$Cu$_{1-x}$ for $x \in \{ 0.3,0.75\} $, detected via the ferromagnetic resonance of a permalloy (Py = Ni$_{80}$Fe$_{20}$) film deposited in a bilayer with the alloy. A thickness

Elementary Again

April 6, 2018
Author(s)
Mark W. Keller
Mark Keller explains how the elementary charge will soon be reinstated in metrology - and why it got sidelined in the first place.

Plasma modification of vertically aligned carbon nanotubes: superhydrophobic surfaces with ultra- low reflectance

November 2, 2017
Author(s)
Christopher S. Yung, Nathan A. Tomlin, Karl Heuerman, Mark W. Keller, Malcolm G. White, Michelle S. Stephens, John H. Lehman
Vertically aligned carbon nanotubes (VACNTs) are excellent broadband (UV–VIS–IR) absorbers of light that can be made even darker with plasma treatments. Modification of VACNTs using O2 and/or CF4 plasmas is shown to have a significant impact on the

Direct time-domain observation of attosecond final-state lifetimes in photoemission from solids

July 1, 2016
Author(s)
Zhensheng Tao, Cong Chen, Tibor Szilvasi, Mark W. Keller, Manos Mavrikakis, Henry C. Kapteyn, Margaret M. Murnane
Attosecond spectroscopic techniques have made it possible to measure differences in transport times for photoelectrons from localized core levels and delocalized valence bands in solids. We report the application of attosecond pulse trains to directly and

Controlling the electronic structure of graphene using surface-adsorbate interactions

July 21, 2015
Author(s)
Piotr Matyba, Adra V. Carr, Cong Chen, David L. Miller, Thomas Orlando, Stefan Mathias, Mark W. Keller, Henry C. Kapteyn, Margaret M. Murnane
Hybridization of atomic orbitals in graphene on Ni(111) opens up a large energy gap of ≈2.8 eV between nonhybridized states at the K point. Here we use alkali-metal adsorbate to reduce and even eliminate this energy gap, and also identify a new mechanism

Suppression of Spin Pumping between Ni80Fe20 and Cu by a Graphene Interlayer

June 7, 2015
Author(s)
William J. Gannett, Mark W. Keller, Hans Nembach, Thomas J. Silva, Ann Chiaramonti Debay
Abstract We compare ferromagnetic resonance measurements of Py (Ni80Fe20) films sputtered onto Cu(111) with and without a graphene (Gr) interlayer grown by chemical vapor deposition before Py deposition. We find the expected damping enhancement from spin

Giant Secondary Grain Growth in Cu Films on Sapphire

August 1, 2013
Author(s)
David L. Miller, Mark W. Keller, Justin Shaw, Katherine P. Rice, Robert Keller, Kyle M. Diederichsen
Single crystal metal films on insulating substrates are attractive for microelectronics and other applications, but they are difficult to achieve on macroscopic length scales. The conventional approach to obtaining such films is epitaxial growth at high

Improved performance of the ECCS experiment at PTB

July 1, 2012
Author(s)
Hansjoerg Scherer, Benedetta Camarota, Mark W. Keller, Sergey Lotkhov
Recent improvements on the ECCS experiment at PTB are reported. A 5-junction single-electron R-pump is shown to shuttle electrons with a relative transfer error of 5×10 -8. Moreover, the relative uncertainty of the setup for the cryogenic capacitor voltage

Electron Counting Capacitance Standard with an improved five-junction R-pump

November 7, 2011
Author(s)
Benedetta Camarota, Hansjoerg Scherer, Sergey Lotkhov, Gerd-Dietmar Willenberg, Franz Josef Ahlers, Mark W. Keller
The Electron Counting Capacitance Standard currently pursued at PTB, aims at the closure of the Quantum Metrological Triangle with a final precision of a few parts in 10 7. This paper reports the considerable progress recently achieved with a new

Theory for a Dissipative Droplet Soliton Excited by a Spin Torque Nanocontact

August 30, 2010
Author(s)
Mark Hoefer, Thomas J. Silva, Mark W. Keller
A distinct type of solitary wave is predicted to form in spin torque oscillators when the free layer has a sufficiently large perpendicular anisotropy. In this structure, which is a dissipative version of the conservative droplet soliton originally studied

Spin-transfer dynamics in spin valves with out-of-plane magnetized CoNi free layers

January 29, 2010
Author(s)
William H. Rippard, Alina M. Deac, Matthew R. Pufall, Justin M. Shaw, Mark W. Keller, Stephen E. Russek, Gerrit E. Bauer, Claudio Serpico
We have measured spin-transfer-induced dynamics in magnetic nanocontact devices having a perpendicularly magnetized Co/Ni free layer and an in-plane magnetized CoFe fixed layer. The frequencies and powers of the excitations agree well with the predictions

Time domain measurement of phase noise in a spin torque oscillator

May 13, 2009
Author(s)
Mark W. Keller, Anthony B. Kos, Thomas J. Silva, William H. Rippard, Matthew R. Pufall
We measure phase noise from the zero crossings of the voltage vs. time waveform of a spin torque nanocontact oscillating in a vortex mode. The power spectrum of the phase noise varies with Fourier frequency f as 1/f 2, consistent with frequency

Why the long-term charge offset drift in Si single-electron tunneling transistors is much smaller (better) than in metal-based ones: Two-level fluctuator stability

August 7, 2008
Author(s)
Neil M. Zimmerman, W H. Huber, Brian J. Simonds, Emmanouel S. Hourdakis, Fujiwara Fujiwara, Yukinori Ono, Yasuo Takahashi, Hiroshi Inokawa, Miha Furlan, Mark W. Keller
A common observation in metal-based (specifically, those with AlOx tunnel junctions) single- electron tunneling (SET) devices is a time-dependent instability known as the long-term charge offset drift. This drift is not seen in Si-based devices. Our aim is

Current Status of the Quantum Metrology Triangle

January 18, 2008
Author(s)
Mark W. Keller
The quantum metrology triangle is a test of the consistency of three quantum electrical standards: the single-electron tunneling current standard, the Josephson voltage standard, and the quantum Hall resistance standard. This paper considers what is known

Uncertainty budget for the NIST Electron Counting Capacitance Standard, ECCS- 1

November 21, 2007
Author(s)
Mark W. Keller, Neil M. Zimmerman, Ali L. Eichenberger
We measure a cryogenic, vacuum-gap capacitor by two methods: 1) charging it with a known number of electrons and measuring the resulting voltage, and 2) using a capacitance bridge traceable to the SI farad. We report a detailed uncertainty budget for the

A single-photon pump

August 25, 2006
Author(s)
Kevin Osborn, Mark W. Keller
We describe a gated quantum dot device called a single-photon pump that produces single photons on demand through the controlled tunneling of individual electrons and holes. Simulations using an InGaAs/GaAs dot show that two modes of operation are possible

HEMT Amplified SET Measurements of Individual InGaAs Quantum Dots

August 25, 2006
Author(s)
Kevin Osborn, Mark W. Keller, Richard Mirin
A High Electron Mobility Transistor (HEMT) is used with a Single Electron Transistor (SET) to measure single electrons tunnelling into individual InGaAs quantum dots. The SET detects the charge motion as an electron tunnels from an underlying n-doped layer

VARIABILITY OF CHARGE NOISE IN Al-BASED SET TRANSISTORS

July 14, 2006
Author(s)
Mark W. Keller, Blaise Jeanneret, Joe Aumentado
We measured the charge noise of four Al-based SET transistors on multiple cooldowns. We found a consistent 1/f component independent of thermal cycling and other treatments, but large variations in the total noise spectrum due to two-level fluctuators.