About

Professor John B. Ketterson is associated with the Department of Physics at Northwestern University. His research group focuses on various aspects of condensed matter physics, including the study of patterned nano-magnet structures. His work involves broadband ferromagnetic resonance measurements, with particular interest in the vortex core resonance that occurs in patterned dots or antidot structures. These materials are of interest due to their potential applications as high-density memory storage in computing. The group also explores atom trapping techniques, as evidenced by the work of doctoral students developing magneto-optical atom traps to create Bose-Einstein condensates of rubidium. Overall, Professor Ketterson's research encompasses experimental investigations into magnetic phenomena at the nanoscale and quantum gas systems, contributing to advancements in magnetic storage technology and atomic physics.

Research topics

• Physics
• Condensed matter physics
• Quantum mechanics
• Optics
• Computer Science
• Materials science
• Geometry
• Chemistry
• Mathematics
• Atomic physics
• Classical mechanics
• Inorganic chemistry
• Engineering
• Electronic engineering
• Optoelectronics
• Chemical physics
• Acoustics
• Crystallography

Selected publications

• Vortex-antivortex states in nanopatterned superconducting films

  Physical Review Applied · 2025-05-02 · 2 citations

  articleSenior author

  We model a periodic thin-film superconducting system containing two differently shaped antidots: circular and equilateral-triangular. In the absence of an external field, the system displays two stable states as a function of the applied current: (i) a vortex-free state at low current and, (ii) above some critical current, a state involving both a vortex and an antivortex pinned to the two respective pinning sites. At still higher currents, the system becomes unstable to repeated nucleation and annihilation of moving vortex-antivortex pairs. The two states have distinct inductive responses. It is noted that these properties open the possibility for these systems to be used as cryogenic circuit or memory elements.

  PublisherDOI

• Nonlinear inductive response of pinned superconducting vortices in artificial pinning sites

  Physical Review Applied · 2024-05-08 · 2 citations

  articleSenior author

  Using the time dependent Ginzburg-Landau equations, we simulate the inductive responses of a variety of thin-film systems containing patterned antidots with different sizes and shapes. The results for all shapes show that the kinetic inductance diverges as the applied current approaches a critical current that is below the BCS depairing current. Exploiting the similarity of the observed current-voltage behavior to that of Josephson junctions, we obtain an empirical equation that well fits the inductivity curve as a function of the applied current.

  PublisherDOI

• Josephson Oscillators Based on Amorphous Superconductors

  IEEE Transactions on Applied Superconductivity · 2023-02-03 · 1 citations

  articleSenior author

  Thin films of amorphous Mo<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_x</i>Ge<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub><italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_x</i> grown with magnetron sputtering are known to exhibit excellent homogeneity and fairly high superconducting transition temperatures (up to 7.5 K). These properties make MoGe thin films suitable to form high-quality tunnel junctions, as demonstrated recently by our group [see Supercond. Sci. Technol. 35, 035008 (2022)]. Here, we report the experimental demonstration of an MoGe/Al/AlO<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_x</i>/(Al)MoGe Josephson oscillator based on amorphous superconductor MoGe, which allows for continuous tuning of the oscillation frequency from about 1 GHz up to tens of GHz. We believe such an oscillator may be useful as a compact on-chip microwave source suitable to control some types of qubits based on Josephson junctions.

  PublisherDOI

• Nonreciprocal spin-wave propagation in YIG/GGG: a limit on the DMI parameter

  Journal of the Korean Physical Society · 2023-06-02 · 2 citations

  articleOpen access
  PublisherOA PDFDOI

• Suhl instabilities in nanoscopic spheroids

  Journal of Magnetism and Magnetic Materials · 2023-09-13

  articleOpen accessSenior author
  PublisherOA PDFDOI

• Suhl Instabilities in Nanoscopic Spheroids

  arXiv (Cornell University) · 2023-05-13

  preprintOpen accessSenior author

  We simulate the magnetization dynamics of a permalloy spheroid of nanoscopic size in zero external field, such that both dipolar and exchange interactions are important. Low excitation power is used to obtain the frequencies and mode patterns of many normal modes. At higher power, non-linear three and four mode couplings between magnons carrying orbital angular momentum are observed to give rise to Suhl instabilities. Suhl's analysis of the selection rules governing the allowed processes is extended to initial states other than uniform precession. These rules are studied and confirmed by the simulations. Both down- and up-conversion are seen as well as three and four-mode processes. General trends are inferred for preferred instabilities among those that are allowed, although the thresholds for some instabilities appear to be very high.

  PublisherOA PDFDOI

• Strategies to perform magnetization reversals in ferromagnets

  OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2023-11-20

  articleOpen access1st authorCorresponding

  Systems and methods for reversing a magnetization in a ferromagnet include a nanometer-scale cylindrical ferromagnetic sample having a height to diameter aspect ratio on the order of 2 or greater. A temporally-varying external field comprising an r.f. Pi pulse is applied to the ferromagnetic sample to cause a precession magnetization vector inclined at an angle with respect to the longest axis of the ferromagnetic sample to continuously rotate around the longest axis. One or more parameters of the temporally-varying external field is continuously adjusted based on at least magnetization dynamics of the ferromagnetic sample and/or an angular dependence of a precession frequency of the ferromagnetic sample.

  PublisherOA PDF

• Investigation of the Critical Currents in Thin-Film MoGe Devices

  IEEE Transactions on Applied Superconductivity · 2023-12-20

  articleSenior author

  We report on flux-flow properties of 50 nm thick thin-film amorphous MoGe bridges of different sizes with and without patterned sub-micron holes with different diameters and spacings. Characterization of the devices was carried out in liquid He at 4.2 K in a magnetic field, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> , applied perpendicular to the device plane. Two critical currents, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c1</sub> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</sub> , were studied. The current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c1</sub> is identified as the onset of a low-resistance state, whereas <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</sub> is the current at which the device switches to a high-resistance state, and the corresponding dependences <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c1</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> ) and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> ) were determined. In the absence of the holes, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c1</sub> decreases monotonically with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> , whereas <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> ) manifests lobes resembling those in the Fraunhofer-like pattern characteristic of Josephson junctions. This behavior may be due to formation of an ordered vortex lattice in some current and field ranges. Introducing the hole-line arrays modifies both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c1</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> ) and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> ) in a way that is most complicated for larger hole diameters.

  PublisherDOI

• Suhl Instabilities in Nanoscopic Spheroids

  SSRN Electronic Journal · 2023-01-01

  preprintOpen accessSenior author
  PublisherDOI

• Realizing the Heteromorphic Superlattice: Repeated Heterolayers of Amorphous Insulator and Polycrystalline Semiconductor with Minimal Interface Defects

  Advanced Materials · 2023-03-12 · 4 citations

  articleOpen access

  Abstract An unconventional “heteromorphic” superlattice (HSL) is realized, comprised of repeated layers of different materials with differing morphologies: semiconducting pc ‐In 2 O 3 layers interleaved with insulating a‐ MoO 3 layers. Originally proposed by Tsu in 1989, yet never fully realized, the high quality of the HSL heterostructure demonstrated here validates the intuition of Tsu, whereby the flexibility of the bond angle in the amorphous phase and the passivation effect of the oxide at interfacial bonds serve to create smooth, high‐mobility interfaces. The alternating amorphous layers prevent strain accumulation in the polycrystalline layers while suppressing defect propagation across the HSL. For the HSL with 7:7 nm layer thickness, the observed electron mobility of 71 cm 2 Vs ‐1 , matches that of the highest quality In 2 O 3 thin films. The atomic structure and electronic properties of crystalline In 2 O 3 /amorphous MoO 3 interfaces are verified using ab‐initio molecular dynamics simulations and hybrid functional calculations. This work generalizes the superlattice concept to an entirely new paradigm of morphological combinations.

  PublisherOA PDFDOI

Recent grants

• Manipulation of Hole-pinned Vortices: Classical and Quantum

  NSF · $510k · 2019–2023

• Collaborative Research: Collective Mode Spectroscopy in Unconventional Superconductors

  NSF · $261k · 2005–2009

• Collaborative Research: Controlled Disorder and Topological Defects in Magnetically Frustrated Thin Film Metamaterials

  NSF · $128k · 2015–2018

• SENSORS: Collaborative Research: Biochemical Sensors and Data Processing for Security Applications

  NSF · $360k · 2003–2007

• IGERT: Quantum Coherent Optical and Matter Systems

  NSF · $3.0M · 2008–2015

Frequent coauthors

• Bharat Bhushan

  280 shared

• Weiqiang Mu

  Northwestern University

  154 shared

• Swastik Kar

  Northeastern University

  148 shared

• Carlos Drummond

  Université de Bordeaux

  147 shared

• K. F. Böhringer

  University of Washington

  147 shared

• Rodolfo Miranda

  Madrid Institute for Advanced Studies

  147 shared

• Amadeo L. Vázquez de Parga

  Madrid Institute for Advanced Studies

  147 shared

• Robert Puers

  KU Leuven

  146 shared

Labs

• Ketterson Research GroupPI

  Not provided

Education

• Ph.D.

  University of Chicago

  1962

• Other

  University of Chicago

  1957