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All Publications

  • Ultrafast oscilloscope based on laser-triggered field emitters OPTICS LETTERS Kealhofer, C., Klopfer, B. B., Skulason, G. E., Juffmann, T., Foreman, S. M., Kasevich, M. A. 2015; 40 (2): 260-263


    Laser-triggered electron emission from sharp metal tips has been demonstrated in recent years as a high brightness, ultrafast electron source. Its possible applications range from ultrafast electron microscopy to laser-based particle accelerators to electron interferometry. The ultrafast nature of the emission process allows for the sampling of an instantaneous radio frequency (RF) voltage that has been applied to a field emitter. For proof-of-concept, we use an RF signal derived from our laser's repetition rate, mapping a 9.28 GHz signal in 22.4 fs steps with 28 mv accuracy.

    View details for DOI 10.1364/OL.40.000260

    View details for Web of Science ID 000347939500034

  • Ultrafast microfocus x-ray source based on a femtosecond laser-triggered tip ANNALEN DER PHYSIK Foreman, S. M., Kealhofer, C., Skulason, G. E., Klopfer, B. B., Kasevich, M. A. 2013; 525 (1-2): L19-L22
  • Advanced sensors for scanning SQUID microscopy IEEE 14th International Superconductive Electronics Conference (ISEC) Kirtley, J. R., Gibson, G. W., Fung, Y. K., KLOPFER, B., Nowack, K., Kratz, P. A., Mol, J., Arpes, J., Forooghi, F., Huber, M. E., Bluhm, H., Moler, K. A. IEEE. 2013
  • Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures NATURE COMMUNICATIONS Kalisky, B., Bert, J. A., Klopfer, B. B., Bell, C., Sato, H. K., Hosoda, M., Hikita, Y., Hwang, H. Y., Moler, K. A. 2012; 3


    In LaAlO(3)/SrTiO(3) heterointerfaces, charge carriers migrate from the LaAlO(3) to the interface in an electronic reconstruction. Magnetism has been observed in LaAlO(3)/SrTiO(3), but its relationship to the interface conductivity is unknown. Here we show that reconstruction is necessary, but not sufficient, for the formation of magnetism. Using scanning superconducting quantum interference device microscopy we find that magnetism appears only above a critical LaAlO(3) thickness, similar to the conductivity. We observe no change in ferromagnetism with gate voltage, and detect ferromagnetism in a non-conducting p-type sample. These observations indicate that the carriers at the interface do not need to be itinerant to generate magnetism. The ferromagnetism appears in isolated patches whose density varies greatly between samples. This inhomogeneity strongly suggests that disorder or local strain generates magnetism in a population of the interface carriers.

    View details for DOI 10.1038/ncomms1931

    View details for Web of Science ID 000306099900049

    View details for PubMedID 22735450