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Hasegawa Group

Research Associate

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Scanning tunneling microscopy (STM) reveals not only atomic structure of surfaces but also electronic states in sub-nanometer areas by tunneling spectroscopy. With a function of spin-polarized (SP-) STM, the microscope also provides local magnetic properties and surface spin structures, and with inelastic tunneling spectroscopy (IETS), various excitation energies can be extracted. In Hasegawa-lab., by using STMs operated in very low temperature and high magnetic field, we have observed various phenomena on nanosize superconductors such as vortex clustering and giant vortex, and peculiar superconducting states in the proximity with ferromagnetic materials. We also study magnetic properties of thin films related with their atomic structure using SP-STM, and their spin excitation with IETS. Modification and control of these properties with an aid of the atom manipulation are one of the targets of our study. Recent subjects include heavy-Fermion materials, such as CeCoIn5; atomic-scale variation in the shape of superconducting gaps was observed.

Proximity effect at superconductor/metal interface. Tunneling spectra taken around an interface between 1ML-Pb layer on Si (blue, normal metal) and a Pb thin film (yellow, super) indicate the penetration of superconductivity into the metal layer with a decay length of 40 nm.
Magnetization curve taken on a nano-size Co island structure formed on Ag surface using spin polarized STM. Because the flips of the tip magnetization occur at ~±0.25T a butterfly-shape curve is observed.

Research Subjects

  1. Superconductivity in local area using low-temperature scanning tunneling microscopy
  2. Fabrication of spin systems by atomic manipulation and their characterization with SP-STM
  3. Local electronic states, superconductivity, and magnetic properties of heavy-Fermion materials
  4. Nano-scalel distribution of potential and spin current by scanning tunneling potentiometry