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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 ultralow temperature and high magnetic field, peculiar local superconducting and topological states that can be found in surface superconductors, whose inversion symmetry is broken, and in the proximity with ferromagnetic materials, have been explored. We have also studied local magnetic properties of spin-spiral structures using SP-STM, spin excitation with SP-IETS, magnetic resonances through the introduction of microwaves, and spin current detection using SP-potentiometry. Recent subjects include heavy-fermion materials, such as CeCoIn5; orbital ordering was observed for the first time in a real space.

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, superconductor) indicate the penetration of superconductivity into the metal layer with a decay length of 40 nm.
Surface-induced orbital ordered states observed on a heavy-fermion material CeCoIn5. In STM images taken on a Co-terminated surface in standard conditions, round-shaped Co atoms are observed (center and upper-left images). On the other hand, in STM images taken in closer distances (lower-right) we observed an ordered phase of dumbbell-shaped d-orbitals. Detailed analysis revealed that the ordered structure is formed only on the surface layer.

Research Subjects

  1. Exploration of peculiar superconducting / topological states using low-temperature STM
  2. Nanoscale measurements of magnetic resonances by SP-STM with microwave
  3. Real-space distribution of spin currents by spin-polarized scanning potentiometry