Highlights

Exploring exotic low-dimensional physical phenomena

Surface Nano Physics Group

Highlights

“Peculiar Rashba splitting originating from the two-dimensional symmetry of the surface”
Phys. Rev. Lett. 103, 156801 (2009)

A peculiar Rashba effect is found at a point in the Brillouin zone, where the time-reversal symmetry is broken, though this symmetry was believed to be a necessary condition for Rashba splitting. This finding obtained experimentally by photoemission measurements on a Bi/Si(111)-(sqrt{3}x sqrt{3}) surface is fully confirmed by a first-principles theoretical calculation. We found that the peculiar Rashba effect is simply understood by the two-dimensional symmetry of the surface, and that this effect leads to an unconventional non-vortical Rashba spin structure at a point with time-reversal invariance.

“Abrupt rotation of the Rashba spin to the direction perpendicular to the surface”
Phys. Rev. Lett. 102, 096805 (2009)

The polarization vector of the Rashba spin, which must be parallel to the two-dimensional (2D) plane in an ideal system, is found to change abruptly and definitely to the direction perpendicular to the surface at the K point of the Brillouin zone of a real hexagonal system, the Tl/Si(111)-(1x1) surface. This finding obtained experimentally by angle-resolved and spin-resolved photoemission measurements is fully confirmed by a first-principles theoretical calculation. We found that the abrupt rotation of the Rashba spin is simply understood by the 2D symmetry of the hexagonal structure.

“Electronic structures of the highest occupied molecular orbital bands of a pentacene ultrathin film”
Phys. Rev. Lett. 98, 247601 (2007)

We report the energy dispersions of the highest occupied molecular orbitals (HOMO)-derived bands of a pentacene (Pn) thin film, whose in-plane structure resemble closely to that of the ab plane of a low-density bulk Pn phase. Our present photoemission result indicates that the overlap of the pi-orbitals of adjacent Pn molecules is larger than what was expected from theoretical calculations. Further, of the two HOMO-derived bands, the large dispersion width of the band with higher binding energy suggest that this one mainly contributes to the band-like charge transport in a Pn crystal.

“Highly Ordered Cobalt-Phthalocyanine Chains on Fractional Atomic Steps: One-Dimensionality and Electron Hybridization”
ACS Nano, 7, 1317 (2013)

Precisely controlled fabrication of low-dimensional, especially the formation of 1D molecular structures with tailored morphologies and electronic properties is at the heart of the nanotechnology research. Here we show that highly ordered cobalt-phthalocyanine chains can be formed by a simple and easy method. We also demonstrate that the substrate surface electrons can propagate along the step arrays and can hybridize with the molecular orbitals. These findings provide a significant step towards readily realization of 1D charge/spin transport, which can be mediated either directly by the molecules or by the surface electrons.

“Valley spin polarization by using the extraordinary Rashba effect on silicon”
Nat. Commun. 4:2073 doi: 10.1038/ncomms3073 (2013)

The addition of the valley degree of freedom to a two-dimensional spin-polarized electronic system provides the opportunity to multiply the functionality of next-generation devices. Here we show the formation of 100% spin polarized valleys by a simple and easy way using the Rashba effect on a system with C3 symmetry. This polarization, which is much higher than those in ordinary Rashba systems, makes the valleys acting as filters that can suppress the backscattering of spin-charge. The present system is formed on a silicon substrate, and therefore opens a new avenue toward the realization of silicon spintronic devices with high efficiency.

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