Dirac fermion reflector by ballistic graphene sawtooth-shaped npn junctions

We have realized a Dirac fermion reflector in graphene by controlling the ballistic carrier trajectory in a sawtooth-shaped npn junction. When the carrier density in the inner p-region is much larger than that in the outer n-regions, the first straight np interface works as a collimator and the collimated ballistic carriers can be totally reflected at the second zigzag pn interface. We observed clear resistance enhancement around the np+n regime, which is in good agreement with the numerical simulation. The tunable reflectance of ballistic carriers could be an elementary and important step for realizing ultrahigh-mobility graphene field effect transistors utilizing Dirac fermion optics in the near future

Clustering Properties of Low-Luminosity Star-Forming galaxies at z = 0.24 and 0.40 in the Subaru Deep Field

We present our analysis on the clustering properties of star-forming galaxies selected by narrow-band excesses in the Subaru Deep Field. Specifically we focus on Halpha emitting galaxies at z = 0.24 and z = 0.40 in the same field, to investigate possible evolutionary signatures of clustering properties of star-forming galaxies. Based on the analysis on 228 Halpha emitting galaxies with 39.8 < log L(Halpha) < 40.8 at z = 0.40, we find that their two-point correlation function is estimated as xi = (r/1.62^{+0.64}_{-0.50} Mpc)^{-1.84 +/- 0.08}. This is similar to that of Halpha emitting galaxies in the same Halpha luminosity range at z = 0.24, xi = (r/1.88^{+0.60}_{-0.49} Mpc)^{-1.89 +/- 0.07}. These correlation lengths are smaller than those for the brighter galaxy sample studied by Meneux et al. (2006) in the same redshift range. The evolution of correlation length between z = 0.24 and z = 0.40 is interpreted by the gravitational growth of the dark matter halos.Comment: 16 pages, 7 figures, PASJ, Vol.60, No.6, in pres

Boundary Scattering in Ballistic Graphene

We report magnetotransport measurements in ballistic graphene/hexagonal boron nitride mesoscopic wires where the charge carrier mean free path is comparable to wire width $W$. Magnetoresistance curves show characteristic peak structures where the peak field scales with the ratio of cyclotron radius $R_\textrm{c}$ and wire width $W$ as $W/R_\textrm{c} = 0.9 \pm 0.1$, due to diffusive boundary scattering. The obtained proportionality constant between $R_\textrm{c}$ and $W$ differs from that of a classical semiconductor 2D electron system where $W/R_\textrm{c} = 0.55$.Comment: 14 pages, 4 figure