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The quantum-spin-Hall (QSH) phase and its helical edge spins of two-dimensional (2D) topological insulators (TIs) are attracting increasing attention. The helical edge spin currents are a favorite to applications in dissipationless spintronic devices with low error rates because the spin currents existing along sample 1D edges are topologically protected in time-reversal symmetry and are easily controlled by external bias voltages. Moreover, combining the 1D edge spin currents with ferromagnetic or superconductor electrodes yields various exciting phenomena and those applications to innovative quantum devices. Nevertheless, reports of 2D TIs and QSH phases (particularly at high temperatures) have been rare and mainly in semiconductor 2D quantum wells. Here, I introduce and discuss how 2D TI states and QSH phases can be created and applied to innovative quantum (spintronic) devices, particularly in atomically thin layers (such as graphene and transition metal dichalcogenide family, which is energetically studied and have demonstrated large topological bulk gaps recently). Research of 2D TIs on atom-thin (or few) layers and those application must open a door to next-generation quantum architectures (such as topological quantum computation utilizing the Majorana fermion). [ABSTRACT FROM AUTHOR]

We report on the anomalous localization effects strongly associated with excess volume of a cobalt catalyst in multiwalled carbon nanotubes (MWNTs) synthesized in nanoporous alumina membranes. These effects bring about the following anomalies in bulk MWNTs: (a) A slight increase in the volume of excess cobalt changes antilocalization (AL) to weak localization (WL), (b) a further increase in excess changes this WL back to the AL, but only in magnetoresistance (MR) oscillation, and (c) even under this AL in MR, AL can not be observed in the conductance versus logarithmic temperature relation. Mechanisms for these anomalies were discussed based on the unique MWNT structures. [ABSTRACT FROM AUTHOR]

We slightly diffuse atoms of electrode materials into one end of multiwalled carbon nanotubes (MWNTs), grown using nanoporous alumina membranes. Diffusion of the light-mass materials (carbon and aluminum) lead to weak localization in Altshuler–Aronov–Spivak oscillation, consistent with past reports. In contrast, we find that diffusion of heavy-mass materials (gold and platinum) at the volume ratio of only about 5% change this weak localization to antilocalization. It is understood by a drastic change of the phase interference caused by the injection of spin-flipped electrons due to spin–orbit interaction in the diffusion region, in the entire part of the MWNTs. We also propose an electron-wave phase switching circuit using this effect. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on Coulomb blockade in a single tunnel junction directly connected to a multiwalled carbon nanotube (MWNT) by utilizing a nanoporous alumina film. The MWNT exhibits a weak localization effect with strong spin flip scattering. Experimental results and analysis suggest that a high-impedance external environment caused by the weak localization in the MWNT can yield Coulomb blockade, in accordance with phase correlation theory in a single junction system. It is also revealed that the Coulomb blockade is very sensitive to phase modulation in the MWNT, which also acts as a high-impedance transmission line. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Correlation of Coulomb blockade (CB) with phase fluctuation caused by mutual Coulomb interaction is reported in an array system of single tunnel junctions directly connected to disordered Ni nanowires. At the voltages lower than CB voltage, temperature dependence of the normalized resistance is classified to the following two regimes by a phase transition temperature (T[sub c]), (1) mutual Coulomb interaction regime (T>T[sub c]) and (2) CB regime (T