Yoshiaki Hirano

Conductance with stochastic resonance in Mn12 redox network without tuning

Artificial neuron-based information processing is one of the attractive approaches of molecular-scale electronics, which can exploit the ability of molecular system for self-assembling or self-organization. The self-organized Mn12/DNA redox network shows nonlinear current-voltage characteristics that can be described by the Coulomb blockade network model. As a demonstration of the nonlinear network system, we have observed stochastic resonance without tuning for weak periodic input signals and thermal noise, which suggests a route to neural network composed of molecular materials.

Nanoscale charge transport in cytochrome c3/DNA network: Comparative studies between redox-active molecules

The redox-active molecule of a cytochrome c3/DNA network exhibits nonlinear current–voltage (I–V) characteristics with a threshold bias voltage at low temperature and zero-bias conductance at room temperature. I–V curves for the cytochrome c3/DNA network are well matched with the Coulomb blockade network model. Comparative studies of the Mn12 cluster, cytochrome c, and cytochrome c3, which have a wide variety of redox potentials, indicate no difference in charge transport, which suggests that the conduction mechanism is not directly related to the redox states. The charge transport mechanism has been discussed in terms of the newly-formed electronic energy states near the Fermi level, induced by the ionic interaction between redox-active molecules with the DNA network.

Nonlinear electric transport in macromolecular system for stochastic computing

Abstract Nonlinearity is the vital factor for stochastic computing. Toward the realization of brain-mimetic function using molecular network, the nonlinear electric properties of molecular systems are investigated in nanoscale with atomic force microscopy and nano-gap electrodes. Nonlinear current–voltage characteristics were observed for {Mo154/152}-ring, cytochrome c, and cytochrome c/DNA networks where the conduction paths includes electron injection into weakly coupled discrete energy levels, electron tunneling through potential well, and electron hopping via Coulomb-blockade network. Stochastic resonance was observed in cytochrome c/DNA network.

√ω-Variation of AC Admittance in the Inhomogeneously Distributed RC Lines

The ac admittance Y(ω) has been analytically derived for the RC lines with locally varying resistance R(x) and capacitance C(x) per unit length under the condition R(x)/C(x) = const. An RC line of this type is found to obey the square-root law Y(ω) ∝√ω for higher frequencies, and to have the advantage of reducing the line length in comparison to the conventional RC line with uniformly distributed R and C.

Spin waves in Mn3Pt

Abstract Spin wave excitation is calculated for the high temperature ordered (F) phase of Mn3Pt by assuming two types of spin structures, single-Q collinear and triple-Q non-collinear structures. It is suggested that precise measurements of spin wave excitation by inelastic neutron scattering could determine uniquely the spin structure of the F-phase.