Masanori Sugahara

Dynamic characteristics of inverter circuits using single electron transistors

We have investigated the basic characteristics of capacitively and resistively coupled single-electron tunneling (SET) inverters as a digital logic circuit. Static and dynamic characteristics have been calculated based on the semiclassical model using the Monte Carlo method. Although a voltage gain larger than unity is found even in a cascade connection of two stages of the SET inverters, they reveal some disadvantages in digital logic application, such as small voltage gain, poor input-output separation, small logic level difference, instability of operating point and oscillating output voltages. The switching delay time is estimated to be on the order of 100 RC, where R and C is resistance and capacitance of a tunnel junction, respectively. The stability of logic voltage levels has also been verified in cross-coupled latch circuits

Complementary Digital Logic Using Resistively Coupled Single-Electron Transistor

A new complementary digital logic based on resistively coupled single-electron transistors (R-SET) was proposed and its basic characteristics were numerically analyzed using the Monte Carlo method. The proposed logic has a logic threshold independent of background polarization charges which induce crucial problems in logic operation in the case of a capacitively coupled logic. In addition, the proposed complementary R-SET logic has larger output voltage swing and better logic level stability than those of a conventional resistance-load R-SET logic. The stability of the logic level of the complementary R-SET logic was investigated by calculating the data retention time of flip-flop circuits, and its dependence on temperature and shot noise was examined. For stable operation of the flip-flop circuit, estimated optimal operation temperature and switching delay time are e 2 /80C t k B and 1500 R t C t , respectively, where C t and R t are capacitance and resistance of the tunnel junction.

Model for Critical Current and Magnetization of Type II Superconductors in Longitudinal Magnetic Fields

The flux‐density distribution and its stability in the mixed state of type II superconductors in the presence of a stationary longitudinal magnetic field are considered in the connection with the critical conduction current and the longitudinal magnetization. It is believed that the theory similates reasonably well the behavior of the superconductors. It is found that the flux pinning by imperfections in the superconductors becomes ineffective in the longitudinal field because of the induced helical vibrations of pinned flux lines.

Superconductive Granular Thin Film and Phase Quantum Tunnel Device

Theoretical considerations show that superconductive granular films can be classified into two groups; \varTheta-superconductors with a definitive phase and N-superconductors with a definitive particle number. It is pointed out that a device made of an N-supercnductor has properties conjugate to the Josephson effect.

Structure-parameter dependence of modality of macroscopic quantum effect in superconductor junction (II). Linked junction

Quantum behaviors of linked junctions of superconductor and normal metal are theoretically studied with the following results. They are classified into two types: type 1 with normal conductance G>Gc and type 2 with G<Gc, where Gc is the critical conductance. Ideal models of type 1 and type 2 are, respectively, prescribed with a set of parameters (gp1, gs=1) and (gp=1, gs1), where gp (parallel mode number) is the number of electronic quantum modes over the cross section of the link and gs (series mode number) is the number of loss oscillators (phonons or photons) which perform energy-exchange interaction with a transitting electron. In the case of superconductor junctions, type 1 shows the Josephson effect and type 2 shows the PQT effect (duality of Josephson effect). The PQT effect is also expected in some normal type 2 junctions.

Dual Conduction Characteristics Observed in Highly Resistive NbN Granular Thin Films

We observed in highly resistive NbN thin films at low temperature dual conduction characteristics in clearly separated two region of their sheet resistance. In the specimens with R Rc, however, the conduction characteristics can be explained supposing the KT effect for charge-soliton pairs.

Single Electron Transfer Logic Gate Family

Single electron transfer logic circuits, where logical bit information is represented by the existence of discrete small current pulses accompanied by single electron tunneling (SET) in a one-dimensional array of small tunnel junctions, have been investigated. The basic operation characteristics of several key circuit elements, such as an SET transmission line, a confluence circuit, a split circuit and a set-reset gate were examined and their correct functionality was verified by Monte Carlo simulation. We have shown that basic logic gates, such as NOT, AND and OR, can be implemented using these circuit elements if we provide periodic single electron clock pulses to the gates. Robustness of these logic gates has also been investigated by calculating the dc bias margin.

Anomalous effect in La2-xSrxCuO4 of doping level x = 1/4n

Anomalous electric response of La 2-x Sr x CuO 4 thin film at Sr doping levels of x 1/4 and 1/16 is observed when charge moves along the c axis. The capacitance C t of the Pd/La 2-x Sr x CuO 4 /SrTiO 3 /Pd structure increases sharply, exceeding the capacitance C STO of the Pd/SrTiO 3 /Pd structure. Oscillatory negative voltage is observed in 4-terminal resistivity measurements of La 2-x Sr x CuO 4 thin film using Pd electrodes at small current. These phenomena are explained by a model of the spatial ordered state in which CuO 2 layers of La 2-x Sr x CuO 4 is replete with O hole pairs.

Anomalous carrier level dependence of normal resistivity of La2−xSrxCuO4

An experimental study is made concerning the dependence of normal resistivity ρ on hole‐carrier level x’ using carefully made La2−xSrxCuO4 sintered specimens. Sharp dips are observed in the ρ vs x’ relation at the carrier levels x’=1/4N (N=1,2,3,...).

Macroscopic Quantum Effect Conjugate to Josephson Effect

A new macroscopic quantum effect with conjugate property to Josephson effect is proposed theoretically. Some experiments are given which reveal real existence of the effect.