Al Tunnel Junctions Research Articles

Measurement of Microwave-Enhanced Energy Gap in Superconducting Aluminum by Tunneling

Al-Al/sub 2/O/sub 3/-Al tunnel junctions were used to measure large increases in the energy gap of superconducting aluminum films in the presence of 10-GHz microwave radiation. When the microwave power was increased at constant temperature, enchancement occurred only for temperatures at which twice the equilibrium energy only for temperatures at which twice the equilibrium energy gap exceeded the photon energy. When the temperature was increased at constant microwave power, enhancement was observed at higher temperatures.

Quantum size effect in SnTe observed by tunnel experiments

AbstractIn SnTe–Al2O3–Al tunnel junctions with size quantization of the electron states in the SnTe electrode, oscillations of the 2nd derivative of the I(U) characteristics were observed at 4 K. From this it was possible to determine a series of points of the E(k) relation perpendicular to the film plane in a range of ±100 meV around the Fermi energy. The results are in agreement with values calculated from band structure data.

Interaction of High-Energy Phonons with Conduction Electrons in Small-Gap Semiconductors

We consider phonon-electron interactions in highly doped III-V and II-VI semiconducting compounds, including nonparabolicity of the conduction band and the spin-orbit interaction. Absorption coefficients are calculated for monochromatic phonons produced by superconducting Sn and Al tunnel junctions, and we predict the possibility of observing directly an interaction of conduction electrons with slow and fast transverse modes, and phonon-induced spin-flip transitions.

Tunneling results with Ni doped electrodes prepared at 80 K

The effect of a Ni impurity layer in one of the electrodes of an AlIAl tunnel junction has been studied for various fabrication temperatures. The results obtained indicate that the strong conductance dip normally obtained is a particle effect rather than a magnetic effect.

743. Photoemissive determination of the barrier profile in AlAl 2O 3Al tunnel junctions : B Korneffel and W Ludwig, Phys Stat Sol (a), 8 (1), Nov 1971, 149–160

743. Photoemissive determination of the barrier profile in AlAl 2O 3Al tunnel junctions : B Korneffel and W Ludwig, Phys Stat Sol (a), 8 (1), Nov 1971, 149–160

Zero-Bias-Conductance-Peak Anomaly of Ta-I-Al Tunnel Junctions at 0.3 K and 90 kG

We have studied the zero-bias-conductance-peak anomaly in a Ta-$I$-Al tunnel junction over a magnetic field range of 1 to 90 kG at a temperature of 0.3 K, and have made a detailed comparison between experiment and the $s\ensuremath{-}d$ exchange theory of electron tunneling. Good agreement between theory and experiment was obtained for the line shape of the conductance peak and its zero-bias temperature dependence. The line shape of the conductance curves found experimentally at high magnetic fields agreed reasonably well with the theory if magnetic-field-induced lifetime broadening was included. There was, however, a serious discrepancy between theory and experiment for the zero-bias magnetoresistance.

Photoemissive determination of the barrier profile in AlAl2O3Al tunnel junctions

The h v dependence of the photoemission current has been investigated in AlAl2O3Al tunnelling structures in the energy interval from 1 to 3.4 eV. The determination of the maximum barrier height φm from the Fowler plot seems to be the most exact method. From the sign reversal and extreme values of the photoemission currents the barrier heights have been determined, too; these additional possibilities will be discussed critically. The potential barrier profile has been obtained from a detailed analysis of the voltage dependence of φm. The influence of field penetration will be discussed. The Thomas-Fermi screening distance has been evaluated to S ≈ 0.5 Å. An AlAl2O3Al-Tunnelstrukturen wurde die h v-Abhängigkeit des Photoemissionsstromes im Energiebereich von 1 bis 3,4 eV untersucht. Die Bestimmung der maximalen Barrierenhöhe φm aus dem „Fowler plot”︁ erscheint am genauesten. Aus der Vorzeichenumkehr sowie den Extremwerten des Photoemissionsstromes wurden ebenfalls die Barrierenhöhen ermittelt: Diese zusätzlichen Möglichkeiten sind einer kritischen Diskussion unterzogen worden. Aus einer detaillierten Analyse der Spannungsabhängigkeit von φm wurde das Potentialbarrierenprofil bestimmt. Der Einfluß der „field penetration”︁ wird diskutiert, für die Thomas-Fermi-Abschirmlänge ergeben sich Werte von S ≈ 0,5 Å.

Logarithmic conductivity of AlAl 2O 3Al tunneling junctions produced by plasma- and by thermal oxidation

The behaviour of plasma and thermally oxidized AlAl 2O 3Al films is investigated using the junction logarithmic conductivity characteristic. The films are shown to exhibit reasonable agreement with the tunneling theory for approximately trapezoidal potential barriers and nonparabolic energy momentum relation in the forbidden band of the insulator. The barrier heights AlAl 2O 3 obtained from the positions of the logarithmic conductivity maxima are in good agreement with those found from photoelectric measurements.

Coherence effects in Mn doped Al-I-Al tunnel diodes

Abstract Coherence effects were studied in Al-I-(Mn)Al tunneling junctions. A decreasing zero bias resistivity anomaly was observed when increasing the barrier-impurity distance, with a correlation length of about 30° A. The anomaly due to the presence of small isolated metallic grains was eliminated.

Zero bias anomalies in AlAl 2O 3Al tunnel junctions doped with Fe

We report the observation of an anomalous conductance maximum at zero bias in iron doped AlAl 2O 3Al tunnel junctions at 4.2°K. This conductance maximum is converted into a resistance maximum at higher doping levels. Magnetic field dependence is also reported.

On the potential barrier shape in Al–Al2O3–Al tunnel junctions

In the conventional theoretical model for the tunnel current through thin Al2O3-layers sandwiched between metal electrodes a potential barrier of convex curvature is assumed. The convex curvature of the barrier is caused by the image potential. However, in this paper it will be shown, by means of the logarithmic derivative of the tunnel current, that a potential barrier of concave curvature leads to noticeably better agreement with experimental data than the convex barrier. It is suggested that a large positive ionic space-charge in the Al2O3-layer causes the concave curvature of the potential barrier.

Temperature dependence of the energy gap in superconducting Al–Al2O3–Al tunnel junctions

The most detailed measurements of the energy gap in Al by the tunneling technique have been made using Al–Al2O3-Pb junctions. Determination of the energy gaps from the I–V curves of these junctions is more precise than previous results using Al–Al2O3–Al tunnel junctions. The chief difficulty with the Al–Al2O3–Al junctions has been the lack of definition in the I–V curves, especially near Tc. Al–Al2O3–Al junctions, in which the energy-gap voltages can be read from the I-V curve with very little ambiguity up to T/Tc ≈ 0.99, are reported here. For the majority of the junctions studied, the temperature dependence of the normalized gap Δ(t)/Δ(0) shows very little scatter (T = 0.34 °K to T = Tc) and agrees closely with the BCS theory. However, a consistent small deviation is observed, with the measured gap values being slightly higher than the BCS prediction. The mean value of 2Δ(0)/kBTc obtained from 21 different junctions is 3.53 with an r.m.s. deviation of ± 0.02.