Kondo-like transport and magnetic field effect of charge carrier fluctuations in granular aluminum oxide thin films

Abstract

Granular aluminum oxide is an attractive material for superconducting quantum electronics. However, its low-temperature normal state transport properties are still not fully understood, while they could be related to the unconventional phenomenon of the superconductivity in this material. In order to obtain useful information on this aspect, a detailed study of charge carrier fluctuations has been performed in granular aluminum oxide films. The results of electric noise measurements indicate the presence of a Kondo-type spin-flip scattering mechanism for the conducting electrons in the normal state, at low temperatures. Moreover, the magnetic field dependence of the noise amplitude suggests that interface magnetic moments are the main source of fluctuations. The identification of the nature of fluctuation processes is a mandatory requirement for the improvement of quality and performance of quantum devices.

Magnetotransport and magnetic properties of amorphous $$\mathrm{NdNi}_5$$ thin films

“…6, a reduction of the 1/f noise amplitude (i.e., a 2 coefficient) is measured by increasing the value of the applied magnetic field, and this effect is enhanced by lowering the temperature. This experimental finding, reported also for granular aluminum oxide thin films 33,34 , gives a further indication in favour of the occurrence of magnetic noise fluctuations to be ascribed to the presence of magnetic impurities found in a Kondo-like regime, as also observed in disordered amorphous alloys 22 .…”

“…In the case of inhomogeneous and disordered material different values of n are possible. In the case of granular aluminum oxide films the value has been obtained 33 , 34 . The experimental data are reproduced for both the models with good accuracy, see green and red lines in Fig.…”

Current-Resistance Effects Inducing Nonlinear Fluctuation Mechanisms in Granular Aluminum Oxide Nanowires

“…Figure 2 shows the temperature dependence of the resistance of all the investigated devices. Differently from the previously analyzed case of AlOx thin films [17], the nanowires are characterized by a monotonic resistivity decrease by increasing the temperature between 8 and 300 K. This decreasing behavior, which is not unusual in high resistive samples, seems to be more pronounced at low temperatures, although the resistance value does not scale with the wire length, probably due to differences of the average wire width and resistivity across the nanowire devices. By using the microstrip (nominally 100 nm-wide) as a reference, it is possible to estimate the room-temperature resistivity of the nanowires ρRT ≈ 5.2 × 10 μΩ cm.…”

“…Conversely, for ρ RT values between 1 × 10 3 and 4 × 10 3 µΩ cm there is an intermediate regime in which the resistance changes very little with temperature and it shows a logarithmic increase at low temperatures (Kondo regime). This is the case of the previously analyzed AlO x thin films [17], which, therefore, have a resistivity temperature dependence different from the nanowires studied here. It is also important to underline that the strictly metallic regime is usually characterized by values of ρ RT that are lower than 10 3 µΩ cm [20].…”

“…Magnetic resistance fluctuations are usually characterized by a noise level increase in the lowtemperature region. This type of fluctuation process, which is already found for granular aluminum oxide thin films, is ascribed to Kondo-like conductivity when the noise level, especially at low temperatures, decreases with an external magnetic field of the order of one thousand Gauss [17,31]. In the case of AlOx nanowires, no magnetic dependence is observed in both DC and AC measurements, even if a noise enhancement is evident by lowering the temperature (for details, see Figure 7).…”