Tunneling and conductivity measurements through the metal-insulator transition in amorphous Nb^Si^ are reported. The authors observe the correlation gap A which varies with resistivity and have related this to the metal-insulator transition as observed in the conductivity. The samples were prepared by a process which allows precise control of the Nb concentration. The results as a function of voltage, temperature, and concentration are compared with current theoretical predictions.PACS numbers: 71.30.+h, 71.50.+t, 72.15.Cz, 73.40.Gk The metal-insulator transition in disordered materials has been recently studied in several transport measurements. 1 " 4 All experiments indicate that there is no minimum metallic conductivity. 3 ' 4 In addition, tunneling measurements have shown a strong anomaly in the density of states at the Fermi level indicative of very strong many-body contributions to the metal-insulator transition. 1 ' 2 Altshuler and Aronov 5 had earlier shown that many-body effects were important. In a phenomenological scaling theory McMillan 6 incorporated both localization and correlation effects on equal footing. He predicted a squareroot singularity N(p) = N(0)[l + (E/A) 1/2 ] in the single-particle density of states at the Fermi level on the metallic side of the transition. This was later verified by the tunneling experiments. The parameter A was interpreted as a correlation gap-the precursor of the energy gap in the single-particle density of states which opens up on the insulating side of the metal-insulator transition. At the metal-insulator (M-I) transition, A goes to zero, N(0) goes to zero, and the energy gap begins to open up.In this Letter we report high-precision tunneling and conductivity measurements through the metal-insulator transition in amorphous Nb x Si xx . Our samples were prepared by simultaneously cosputtering Nb and Si onto a substrate producing a shallow concentration gradient. Unlike previous measurements which had difficulty in producing controlled, uniform concentration changes, our method allowed us to measure the properties of the amorphous material in a controlled and systematic way as we moved through the M-I transition in small, uniform increments. As in previous experiments we have observed a correlation gap A which varies with resistivity. However unlike previous experiments we have made low-temperature transport measurements to correlate our tunneling results directly with the metal-insultor transition. In addition we have observed the metal-insulator transition by the onset of the breakdown of the single-step tunneling process when the energy gap appears at the Fermi energy and localized states appear in the Nb^Sii^. By controlling concentration as easily as voltage and temperature we can obtain experimental relationships among them and in this Letter these are presented and compared with current theoretical predictions.Our samples were prepared by cosputtering Nb and Si from separate targets onto sapphire substrates (see inset in Fig. 1). The films had a thickness...
The Zeeman energy splitting 5 of the superconducting tunneling conductances measured in a magnetic field gives a measure of both the g factor of the conduction electrons and also the l =0 antisymmetric Fermi-liquid parameter 6 . We show how a technique of Fourier analysis, known as cepstral analysis, can be used to measure the Zeeman splitting directly from the total conductance. This technique allows measurement of Fermi-liquid effects which are thought to be of particular importance in high-T, vanadium-based compounds. We present some results on the recent data of Bending, Beasley, and Tsuei on V3Ga in which the g factor is found to be nearly 2.0.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.