Zero-Bias Anomalies in Normal Metal Tunnel Junctions

Abstract

than two orders of magnitude by the presence of 1% Ni 2+ ions). Ni 2+ emission may also be excited through the Mn 2+ bands near 4300 A, but these are superimposed on a 3 T 1 band of Ni 2+ . Particularly interesting is the fact that the efficiency of Mn 2+ -Ni 2+ energy transfer is high even for very low Ni 2+ concentration. For example, in MnF 2 containing 15 ppm Ni 2+ ions, the quantum efficiency for Ni 2+ emission is about 30% at 4.2°K when exciting the 4 7\ band of Mn 2+ . To illustrate this figure somewhat differently, consider a sphere about each Ni 2+ ion such that all Mn 2+ ions within the sphere transfer their excitation to Ni 2+ , while those outside do not. The radius of the sphere so calculated for MnF 2 containing 15 ppm Ni 2+ ions is about 60 A. These findings indicate that energy transport between Mn 2+ ions is extremely long range, just as suggested previously for nickel compounds. 2 We are grateful to C. G. B. Garrett and G. K. Wertheim for several helpful suggestions on the manuscript.

Oxidation of metals at the chromium oxide interface

“…The observed current-voltage curve of the resulting film was strongly reminiscent of the so-called ''giant resistance peak'' observed by Rowell and Shen on Cr-I-Ag tunnel junctions. 17 The insulator ''I'' in their junctions was also fabricated by oxidation of a Cr film, and the anomaly attributed to the presence of magnetic CrO 2 and Cr 2 O 3 . Angle-resolved x-ray photoemission ͑ARXPS͒ investigations of these films, 18 allowed us to differentiate between CrO 2 and Cr 2 O 3 .…”

“…In one approach, samples were made of a thin Cr film ͑30 nm thick͒ sputtered on a clean Si wafer and oxidized in partial oxygen pressure. We reproduced the synthesis route of Rowell and Shen, 17 with the samples heated 14 h at 470 K in 730 mbar oxygen partial pressure. The observed current-voltage curve of the resulting film was strongly reminiscent of the so-called ''giant resistance peak'' observed by Rowell and Shen on Cr-I-Ag tunnel junctions.…”

“…1. Pb was evaporated on top of samples fabricated by the approach of Rowell and Shen, 17 while the Co was evaporated on the epitaxial Cr 2 O 3 /CrO 2 samples on single-crystal TiO 2 . As expected, Cr 2p corelevel spectra show that the clean surface is dominated by the stable Cr 2 O 3 surface oxide.…”

Nonequilibrium STM model for Kondo resonance at a surface

“…The behavior is similar to another important zero-bias phenomenon besides the Kondo resonance, the so-called zero-bias anomaly. [51] If we subtract the dip from total dI/dV curve we get the Kondo resonance Peak (solid-line).…”

Spin blockade effects in chromium oxide intergrain magnetoresistance

“…This low-bias conductivity is strongly reminiscent of the so-called giant resistance peak observed by Rowell and Shen on Cr-I-Ag tunnel junctions. 17 This insulator ''I'' was fabricated by oxidation of a Cr film, and the anomaly attributed to the presence of magnetic CrO 2 and Cr 2 O 3 ! We can directly superpose our resistance versus bias curve to the Rowell and Shen results if we scale down our bias voltage scale by a factor of 10.…”