Conductance quantization at room temperature in magnetic and nonmagnetic metallic nanowires

Abstract

This paper shows that conductance quantization at room temperature is a physical and reliable observation. This is demonstrated by conductance histograms taking all ͑12 000͒ consecutive nanowire conductance experiments in Au at room temperature. On the other hand, conductance curves in Ni, a room-temperature ferromagnet, show staircase-quantized behavior, but the histograms do not show quantized peaks, most probably due to the lifting of the spin degeneracy. ͓S0163-1829͑97͒50108-1͔Recent experimental results using scanning tunneling microscopy ͑STM͒, 1,2 mechanically controllable break junctions, 3 and quantum table-top experiments using household macroscopic wires 4,5 have shown conductance quantization ͑CQ͒ in metallic nanowires at room temperature ͑RT͒. Previous to these experiments, CQ was predicted theoretically 6,7 in these nanostructures. Metallic nanowires ͑NW͒ are obtained by breaking a contact between two metallic electrodes. The contact does not break cleanly but is stretched into many nanofilaments. 4,5 At the last stages, one thread remains, and quantum-mechanical effects take over. This happens in all the experiments mentioned above. 1-5 If, simultaneously to the formation, stretching, and breakage of the NW, its conductance is measured, a staircase dependence is found just before it breaks. Conductance histograms using up to 100-200 such curves have been reported showing CQ peaks. However, some criteria have been always used to select the conductance curves with which the histogram is built. The metallic nanowire formation has been also predicted by molecular-dynamics simulations, 8 and recent scanning electron microscopy and chemical analysis experiments have displayed it in real time as a macroscopic metallic contact breaks. 5,9 In this work histograms built using all ͑up to 12 000͒, consecutive conductance curves are presented for Au, Pt, and Ni nanowires at RT. This is ϳ100 times more than any previously reported experiments and without histogram sample selection. The conductance histogram for Au at RT and in air shows clear CQ peaks. The histogram for Ni electrodes does not show CQ peaks, even though the conductance shows a stepped behavior, most probably due to the lifting of the spin degeneracy.The experiments are performed in a home-built STM at RT in air. Two high-purity polycrystalline macroscopic electrodes with a few tens of mV potential difference between them, are brought in and out of contact. The current flowing through is measured with a current-voltage ͑I-V͒ converter working at 10 5 gain ͑100-mV/A, 3-s settling time͒. The position of one electrode is fixed, while the other is moved with a piezoelectric actuator driven with a triangular wave. The electrode speed is controlled by varying the amplitude and/or the frequency of this signal. The output of the I-V converter ͑the current signal͒ is measured with a LeCroy 9354AM oscilloscope, with a 500-MHz bandwidth and a 5-G sample/s sampling rate. The current data acquisition is trig-

Fine structure constant and quantized optical transparency of plasmonic nanoarrays

“…Such breakdown is usually caused by electromigration [20][21][22] and/or defects 23,24 . It is known that the contact resistance of a narrow breakdown/contact channel is quantized 25,26 . The dependence of the strength of electromagnetic fields near the edges of a nanopillar on its diameter and the array period would affect electromigration and result in variations in breakdown channels.…”

Plastic Flowlike Deformation and Its Relation to Aperiodic Peaks in Conductance Histograms of Molybdenum Nanocontacts

“…For NCs made of noble metals, especially gold (Au), the conductance decreases in a stepwise fashion during the breaking process, and several peaks are observed at integer multiples of G 0 in the histogram of the time-conductance traces. 1,2,6,9,10,18,19) From Sharvin's formula 30) and numerical calculations, 3, 4, 11-15, 17, 20, 31-35) the conductance value 1G 0 was interpreted to correspond to contacts having the minimum possible cross section, i.e., single-atom contacts. However, in the conductance histograms of NCs made of other metals, except Au, copper, silver (Ag), and aluminum 36,37) , the features of conductance quantization have not been observed or even no peak has been observed.…”

“…However, in the conductance histograms of NCs made of other metals, except Au, copper, silver (Ag), and aluminum 36,37) , the features of conductance quantization have not been observed or even no peak has been observed. 10,38) Therefore, from the conductances of NCs made of such metals, we cannot simply deduce the corresponding structures. Consequently, the relationship between the NC structure and the conductance has been predicted on the basis of calculations using simple hypothetical models.…”

Electron Transport in Magnetic Quantum Point Contacts

“…∆G = G 0 2 = e 2 h . Indeed, half-integer conductance quanta have been observed in both magnetic-and non-magnetic point contacts, particularly in external magnetic fields [43][44][45][46][47][48][49][50].…”

“…If only one type of electrons (spin-up or spin-down) contributes to the conductance through fully spin-polarized channels, Eq. (1) may be written as [43]:…”