Title :
Subharmonic photon-assisted tunneling effect in Superconducting NbN tunnel junctions
Author :
Uzawa, Yoshinori ; Takeda, Masanori ; Kawakami, Akira ; Wang, Zhen
Author_Institution :
Kansai Adv. Res. Center, Nat. Inst. of Inf. & Commun. Technol., Kobe, Japan
fDate :
6/1/2005 12:00:00 AM
Abstract :
We investigated subharmonic gap structures in the current-voltage (I-V) characteristics of NbN tunnel junctions by observing frequency response using a quasioptical mixer configuration. We chose a 10.5-μm-long by 0.6-μm-wide junction for the mixer so that the junction behaved as a distributed element at submillimeter-wave frequencies in wideband observations. In the presence of electromagnetic waves, subharmonic photon-assisted tunneling steps with a voltage width of hf/2e could clearly be observed below and above the half-gap voltage in the I-V curves of junctions at measured frequencies from 600 to 950 GHz, where h is Planck´s constant, f is frequency, and e is electron charge. This evidence is consistent with a consequence of multiple Andreev reflection at low transmissions or multiparticle tunneling.
Keywords :
frequency response; niobium compounds; submillimetre wave mixers; superconducting junction devices; superconductive tunnelling; 600 to 950 GHz; I-V curves; NbN; Planck constant; current-voltage characteristics; electromagnetic waves; electron charge; frequency response; multiparticle tunneling; multiple Andreev reflection; quasioptical mixer configuration; subharmonic gap structures; subharmonic photon-assisted tunneling effect; submillimeter wave frequeny; superconducting NbN tunnel junctions; Charge measurement; Current measurement; Electromagnetic scattering; Frequency measurement; Frequency response; Hafnium; Josephson junctions; Tunneling; Voltage; Wideband; Multiple Andreev reflection; NbN tunnel junctions; subharmonic gap structures; subharmonic photon-assisted tunneling;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
DOI :
10.1109/TASC.2005.849760