Measurements are reported of the current-voltage (I-V) characteristics of externally shunted oxide-barrier tunnel junctions at temperatures T and critical currents Ic such that the Josephson coupling energy (2e)Ic is comparable to the thermal energy k T. The measurements are in complete quantitative agreement with the theory of Ambegaokar and Halperin in the limit that the dimensionless parameter βc=(2e) (IcCσ2)1, where C is the capacitance and σ the total conductance of the shunted junction. Measurements for larger values of βc are in qualitative agreement with the theory of Kurkijärvi and Ambegaokar. In addition, the Ambegaokar-Halperin theory is generalized to include the cos pair-quasiparticle interference term. It is concluded that a measurement of the cos term using only the I-V characteristic will be difficult.
ASJC Scopus subject areas
- Condensed Matter Physics