Condensed-Matter Physics & Materials Science Seminar

The current-phase relation (CPR) of a Josephson junction reveals valuable information about the microscopic processes and symmetries that
influence the supercurrent. For the work described in this talk, we have studied the CPR of graphene-based Jospehson junctions, inspired by
previous theoretical predictions [1, 2] of a departure from the usual sinusoidal functionality, or skewness, of the CPR.
The experimental data was obtained by incorporating the junction into an rf SQUID geometry coupled to a dc SQUID magnetometer, a technique
usually referred to as phase-sensitive SQUID interferometry, which allows for the direct measurement of the phase difference across the junction.
While some of the predictions from theory - like the departure of the CPR from sinusoidal behavior, its symmetry with carrier nature and the
de-skewing with increasing temperature - were qualitatively observed, others were inconsistent with the experimental data. Perhaps the most
important disparity was that of the functionality of the skewing, which we found to vary linearly with critical current (Ic), independent of the carrier
density/temperature combination used to attain Ic. It is worth mentioning that our measurements have prompted renewed theoretical interest in
this system, culminating in the modification of the original model to include the effects of temperature [3], and a recent publication [4] venturing
an explanation for the observed linearity of the CPR skewness with Ic.
References
[1] M. Titov and C. W. J. Beenakker, Phys. Rev. B, 74, 041401(R) (2006).
[2] A. M. Black-Scha_er and S. Doniach, Phys. Rev. B, 78, 024504 (2008).
[3] A. M. Black-Scha_er and J. Linder, Phys. Rev. B, 82, 184522 (2010).
[4] I. Hagym_asi, A. Korm_anyos, J. Cserti, Phys. Rev. B, 82, 134516 (2010