Quantum charge fluctuations in a superconducting grain
Abstract
We consider charge quantization in a small superconducting grain that is contacted by a normalmetal electrode and is controlled by a capacitively coupled gate. At zero temperature and zero conductance G between the grain and the electrode, the charge Q as a function of the gate voltage V_{g} changes in steps. The step height is e if Δ<E_{c} , where Δ and E_{c} are, respectively, the superconducting gap and the charging energy of the grain. Quantum charge fluctuations at finite conductance remove the discontinuity in the dependence of Q on V_{g} and lead to a finite step width ∝G^{2}Δ . The resulting shape of the Coulomb blockade staircase is of a novel type. The grain charge is a continuous function of V_{g} while the differential capacitance, dQ/dV_{g} , has discontinuities at certain values of the gate voltage. We determine analytically the shape of the Coulomb blockade staircase also at nonzero temperatures.
 Publication:

Physical Review B
 Pub Date:
 September 2005
 DOI:
 10.1103/PhysRevB.72.104507
 arXiv:
 arXiv:condmat/0502657
 Bibcode:
 2005PhRvB..72j4507H
 Keywords:

 74.50.+r;
 73.23.Hk;
 72.10.Fk;
 74.20.Fg;
 Tunneling phenomena;
 point contacts weak links Josephson effects;
 Coulomb blockade;
 singleelectron tunneling;
 Scattering by point defects dislocations surfaces and other imperfections;
 BCS theory and its development;
 Condensed Matter  Mesoscale and Nanoscale Physics;
 Condensed Matter  Superconductivity
 EPrint:
 12 pages, 3 figures