Quantum fluctuations in the cohesive force of metallic nanowires

Based on the recent free-electron model for cohesion in narrow metallic constrictions by Stafford, Baeriswyl, and Burki [Phys. Rev. Lett. 79, 2863 (1997)] we calculate the quantum fluctuations in the cohesive force versus elongation. The fluctuations are dominated by states near the Fermi energy, thus explaining their apparently universal magnitude of order epsilon(F)/lambda(F). We present numerical results for the force fluctuations in a simple geometry and show that they are well described by the contributions of a few classical periodic orbits in the Balian-Bloch trace formula for the density of states of transverse motion. [S0163-1829(99)51812-2].