Ab initio non-equilibrium Green's function study on the growth of metallic bridge in mixed conductor atomic switch

A novel atomic switch [1] composed of a mixed conductor, Ag$_{2}$S or Cu$_{2}$S, has attracted much attention. To investigate the electronic properties of the atomic switch, we have examined interface structure and electron transport of Ag/Ag$_{2}$S/Ag and Cu/Cu$_{2}$S/Cu using ab initio non-equilibrium Green's function method. In Ag/Ag$_{2}$S/Ag, we found a spontaneous growth of a metallic bridge composed of a Ag atomic chain when a unidirectional stress is applied to Ag$_{2}$S [2]. On the contrary, a metallic bride does not appear in Ag$_{2}$S and Cu$_{2}$S without stress. We also examined the influence of Ag/Cu addition on the structural and transport properties of Ag$_{2}$S and Cu$_{2}$S atomic switches, and found that the Ag/Cu addition leads to the metallization in the both systems. However, clear growth of the atomic bridge is confirmed only in Ag/Ag$_{2+\delta }$S/Ag. The metallic nature in Cu/Cu$_{2+\delta }$S/Cu is related to the growth of electron charge network at the Fermi level. 1) K. Terabe, et al., Nature 433, 47 (2005). 2) Z. Wang, T. Kadohira, T. Tada, S. Watanabe, Nano Letters 7, 2688 (2007).