Transient doping in atomic chains -- a case study in time-resolved STM

Doping one-dimensional (1D) systems is notoriously difficult due to the structural disorder created by the dopants. The Si(553)-Au surface features an array of step edges with 1D chains of dangling bonds. These chains have a 1x3 ordered ground state [1]. Using a scanning tunneling microscope we inject electrons from the tip into these step-edge chains and we observe that the periodicity of the atomic chains changes from the 1x3 ordered ground state to a 1x2 ordered excited state with increasing tunneling current. The threshold current for this transition is reduced at lower temperatures. In conjunction with first principles density-functional calculations we conclude that the 1x2 phase is created by transient doping of the atom chains [2]. Random telegraph fluctuations between two levels of the tunneling current provide direct access to the dynamics of the phase transition, revealing a monostable state, and lifetimes in the millisecond range. Our method provides a possible avenue to map out a doping-dependent phase diagram in cases where conventional impurity doping is problematic. \\[4pt] [1] S.C. Erwin, F.J. Himpsel, Nat. Comm. 1:58 (2010).\\[0pt] [2] S. Polei et al., PRL 111, 156801 (2013).