Modeling Green's function measurements with two-tip scanning tunneling microscopy

Abstract

A double-tip scanning tunneling microscope with nanometer-scale tip separation has the ability to access the single-electron Green's function in real and momentum spaces based on second-order tunneling processes. Experimental realization of such measurements has been limited to quasi-one-dimensional systems due to the extremely small signal size. Here we propose an alternative approach to obtain such information by exploiting the current-current correlations from the individual tips and present a theoretical formalism to describe it. To assess the feasibility of our approach we make a numerical estimate for an ∼25-nm Pb nanoisland and show that the wave function in fact extends from tip to tip and the signal depends less strongly on increased tip separation in the diffusive regime than the one in alternative approaches relying on tip-to-tip conductance.

Fabrication of on-chip probes for double-tip scanning tunneling microscopy

“…Scanning tunneling microscopy using two tips simultaneously in tunneling, also called double-tip STM, often relies on two individually driven metal wire probes brought into close proximity to locally probe resistivity [1][2][3] or to access the proposed electron correlations at the nanoscale [4][5][6][7][8][9][10][11]. Achieving tip separation down to the nanometer scale, a long standing goal in multiprobe STM, has proven challenging and is limited by the radius of curvature of the two tips [12] and requires sophisticated navigation routines [13,14].…”