Nanoscopic interferometer model for spin resonance in current noise

We study a model for the observed phenomenon of electron spin resonance (ESR) at the Zeeman frequency as seen by a scanning tunneling microscope (STM) via its current noise. The model for this ESR-STM phenomenon allows the STM current to flow in two arms of a nanoscopic interferometer, one arm has direct tunneling from the tip to the substrate while the second arm has tunneling through two spin states. We evaluate analytically the noise spectrum for nonpolarized leads, as relevant to the experimental setup. We show that spin-orbit interactions allow for an interference of two tunneling paths resulting in a resonance effect.