Differentiation of Surface and Bulk Conductivities via Four-probe Spectroscopy

A large number of materials have localized electronic states present on their surfaces. Understanding and controlling the electronic properties of these states does not only constitute the foundations of surface science but also the modern electronic devices. Being studied with mature surface analytic techniques like STM and ARPES, local electronic properties of surface states can be characterized very well. However, little is known about the electron transport through these 2D surface states which can present completely different characteristics than the transport through the underlying 3D bulk. During the last decade however, the demand for understanding the transport through surface states increased significantly due to constantly decreasing size of microelectronic devices and discovery of new materials like topological insulators (TIs) and other 2D layered materials with surface states hosting new and interesting transport properties.