2026/10/14(Wed) 14:00 -16:00 一樓演講廳 1F, Auditorium
Title
Probing spin-dependent charge transport at single-nanometer length scales
Speaker
Prof. Dr. Matthias Bode (Chair of Experimental Physics II, University of Würzburg, Germany)Abstract
Scanning tunneling microscopy (STM) has become a standard tool in surface science. It not only allows for the imaging of surfaces down to the atomic scale, the analysis of standing waves of hot charge carriers also opened the door to elucidate local electronic properties with unprecedented resolution. This technique, known as quasiparticle interference (QPI) mapping, detects maxima and minima of the differential conductance dI/dU generated by the coherent scattering of electronic states at defects, such as step edges, surface impurities, or adatoms.
It is a severe limitation, however, that the same STM tip is simultaneously used to inject and to detect the charge carriers, i.e., after injection, the quasiparticle needs to be “routed back” for detection. Therefore, it is virtually impossible to spatially map the charge density which results from scattering, refraction, and diffraction around a given quasiparticle injection point. To circumvent this limitation, multi-probe STMs have been utilized to measure transport. However, due to the finite diameter of STM tips, this technique is limited to distances > 30 nm.
The so-called molecular nanoprobe (MONA) technique represents an alternative approach. Here, charge carriers are locally injected by a STM tip, propagate across the surface, and are detected by a single molecule via a reversible electron-induced switching process, such as a tautomerization. Charge transport in surface states, anisotropic transport, and the damping and coherent superposition of quantum-mechanical waves has been experimentally demonstrated (see Fig. 1).
In this presentation, I will review the recent development and discuss spin-polarized (SP) MONA using magnetic STM tips. For the spin–momentum-locked surface state of the Rashba alloy BiAg2 we show that the current direction inverses as the tip magnetization is reversed by an external field. In a proof-of-principle experiment we apply SP-MONA to investigate how a single Gd cluster influences the spin-dependent charge transport of the Rashba surface alloy.
Language
演講語言 (Language): in English