Probing ultrafast spin dynamics with optical pump–probe scanning tunnelling microscopy

Abstract

Studies of spin dynamics in low-dimensional systems are important from both fundamental and practical points of view. Spin-polarized scanning tunnelling microscopy allows localized spin dynamics to be characterized and plays important roles in nanoscale science and technology. However, nanoscale analysis of the ultrafast dynamics of itinerant magnetism, as well as its localized characteristics, should be pursued to advance further the investigation of quantum dynamics in functional structures of small systems. Here, we demonstrate the optical pump-probe scanning tunnelling microscopy technique, which enables the nanoscale probing of spin dynamics with the temporal resolution corresponding, in principle, to the optical pulse width. Spins are optically oriented using circularly polarized light, and their dynamics are probed by scanning tunnelling microscopy based on the optical pump-probe method. Spin relaxation in a single quantum well with a width of 6 nm was observed with a spatial resolution of ∼ 1 nm. In addition to spin relaxation dynamics, spin precession, which provides an estimation of the Landé g factor, was observed successfully.

Direct observation and control of hydrogen-bond dynamics using low-temperature scanning tunneling microscopy

“…More recently, time-resolved STM techniques with the order of nanoseconds or picoseconds has been achieved by combining a short electric [276] or optical pulse [277]. These techniques are yet too immature to trace adsorbate reactions, but further development of time-resolved STM will allow us to unveil H-bond dynamics at the spatial and temporal limits.…”

Vibron-assisted spin relaxation at a metal/organic interface

“…Notably, by assuming = 1 meV (a realistic value for a molecule physisorbed on a surface) we can estimate t to be 26 ns for g = 4 and about an order of magnitude smaller if g = 3, with a current of the order of 1 nA. Since nanosecond resolution has been recently achieved in pump-probe spSTM experiments [29][30][31][32], a verification of our proposed vibroninduced spin relaxation at hybrid interfaces is possible.…”

“…This consists in performing time-resolved spin-polarized scanning tunneling microscopy (spSTM) experiments which probe well-defined molecules on a substrate. We will show that the required time resolution is indeed achievable with this technique [29][30][31][32]. The article is organized as follows: First, we introduce the proposed model and we describe the employed theoretical methods (Sec.…”

Scanning Probe Characterization of Heterostructured Colloidal Nanomaterials

“…with unprecedented spatial resolution, as well as accessing complex material properties, moving beyond the realm of electrical characterization. A few prominent examples are (a) understanding spin dynamics by use of pump−probe STM, 255 (b) understanding the dynamics of photoexcited charges by use of time-resolved EFM measurements, and (c) understanding thermoelectricity in molecular junctions by use of custom-built STM. 256 A portion of future thrusts in SPM measurements will likely be geared toward acquiring atomic-scale to nanoscale information within materials scaled up to be utilized for specific applications.…”