Critical role of parallel momentum in quantum well state couplings in multi-stacked nanofilms: an angle resolved photoemission study

TL;DR

This study uses ARPES to reveal how parallel momentum influences the coupling of quantum well states in multi-stacked nanofilms, identifying distinct regimes of strong and weak coupling across interfaces.

Contribution

It demonstrates the critical role of parallel momentum in quantum well state coupling and uncovers two regimes of electronic interaction in bimetallic nanofilms, supported by DFT calculations.

Findings

Strong coupling regime leads to new quantum well states.

Weak coupling regime retains individual layer states.

Parallel momentum determines coupling strength and regime.

Abstract

We use angle resolved photoemission spectroscopy (ARPES) to investigate the coupling of electron quantum well states (QWS) in epitaxial thin Pb and Ag films. More specifically, we investigate the Ag/Si, Pb/Si, and Pb/Ag/Si systems. We found that the parallel momentum plays a very profound role determining how two adjacent quantum wells are coupled electronically across the interface. We revealed that in the Pb/Ag bimetallic system, there exist two distinctly different regimes in the energy versus momentum (E vs. k) space. In one regime the electronic states in Ag and Pb are strongly coupled resulting in a new set of quantum well states for the bi-metallic system. In the other regime the electronic states in individual metallic layers are retained in their respective regions, as if they are totally decoupled. This result is corroborated by calculations using density functional theory. We further unravel the underlying mechanism associated with the electron refraction and total internal reflection across the interface.