Tunnelling stands as a cornerstone process in quantum mechanics, allowing a wave packet to traverse an energetically impassable barrier with a certain probability. At the atomic scale, tunnelling effects play a vital role in molecular biology, influencing enzyme catalysis, triggering DNA mutations, and setting off olfactory signaling cascades.
In the realm of light-induced chemical reactions, charge and energy transfer, and radiation emission, photoelectron tunnelling plays a pivotal role. As optoelectronic chips and devices approach the sub-nanometer atomic scale, quantum tunneling effects between channels become significantly pronounced.
Real-time imaging of electron tunneling dynamics within complex structures holds immense scientific importance, propelling the advancement of tunneling transistors and ultrafast optoelectronic devices. The influence of neighboring atoms on electron tunneling dynamics remains a crucial scientific challenge in quantum physics, quantum chemistry, nanoelectronics, and related fields.
In a recent publication in Light Science & Application titled "Tunnelling of electrons via the neighboring atom," a team of scientists from Hainan University and East China Normal University presented a prototype system, a van der Waals complex Ar-Kr+, with an internuclear distance of 0.39 nm. This system was designed to track electron tunneling via the neighboring atom at the sub-nanometer scale.
The intrinsic electron localization of the highest occupied molecular orbital of Ar-Kr indicates a preference for electron removal from the Kr site in the first ionization step. The electron hole, assisted by the site in Ar-Kr+, ensures that the second electron is predominantly removed from the Ar atom in the second ionization step, with the possibility of direct tunneling to the continuum from the Ar atom or via the neighboring Kr+ ionic core.
Utilizing the improved Coulomb-corrected strong-field approximation (ICCSFA) method developed by the team, capable of considering Coulomb interaction during tunnelling, the scientists monitored the photoelectron transverse momentum distribution to track tunnelling dynamics. This revealed two effects: strong capture and weak capture of tunneling electrons by the neighboring atom.
The electron emitted from the Ar atom is initially trapped in highly excited transient states of the Ar-Kr+* before eventually releasing to the continuum. The study employed a linearly polarized pump laser pulse to prepare the Ar-Kr+ ion and a time-delayed elliptically polarized probe laser pulse to track the electron transfer-mediated electron tunnelling dynamics (e2, orange arrow).
This groundbreaking work sheds light on the critical role of neighboring atoms in electron tunnelling within sub-nanometer complex systems. The discovery offers a fresh perspective on understanding the Coulomb effect under potential barriers in electron tunnelling dynamics, solidifying high harmonic generation and establishing a robust research foundation for probing and controlling the tunnelling dynamics of complex biomolecules.
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