[Paper Review] Single-molecule junctions map the interplay between electrons and chirality

Anil Kumar Singh, Kévin Martin+5 more|arXiv (Cornell University)|Aug 22, 2024

Molecular Junctions and Nanostructures4 citations

TL;DR

This study demonstrates that single-molecule junctions based on helicene molecules exhibit dual functionality as both a magnetic diode and a spin valve, enabling atomic-scale mapping of distinct electron-chirality interactions. The coexistence of spin-dependent transport and magnetic field-induced rectification reveals two separate electron-chirality coupling mechanisms: spin-orbit coupling and chiral-induced spin filtering, advancing spintronic device design at the molecular level.

ABSTRACT

The interplay of electrons with a chiral medium has a diverse impact across science and technology, influencing drug separation, chemical reactions, and electronic transport. In particular, such electronchirality interactions can significantly affect charge and spin transport in chiral conductors, ranging from bulk semiconductors down to individual molecules. Consequentially, these interactions are appealing for spintronic manipulations. However, an atomistic mapping of the different electron chirality interactions and their potential for spintronics has yet to be reached. Here, we find that single molecule junctions based on helicene molecules behave as a combined magnetic diode and spin valve device. This dual functionality is used to identify the coexistence of different electron chirality interactions at the atomic scale. Specifically, we find that the magnetic diode behavior arises from an interaction between the angular momentum of electrons in a chiral medium and magnetic fields, whereas the spin valve functionality stems from an interaction between the electron spin and a chiral medium. The coexistence of these two interactions in the same atomic scale system is then used to identify the distinct properties of each interaction. This work uncovers the different electron chirality interactions available at the atomic level. The found concurrent existence of such interactions can broaden the available methods for spintronics by combining their peculiar functionalities.

Motivation & Objective

• To map the interplay between electrons and chirality at the atomic scale using single-molecule junctions.
• To identify and distinguish between different electron-chirality interactions influencing charge and spin transport.
• To explore the potential of chiral molecules as multifunctional components in spintronic devices.
• To establish a platform for probing spin-dependent transport mechanisms in chiral nanostructures.

Proposed method

• Fabrication of single-molecule junctions using helicene molecules via mechanical break junction techniques.
• Measurement of current-voltage characteristics under applied magnetic fields to probe spin and charge transport.
• Use of chiral molecular geometry to induce spin-dependent electron transport and magnetic rectification.
• Analysis of magnetic diode behavior to isolate electron angular momentum coupling with magnetic fields.
• Investigation of spin valve functionality to identify spin-momentum locking in chiral media.
• Comparison of experimental results with theoretical models to disentangle distinct electron-chirality interactions.

Experimental results

Research questions

• RQ1 How do electron-chirality interactions manifest in single-molecule junctions at the atomic scale?
• RQ2 What physical mechanisms underlie the observed magnetic diode and spin valve behaviors in helicene-based junctions?
• RQ3 Can both spin-dependent transport and magnetic field-induced rectification coexist in the same molecular system?
• RQ4 What is the origin of the observed spin filtering and angular momentum coupling in chiral conductors?
• RQ5 How can these dual functionalities be leveraged for advanced spintronic applications?

Key findings

• Single-molecule helicene junctions exhibit concurrent magnetic diode behavior due to coupling between electron angular momentum and external magnetic fields.
• The junctions also function as spin valves, indicating a separate interaction between electron spin and the chiral molecular environment.
• The coexistence of both functionalities allows for the unambiguous identification of two distinct electron-chirality interactions at the atomic scale.
• The magnetic diode effect arises from chiral-induced spin-orbit coupling, while the spin valve effect stems from chiral-induced spin filtering.
• These findings demonstrate that helicene-based junctions can serve as a dual-functional platform for probing and utilizing electron-chirality interactions.
• The results open new pathways for designing multifunctional spintronic devices by combining spin filtering and magnetic rectification in a single molecular component.