About chirality, tunneling and light fields

Electrons in motion: in chirality, tunneling and light fields

Schematic view of sub-barrier and continuous electron dynamics in strong field ionization (a) and principles of chiral attoclock (b) and sub-loop-gated photoelectron interferometry (c) techniques. In (a), ionization takes place as part of the first bound electron wave packet tunnels across the target potential barrier dropped by the strong laser field. The released electron is then scattered over the ionic potential in continuum. In (b), randomly oriented molecules are ionized in a pair of circular co-rotational by a two-color laser field E

Will an electron escaping a molecule through a quantum tunnel behave differently depending on whether the molecule is left- or right-handed?

Chemists borrowed the terms “left-handed” and “right-handed” from anatomy to describe molecules characterized by a certain type of asymmetry. To explore the concept of chirality, look at your hands with your palms facing up. Frankly, the two are mirror images of each other. But even if we try to overlap them, they will not completely overlap. Such objects, called “chiral”, can be found in nature at all scales, from galaxies to molecules.

We experience chirality every day not only when we pick up an object or put on our shoes, but also when we eat or breathe: our taste and smell can distinguish between two mirror images of a chiral molecule. In fact, our bodies are so sensitive to chirality that a molecule can be a drug and its mirror image a poison. Therefore, chirality is very important in pharmacology, where 90 percent of the drugs synthesized are chiral compounds.

Chiral molecules have special symmetry properties that make them excellent candidates for the study of fundamental phenomena in physics. Recently, Prof. from CNRS/University of Bordeaux. Yann Mairesse and Prof. from the Weizmann Institute’s Department of Complex Systems Physics. Research teams led by Nirit Dudovich have used chirality to shed new light on one of the most intriguing quantum phenomena: the tunneling process.

Tunneling is a phenomenon where quantum particles cross seemingly impossible physical barriers. Since this movement is forbidden in classical mechanics, it is very difficult to form an intuitive picture of its dynamics. To create a tunnel in the chiral molecules, the researchers exposed them to an intense laser field. “The molecules’ electrons are naturally bound around the nuclei by an energy barrier,” explains Mairesse. “You can imagine electrons as air trapped inside an inflatable balloon. Powerful laser fields are capable of reducing the thickness of the balloon enough that some air can pass through it, even though the balloon has no holes.”

Mairesse, Dudovich and their team set out to examine an as yet unexplored aspect of tunneling: the moment a chiral molecule encounters a chiral light field and the way its brief encounters affect electron tunneling. “We were very excited to discover the connection between chirality and tunneling. We wanted to learn more about what tunneling would look like under these particular conditions,” Dudovich says.

It takes only a few hundred attoseconds for an electron to escape from an atom or molecule. Many of the processes studied in Mairesse and Dudovich’s labs characterize such small time frames. The two teams asked the question: How does the chirality of a molecule affect the escape of an electron?

“We used a laser field that rotates in time to spin the barrier around the chiral molecules,” says Mairesse. “Following the balloon metaphor, if the laser field rotates horizontally, you would expect the air to exit the balloon in the horizontal plane, following the direction of the laser field. What we found is that if the balloon is chiral, the air will fly out of the balloon, either toward the ground or the ceiling, depending on the direction of rotation of the laser. So out of the chiral tunnel. The electrons exit with the memory of the barrier’s spin direction. This is very similar to the effect of a corkscrew, but on the scale of nanometers and attoseconds.”

Thus, the two teams discovered that the probability of an electron tunneling through, the electron tunneling step, and the timing of the tunneling event depend on the molecule’s chirality. These exciting results lay the groundwork for further studies that will use the unique symmetry properties of chiral molecules to investigate the fastest processes occurring in light matter interaction.

The article was published in the journal Physical Examination X.

More information:
E. Bloch et al., Uncovering the Effect of Molecular Chirality on Tunnel Ionization Dynamics, Physical Examination X (2021). DOI: 10.1103/PhysRevX.11.041056

Provided by the Weizmann Institute of Science

Quotation: Stray electrons: In chirality, tunneling and light fields (2022, 23 Dec), retrieved Dec 23, 2022 from https://phys.org/news/2022-12-electrons-chirality-tunneling-fields.html

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