Researchers create a nanoscale slalom course for electrons

A research team led by professors from the Department of Physics and Astronomy has created a serpentine path for electrons, impregnating them with new properties that could be useful in future quantum devices.

Jeremy Levy, a distinguished professor of condensed matter physics, and Patrick Irvin, research professor, are co-authors of the article “Engineered spin-orbit interactions in LaAlO₃/ SrTiO₃-based 1D serpentine electron waveguides “, published in Advances in science on November 25.

“We already know how to ballistically shoot electrons through one-dimensional nanowires made from these oxide materials,” says Levy. “What’s different here is that we’ve changed the environment for electrons, forcing them to weave left and right as they travel. This motion changes the properties of the electrons, giving rise to new behavior.”

The work is led by a recent PhD. recipient, Dr. Megan Briggeman, whose thesis was devoted to developing a platform for “quantum simulation” in one dimension. Briggeman is also the lead author of a related work published earlier this year in Science, where a new family of electronic phases has been discovered in which electrons travel in packets of 2, 3 and more at a time.

Electrons behave very differently when forced to exist along a straight line (i.e. in one dimension). It is known, for example, that the spin and charge components of electrons can split and travel at different speeds through a 1D wire. These bizarre effects are fascinating and also important for the development of advanced quantum technologies such as quantum computers. Movement along a straight line is just one of the many possibilities that can be created using this quantum simulation approach. This publication explores the consequences of making electrons move from side to side as they run down and otherwise the linear path.

A recent proposal for topologically protected quantum computing exploits so-called “Majorana fermions”, particles that can exist in 1D quantum wires when certain ingredients are present. The LaAlO₃/ SrTiO₃ the system, it turns out, has most but not all of the required interactions. It lacks a sufficiently strong “spin-orbit interaction” that can produce the conditions for Majorana fermions. One of the main findings of this latest work by Levy is that spin-orbit interactions can indeed be engineered through the serpentine motion that electrons are forced to undertake.

In addition to identifying new engineered spin-orbit couplings, the periodic repetition of the serpentine path creates new ways for electrons to interact with each other. The experimental result of this is the existence of fractional conductances that deviate from those expected for individual electrons.

These slalom courses are created using a nanoscale drawing technique similar to an Etch A Sketch toy, but with a point size that is a trillion times smaller in the area. These paths can be sketched and erased over and over again, each time creating a new type of path for electrons to travel through. This approach can be thought of as a way to create quantum materials with reprogrammable properties. Materials scientists synthesize materials in a similar way, extracting atoms from the periodic table and forcing them to arrange them in periodic matrices. Here the lattice is artificial: a zigzag of movement occurs in a space of ten nanometers instead of in a sub-nanometer atomic distance.

Levy, who is also director of the Pittsburgh Quantum Institute, said this work contributes to one of the main goals of the Second Quantum Revolution, which is to explore, understand and exploit the whole nature of quantum matter. A better understanding and the ability to simulate the behavior of a wide range of quantum materials will have far-reaching consequences. “This research is part of a larger effort here in Pittsburgh to develop new sciences and technologies related to the second quantum revolution,” he said.