Experiments in twisted, layered quantum materials offer new picture of how electrons behave

June 8, 2022

Below is from an article by Tom Garlinghouse for the Department of Physics (June 8, 2022).

A recent experiment detailed in the journal Nature is challenging our picture of how electrons behave in quantum materials. Using stacked layers of a material called tungsten ditelluride, researchers have observed electrons in two dimensions behaving as if they were in a single dimension — and in the process have created what the researchers assert is a new electronic state of matter. 

“This is really a whole new horizon,” said Sanfeng Wu, assistant professor of physics at Princeton University and the senior author of the paper. “We were able to create a new electronic phase with this experiment — basically, a new type of metallic state.”

Our current understanding of the behavior of interacting electrons in metals can be described by a theory that works well with two- and three-dimensional systems, but breaks down when describing the interaction of electrons in a single dimension.

“This theory describes the majority of the metals that we know,” said Wu. “It states that electrons in metal, though strongly interacting, should behave like free electrons, except that they may have different values in some characteristic quantities, such as the mass and magnetic moment."

In one-dimensional systems, however, this “Fermi liquid theory” gives way to another theory, “the Luttinger liquid theory,” to describe the interaction between electrons.

“Luttinger liquid theory provides a basic starting point to understand interacting electrons in one dimension,” said Wu. “Electrons in a one-dimensional lattice are so strongly correlated with one another that, in a sense, they begin not to act like free electrons."

The Fermi liquid theory was first put forward by the Nobel Prize winner L.D. Landau. Luttinger’s theory went through a long process of refinement before it became widely accepted by physicists. A theoretical model was first proposed by Japanese Nobel Prize winner Shinichiro Tomonaga in the 1950s, said Wu, and was independently formulated by J.M. Luttinger later in 1963. Luttinger, however, provided an inadequate solution and so Princeton mathematician and physicist Elliott Lieb, today the Eugene Higgins Professor of Physics, Emeritus, took up the challenge in 1965, eventually providing a correct solution. Another physicist and Nobel Prize laureate, F. Duncan Haldane, Princeton’s Sherman Fairchild University Professor of Physics, then used the model in 1981 to understand the interaction effects of one-dimensional metals. Haldane coined the term “Luttinger liquids” and laid the foundation for the modern theory of Luttinger liquids as a general description for one-dimensional metals.

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