Study observes the behavior of Luttinger's liquid in a quasi-2D system

Study observes the behavior of Luttinger’s liquid in a quasi-2D system

Study observes the behavior of Luttinger's liquid in a quasi-2D system

Image showing: (a) the conventional (quasi-)1D Luttinger’s liquid with parallel chain networks, (b) the theoretically proposed crossed sliding Luttinger’s liquid model with spatially separated planar parallel chain networks, and (c) the liquid 2D Luttinger in η-Mo4O11, where the orthogonal orbital components of electrons flowing along different chains guarantee the minor inter-lattice interactions. Credit: Du et al

Luttinger liquids are typically paramagnetic materials exhibiting non-Fermi liquid behavior, such as molybdenum oxides. These “liquids” and their fascinating properties have so far only been observed in 1D and near-1D compounds, such as blue bronze. A0.3moo3 (A= K, Rb, Tl) and purple bronze Li0.9month6O17.

Researchers from Tsinghua University, ShanghaiTech University and other institutes in China recently observed the prototypical behavior of Luttinger’s liquid in η-Mo4O11,a charge density wave material with a quasi-2D crystal structure. Their findings, published in Natural Physicscould pave the way for exploring the behavior of non-Fermi liquids in other 2D and 3D quantum materials.

“In our previous work, we identified the Luttinger liquid phase in the normal state of blue bronzes, which is not surprising due to its quasi-1D nature,” said Lexian Yang and Yulin Chen, two of the researchers who conducted the study.

“We then noticed that a large family of molybdenum oxides shares a common building unit: chains of Mo-O octahedra. But in some of them, like η-Mo4O11quasi-1D warps intersect and weave into a quasi-2D structure.”

Materials with quasi-2D structures, such as the material examined by Yang, Chen and their colleagues, have attracted considerable research attention, with physicists wondering if they could preserve some properties of 1D materials, including the behavior Luttinger’s liquid. Initially, the researchers did not expect to observe this behavior, so they were very surprised when they did.

In their experiments, they used quasi-2D η-Mo4O11 samples with a layered structure. The advantage of using these samples is that they can be easily cleaved to expose large flat surfaces, making them easier to examine.

“To protect our samples from contamination, we studied the sample in an ultra-high vacuum environment by exciting electrons inside the crystals using monochromatic light,” Yang and Chen explained. “We then collected these excited electrons, or photoelectrons, and analyzed their energy and momentum to infer their initial status inside the sample.”

To examine their samples, Yang and his colleagues used a spectroscopic technique known as angular-resolved photoemission spectroscopy (ARPES), which allows researchers to directly visualize the electronic structure of materials. This technique can be applied to countless different types of materials and was previously also used to examine high temperature superconductors, topological quantum materials and transition metal dichalcogenides.

“We have shown that Luttinger’s liquid physics, which was previously considered a prototype for 1D behavior, can be extended to quasi-2D systems,” Yang and Chen said. “This extension can help us understand other puzzling non-Fermi liquid behaviors in 2D or even 3D systems. Luttinger’s liquid behavior is a rare example of an exactly solvable model for interacting systems. Although it has long been considered the “standard model” for 1D metals, theorists have proposed that it is related to non-Fermi liquid behaviors in different systems such as the normal state of high-temperature cuprate superconductors.

The recent findings collected by this team of researchers represent an important step towards achieving a unified understanding of the behaviors of non-Fermi liquids in 2D and 3D systems. Their work could therefore soon inspire new studies exploring the behavior of Luttinger liquids and other non-Fermi liquid states in other materials.

“Our future research is already underway,” Yang and Chen added. “Our first step will be to explore and find more material systems (low-dimensional molybdenum oxides and beyond) containing suspected Luttinger’s liquid. Second, to know the common behavior of Luttinger’s liquid in different materials, their similarities and their differences will help unveil the underlying physical laws. Third, and most interestingly, the interactions between other degrees of freedom and Luttinger’s liquid that might lead to long-range ordered states deserve further exploration.”

More information:
X. Du et al, Crossed Luttinger liquid hidden in quasi two-dimensional material, Natural Physics (2022). DOI: 10.1038/s41567-022-01829-z

L. Kang et al, band-selective Holstein polaron in Luttinger liquid material A0.3MoO3 (A=K,Rb), Nature Communication (2021). DOI: 10.1038/s41467-021-26078-1

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