Physicists find room-temperature, 2D-to-1D topological transition
Rice-led team toggles side- and edge-conduction states in bismuth iodide crystals

Date:
August 24, 2021
Source:
Rice University
Summary:
Physicists have discovered a room-temperature transition between
1D and 2D electrical conduction states in the topological insulator
bismuth iodide.



FULL STORY ==========================================================================
A Rice University team and its collaborators have discovered a
room-temperature transition between 1D and 2D electrical conduction
states in topological crystals of bismuth and iodine.


========================================================================== Researchers found they could toggle the material, crystalline chains
of bismuth iodide (Bi4I4), between low- and high-order conduction
states at a transition temperature around 80 degrees Fahrenheit. The
research is available online this week in the American Physical Society
journal Physical Review Xand was conducted by physicists from Rice; the University of Texas at Dallas; the University of California, Berkeley;
Ohio State University; and other institutions.

Bi4I4 is a topological insulator, a material that's conductive on its
surface or edges but not its interior. The crystal lattice of Bi4I4
undergoes a subtle shift at the transition temperature. The shift changes
the material's electronic behavior, and the study showed this change,
or "phase transition," is the boundary between 1D and 2D topological
conduction states.

The high-temperature 2D state features electrical conduction around
four sides of the rectangular crystals. Rice physicists Ming Yi, Jianwei
Huang and their collaborators discovered conduction transitioned to 1D
edges as the material was cooled below 80 degrees.

"This is the first evidence suggesting that the low-temperature state
is actually a higher order topological insulator where conduction is
happening on the crystal hinges as opposed to the surfaces," said Yi,
an assistant professor of physics and astronomy and co-corresponding
author of the PRX study. "Imagine starting in the high-temperature state,
where you have an insulating bulk and conduction surfaces around the sides
of the material. As soon as you go through this structural distortion,
the conduction is confined to the one-dimensional hinges where these
sides meet." In most materials, the differences between phases --
like solid ice or liquid water -- arise from different organizational symmetries of their constituent parts. In the 1980s, physicists discovered phases of matter with identical symmetries. These were eventually shown
to arise from topological properties, "protected" quantum states that
are of growing interest for quantum computation.



==========================================================================
Yi said the dimensional change in electrical conduction mediated by
Bi4I4's phase transition could potentially be used for engineering an electrical switch operated by changing temperature.

"This transition happens at room temperature," Yi said. "It's a
first-order phase transition, which means the change happens very
suddenly. It's a tiny shift of the crystal lattice that directly impacts
the electrical conduction on the crystal boundaries." Huang, a Rice postdoctoral research associate and the study's lead author, said labs worldwide are racing to find and catalog topological materials, and
physicists have only recently begun classifying them into subfamilies.

While Bi4I4's combination of properties is unique, Huang said this week's discovery could aid the search for similar topological materials.

"Our findings are consistent with recent theoretical predictions of
higher- order topological insulators that are beyond the scope of the established topological materials databases," he said.



==========================================================================
Yi's lab and collaborators in the lab of UC Berkeley co-corresponding
author Robert Birgeneau used an experimental technique called
angle-resolved photoemission spectroscopy (ARPES) to map Bi4I4's
electronic band features.

"ARPES is the best probe for looking at topological materials because
there's a very distinct signature that will tell if materials are
topological or not," she said.

To distinguish between the 1D and 2D conduction states, her team had
"to look at different surfaces, and that is extremely difficult to do,"
Yi said.

Yi said critical contributions came from UT Dallas co-corresponding
authors Fan Zhang, who provided theoretical guidance and prediction,
and Bing Lv, whose lab synthesized Bi4I4 crystals that were as much as
a centimeter long, a millimeter wide and hundreds of microns thick. The
size of the crystals allowed Huang to make crucial ARPES measurements
on both the tops and sides of the materials.

Additional study co-authors include Han Wu, Yucheng Guo and Yichen Zhang
of Rice; Ji Seop Oh of both Rice and UC Berkeley; Sheng Li, Xiaoyuan
Liu, Nikhil Dhale and Yan-Feng Zhou of UT Dallas; Chiho Yoon of both UT
Dallas and Seoul National University in South Korea; Makoto Hashimoto and Donghui Lu of the SLAC National Linear Accelerator; Jonathan Denlinger
of Lawrence Berkeley National Laboratory; Xiqu Wang of the University
of Houston; and Chun Ning Lau of Ohio State.

The research was mainly supported by the National Science Foundation's Designing Materials to Revolutionize and Engineer our Future program
(1921847, 1921798, 1921581, 1922076), the primary program by which
NSF participates in the Materials Genome Initiative for Global
Competitiveness.

========================================================================== Story Source: Materials provided by Rice_University. Original written
by Jade Boyd. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jianwei Huang, Sheng Li, Chiho Yoon, Ji Seop Oh, Han Wu, Xiaoyuan
Liu,
Nikhil Dhale, Yan-Feng Zhou, Yucheng Guo, Yichen Zhang, Makoto
Hashimoto, Donghui Lu, Jonathan Denlinger, Xiqu Wang, Chun Ning Lau,
Robert J.

Birgeneau, Fan Zhang, Bing Lv, Ming Yi. Room-Temperature Topological
Phase Transition in Quasi-One-Dimensional Material Bi4I4. Physical
Review X, 2021; 11 (3) DOI: 10.1103/PhysRevx.11.031042 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210824135314.htm

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