Quantum computing: Exotic particle had an 'out-of-body experience'
An unexpected finding could advance quantum computers and high-
temperature superconductors

Date:
August 24, 2021
Source:
DOE/Lawrence Berkeley National Laboratory
Summary:
Scientists have taken a clear picture of electronic particles that
make up a mysterious magnetic state called quantum spin liquid
(QSL). The achievement could facilitate the development of superfast
quantum computers and energy-efficient superconductors. The
scientists are the first to capture an image of how electrons
in a QSL decompose into spin- like particles called spinons and
charge-like particles called chargons.



FULL STORY ========================================================================== Scientists have taken the clearest picture yet of electronic particles
that make up a mysterious magnetic state called quantum spin liquid (QSL).


==========================================================================
The achievement could facilitate the development of superfast quantum
computers and energy-efficient superconductors.

The scientists are the first to capture an image of how electrons in a
QSL decompose into spin-like particles called spinons and charge-like
particles called chargons.

"Other studies have seen various footprints of this phenomenon, but we
have an actual picture of the state in which the spinon lives. This
is something new," said study leader Mike Crommie, a senior faculty
scientist at Lawrence Berkeley National Laboratory (Berkeley Lab) and
physics professor at UC.

"Spinons are like ghost particles. They are like the Big Foot of quantum physics -- people say that they've seen them, but it's hard to prove that
they exist," said co-author Sung-Kwan Mo, a staff scientist at Berkeley
Lab's Advanced Light Source. "With our method we've provided some of the
best evidence to date." A surprise catch from a quantum wave In a QSL,
spinons freely move about carrying heat and spin -- but no electrical
charge. To detect them, most researchers have relied on techniques that
look for their heat signatures.



==========================================================================
Now, as reported in the journal Nature Physics, Crommie, Mo, and their
research teams have demonstrated how to characterize spinons in QSLs by directly imaging how they are distributed in a material.

To begin the study, Mo's group at Berkeley Lab's Advanced Light Source
(ALS) grew single-layer samples of tantalum diselenide (1T-TaSe2) that
are only three-atoms thick. This material is part of a class of materials called transition metal dichalcogenides (TMDCs). The researchers in Mo's
team are experts in molecular beam epitaxy, a technique for synthesizing atomically thin TMDC crystals from their constituent elements.

Mo's team then characterized the thin films through angle-resolved photoemission spectroscopy, a technique that uses X-rays generated at
the ALS.

Using a microscopy technique called scanning tunneling microscopy (STM), researchers in the Crommie lab -- including co-first authors Wei Ruan,
a postdoctoral fellow at the time, and Yi Chen, then a UC Berkeley
graduate student -- injected electrons from a metal needle into the
tantalum diselenide TMDC sample.

Images gathered by scanning tunneling spectroscopy (STS) -- an imaging technique that measures how particles arrange themselves at a particular
energy -- revealed something quite unexpected: a layer of mysterious
waves having wavelengths larger than one nanometer (1 billionth of a
meter) blanketing the material's surface.



==========================================================================
"The long wavelengths we saw didn't correspond to any known behavior of
the crystal," Crommie said. "We scratched our heads for a long time. What
could cause such long wavelength modulations in the crystal? We ruled out
the conventional explanations one by one. Little did we know that this was
the signature of spinon ghost particles." How spinons take flight while chargons stand still With help from a theoretical collaborator at MIT, the researchers realized that when an electron is injected into a QSL from the
tip of an STM, it breaks apart into two different particles inside the QSL
-- spinons (also known as ghost particles) and chargons. This is due to
the peculiar way in which spin and charge in a QSL collectively interact
with each other. The spinon ghost particles end up separately carrying
the spin while the chargons separately bear the electrical charge.

In the current study, STM/STS images show that the chargons
freeze in place, forming what scientists call a star-of-David charge-density-wave. Meanwhile, the spinons undergo an "out-of-body
experience" as they separate from the immobilized chargons and move
freely through the material, Crommie said. "This is unusual since
in a conventional material, electrons carry both the spin and charge
combined into one particle as they move about," he explained. "They don't usually break apart in this funny way." Crommie added that QSLs might
one day form the basis of robust quantum bits (qubits) used for quantum computing. In conventional computing a bit encodes information either as
a zero or a one, but a qubit can hold both zero and one at the same time,
thus potentially speeding up certain types of calculations.

Understanding how spinons and chargons behave in QSLs could help advance research in this area of next-gen computing.

Another motivation for understanding the inner workings of
QSLs is that they have been predicted to be a precursor to exotic superconductivity. Crommie plans to test that prediction with Mo's help
at the ALS.

"Part of the beauty of this topic is that all the complex interactions
within a QSL somehow combine to form a simple ghost particle that just
bounces around inside the crystal," he said. "Seeing this behavior
was pretty surprising, especially since we weren't even looking for it." ========================================================================== Story Source: Materials provided by
DOE/Lawrence_Berkeley_National_Laboratory. Note: Content may be edited
for style and length.


========================================================================== Related Multimedia:
* Images_and_illustrations ========================================================================== Journal Reference:
1. Wei Ruan, Yi Chen, Shujie Tang, Jinwoong Hwang, Hsin-Zon Tsai,
Ryan L.

Lee, Meng Wu, Hyejin Ryu, Salman Kahn, Franklin Liou, Caihong
Jia, Andrew Aikawa, Choongyu Hwang, Feng Wang, Yongseong Choi,
Steven G. Louie, Patrick A. Lee, Zhi-Xun Shen, Sung-Kwan Mo,
Michael F. Crommie. Evidence for quantum spin liquid behaviour in
single-layer 1T-TaSe2 from scanning tunnelling microscopy. Nature
Physics, 2021; DOI: 10.1038/s41567-021- 01321-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210824174405.htm

--- up 15 weeks, 4 days, 22 hours, 45 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)