Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


First Direct Observations of Spinons and Holons

The theory has been around for more than 40 years, but only now has it been confirmed through direct and unambiguous experimental results. Working at the Advanced Light Source (ALS) of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, a team of researchers has observed the theoretical prediction of electron “spin-charge separation” in a one-dimensional solid. These results hold implications for future developments in several key areas of advanced technology, including high-temperature superconductors, nanowires and spintronics.
Spectral data from an ARPES study at Beamline 7.0.1 of Berkeley Lab’s Advanced Light Source revealed the two discrete peaks (blue for the holon and red for the spinon) that form the signature signal of a spin-charge separation event.

Just as the body and wheels of a car are thought to be intrinsic parts of a whole, incapable of separate and independent actions, i.e., the body goes right while the wheels go left, so, too, are electrical charge and spin intrinsic components of an electron. Except, according to theory, in one-dimensional solids, where the collective excitation of a system of electrons can lead to the emergence of two new particles called “spinons” and “holons.” A spinon carries information about an electron’s spin and a holon carries information about its charge, and they do so as separate and independent entities. Numerous experiments have tried to confirm the creation of spinons and holons, referred to as spin-charge separation, but it took the technological advantages offered at ALS Beamline 7.0.1, also known as the Electronic Structure Factory (ESF), to achieve success.

In a paper published in the June 2006 issue of the journal Nature-Physics, researchers have reported the observation of distinct spinon and holon spectral signals in one-dimensional samples of copper oxide, SrCuO2, using the technique known as ARPES, for angle-resolved photoemission spectroscopy. The research was led by Changyoung Kim, at Yonsei University, in Seoul, Korea, ALS scientist Eli Rotenberg, and Zhi-Xun Shen of Stanford University, a leading authority on the use of ARPES technology. Co-authoring the Nature-Physics paper with them were Bum Joon Kim and Hoon Koh, plus S.J. Oh, H. Eisaki, N. Motoyama, S. Uchida, T. Tohyama, and S. Maekawa.

“There have been claims of observing the two peak spectral structures of spin-charge separation in the past, but they turned out to be wrong or have plenty of ambiguity. This was primarily because those results were obtained from complicated materials and were not theoretically backed up,” said Kim, who has spent several years investigating the spin-charge separation phenomenon. “Our observations using ARPES are direct and the results are unambiguous because they were obtained from a simple material that left little room for misinterpretation. Also, our results are theoretically backed up.”

Said Shen, “Our results confirming the idea of spin-charge separation are important because they reveal deep insights into the quantum system - and the beauty and subtleties associated with it. From this study we know more about how the collective behavior of a system of particles can be so fundamentally different from that of the constituent individuals.”

The idea behind spin-charge separation is that electrons behave differently when their range of motion is restricted to a single dimension, as opposed to three or even two dimensions. When moving through one dimension, for example, the electrons are lined up head-to-tail, making the repulsive force between their negative electrical charges overridingly dominant. The restricted movement of electrons through one-dimensional material was expected to give rise to collective effects that would be strong enough to break the information flow of spin and charge from a single electron.

ARPES is an excellent tool for observing spin-charge separation and other collective effects involving electrons. In this technique, x-rays are flashed on a sample causing electrons to be emitted through the photoelectric effect. Measuring the kinetic energy of emitted electrons and the angles at which they are ejected identifies their velocity and scattering rates. This in turn yields a detailed picture of the electron energy spectrum. Ordinarily, the removal of an electron from a crystal creates a hole, a vacant positively-charged energy space. This hole carries information on both the spin and the charge, as observed in a single peak of an ARPES spectrum. If spin-charge separation occurs, the hole decays into a spinon and a holon and two peaks in the ARPES spectrum are observed.

ALS Beamline 7.0.1 utilizes a state-of-the-art undulator magnetic insertion device to generate beams of x-rays with properties similar to that of a laser. These coherent and tunable x-ray beams are a hundred million times brighter than those from the best x-ray tubes and provide an exceptionally high degree of angular resolution for ARPES experiments.

Said Rotenberg, who manages the beamline and oversees research at the ESF experimental station, “At the ESF we have the advantage of being able to survey relatively large amounts of reciprocal space to locate where the interesting correlated effects are occurring. Our data not only shows a clear separation of ARPES spectral peaks, it can also be compared to theory to obtain spectral functions, which, in principle, can provide detailed information about the dynamics of spinons and holons.”

High-temperature superconducting copper oxides, or cuprates, with their ability to lose all electrical resistance at transition temperatures far above those of metal superconductors, have become valuable tools for research even though scientists still do not know why they work. Central to many of the leading theories that attempt to explain high-temperature superconductivity in cuprates is the existence of spin-charge separation in one-dimensional systems.

Said Kim, “Our experimental confirmation of this spin-charge separation should provide more confidence in these theories.”

Another area in which spinons and holons could play an important role is in the development of nanowires, one-dimensional hollow tubes through which the movement of electrons is so constrained that quantum effects dominate.

Nanowires are expected to be key components in future nanotechnologies, including optoelectronics, biochemical sensing, and thermoelectrics.

Said Rotenberg, “The transport of electrons through nanowires will be subject to spin-charge separation and it will be very helpful to have experimental as well as theoretical understanding of this phenomenon as nanowire technology advances.”

The creation of spinons and holons in one-dimensional systems is also expected to have an impact on the future of spintronics, a technology in which the storage and movement of data will be based on the spin of electrons, rather than just on charge, as with our current electronic technology. Spin-based electronic devices promise to be smaller, faster and far more versatile than today’s devices.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.

Lynn Yarris | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht Researchers discover link between magnetic field strength and temperature
21.08.2018 | American Institute of Physics

nachricht Smallest transistor worldwide switches current with a single atom in solid electrolyte
17.08.2018 | Karlsruher Institut für Technologie (KIT)

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: It’s All in the Mix: Jülich Researchers are Developing Fast-Charging Solid-State Batteries

There are currently great hopes for solid-state batteries. They contain no liquid parts that could leak or catch fire. For this reason, they do not require cooling and are considered to be much safer, more reliable, and longer lasting than traditional lithium-ion batteries. Jülich scientists have now introduced a new concept that allows currents up to ten times greater during charging and discharging than previously described in the literature. The improvement was achieved by a “clever” choice of materials with a focus on consistently good compatibility. All components were made from phosphate compounds, which are well matched both chemically and mechanically.

The low current is considered one of the biggest hurdles in the development of solid-state batteries. It is the reason why the batteries take a relatively long...

Im Focus: Color effects from transparent 3D-printed nanostructures

New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference

Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

All Focus news of the innovation-report >>>



Industry & Economy
Event News

LaserForum 2018 deals with 3D production of components

17.08.2018 | Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

Latest News

Air pollution leads to cardiovascular diseases

21.08.2018 | Ecology, The Environment and Conservation

Researchers target protein that protects bacteria's DNA 'recipes'

21.08.2018 | Life Sciences

A paper battery powered by bacteria

21.08.2018 | Power and Electrical Engineering

Science & Research
Overview of more VideoLinks >>>