Nav: Home

Unlocking the secrets of metal-insulator transitions

November 08, 2018

UPTON, NY - By using an x-ray technique available at the National Synchrotron Light Source II (NSLS-II), scientists found that the metal-insulator transition in the correlated material magnetite is a two-step process. The researchers from the University of California Davis published their paper in the journal Physical Review Letters. NSLS-II, a U.S. Department of Energy (DOE) Office of Science user facility located at Brookhaven National Laboratory, has unique features that allow the technique to be applied with stability and control over long periods of time.

"Correlated materials have interesting electronic, magnetic, and structural properties, and we try to understand how those properties change when their temperature is changed or under the application of light pulses, or an electric field" said Roopali Kukreja, a UC Davis professor and the lead author of the paper. One such property is electrical conductivity, which determines whether a material is metallic or an insulator.

If a material is a good conductor of electricity, it is usually metallic, and if it is not, it is then known as an insulator. In the case of magnetite, temperature can change whether the material is a conductor or insulator. For the published study, the researchers' goal was to see how the magnetite changed from insulator to metallic at the atomic level as it got hotter.

In any material, there is a specific arrangement of electrons within each of its billions of atoms. This ordering of electrons is important because it dictates a material's properties, for example its conductivity. To understand the metal-insulator transition of magnetite, the researchers needed a way to watch how the arrangement of the electrons in the material changed with the alteration of temperature.

"This electronic arrangement is related to why we believe magnetite becomes an insulator," said Kukreja. However, studying this arrangement and how it changes under different conditions required the scientists to be able to look at the magnetite at a super-tiny scale.

The technique, known as x-ray photon correlation spectroscopy (XPCS), available at NSLS-II's Coherent Soft X-ray scattering (CSX) beamline, allowed the researchers to look at how the material changed at the nanoscale--on the order of billionths of a meter.

"CSX is designed for soft x-ray coherent scattering. This means that the beamline exploits our ultrabright, stable and coherent source of x-rays to analyze how the electron's arrangement changes over time," explained Andi Barbour, a CSX scientist who is a coauthor on the paper. "The excellent stability allows researchers to investigate tiny variations over hours so that the intrinsic electron behavior in materials can be revealed."

However, this is not directly visible so XPCS uses a trick to reveal the information.

"The XPCS technique is a coherent scattering method capable of probing dynamics in a condensed matter system. A speckle pattern is generated when a coherent x-ray beam is scattered from a sample, as a fingerprint of its inhomogeneity in real space," said Wen Hu, a scientist at CSX and co-author of the paper.

Scientists can then apply different conditions to their material and if the speckle pattern changes, it means the electron ordering in the sample is changing. "Essentially, XPCS measures how much time it takes for a speckle's intensity to become very different from the average intensity, which is known as decorrelation," said Claudio Mazzoli, the lead beamline scientist at the CSX beamline. "Considering many speckles at once, the ensemble decorrelation time is the signature of the dynamic timescale for a given sample condition."

The technique revealed that the metal-insulator transition is not a one step process, as was previously thought, but actually happens in two steps.

"What we expected was that things would go faster and faster while warming up. What we saw was that things get faster and faster and then they slow down. So the fast phase is one step and the second step is the slowing down, and that needs to happen before the material becomes metallic," said Kukreja. The scientists suspect that the slowing down occurs because, during the phase change, the metallic and insulating properties actually exist at the same time in the material.

"This study shows that these nanometer length scales are really important for these materials," said Kukreja. "We can't access this information and these experimental parameters anywhere else than at the CSX beamline of NSLS-II."
-end-
This research was funded by the National Science Foundation, the Air Force Office of Scientific Research, and the University of California's Multicampus Research Programs and Initiatives.

Related Links

An electronic version of this news release with related graphics: https://www.bnl.gov/newsroom/news.php?a=113208

Scientific Paper: "Orbital Domain Dynamics in Magnetite below the Verwey Transition"

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization.

Follow @brookhavenlab on Twitter and Facebook

Media contact: Peter Genzer [genzer@bnl.gov], (631) 344-3174, or Karen McNulty Walsh [kmcnulty@bnl.gov], (631) 344-8350

DOE/Brookhaven National Laboratory

Related Electrons Articles:

Deceleration of runaway electrons paves the way for fusion power
Fusion power has the potential to provide clean and safe energy that is free from carbon dioxide emissions.
Shining light on low-energy electrons
The classic method for studying how electrons interact with matter is by analyzing their scattering through thin layers of a known substance.
Ultrafast nanophotonics: Turmoil in sluggish electrons' existence
An international team of physicists has monitored the scattering behavior of electrons in a non-conducting material in real-time.
NASA mission uncovers a dance of electrons in space
NASA's MMS mission studies how electrons spiral and dive around the planet in a complex dance dictated by the magnetic and electric fields, and a new study revealed a bizarre new type of motion exhibited by these electrons.
'Hot' electrons don't mind the gap
Rice University scientists discover that 'hot' electrons can create a photovoltage about a thousand times larger than ordinary temperature differences in nanoscale gaps in gold wires.
Electrons used to control ultrashort laser pulses
We may soon get better insight into the microcosm and the world of electrons.
Supercool electrons
Study of electron movement on helium may impact the future of quantum computing.
Two electrons go on a quantum walk and end up in a qudit
There is a variety of physical systems that can be used to implement a separate quantum bit, but significantly less research has been done into systems of several qubits or qudits.
Radiation that knocks electrons out and down, one after another
Researchers at Japan's Tohoku University are investigating novel ways by which electrons are knocked out of matter.
Controlling electrons in time and space
A new method has been developed to control electrons being emitted from metal tips.

Related Electrons Reading:

Pushing Electrons
by Daniel P. Weeks (Author)

The Electron
by Dennis Morris (Author)

My First Science Textbook: Electrons
by Mary Wissinger (Author), Genius Games (Contributor), John Coveyou (Contributor), Harriet Kim Anh Rodis (Contributor)

Electrons, The Building Blocks of the Universe and the Elemental Kingdom
by Ascended Master Teaching Foundation

Electron in Action
by Steve Kinney (Author)

Scanning Electron Microscopy and X-Ray Microanalysis
by Joseph I. Goldstein (Author), Dale E. Newbury (Author), Joseph R. Michael (Author), Nicholas W.M. Ritchie (Author), John Henry J. Scott (Author), David C. Joy (Author)

Pushing Electrons: A Guide for Students of Organic Chemistry, 3rd
by Daniel P. Weeks (Author)

Interacting Electrons: Theory and Computational Approaches
by Richard M. Martin (Author), Lucia Reining (Author), David M. Ceperley (Author)

Scanning Electron Microscopy and X-Ray Microanalysis: Third Edition
by Joseph Goldstein (Author), Dale E. Newbury (Author), David C. Joy (Author), Charles E. Lyman (Author), Patrick Echlin (Author), Eric Lifshin (Author), Linda Sawyer (Author), J.R. Michael (Author)

There Are No Electrons: Electronics for Earthlings
by Kenn Amdahl (Author)

Best Science Podcasts 2018

We have hand picked the best science podcasts for 2018. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Unintended Consequences
Human innovation has transformed the way we live, often for the better. But as our technologies grow more powerful, so do their consequences. This hour, TED speakers explore technology's dark side. Guests include writer and artist James Bridle, historians Yuval Noah Harari and Edward Tenner, internet security strategist Yasmin Green, and journalist Kashmir Hill.
Now Playing: Science for the People

#499 Technology, Work and The Future (Rebroadcast)
This week, we're thinking about how rapidly advancing technology will change our future, our work, and our well-being. We speak to Richard and Daniel Susskind about their book "The Future of Professions: How Technology Will Transform the Work of Human Experts" about the impacts technology may have on professional work. And Nicholas Agar comes on to talk about his book "The Sceptical Optimist" and the ways new technologies will affect our perceptions and well-being.