Nav: Home

Lining up surprising behaviors of superconductor with one of the world's strongest magnets

August 08, 2018

UPTON, NY--What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that have a "super" ability to conduct electricity when chilled by liquid nitrogen? A team of scientists set out to answer this question in one such superconductor made of the elements lanthanum, strontium, copper, and oxygen (LSCO). They discovered that the electrical resistance of this copper-oxide compound, or cuprate, changes in an unusual way when very high magnetic fields suppress its superconductivity at low temperatures.

"The most pressing problem in condensed matter physics is understanding the mechanism of superconductivity in cuprates because at ambient pressure they become superconducting at the highest temperature of any currently known material," said physicist Ivan Bozovic, who leads the Oxide Molecular Beam Epitaxy Group at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and who is a coauthor of the Aug. 3 Science paper reporting the discovery. "This new result--that the electrical resistivity of LSCO scales linearly with magnetic field strength at low temperatures--provides further evidence that high-temperature superconductors do not behave like ordinary metals or superconductors. Once we can come up with a theory to explain their unusual behavior, we will know whether and where to search for superconductors that can carry large amounts of electrical current at higher temperatures, and perhaps even at room temperature."

Cuprates such as LSCO are normally insulators. Only when they are cooled to some hundred degrees below zero and the concentrations of their chemical composition are modified (a process called doping) to a make them metallic can their mobile electrons pair up to form a "superfluid" that flows without resistance. Scientists hope that understanding how cuprates achieve this amazing feat will enable them to develop room-temperature superconductors, which would make energy generation and delivery significantly more efficient and less expensive.

In 2016, Bozovic's group reported that LSCO's superconducting state is nothing like the one explained by the generally accepted theory of classical superconductivity; it depends on the number of electron pairs in a given volume rather than the strength of the electron pairing interaction. In a follow-up experiment published the following year, they obtained another puzzling result: when LSCO is in its non-superconducting (normal, or "metallic") state, its electrons do not behave as a liquid, as would be expected from the standard understanding of metals.

"The condensed matter physics community has been divided about this most basic question: do the behaviors of cuprates fall within existing theories for superconductors and metals, or are there profoundly different physical principles involved?" said Bozovic.

Continuing this comprehensive multipart study that began in 2005, Bozovic's group and collaborators have now found additional evidence to support the latter idea that the existing theories are incomplete. In other words, it is possible that these theories do not encompass every known material. Maybe there are two different types of metals and superconductors, for example.

"This study points to another property of the strange metallic state in the cuprates that is not typical of metals: linear magnetoresistance at very high magnetic fields," said Bozovic. "At low temperatures where the superconducting state is suppressed, the electrical resistivity of LSCO scales linearly (in a straight line) with the magnetic field; in metals, this relationship is quadratic (forms a parabola)."

In order to study magnetoresistance, Bozovic and group members Anthony Bollinger, Xi He, and Jie Wu first had to create flawless single-crystal thin films of LSCO near its optimal doping level. They used a technique called molecular beam epitaxy, in which separate beams containing atoms of the different chemical elements are fired onto a heated single-crystal substrate. When the atoms land on the substrate surface, they condense and slowly grow into ultra-thin layers, building a single atomic layer at a time. The growth of the crystal occurs in highly controlled conditions of ultra-high vacuum to ensure that the samples do not get contaminated.

"Brookhaven Lab's key contribution to this study is this material synthesis platform," said Bozovic. "It allows us to tailor the chemical composition of the films for different studies and provides the foundation for us to observe the true properties of superconducting materials, as opposed to properties induced by sample defects or impurities."

The scientists then patterned the thin films onto strips containing voltage leads so that the amount of electrical current flowing through LSCO under an applied magnetic field could be measured.

They conducted initial magnetoresistivity measurements with two 9 Tesla magnets at Brookhaven Lab--for reference, the strength of the magnets used in today's magnetic resonance imaging (MRI) machines are typically up to 3 Tesla. Then, they brought their best samples (those with the best structural and transport qualities) to the Pulsed Field Facility. Located at DOE's Los Alamos National Laboratory, this international user facility is part of the National High Magnetic Field Laboratory, which houses some of the strongest magnets in the world. Scientists at the Pulsed Field Facility placed the samples in an 80 Tesla pulsed magnet, powered by quick pulses, or shots, of electrical current. The magnet produces such large magnetic fields that it cannot be energized for more than a very short period of time (microseconds to a fraction of a second) without destroying itself.

"This large magnet, which is the size of a room and draws the electricity of a small city, is the only such installation on this continent," said Bozovic. "We only get access to it once a year if we are lucky, so we chose our best samples to study."

In October, the scientists will get access to a stronger (90 Tesla) magnet, which they will use to collect additional magnetoresistance data to see if the linear relationship still holds.

"While I do not expect to see something different, this higher field strength will allow us to expand the range of doping levels at which we can suppress superconductivity," said Bozovic. "Collecting more data over a broader range of chemical compositions will help theorists formulate the ultimate theory of high-temperature superconductivity in cuprates."

In the next year, Bozovic and the other physicists will collaborate with theorists to interpret the experimental data.

"It appears that the strongly correlated motion of electrons is behind the linear relationship we observed," said Bozovic. "There are various ideas of how to explain this behavior, but at this point, I would not single out any of them."
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

Follow @BrookhavenLab on Twitter or find us on Facebook.

DOE/Brookhaven National Laboratory

Related Magnetic Field Articles:

Scholes finds novel magnetic field effect in diamagnetic molecules
The Princeton University Department of Chemistry publishes research this week proving that an applied magnetic field will interact with the electronic structure of weakly magnetic, or diamagnetic, molecules to induce a magnetic-field effect that, to their knowledge, has never before been documented.
Origins of Earth's magnetic field remain a mystery
The existence of a magnetic field beyond 3.5 billion years ago is still up for debate.
New research provides evidence of strong early magnetic field around Earth
New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed.
Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.
Adhesive which debonds in magnetic field could reduce landfill waste
Researchers at the University of Sussex have developed a glue which can unstick when placed in a magnetic field, meaning products otherwise destined for landfill, could now be dismantled and recycled at the end of their life.
Earth's last magnetic field reversal took far longer than once thought
Every several hundred thousand years or so, Earth's magnetic field dramatically shifts and reverses its polarity.
A new rare metals alloy can change shape in the magnetic field
Scientists developed multifunctional metal alloys that emit and absorb heat at the same time and change their size and volume under the influence of a magnetic field.
Physicists studied the influence of magnetic field on thin film structures
A team of scientists from Immanuel Kant Baltic Federal University together with their colleagues from Russia, Japan, and Australia studied the influence of inhomogeneity of magnetic field applied during the fabrication process of thin-film structures made from nickel-iron and iridium-manganese alloys, on their properties.
'Magnetic topological insulator' makes its own magnetic field
A team of U.S. and Korean physicists has found the first evidence of a two-dimensional material that can become a magnetic topological insulator even when it is not placed in a magnetic field.
Scientists develop a new way to remotely measure Earth's magnetic field
By zapping a layer of meteor residue in the atmosphere with ground-based lasers, scientists in the US, Canada and Europe get a new view of Earth's magnetic field.
More Magnetic Field News and Magnetic Field Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Making Amends
What makes a true apology? What does it mean to make amends for past mistakes? This hour, TED speakers explore how repairing the wrongs of the past is the first step toward healing for the future. Guests include historian and preservationist Brent Leggs, law professor Martha Minow, librarian Dawn Wacek, and playwright V (formerly Eve Ensler).
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.