Imaging electron pairing in a simple magnetic superconductor

Jul 14, 2013
jAnticipated electronic structure of a heavy fermion superconductor. a, Schematic representation of the crystal unit cell of CeCoIn5. b, Schematic of the typical evolution of the k-space electronic structure observed as hybridization splits the light band into two heavy bands, and the consequential effects on the density of statesN(E). Credit: Nature Physics DOI: 10.1038/nphys2671

In the search for understanding how some magnetic materials can be transformed to carry electric current with no energy loss, scientists at the U.S. Department of Energy's Brookhaven National Laboratory, Cornell University, and collaborators have made an important advance: Using an experimental technique they developed to measure the energy required for electrons to pair up and how that energy varies with direction, they've identified the factors needed for magnetically mediated superconductivity-as well as those that aren't.

"Our measurements distinguish energy levels as small as one ten-thousandth the energy of a single photon of light-an unprecedented level of precision for electronic matter visualization," said Séamus Davis, Senior Physicist at Brookhaven the J.G. White Distinguished Professor of Physical Sciences at Cornell, who led the research described in Nature Physics. "This precision was essential to writing down the mathematical equations of a theory that should help us discover the mechanism of magnetic superconductivity, and make it possible to search for or for zero-loss energy applications."

The material Davis and his collaborators studied was discovered in part by Brookhaven physicist Cedomir Petrovic ten years ago, when he was a graduate student working at the National High Magnetic Field Laboratory. It's a compound of cerium, cobalt, and that many believe may be the simplest form of an unconventional superconductor-one that doesn't rely on vibrations of its to pair up current-carrying electrons. Unlike employing that mechanism, which must be chilled to near absolute zero (-273 degrees Celsius) to operate, many unconventional superconductors operate at higher temperatures-as high as -130°C. Figuring out what makes electrons pair in these so-called could one day lead to room-temperature varieties that would transform our .

The main benefit of CeCoIn5, which has a chilly operating temperature (-271°C), is that it can act as the "hydrogen atom" of magnetically mediated superconductors, Davis said-a test bed for developing theoretical descriptions of magnetic superconductivity the way hydrogen, the simplest atom, helped scientists derive for the quantum mechanical rules by which all atoms operate.

"Scientists have thought this material might be 'the one,' a compound that would give us access to the fundamentals of magnetic superconductivity in a controllable way," Davis said. "But we didn't have the tools to directly study the process of electron pairing. This paper announces the successful invention of the techniques and the first examination of how that material works to form a magnetic superconductor."

The method, called quasiparticle scattering interference, uses a spectroscopic imaging scanning tunneling microscope designed by Davis to measure the strength of the "glue" holding electron pairs together as a function of the direction in which they are moving. If magnetism is the true source of electron pairing, the scientists should find a specific directional dependence in the strength of the glue, because magnetism is highly directional (think of the north and south poles on a typical bar magnet). Electron pairs moving in one direction should be very strongly bound while in other directions the pairing should be non-existent, Davis explained.

To search for this effect, Davis group members Milan P. Allan and Freek Massee used samples of the material made by Petrovic. "To make these experiments work, you have to get the materials exactly right," Davis said. "Petrovic synthesized atomically perfect samples."

With the samples held in the microscope far below their superconducting temperature, the scientists sent in bursts of energy to break apart the electron pairs. The amount of energy it takes to break up the pair is known as the superconducting energy gap.

"When the pairs break up, the two electrons move off in opposite directions. When they hit an impurity in the sample, that makes a kind of interference, like waves scattering off a lighthouse," Davis explained. "We make movies of those standing waves. The interference patterns tell us the direction the electron was traveling for each energy level we send into the system, and how much energy it takes to break apart the pairs for each direction of travel."

The instrument uses the finest energy resolution for electronic matter visualization of any experiment ever achieved to tease out incredibly small energy differences-increments that are a tiny fraction of the energy of a single photon of light. The precision measurements revealed the directional dependence the scientists were looking for in the superconducting energy gap.

"Our job as scientists is to write down an equation and solve it to give a quantitative description of what we observed, and then use it to describe how magnetic superconductivity works and make and test predictions about how certain new materials will behave," Davis said.

One of the most important things the theory will do, he explained, will be to help separate the "epiphenomena," or side effects, from the true phenomena-the fundamental elements essential for superconductivity.

"Once you know the fundamental issues, which is what these studies reveal, it greatly enhances the probability of discovering a new material with the correct characteristics because you know what you are looking for-and you know what to avoid. We are very enthusiastic that we will be able to provide the theoretical tools for identifying the stuff to avoid when trying to make magnetic superconductors with improved properties," Davis said.

Explore further: 'Long-awaited explanation' for mysterious effects in high-temperature superconductors

More information: "Imaging Cooper pairing of heavy fermions in CeCoIn5" Nature Physics.dx.doi.org/10.1038/nphys2671

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Minich
1 / 5 (2) Jul 14, 2013
"" The Cooper pairing mechanism of heavy fermion
superconductors1–4, long thought to be due to spin
fluctuations5–7, has not yet been determined

for the first time in any heavy fermion
superconductor, we determine the detailed structure of its
multiband energy gaps delta(k). ""
It is consistent with Minich's Modified Band Theory of superconducticity
http://physicsfor...sy.htm#5
that denyes cooper pairing at all!
vacuum-mechanics
1 / 5 (7) Jul 15, 2013
"Our measurements distinguish energy levels as small as one ten-thousandth the energy of a single photon of light-an unprecedented level of precision for electronic matter visualization," said Séamus Davis, Senior Physicist at Brookhaven the J.G. White Distinguished Professor of Physical Sciences at Cornell, who led the research described in Nature Physics. "This precision was essential to writing down the mathematical equations of a theory that should help us discover the mechanism of magnetic superconductivity ….


Before discovering of the mechanism of magnetic superconductivity, maybe this physical view of a rotating electron mechanism which explains how it creates magnetic field could give a hint…
http://www.vacuum...21〈=en
Minich
1 / 5 (2) Jul 15, 2013
It is consistent with Minich's Modified Band Theory of superconducticity that denyes cooper pairing at all!
LOL, how the imaging of Cooper pairing can be consistent with theory, which denies the existence of such pairing?


How do You distingwish?
1. Pair of electrons the first electron is in state one and the second electron is in state second.
2. One electron is in coherent superposition the same electron is in state one and the same electron is in state second.

Why do You think that suggested experiment recognizes the difference?
:)
ValeriaT
1 / 5 (1) Jul 15, 2013
This is not relevant to my question: "how the imaging of Cooper pairing can be consistent with theory, which denies the existence of such pairing"?
Minich
1 / 5 (3) Jul 15, 2013
Think youself, please.It is elementary fact of using ARPES one electron fitting.

To become correct Arpes must detect two electron pairs, not one electron wave function.
Where do You see pair selection in this experiment?
Minich
1 / 5 (3) Jul 15, 2013
So ArPES studies give experiment resuts for nonparing theory. IE gap values for for MOdified Band theory.
aroc91
not rated yet Jul 18, 2013
This is not relevant to my question: "how the imaging of Cooper pairing can be consistent with theory, which denies the existence of such pairing"?


Your question? I could have sworn natello wrote that. Oh wait, sockpuppets.

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