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Uncovering an Odd Form of Superconductivity

An innovative technique will allow scientists to probe superconductivity involving an unusual type of electron pairing called odd-frequency pairing.

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For more than a century, physicists have pondered the origin of superconductivity—the ability of certain materials to conduct electricity without resistance. Today, conventional superconductivity is fairly well understood, but other forms of the phenomenon remain mysterious. Debmalya Chakraborty and Annica Black-Schaffer at Uppsala University, Sweden, have proposed an experimental probe for one type of unconventional superconductivity [1]. The researchers hope that their technique will lead to a much better understanding of the phenomenon.

The mechanism behind superconductivity is the formation of particle-like entities called Cooper pairs—bound states of two electrons. Ordinary superconductivity involves even-frequency pairing, in which the Cooper pairs have an even symmetry with respect to time. Chakraborty and Black-Schaffer are concerned with odd-frequency pairing, whereby the pairs have an odd symmetry in time. Odd-frequency pairing is thought to exist in many superconducting systems—including in structures that combine superconductors with magnetic materials—but until now, scientists have lacked a method for directly detecting it.

Newly Discovered Type of “Strange Metal” – Material That Shares Fundamental Quantum Attributes With Black Holes

A new discovery could help scientists to understand “strange metals,” a class of materials that are related to high-temperature superconductors and share fundamental quantum attributes with black holes.

Scientists understand quite well how temperature affects electrical conductance in most everyday metals like copper or silver. But in recent years, researchers have turned their attention to a class of materials that do not seem to follow the traditional electrical rules. Understanding these so-called “strange metals” could provide fundamental insights into the quantum world, and potentially help scientists understand strange phenomena like high-temperature superconductivity.

Now, a research team co-led by a Brown University physicist has added a new discovery to the strange metal mix. In research published in the journal Nature, the team found strange metal behavior in a material in which electrical charge is carried not by electrons, but by more “wave-like” entities called Cooper pairs.

Discovery of segmented Fermi surface induced by Cooper pair momentum on a hybrid material platform

In a new report now published in Science, primary authors Zhen Zhu, Michal Papaj, and an international research team in physics, materials science, and condensed matter at the Jiao Tong University, China, Massachusetts Institute of Technology, U.S., and the Chinese Academy of Sciences discovered the Fermi surface of supercurrent-induced quasiparticles in a superconducting system for the first time. This discovery comes 50 years after the initial theoretical prediction was made by physicist Peter Fulde and revealed the impact of the finite Cooper pair momentum on the quasiparticle spectrum. In condensed matter physics, Cooper pairs are a pair of electrons with opposite spins loosely bound due to electron-lattice interactions. Superconductivity is based on their condensation to Bosonic states at low temperatures. The interplay of superconductivity and magnetic fields leads to the phenomenon of a 'segmented Fermi surface." A leading author of this work, MIT Professor of Physics Liang Fu, outlined the significance of this discovery.

Researchers identify new type of superconductor

Until now, the history of superconducting materials has been a tale of two types: s-wave and d-wave.

Now, Cornell researchers—led by Brad Ramshaw, the Dick & Dale Reis Johnson Assistant Professor in the College of Arts and Sciences—have discovered a possible third type: g-wave.

Their paper, "Thermodynamic Evidence for a Two-Component Superconducting Order Parameter in Sr2RuO4," published Sept. 21 in Nature Physics. The lead author is doctoral student Sayak Ghosh, M.S. '19.

Electrons in superconductors move together in what are known as Cooper pairs. This "pairing" endows superconductors with their most famous property—no electrical resistance—because, in order to generate resistance, the Cooper pairs have to be broken apart, and this takes energy.

Hole-y Superconductor: Entirely New State of Matter Discovered

In a finding that reveals an entirely new state of matter, research published in the journal Science shows that Cooper pairs, electron duos that enable superconductivity, can also conduct electricity like normal metals do.

For years, physicists have assumed that Cooper pairs, the electron duos that enable superconductors to conduct electricity without resistance, were two-trick ponies. The pairs either glide freely, creating a superconducting state, or create an insulating state by jamming up within a material, unable to move at all.

But in a new paper published today (November 14, 2019) in Science, a team of researchers has shown that Cooper pairs can also conduct electricity with some amount of resistance, as regular metals do. The findings describe an entirely new state of matter, the researchers say, that will require a new theoretical explanation.

“There had been evidence that this metallic state would arise in thin film superconductors as they were cooled down toward their superconducting temperature, but whether or not that state involved Cooper pairs was an open question,” said Jim Valles, a professor of physics at Brown University and the study’s corresponding author. “We’ve developed a technique that enables us to test that question and we showed that, indeed, Cooper pairs are responsible for transporting charge in this metallic state. What’s interesting is that no one is quite sure at a fundamental level how they do that, so this finding will require some more theoretical and experimental work to understand exactly what’s happening.”

For superconductors, discovery comes from disorder

Discovered more than 100 years ago, superconductivity continues to captivate scientists who seek to develop components for highly efficient energy transmission, ultrafast electronics or quantum bits for next-generation computation. However, determining what causes substances to become—or stop being—superconductors remains a central question in finding new candidates for this special class of materials.

In potential superconductors, there may be several ways electrons can arrange themselves. Some of these reinforce the superconducting effect, while others inhibit it. In a new study, scientists at the U.S. Department of Energy's (DOE) Argonne National Laboratory have explained the ways in which two such arrangements compete with each other and ultimately affect the temperature at which a material becomes superconducting.

In the superconducting state, electrons join together into so-called Cooper pairs, in which the motion of electrons is correlated; at each moment, the velocities of the electrons participating in a given pair are opposite. Ultimately, the motion of all electrons is coupled—no single electron can do its own thing—which leads to the lossless flow of electricity: superconductivity.

Cooper Pairs

Introduction In the field of superconductivity, Cooper pairs play a fundamental role. Named after physicist Leon Cooper, a Cooper pair is a bound state of two electrons (or other fermions) with opposite momenta (i.e., moving in opposite directions) and opposite spins, effectively forming a boson. Formation of Cooper Pairs Electrons in a material are usually repelled from each other due to…

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Josephson Effect

Introduction The Josephson Effect is a quantum mechanical phenomenon involving pairs of superconductors separated by a thin insulating barrier, known as a Josephson junction. This effect, named after the British physicist Brian D. Josephson, who predicted it in 1962, allows for the tunneling of Cooper pairs across the barrier, leading to a supercurrent. AI generated image of two electrons bound…

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Hole-y Superconductor: Entirely New State of Matter Discovered

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