A UCSB postdoctoral scholar in physics discovers a counterintuitive phenomenon: the coexistence of superconductivity with dissipation
For his doctoral dissertation in the Goldman Superconductivity Research Group at the University of Minnesota, Yu Chen, now a postdoctoral researcher at UC Santa Barbara, developed a novel way to fabricate superconducting nanocircuitry. However, the extremely small zinc nanowires he designed did some unexpected — and sort of funky — things.
Chen, along with his thesis adviser, Allen M. Goldman, and theoretical physicist Alex Kamenev, both of the University of Minnesota, spent years seeking an explanation for these extremely puzzling effects. Their findings appear this week in Nature Physics.
"We were determined to figure out how we could reconcile the strange phenomena with the longstanding rules governing superconductivity," said lead author Chen. "The coexistence of superconductivity with dissipation, which we observed, is counterintuitive and bends the rules as we know them."
Typically superconductivity and dissipation are thought to be mutually exclusive because dissipation, a process in thermodynamic systems whereby electric energy is transformed into heat, is a feature of a normal — versus a superconductive — state.
"But we discovered that superconductivity and dissipation can coexist under rather generic conditions in what appears to be a universal manner," Chen said.
After long and careful work, which involved both experimental and theoretical efforts, the researchers found an explanation that fits. Behind all of the observed phenomena is a peculiar nonequilibrium state of quasiparticles — electron-like excitations that formed in the nanowires Chen designed.
The quasiparticles are created by phase slips. In a superconductive state, when supercurrent flows through the nanowire, the quantum mechanical function describing the superconductivity of the wire evolves along the length of the wire as a spiral shaped like a child's Slinky toy. From time to time, one of the revolutions of the spiral contracts and disappears altogether. This event is called a phase slip. This quirk generates quasiparticles, giving rise to a previously undiscovered voltage plateau state where dissipation and superconductivity coexist.
"The most significant achievement was making the nanowires smaller and cooler than anyone had done previously," Kamenev said. "This allowed the quasiparticles to travel through the wire faster and avoid relaxation. This leads to a peculiar nonthermal state, which combines properties of a superconductor and a normal metal at the same time."
In addition to discovering this unique phenomenon, the team also found another heretofore-unseen property in the voltage plateau. When a magnetic field is turned on in the voltage plateau state, rather than shrinking the superconducting region, which is what would usually occur, the superconducting area expands and is enhanced.
"This is an unexpected property of very small nanowires," said Goldman.
This state appears to be universal for ultra-small superconducting circuitry like Chen's, which features ideal contacts between the nano-elements and the leads. Such nanoscale superconductors may be key components in future superconducting computer systems.
"Our findings demonstrate that superconducting nanocircuits can be used as a simple, but rather generic platform to investigate nonequilibrium quantum phenomena," Chen concluded.
"Now we need to explore the parameters of nanowires that give rise to the effect and those that don't," Goldman said. "We also need to examine the behavior of wires of different lengths and different materials in order to further define the parameters."
Julie Cohen | Eurek Alert!
New record in materials research: 1 terapascals in a laboratory
22.07.2016 | Universität Bayreuth
Mapping electromagnetic waveforms
22.07.2016 | Max-Planck-Institut für Quantenoptik
Researchers at the U.S. Department of Energy's (DOE) Ames Laboratory have discovered an unusual property of purple bronze that may point to new ways to achieve high temperature superconductivity.
While studying purple bronze, a molybdenum oxide, researchers discovered an unconventional charge density wave on its surface.
Munich Physicists have developed a novel electron microscope that can visualize electromagnetic fields oscillating at frequencies of billions of cycles per second.
Temporally varying electromagnetic fields are the driving force behind the whole of electronics. Their polarities can change at mind-bogglingly fast rates, and...
Breakup of continents with two speed: Continents initially stretch very slowly along the future splitting zone, but then move apart very quickly before the onset of rupture. The final speed can be up to 20 times faster than in the first, slow extension phase.phases
Present-day continents were shaped hundreds of millions of years ago as the supercontinent Pangaea broke apart. Derived from Pangaea’s main fragments Gondwana...
Scaffolding and specialised workers help with the delivery – Heidelberg biochemists gain new insights into biogenesis
A type of scaffolding on which specialised workers ply their trade helps in the manufacturing process of the two subunits from which the ribosome – the protein...
Scientists at the Helmholtz Zentrum München have developed a new mass spectrometry imaging method which, for the first time, makes it possible to analyze hundreds of metabolites in fixed tissue samples. Their findings, published in the journal Nature Protocols, explain the new access to metabolic information, which will offer previously unexploited potential for tissue-based research and molecular diagnostics.
In biomedical research, working with tissue samples is indispensable because it permits insights into the biological reality of patients, for example, in...
15.07.2016 | Event News
15.07.2016 | Event News
11.07.2016 | Event News
25.07.2016 | Materials Sciences
25.07.2016 | Machine Engineering
25.07.2016 | Materials Sciences