New clues important to our understanding of superconductivity are provided by precise measurements of electronic states
Researchers at RIKEN’s Discovery Research Institute in Wako, in collaboration with researchers from Cornell University in the US, and Kyoto University, have refined a method that measures small electronic excitations in superconductors. Comparisons of these properties for different materials have provided valuable clues towards our understanding of superconductivity.
The classical theory of superconductivity describes the superconducting state arising through the pairing of electrons into pairs. The properties of these electron pairs, however, are difficult to model mathematically. Physicists therefore prefer to describe them as a virtual single ‘quasiparticle’. “Although these quasiparticles are fictitious, they really govern the electronic states of superconductors, particularly at low energies,” explains Tetsuo Hanaguri from the research team.
Many details of the electronic states of quasiparticles and the precise amount of energy it takes to break up the electron pairs are difficult to measure, and remain poorly understood. This ‘break-up energy’, referred to as the ‘superconducting gap’, is traditionally considered as being directly related to the critical temperature where superconductivity persists. The larger the gap, the greater the difficultly to break up the electron pairs, thus the higher the critical temperature is for superconductivity. However, this relation has never been confirmed for the so-called ‘high-temperature’ superconductors, whose mechanism of superconductivity remains a mystery.
Reporting in the journal Nature Physics1, the RIKEN researchers have now measured the properties of the quasiparticles using a scanning tunneling microscope that scans the surface of a superconducting material with an atomic resolution and records tiny variations in the electronic structure. However, the observed periodic variations in the electronic properties are difficult to analyze as a number of effects contribute to these regular patterns. Therefore, Hanaguri and colleagues developed a novel mathematical technique to successfully pick out the quasiparticle signatures.
This mathematical technique allows the researchers to characterize several materials and compare their superconducting properties. Surprisingly, the relative variation in the superconducting gap was found to be the same for two different high-temperature superconductors, although their critical temperature differs by a factor of three. This shows that, contrary to conventional assumptions, the superconducting state is influenced by more than just the size of the superconducting gap.
To better understand the relation between superconducting gap and superconductivity, Hanaguri says that further measurements are needed to determine the effect of temperature and magnetic field on the quasiparticles. Ultimately, these measurements may provide vital clues on the fundamental mechanisms governing high-temperature superconductors.
1. Hanaguri, T., Kohsaka, Y., Davis, J. C., Lupien, C., Yamada, I., Azuma, M., Takano, M., Ohishi, K., Ono, M. & Takagi, H. Quasiparticle interference and superconducting gap in Ca2–xNaxCuO2Cl2. Nature Physics 3, 865–871 (2007).
Prototype device for measuring graphene-based electromagnetic radiation created
28.10.2016 | Lomonosov Moscow State University
Steering a fusion plasma toward stability
28.10.2016 | American Physical Society
Physicists from the University of Würzburg have designed a light source that emits photon pairs. Two-photon sources are particularly well suited for tap-proof data encryption. The experiment's key ingredients: a semiconductor crystal and some sticky tape.
So-called monolayers are at the heart of the research activities. These "super materials" (as the prestigious science magazine "Nature" puts it) have been...
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
28.10.2016 | Power and Electrical Engineering
28.10.2016 | Physics and Astronomy
28.10.2016 | Life Sciences