Figure: A phase diagram shows the evolution of superconducting transition temperature (Tc) as a function of magnetic field and density of charge carriers (hole doping). Microwave flux-flow experiments developed at SFU provide a new trajectory for exploring the phase diagram.
A new signature of vortex fluctuations in high temperature superconductors
The motivation – Copper-oxide (cuprate) high temperature superconductors remain one of the most mysterious classes of material even 30 years after their discovery. They are the focus of a world-wide effort to understand the broader class of quantum materials – materials that require the solution of a hard quantum problem in order to predict their behaviour. An interesting but controversial possibility is that even outside the high temperature superconducting phase, superconductivity may persist locally, in the form of short-range superconducting order, with long-range properties, such as zero electrical resistance, destroyed by the proliferation of whirlpools of supercurrent called vortices.
The development – The Broun group in the Physics Department at Simon Fraser University has systematically studied the behaviour of vortices in a wide range of high temperature superconductors at low temperatures. To do this, the authors developed sensitive new techniques that shake the vortices at microwave frequencies, thereby allowing their properties to be studied independently of forces that pin the vortices in place. They discovered that vortices in this type of superconductor display an unusual resistive response that depends logarithmically on temperature. Most significantly, the measurements suggest that this behaviour is not a property of the metallic state that the superconductivity emerges from, but a property of the vortices themselves, and point to the existence of vortices outside the superconducting phase.
Its significance – At present, high temperature cuprate superconductors can remain superconducting up to about half that of room temperature; it would be of great technological benefit to extend this temperature range higher. The identification of vortices outside the superconducting phase is an important step in understanding the mechanisms that currently limit superconducting transition temperatures.
Read the paper – “Logarithmic upturn in low-temperature electronic transport as a signature of d-wave order in cuprate superconductors” by Zhou, XQ; Peets, DC; Morgan, B; Huttema, WA; Murphy, NC; Thewalt, E; Truncik, CJS; Turner, PJ; Koenig, AJ; Waldram, JR; Hosseini, A; Liang, RX; Bonn, DA; Hardy, WN; Broun, DM. Physicial Review Letters 121:267004 (2018). DOI: 10.1103/PhysRevLett.121.267004.
Website article compiled by Jacqueline Watson with Theresa Kitos