Seeing Superconductivity with the CES Director
"One hundred years ago, people thought physics was understood, and they were proven wrong. Similarly today, some of the key issues in physics that people may think are solved are not solved at all," said Séamus Davis, Director of the Center for Emergent Superconductivity, or CES.
Superconductivity can be considered part of a much larger research area termed macroscopic quantum physics that also includes superfluidity, supersolidity and even the Higgs field. Davis explains that in these systems the mysteries of nature become particularly apparent, the laws of physics appear to contradict everyday experience and big fundamental questions can be found. And that is where Davis' passions lie.
A classically trained physicist and member of the U.S. National Academy of Sciences, Davis wants to know the answers.
To answer fundamental questions of electron activity, Davis and his colleagues at the center are visualizing and measuring the properties of electrons in crystals of exotic "high temperature" superconductors.
The only Energy Frontier Research Center dedicated to studying superconductivity, CES aims to understand and control established superconductors while discovering some new ones. A superconductor allows resistance-free electrical conduction through the material when the material is below a certain critical temperature. Currently, several high-temperature superconducting materials can superconduct when cooled with liquid nitrogen (-196 ◦C). Davis believes there's no reason why there can't be room temperature superconductivity, a discovery that would revolutionize efficiency in energy transport and usage beyond all current standards.
One of the fascinating mysteries in cuprate superconductivity is the pseudogap, a phase of matter that exists in the transition between the material's insulating and superconducting phases. To explore where the pseudogap phase comes from, Davis and his colleagues are obtaining atomic-resolution images of electronic structure of high-temperature superconductors.
They are acquiring these images with a spectroscopic imaging-scanning tunneling microscope, or SI-STM, of the type that Davis developed over a decade ago, first at University of California at Berkeley and then at Cornell University. This instrument is one of a few of its kind in the United States. Davis' second-generation instrument is at Brookhaven National Laboratory.
Davis and colleagues analyze high-temperature superconductors synthesized with strategic doping levels, ranging across all three phases (insulating, pseudogap, and superconducting), and established that the pseudogap state appears locally at the nanoscale when the "parent" insulator state is doped or altered to make it conducting. The population of these nanoscale pseudogap regions grows until they all touch each other at higher doping levels and the completely ordered superconductor phase is achieved. The discovery has implications for designing higher temperature cuprate superconductors down the road.
While all scanning tunneling microscopes are designed to look at individual atoms on the surface of a material using a tip so sharp that it terminates with a single atom, the SI-STM of CES is rather special. "SI-STMs are engineered better than conventional STMs at every turn and they are not physically doing the same thing," said Davis.
At Cornell and Brookhaven, the instruments are in labs that protect against all vibrations, and unlike a regular STM, the tip can hover stationary for months just picometers over each surface without crashing – there is that much stability. With this stability comes spatial and energy resolution plus vastly enhanced signal-to-noise ratios for visualizing electronic matter.
Davis manages to publish time and time again in Science and Nature, a feat that he shrugs off. "The necessary standard for publishing there is very useful. Aspiring to those journals is a helpful way to calibrate your work."
He maintains that he and his colleagues just do the best job they can, all the time, and that the papers come from combined efforts within big collaborations. Indeed it's the teamwork, the scientific conversations with students, postdocs and coworkers and the discussion of new ideas that he deeply enjoys.
Generating the data that eventually goes into one SI-STM figure takes up to a week, summing gigabytes of data per experiment, terabytes per manuscript. Therefore, the challenge moves from can I measure it? to can I work up this data? Here Davis got help from his wife, physicist Kathy Selby, who suggested he make a movie of the data in such a way as to ultimately allow for the extraction of electronic structure information.
Although Selby is a senior lecturer in physics at Cornell, the pair maintains relatively separate physics spheres. Selby, a scholar, expert and teacher of the Irish Celtic fiddle, is heavily interested in the physics of music. Their two children, Michael and Owen, both take music lessons, yet Davis is untrained.
Of his extracurricular passions, Davis is keen on history, literature and aspires to speak Latin; although given the demands on his time, fluency may have to wait until retirement. It's not all work, however. Davis and his family take vacations in his native Ireland, where science is surely never far from the mind of someone who seems to enjoy it as much as Davis.