Electronic disruption prods Mott insulator's conversion to metallic state
In a relatively recently discovered class of materials, known as spin-orbit Mott insulators, theorists have predicted the emergence of new properties at points just beyond the insulating state, when electronic manipulation can transform these compounds into conducting metals.
Images obtained through scanning tunneling spectroscopy show the transformation of a compound of strontium, iridium and oxygen -- part of a mysterious class of materials known as spin-orbit Mott insulators. By introducing charge carriers within the compound by replacing 40 percent of the iridium ions with ruthenium, researchers from Boston College were able to reveal the microscopic mechanisms that transform these insulators into a metallic state. The images reveal ruthenium effectively created features within the compound that resembled minute metallic puddles. As the amount of additional ruthenium was increased, the puddles 'percolate,' coalescing to form a metal across which charges freely flow.
Credit: Nature Communications
A better understanding of electrons near this transition, theorists have predicted, could allow these new Mott insulators to pave the way to discoveries in superconductivity, new topological phases of matter, and new forms of unusual magnetism.
What scientists have lacked is experimental evidence that reveals the microscopic mechanisms that actually drive one of these spin-orbit Mott insulators to become a metal.
Now a team of physicists at Boston College report in Nature Communications that they manipulated a compound of strontium, iridium and oxygen – Sr3Ir207 – with a substitution of ruthenium metal ions, successfully driving the material into the metallic regime, and mapping this previously uncharted transformation as it took place, giving scientists a unique view into the workings of these insulators.
Spin-orbit Mott insulators are so named because of their complex electronic properties. Within these novel materials, there is a repulsive interaction between electrons that tends to drive the electrons to a stand still. This tendency is bolstered by the lowering of the electron's energy via a strong interaction between the electron's magnetic field and its orbital motion around the nucleus.
This delicate interplay between repulsive action, known as Coulomb interaction, and the coupling between electrons' spin and orbital motion has allowed scientists to define this class of materials as spin-orbit Mott insulators.
Boston College Assistant Professor of Physics Stephen D. Wilson said the team succeeded in driving the insulator-to-metal transformation by replacing 40 percent of the iridium ions with ruthenium, thereby creating a metal alloy. That event introduced charge carriers, which have proven successful in destabilizing the so-called Mott phase in the transformation of compounds in this class of insulators.
Scanning tunneling microscopy revealed ruthenium effectively created features within the compound that resembled minute metallic puddles, said Wilson, one of the lead researchers on the project. As the amount of additional ruthenium was increased, the puddles began to "percolate," coalescing to form a metal across which charges freely flow, he added.
"The addition of ruthenium introduces charge carriers, but at a low ratio of ruthenium to iridium they simply stay put in these little metallic puddles, which are symptoms of strong correlated electrons," Wilson said. "These electrons are stable and wouldn't move much. But when we stepped up the disruption by increasing the amount of ruthenium, the puddles moved together and achieved a metallic state."
The behavior in this particular compound parallels what researchers have seen in Mott insulators that play host to such phenomenon as high temperature superconductivity, said Wilson, who will discuss his research at the upcoming annual meeting of the American Physical Society.
By pinpointing exactly where this transformation takes place, the team's findings should help to lay the groundwork in the scientific search for new electronic phases within spin-orbit Mott insulators, said Wilson, who co-authored the report with his Boston College Department of Physics colleagues Professor Vidya Madhavan, Professor Ziqiang Wang, and Assoc. Prof. Fr. Cyril P. Opeil, SJ.
BC graduate students Chetan Dhital, the lead author of the paper, Tom Hogan, Wenwen Zhou, Xiang Chen, Zhensong Ren, Mani Pokharel, and M. Heine also contributed to the project. Scientists at the Oak Ridge National Laboratory, the U.S. National Institute of Standards and Technology and the Canadian Center for Neutron Research also collaborated on the research.
Ed Hayward | EurekAlert!
Young Scientist Discovers Magnetic Material Unnecessary to Create Spin Current
27.07.2015 | Argonne National Laboratory
Quantum dots light the way
21.07.2015 | The Agency for Science, Technology and Research (A*STAR)
Researchers have developed an ultrafast light-emitting device that can flip on and off 90 billion times a second and could form the basis of optical computing.
Joint BioEnergy Institute study identifies bacterial protein that is key to protecting rice against bacterial blight
A bacterial signal that when recognized by rice plants enables the plants to resist a devastating blight disease has been identified by a multi-national team...
Researchers in the Cockrell School of Engineering at The University of Texas at Austin are one step closer to delivering smart windows with a new level of energy efficiency, engineering materials that allow windows to reveal light without transferring heat and, conversely, to block light while allowing heat transmission, as described in two new research papers.
By allowing indoor occupants to more precisely control the energy and sunlight passing through a window, the new materials could significantly reduce costs for...
Argonne scientists used Mira to identify and improve a new mechanism for eliminating friction, which fed into the development of a hybrid material that exhibited superlubricity at the macroscale for the first time. Argonne Leadership Computing Facility (ALCF) researchers helped enable the groundbreaking simulations by overcoming a performance bottleneck that doubled the speed of the team's code.
While reviewing the simulation results of a promising new lubricant material, Argonne researcher Sanket Deshmukh stumbled upon a phenomenon that had never been...
A NASA camera on the Deep Space Climate Observatory (DSCOVR) satellite has returned its first view of the entire sunlit side of Earth from one million miles away.
The color images of Earth from NASA's Earth Polychromatic Imaging Camera (EPIC) are generated by combining three separate images to create a...
23.07.2015 | Event News
10.07.2015 | Event News
25.06.2015 | Event News
27.07.2015 | Materials Sciences
27.07.2015 | Information Technology
27.07.2015 | Power and Electrical Engineering