Scientists Study the Insulator-Superconductor Transition of Copper-Oxide Compound in Fine Detail
April 11, 2016 | BNLEstimated reading time: 4 minutes
Using a highly controlled deposition technique, scientists from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have synthesized ultrathin films containing multiple samples of a copper-oxide compound to study the compound's electronic behavior at near absolute zero, or minus 459 degrees Fahrenheit. This technique, as described in a paper published in this week's Online Early Edition of the Proceedings of the National Academy of Sciences, is helping scientists understand how electrons behave as this material transitions from being an insulator to a superconductor capable of carrying electric current with no resistance.
"We are trying to understand the mechanism of the insulator-superconductor transition in a family of compounds called the cuprates. These compounds become superconducting at relatively high temperatures—minus 200 degrees Fahrenheit—in comparison to most superconducting materials, which require temperatures within a few degrees of absolute zero," said Jie Wu, lead author on the paper and a physicist in Brookhaven Lab's Condensed Matter Physics and Materials Science Department. "Characterizing this mechanism may provide insight into how we can make the superconducting temperature even higher, possibly even reaching room temperature."
This capability would enable electricity to be transferred much more efficiently. "Imagine a power line that carries electricity without any energy loss. We could wire the whole planet, resulting in trillions of dollars in savings and reduced environmental impact," said Wu.
Insulator-superconductor transition
In their native state, cuprates are insulators; they do not readily conduct electricity. But cuprates can become superconducting when chemically "doped" with strontium atoms, which produce free-moving electrons that pair up in the crystalline copper-oxide layers where superconductivity is known to occur.
At a certain reduced doping level, however, superconductivity weakens and eventually disappears. As the cuprates' superconducting temperature is lowered to near absolute zero, resistance increases somewhat (a characteristic of insulators) yet conductivity remains quite high (a characteristic of metals). The nature of this strange "insulating" state has been a puzzle to scientists for years.
Solving the puzzle requires a method of fine-tuning the doping level to incrementally approach the quantum critical point—the "tipping" point at which a material is on the cusp of transitioning from one state of electronic order to another, similar to the phase change that happens when ice melts into liquid water. It also requires a highly sensitive way to measure the electronic changes corresponding with the different doping levels.
One film, many samples
To study the insulator-superconductor transition in fine detail, the scientists synthesized films of a compound containing lanthanum, strontium, copper, and oxygen. They used a combinatorial molecular beam epitaxy system at Brookhaven that places materials onto a substrate, atom by atom, in a layered manner and at tightly controlled deposition rates.
Through photolithography, a technique of transferring a geometric pattern onto a substrate, the scientists patterned single-crystal films into a linear "combinatorial" library containing 30 samples, each with a slightly different chemical doping level near the quantum critical point. To provide the electrical contact needed to measure the resistivity of the samples, they evaporated gold pads onto the films' surface.
"We programmed the system to vary the doping level continuously and very precisely at a set minute increment," said Ivan Bozovic, co-author on the paper and a senior physicist in Brookhaven's Condensed Matter Physics and Materials Science Department.
The scientists then measured the electrical resistivity of the samples with varying temperatures, magnetic fields, and doping levels near the quantum critical point. Two types of measurements were taken: one parallel to the electrical current (longitudinal resistivity) and one perpendicular (Hall resistivity).
"The Hall resistivity is much more sensitive because it measures the voltage at a particular cross section of the sample. Longitudinal resistivity averages the whole section," said Wu. "Our Brookhaven team is the first to use this more localized approach that can give us a direct measurement of the density of mobile electrons."
Page 1 of 2
Suggested Items
DuPont Showcases AI Innovations Featuring Advanced Interconnects at 2024 International Electronic Circuits Exhibition
05/13/2024 | DuPontDuPont announced it will showcase its comprehensive range of advanced circuit materials and solutions at the 2024 International Electronic Circuits Exhibition in Shanghai. With a product portfolio that includes fine line, signal integrity, power and thermal management, DuPont will exhibit at Booth #8L06 at the National Exhibition and Convention Center (NECC) from May 13 to 15.
MKS’ Atotech to Participate in ECTC
05/10/2024 | MKS’ AtotechAt this year’s 74th IEEE Electronic Components and Technology Conference (ECTC), MKS’ Atotech will present and demonstrate its latest product and service innovations.
The Chemical Connection: Reducing Etch System Water Usage, Part 2
05/02/2024 | Don Ball -- Column: The Chemical ConnectionIn my last column, I reviewed some relatively simple ways to reduce water usage in existing etch systems: cutting down cooling coil water flow, adding chillers to replace plant water for cooling, lowering flow rate nozzles for rinses, etc. This month, I’ll continue with more ways to control water usage in your etcher. Most of these are not easily retrofittable to existing equipment but should be given serious consideration when new equipment is contemplated. With the right combination of add-ons, it is possible to bring the amount of water used in an etch system to almost zero.
Designer’s Notebook: What Designers Need to Know About Manufacturing, Part 2
04/24/2024 | Vern Solberg -- Column: Designer's NotebookThe printed circuit board (PCB) is the primary base element for providing the interconnect platform for mounting and electrically joining electronic components. When assessing PCB design complexity, first consider the component area and board area ratio. If the surface area for the component interface is restricted, it may justify adopting multilayer or multilayer sequential buildup (SBU) PCB fabrication to enable a more efficient sub-surface circuit interconnect.
Insulectro’s 'Storekeepers' Extend Their Welcome to Technology Village at IPC APEX EXPO
04/03/2024 | InsulectroInsulectro, the largest distributor of materials for use in the manufacture of PCBs and printed electronics, welcomes attendees to its TECHNOLOGY VILLAGE during this year’s IPC APEX EXPO at the Anaheim Convention Center, April 9-11, 2024.