Superconducting materials（超导材料） , which transmit power resistance-free, are found to perform optimally²（最佳，最适宜） when high- and low-charge density³ varies on the nanoscale level, according to research performed at the Department of Energy's Oak Ridge⁴ National Laboratory. In research toward better understanding the dynamics⁵ behind high-temperature superconductivity, the ORNL scientists rewrote computational code for the numerical Hubbard model that previously⁶ assumed copper-compound superconducting materials known as cuprates to be homogenous⁷（同质的，同类的） — the same electron density — from atom to atom.

Lead author Thomas Maier and colleagues Gonzalo Alvarez, Michael Summers and Thomas Schulthess received the Association for Computing⁸ Machinery⁹ Gordon Bell Prize two years ago for their high-performance computing application. The application has now been used to examine the nanoscale inhomogeneities（不均一，不同类） in superconductors that had long been noticed but left unexplained.

The paper is published in Physical Review Letters.

"Cuprates and other chemical compounds used as superconductors require very cold temperatures, nearing absolute zero, to transition from a phase of resistance to no resistance," said Jack¹⁰ Wells, director of the Office of Institutional Planning and a former Computational Materials Sciences group leader.

Liquid nitrogen is used to cool superconductors into phase transition（相变） . The colder the conductive material has to get to reach the resistance-free superconductor phase, the less efficient and more costly¹¹ are superconductor power infrastructures¹³. Such infrastructures include those used on magnetic levitation¹⁴ trains, hospital Magnetic Resonance¹⁵ Imaging, particle accelerators and some city power utilities.

In angle-resolved photoemission（光电发射） experiments and transport studies on a cuprate（铜酸盐） material that exhibits striped electronic inhomogeneity, scientists for years observed that superconductivity is heavily affected¹⁶ by the nanoscale features and in some respect even optimized¹⁷.

"The goal following the Gordon Bell Prize was to take that supercomputing application and learn whether these inhomogenous stripes increased or decreased the temperature required to reach transition," Wells said. "By discovering that striping leads to a strong increase in critical temperature, we can now ask the question: is there an optimal¹ inhomogeneity?"

In an ideal world, a material could become superconductive at an easily achieved and maintained low temperature, eliminating much of the accompanying cost of the cooling infrastructure¹².

"The next step in our progress is a hard problem," Wells said. "But from our lab's point of view（观点，立场） , all of the major tools suited for studying this phenomenon — the computational codes we've written, the neutron¹⁸ scattering¹⁹ experiments that allow us to examine nanoscale properties — are available to us here."