Irish and Chinese scientists Discover New Method to Improve Conductance In Materials

20 March 2019

Researchers from AMBER, the Science Foundation Ireland Research Centre for Advanced Materials and BioEngineering, the School of Physics and the CRANN Institute, at Trinity College Dublin, have today announced the development of a new method to majorly improve conductance in materials (otherwise known as two-dimensional 2D systems). This discovery could have significant impacts in the fields of ultra-fast electronics and, possibly, energy.

Conductance is the degree to which an object conducts electricity. It is a property that some materials such as metals have naturally making them highly valued in modern electronics. To make a material more conductive two strategies can be taken: the material can either have a lot of charge carriers, increasing charge-carrier density; or the material can have a high charge-carrier mobility, meaning the charge carriers move more efficiently. By increasing the carrier density of a two dimensional material, the charged impurity increases largely. This often results in electron-electron scattering, meaning a decrease in efficiency and mobility of the charge. In this latest breakthrough, Professor Stefano Sanvito and his team at AMBER have discovered that the surface state of Weyl semimetal NbAs can overcome such a limit and maintain a high mobility even in the presence of a high carrier density.

Combined with the high mobility value, a record-high surface sheet conductance was achieved up to 5~100 S/□. This far exceeds that of conventional 2D electron gas, quasi-2D metal films, and topological insulator surface states.

The new study is published in Nature Materials* a leading international science journal. The study was led by AMBER researchers at the School of Physics and CRANN Institute, Trinity College and scientists at Fudan University, China.

Professor Mick Morris, Director of AMBER and Professor in Trinity’s School of Chemistry, said: “Fundamental research is the cornerstone of AMBER’s work and today’s announcement further enhances our proven track record of pushing the boundaries of science to discover real solutions that can improve people’s lives. AMBER is home to some of the world’s leading scientists, engineers and investigators – leaders in their fields – who use their vast knowledge and expertise to discover, improve and exploit materials science. I wish to congratulate Stefano and his team on this exciting development and its publication in Nature Materials, the world’s leading multidisciplinary science journal.”

Professor Stefano Sanvito lead AMBER Investigator on the project, Professor in Trinity’s School of Physics and Director of the CRANN Institute, commented: “This discovery builds on our previous work on the Quantum Hall effect based on Weyl orbits in cadmium arsenide. We attribute the origin of the ultra-high surface conductance to the disorder-tolerant nature of the Fermi arcs. Our results present the first transport evidence for the low-dissipation property of Fermi arcs in Weyl semimetal NbAs surface states and establish it as an excellent 2D metal with supreme conductivity for both fundamental studies and potential electronic applications. I would like to thank my colleagues at Fudan University in China for their collaboration on this project and of my former student, Dr. Narayan, with whom I have developed the theory. Given the complexity of the phenomena investigated, it would have been extremely difficult to perform the study within a single research group.”

In order to study its surface transport properties, the scientists in Fudan first developed a new approach to synthesise the high-quality nanostructures of Weyl semimetal NbAs with tunable Fermi levels. Because of their large surface-to-bulk ratio, the 2D surface state exhibits dominant quantum oscillations with multiple large Fermi surfaces that give rise to a high sheet carrier density, even though the bulk Fermi level locates near the Weyl nodes. The Irish team in AMBER provided the theoretical support to explain the results and interpret the data.

https://www.nature.com/articles/s41563-019-0320-9