Fundamental Properties of Superconductors and Mesoscale Devices

Harvard University, Cambridge MA

Investigators

Abstract

This Condensed Matter Physics project, involving experiment and data analysis, and theoretical modeling, will study the physical properties of nanoscale device structures, fabricated of superconducting, normal metal, ferromagnetic, and organic conductors. One of the most active issues in fundamental research in superconductivity is clarification of how superconductivity is weakened and eventually destroyed by quantum phase-slip processes in a superconducting wire as it is made thinner and thinner, approaching the true one-dimensional limit. This issue also has potential practical importance in setting a limit on miniaturization of superconductive electronics. Experiments involving controlled external damping are planned to clarify the role of dissipative processes in suppressing quantum phase slips, and perhaps driving a phase transition at T = 0 to a truly zero resistance state. The effect of heating on I-V characteristics at finite current levels also needs to be understood. Other planned experiments study charge and spin transfer between ferromagnetic and superconducting metals in geometries involving nanometer length scales. Such experiments probe the length scales required for possible applications in quantum computing and tests of Bell's inequality. Research will also be done on carbon nanotubes, using Raman scattering to determine the chirality of individual nanotubes used in transport and scanned probe measurements, to eliminate a major source of uncertainty in the interpretation of experimental data. Students and postdocs involved in this project will become expert in techniques of fabrication and measurement of nanostructures, essential to development of modern technology. Experimental measurements and theoretical analysis will be carried out to increase our understanding of the physical properties of nanoscale device structures fabricated of a wide range of materials: superconducting, normal metal, ferromagnetic, and organic. In addition to the pursuit of scientific knowledge and intellectual understanding, this work will have broader impact in two separate directions: (1) Understanding of the unique quantum properties of materials when their dimensions are reduced to the nanometer scale is essential to exploiting opportunities and avoiding barriers to technological progress as the miniaturization epitomized by Moore's Law proceeds in the future. (For example, a superconducting wire becomes resistive if its diameter is reduced too much.); (2) Researchers in this program (ranging from undergraduates to postdocs and visiting faculty) receive thorough exposure to a wide range of fabrication, measurement, and interpretation skills, which provides excellent preparation for careers in academia, industry, and government.