Field Dependent Penetration Depth in Unconventional Superconductors

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

The temperature and magnetic field dependence of the London penetration depth of a superconductor yields direct information about the underlying quantum state. This individual investigator project will use high resolution penetration depth measurements to explore Andreev bound states, a new quantum phenomena that arises from the unconventional angular momentum state of the charged pairs in high temperature superconductors. Andreev states modify the energy spectrum and significantly influence the electromagnetism of these materials. These states are greatly enhanced in superconductors containing defects of nanometer size produced by heavy ion irradiation. The penetration depth in irradiated samples will be studied in order to explore how high temperature superconductivity changes when nanoscale structures are introduced into a crystal. If fully successful, this project will add a new spectroscopy of the pairing state, a new chapter in the electromagnetic properties of superconductors and a window into the behavior of high temperature superconductivity at the nanoscale. The students and postdoctoral researchers involved in this research will obtain training and experience in modern electronic instrumentation, cryogenics, graphical computer programming, electron microscopy, materials characterization and research at national accelerator facilities. This will provide them with skills useful in many scientific or technological careers. %%% The ability to shield a magnetic field is a property shared by all superconductors. The degree of shielding is determined by a quantity known as the London penetration depth. This individual investigator project will use high resolution measurements of the penetration depth to explore a new class of quantum phenomena called Andreev bound states that arise in high temperature superconductors. Andreev states are unique to these "unconventional" materials and can provide a new tool with which to understand them. The question of how high temperature superconductivity is modified in devices of nanometer size remains an outstanding problem. Andreev states will be particularly important in this realm and experiments are proposed to understand their role. Superconductors have a potentially huge technological impact, largely by virtue of their unusual electromagnetic properties. This project will lead to a deeper understanding of these properties and if fully successful, to a hybridization of high temperature superconductivity and nanoscience. The project will train students and postdoctoral researchers in modern electronic instrumentation, cryogenics, graphical computer programming, electron microscopy, materials characterization and research at national accelerator facilities. These skills will be important for research in industrial, academic, or government research. ***