Penetration Depth in Organic Superconductors

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

Nontechnical Abstract Organic conductors represent a class of carbon-based materials where pressure and temperature may induce transformations from one kind of electronic behavior to another. A striking example is the transformation from magnetism into superconductivity which will be the focus of this project. Experiments are planned to measure a quantity called the magnetic penetration depth, whose behavior provides a window into the microscopic behavior of electrons in the superconducting state. This work will build upon novel techniques previously developed in this lab to measure the penetration depth. How organic superconductivity differs from its counterpart in ordinary metals and high temperature superconductors, how it evolves from magnetism and what ultimately causes it to occur will be the key questions this project will try to answer. Complex electronic materials of this type will undoubtedly play a role in future computational and micro mechanical devices. Understanding the physical principles that govern their behavior is critical in the same way that understanding the behavior of silicon was to the computer revolution. This program will provide training for both undergraduate and graduate students in low noise, high frequency electronic instrumentation, cryogenics, computer simulation and high pressure methods. It will also provide these students with the intellectual challenge of understanding the complex behavior of newly synthesized materials and help forge links between physics, chemistry, electrical engineering and material science. Technical Abstract Organic conductors are synthetic metals composed of carbon-based molecules. By changing temperature and pressure they transform from metals into insulators, magnets or superconductors. Determining the general principles that govern these electronic transformations is one of the central unsolved problems in condensed matter physics. This project will focus on high frequency magnetic measurements in a class of organic materials for which high quality, single crystals are readily available. The experiments will utilize electronic oscillator techniques developed in this lab to measure the magnetic penetration length, a quantity fundamental to all superconductors. By studying how the penetration depth changes in response to pressure, temperature, magnetic field and chemical substitution, a window will be opened into the underlying quantum state of the superconductor. The themes will be how organic superconductivity differs from its counterpart in conventional metals and high temperature superconductors, how it evolves under pressure from the magnetic phase and ultimately what causes organic materials to become superconductors. The program will provide training for both undergraduates and graduate students in low noise, high frequency electronic instrumentation, cryogenics, magnetic measurements and high-pressure techniques. It will also provide students with the intellectual challenge of understanding the complex behavior of newly synthesized materials.