Colloquium: “Inhomogeneous Superconductivity, Pulsed Magnetic Fields, and an Abundance of Data” — October 28, 2021 at 4 PM
Dr. Charles C. Agosta
Director of the 3/2 Engineering Program
Former Chair of the Department of Physics
Thursday, October 28, 2021, 4 PM
George P. Williams, Jr. Lecture Hall, (Olin 101)
Video Link will be available if needed
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Welcome Back to in-person Colloquiums!
A reception will be held in Olin Lounge* at 3:30 PM prior to the colloquium. All interested persons are cordially invited to attend.
* We encourage all to wander out to the front entrance of the building or up to the Observatory Deck on the 3rd floor to enjoy their refreshments.
Superconductivity, more than one hundred years after its discovery, has no universal underlying microscopic, quantum mechanical, explanation, that we know of. It is the biggest unsolved problem in condensed matter physics. At Clark University, we study various correlated electron states using high magnetic fields, low temperatures, and high pressures, with the hope that we can contribute to the understanding of how electrons behave in metals. After an introduction, this talk will concentrate on the subject of inhomogeneous superconductivity. The story begins in 1960 when Clogston and Chandrasekhar claimed there was an ultimate magnetic field that would destroy superconductivity, when the energy to flip an electron spin in a magnetic field (Zemann energy) exceeded the binding energy of the Cooper pairs (superconducting energy gap). This limit is commonly called the Pauli paramagnetic limit HP. In 1964 Fulde and Ferrell in the US and Larkin and Ovchinnikov in Russia predicted that in a clean superconductor where the magnetic field can reach HP, an exotic inhomogeneous superconducting phase (the FFLO state) can be stabilized at fields greater than HP. Most superconductors cannot reach fields as high as HP, because vortices destroy superconductivity at lower fields. We have discovered that the highly anisotropic crystalline organic superconductors have the ability to suppress the effects of vortices, and support the highly sought after FFLO superconducting state. We will present rf penetration depth and specific heat data in magnetic fields up to 35 tesla, and temperatures down to 60 mK that are consistent with the FFLO state. We will also describe our unique pulsed magnetic field apparatus that reaches fields of 50 tesla, and our rf penetration depth measurement system that we use to investigate the properties of materials.
Faculty Biogragphy (http://www2.clarku.edu/faculty/facultybio.cfm?id=339&progid=25)