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Date: May 18, 2022
Speaker: Dr. Randolph “Rand” Elmquist, Physicist, NIST, Gaithersburg, MD
Quantum Measurement Division; Fundamental Electrical Measurements Group
Title: Quantum Hall Array Structures Apply Quantized Resistance in the Wider World
Time: 1:00 p.m. Talk goes from 1:00 - 3:00 p.m. Attendees can sign in any time after 12:30 p.m.
Abstract: Degeneracy in the Landau levels of monolayer graphene allows a stable and precise quantum Hall (QH) resistance plateau at ≈12.9 k(ohm) that is used for precise metrology. When single Hall bars are connected in certain array circuits, they attain a wider range of values depending on the topological arrangement, and we have demonstrated highly precise QH array values using epitaxial graphene. One application of such arrays is direct connection between a macroscopic mass and the defined electrical power unit in a single experiment, in which the current used to levitate the mass in a magnetic field passes through a graphene quantum Hall standard. Any rational value of resistance is possible if the array surface area is large enough or the Hall bar array and interconnections can be shrunk to fit on a monolayer graphene sample. We are exploring how these arrays function and the physical limits on integration. This research will permit experimental development of quantum current sources, quantum rheostats, and the like. These are interesting as engineering problems, and the microscopic workings of QH systems are central in our exploration of these systems.
Biography: Randolph E. Elmquist directs the Quantum Conductance project at the National Institute of Standards and Technology. Working for the past thirty-two years in the field of electrical and quantum metrology, he has contributed to the experimental design and measurement of the electronic Kilogram and calculable impedance standards for the determination of the von Klitzing constant and alpha, the unitless fine-structure constant. He leads the development of cryogenic current comparator systems, the quantum Hall effect, and graphene electronic devices for metrology. He graduated with the PhD degree in Physics from the University of Virginia and is a member of the American Physical Society and a senior member of the Institute of Electrical and Electronics Engineers.
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