Prozorov_18 - PHYSICS 222 Introduction to Classical Physics...

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Unformatted text preview: PHYSICS 222 Introduction to Classical Physics II Prof. Ruslan Prozorov Iowa State University Fall 2011 LECTURE 18 Superconductivity: (100 years since the discovery) some slides for this lecture were contributed by Prof. Peter Kes (Leiden) temperature scales http://www.magnet.fsu.edu/education/tutorials/magnetacademy/superconductivity101/page4.html PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 2 26 October 1911 : zero resistance! PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 3 superconductivity and superfluidity PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 4 the prize… not for superconductivity but the discovery of superconductivity appears in his Nobel lecture PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 5 is a superconductor a perfect metal? No, in addition to R = 0, superconductors exhibit Meissner – Ochsenfeld effect (1933) – they expel magnetic flux Walther Meissner Robert Ochsenfeld Normal Hc 800 H (Oe) 600 Superconductor 400 200 0 0 1 2 3 4 5 6 7 8 T (K) PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 6 superconductivity is common PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 7 NO – it is a NEW state of matter H c 0 1 T Tc 2 Magnetic field Hc(T=0) normal B0 superconducting Temperature Tc(H=0) Faraday law does not work inside bulk superconductor!! PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 8 two types of superconductors Magnetic field Hc2 type – II superconductor Hc normal mixed Hc1 B0 superconducting Temperature PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University Tc(H=0) 5 October 2011 9 the timeline PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 10 what happens to electrons? to explain superconductivity, we need to have all electrons to be in the same quantum state. However, as we learned before, Pauli principle prohibits that! What is the solution? To form a bound state (“Cooper Pair”) that will have spin = 0. These pairs are bosons, so they do NOT obey Pauli principle. How does this work? We need attraction between electrons. PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 11 The BCS theory of superconductivity John Bardeen, Leon Cooper, and John Schrieffer BARDEEN, J., L. N. COOPER & J. R. SCHRIEFFER. Theory of Superconductivity, In The Physical Review, Second Series, Vol. 108, No. 5, p.1175-1204. Lancaster, PA, 1957. The complete issue in original blue printed wrappers. WITH: The Physical Review, Second Series, Vol. 104, No. 4 and Vol. 106, No.1, both in original wrappers. $5000. PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 12 Josephson effect Brian D. Josephson super-current can flow through a thin insulator! used in devices called Superconducting Quantum Interference Device (SQUID) as extremely sensitive voltmeters and magnetometers PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 13 major applications PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 14 really big magnets PHYS222 - Lecture 18 - Prof. Ruslan Prozorov - Iowa State University 5 October 2011 15 ...
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