The discovery of fluxoid quantization:

Transcription

1 The discovery of fluxoid quantization: 2e eor not 2e R.Doll M.Näbauer Dietrich Einzel Walther-Meißner-Institut tit t für Tieftemperaturforschung t f Bayerische Akademie der Wissenschaften D Garching Outline Theoretical insights: then and now The Doll-Näbauer experiment The Deaver-Fairbank experiment The IBM conference 1961 Post 1961 B.S.Deaver W.Fairbank 75th Annual Meeting 2011, DPG Spring Meeting, Condensed Matter Section, Dresden, March 13 18, 2011

2 Theoretical insights: then and now Consider particles of mass km 0 and charge ke: charged bosons fermion pairs condensate: qm (bosonic) wave function Madelung representation magnitude: condensate density phase: uniqueness requirement 2

3 Theoretical insights: then and now The condensate density n s (T) off-diagonal long-range order BCS 1957: pairing hypothesis implies k=2 more theories for n s (T)/k Gor kov, 1958 Landau, Ginzburg London s (near T c c) 1950 (near T c c) 1935, 1950 n s (T) k k 3

4 Theoretical insights: then and now condensate current density canonical momentum gauge invariance Bohr- Sommerfeld quantization fluxoid quantization 4

5 =hc/ke: what was known in 1961? Nambu-Goldstone mode 1 BCS, 1957: no prediction of fluxoid quantization 2 Fritz London 1950: k=1 3 Lars Onsager 1959: k=2 2 private communication with W. M. Fairbank 4 5 rumours 1960: k=n NB Byers &CNY Yang 1961: k=2 N: number of particles experimental pairing correlations imply hc/2e periodicity of the free energy check required! 5

6 The Doll-Näbauer experiment 1934 Walther Meißner accepts the chair of Technical Physics at the TU Munich 1943 WWII: Meißner s Institute moves to Herrsching/Ammersee into two barracks 1946 Walther Meißner founds the Commission of Low Temperature Research (CLTR) in the Bavarian Academy of Sciences during his presidentship Robert Doll joins the CLTR (diploma 1953, PhD 1959) 1951 Martin Näbauer joins the CLTR (diploma 1949, PhD 1955, VL 1958) W. Meißner The Herrsching barracks ( ) M. Näbauer R. Doll (88 years) 6

7 The Doll-Näbauer experiment 1960 Doll and Näbauer start experiment to measure the fluxoid in a (Pb) superconducting hollow cylinder in Herrsching (Meißner not involved!) 1961 April Clear evidence for quantized flux, however, with 0 =½ (hc/e) June 15 Näbauer attends the IBM conference in Yorktown Heights June 19 Submission to PRL by Robert Doll after considerable time delay 7

8 The Deaver-Fairbank experiment 1952 William Fairbank joins the Faculty of Physics at Duke University, Durham. Collaboration with Fritz London on 3 He Fermi-Dirac degeneracy temperature. Idea of measuring the fluxoid quantum in superconductors William Fairbank joins the Faculty of Physics at Stanford University (invited by Felix Bloch) Bascom S. Deaver accepts Fairbank s offer to do his PhD work on the measurement of quantized flux in a superconducting hollow cylinder Fritz London W.M. Fairbank B.S. Deaver Jr. (80 years) 8

9 The Deaver-Fairbank experiment 1960 Deaver starts his experiment to measure the fluxoid in a superconducting hollow cylinder at Stanford May Clear evidence for quantized flux, however, with 0 =½ (hc/e). June 15 Bill Little attends the IBM conference in Yorktown Heights. June 16 Submission to PRL by Deaver and Fairbank. 9

10 The IBM conference, June 15 17, 1961 IBM Conference of Fundamental Research in Superconductivity, it Yorktown Heights, N. Y. June 14: Bill Little meets Martin Näbauer in his hotel room. L.: Is the flux quantized? ( Ist der Fluss quantisiert? ) N.: Sure! ( Ja freilich ist er quantisiert! ) June 15: Martin Näbauer presents a talk on the flux quantization effect observed in Herrsching/Bavaria Bill Little presents his own talk and afterwards shows the data on the flux quantization effect observed by Deaver and Fairbank in Stanford/California. W.A. Little (80 years) After a heated discussion everybody in the audience is convinced that k=2 is needed to understand both experimental data sets. Little: It came as a big surprise and some relief that both parties had recognized the factor of two 10

11 Post Doll and Näbauer receive Awards from both the Academy of Sciences in Munich and Göttingen. BA-Medal Bene Merenti for Robert Doll in Martin Näbauer dies unexpectedly the day before signing the contract for a professorship p at the TU Munich Bascom Deaver starts his career as a Professor at the University of Virginia The CLTR moves from Herrsching to Garching (20 km north of Munich) and is renamed 1982 into Walther-Meißner Institute (WMI) Robert Doll retires, but continues to frequent the WMI almost daily, dealing with various problems in physics, even theory (Ginzburg-Landau) Bascom Deaver receives various Awards for good teaching, such as the George B. Pegram Award for Excellence in Teaching of Physics (May) Bascom Deaver retires, but continues to have his research lab at UVA. (168)Bascom (16.8.) Deaver can celebrate his 80th birthday in the best of health (16.1.) Robert Doll can celebrate his 88th birthday in the best of health. 11

12 Summary: 50 years of fluxoid quantization BCS theory (1957) has side aspects (fluxoid quantization), which have remained unrecognized until as late as Remarkable coincidences on the Bavarian and Californian side: basic idea, starting time (around 1960), duration (until 1961), IBM conference, PRL Complete agreement of both parties w.r.t. fluxoid quantum showing the pair charge. Therefore Doll/Näbauer and Deaver/Fairbank should always be cited together. The existence of quantized flux in superconductors ranks as one of the most exciting experimental discoveries of the last century. R. Doll M. Näbauer B.S. Deaver Jr. W.M. Fairbank 12

13 Appendix: Fritz London s footnote The famous footnote in the book Superfluids by Fritz London, 1950 A1

14 Appendix: The difference between flux and fluxoid superconducting hollow cylinder: trapped flux differs from fluxoid d R L i H ext London-BCS magnetic penetration depth A2

15 Appendix: the energy gap (T) Ginzburg-Landau regime low temperature limit interpolation procedure for (T) 1 2 (T) 2 (0) EX k=1 k=5 k= T/T c 1.0 A3

16 Appendix: the superfluid density n s (T) Ginzburg-Landau regime 1 EX k=1 k5 k=5 low temperature limit k=2 interpolation procedure for n s (T) n s (T) n T/T c A4

17 Appendix: how to connect with the BCS gap energy gap 1 superfluid density rfluid den nsity, gap 2 (T) 2 (0) n s (T) n scaling behavior: vs. near T c super relative deviation T/T c 1.0 A5

18 Appendix: BCS spin susceptibility, analytic results BCS spin susceptibility Y(T)/Y int (T) Y(T) quasiparticle Yosida function Ginzburg-Landau expansion a /k/ T) 2 B low-t expansion: b (k B T/, c exp( /k B T) a, b c known to all orders! a funct tion Yosid 0 Y int (T) Y GL (T) Y LT (T) Y Y int 0.1 T/T c T/T Y A6

19 Appendix: BCS energy gap and the -function pair binding energy order parameter e energy spectrum develops gap superfluid density order parameter e Ginzburg-Landau A7

20 Appendix: On nonequilibrium superconductivity Nambu matrices dynamics in phase space gradients collisions von-neuman equation (integro-differential eq.) external potentials interactions, collective modes integral equations order parameter dynamics: gauge mode/collective modes conservation vs. relaxation laws elastic vs. inelastic scattering observables ; vertex A8

21 Appendix: 2e or not 2e in the Doll-Näbauer experiment A9

22 Appendix: Doll/Näbauer publication in Z. Physik A10