Aspects of of Intrinsic Josephson Tunneling

Transcription

1 Aspects of of Intrinsic Josephson Tunneling D. Winkler, 1,2 A. Yurgens, 1 V.M. Krasnov, 1 Y.S. Sudershan, 1 T. Claeson, 1 E. J. Tarte, 3 M.G. Blamire 3 Chalmers University of Technology and Göteborg University Department of Microelectronics and Nanoscience, SE Göteborg, Sweden 2) Imego Institute Aschebergsg 46, Building 11, SE Göteborg, Sweden 3) IRC in Superconductivity, University of Cambridge Madingley Rd, Cambridge, CB3 0HE, UK Microelectronics S Göteborg, and Sweden, Nanoscience, Chalmers winkler@fy.chalmers.se University of Technology and Göteborg University

2 Contents Background and the system Ways of making small junctions The experimental toolbox Recent work and some understanding The pseudogap vs. superconducting gap and T, H, HgBr 2 Interlayer coupling and pressure Bi2212 films Conclusions

3 KLEINER AND MÜLLER GOTHENBURG UNIVERSITY

4 INTRINSIC JOSEPHSON JUNCTIONS CURRENT (ma) Bi2212 single crystal A B I stacks 'large' mesa GOTHENBURG UNIVERSITY intrinsic junctions intrinsic Josephson effect q a) b) CuO Ca CuO SrO BiO BiO SrO CuO Ca CuO S' S S' S' S S' S' S VOLTAGE (mv) I V

5 MESA STRUCTURES - using photolithography area ~ µm^2 Advantages: specified number of junctions small volume less defects less heating height ~ Å (in situ controlled) Ar ion etching or Appl. Phys. Lett. 70, 1760 (1997) Chemical etching (EDTA)

6 CaF 2 gold photoresist Bi2212 CROSS-BAR PHOTOLITHOGRAPHY photoresist gold FIB track CaF 2 Bi2212 photoresist gold CaF 2 Bi2212

7 GOTHENBURG UNIVERSITY FABRICATION OF MESAS OF Bi2212 INTRINSIC JOSEPHSON JUNCTIONS USING A FOCUSSED ION BEAM

8 GOTHENBURG UNIVERSITY FABRICATION OF MESAS OF Bi2212 INTRINSIC JOSEPHSON JUNCTIONS USING A FOCUSSED ION BEAM

9 The experimental toolbox! Charge transport, current-voltage! Temperature! Magnetic field! Pressure! Intercalation! Irradiation with heavy ions! Light and microwaves! Number of Cu-O planes

10 RECENT WORK ON Bi2212 INTRINSIC JUNCTIONS! Pseudogap in the c-axis tunneling! Interlayer coupling theory and intrinsic Josephson effects! A pressure-induced increase of 2 3 times in I c of both Bi2212 and Bi2201- single crystals in contrast to 2-6% increase of T c! Vortex dynamics related work! The c-axis magnetoresistance peak effect in Bi2212 determined by the zero-field sub-gap current-voltage characteristics. 60-fold increase at 6 T.! Mapping the vortex magnetic phase diagram from I-V! The influence of 5 GeV Pb + ion radiation was studied. I c has a peak at 1/3 of the matching field B φ! Multiple valued critical current! Zero-voltage-state lifetime measurements! Critical current switching distribution! Phase-locking between junctions in a stack S ! Göteborg, Comparison Sweden, to numerical winkler@fy.chalmers.se simulations

11 PSEUDOGAP versus the SUPERCONDUCTING GAP two scenarios... (From J.L. Tallon and J.W. Loram)

12 PSEUDOGAP GOTHENBURG UNIVERSITY (Krasnov et al. PRL84, 5860 (2000))

13 di/dv PSEUDOGAP GOTHENBURG UNIVERSITY

14 PSEUDOGAP GOTHENBURG UNIVERSITY (Winkler et al., Supercond. Sci. Technol. 12, (1999))

15 HgBr 2 intercalation Decrease of the c-axis critical current less heating about one week at C Jin-Ho Choy, Seong-Ju Hwang, and Nam-Gyu Park J. Am. Chem. Soc. 119, 1624 (1997) Tord Claeson

16 PSEUDOGAP GOTHENBURG UNIVERSITY (Krasnov et al. PRL84, 5860 (2000))

17 I(mV) I (ma) intrinsic Josephson junctions (HgBr2) Bi-2212 T = 4.2 K 10 intrinsic Josephson junctions I(mA) V(mV) The intercalation does not change the quality of I-V's Tord Claeson V(mV)

18 di/dv (ms) Tc = 66 K 4.2 K 38 K 50 K di/dv (ps) di/dv (ms) di/dv(kω -1 ) = 1.068e-3 V(mV) % of data presented V (mv) K 10 Tc = 66K 92 K V/10 (mv) RESISTANCE TEMPERATURE (K) Tord Claeson

19 Two intercalated samples GOTHENBURG UNIVERSITY K Tc = K K Tc = 66 K di/dv (ms) K 110 K 60 K 78 K di/dv (ms) K 56 K 5 81 K 65 K V(mV) HgBr -Bi2212; 2 (4.2) = 31 mev V(mV) (Τ) / (4.2) pristine Bi2212; (4,2) = 12.5 mev 1 (4,2) = 18.5 mev 2 BCS Superconducting & pseudogap structures Microelectronics and Nanoscience, Chalmers University of 50Technology and Göteborg University TEMPERATURE (K) Tord Claeson

20 Magnetic field dependence H I c for Bi2212 Superconducting gap and pseudogap di/dv (ms) Bi2212 (S875b) H=0T H=14T T=40K T=60K T=72K T=80K V (Volt) (Krasnov et al. cond-mat/ , 29 June 2000)

21 Intercalated HgBr2- Bi2212 mesa at 4.2 K di/dv (ms) V s (mv) σ(h)-σ(0) (µs) T=4.2K H (T) I=0 HgBr 2 -Bi V (Volt) H=0T H=2T H=4T H=6T H=10T H=14T a) b) H (T)

22 H I c pure Bi2212 di/dv (ms) 10 5 a) T =72K S875b H=0T H=1T H=2T H=4T H=7T H=10T H=12T H=14T di/dv (ms) 10 5 b) T =80K Bi2212 H=0T H=1T H=2T H=4T H=6T H=10T H=14T V (Volt)

23 INTERLAYER COUPLING AND PRESSURE

24 PENETRATION DEPTH λ c = cφ0 2 8π sj c

25 PRESSURE GOTHENBURG UNIVERSITY δ a a δ c c δ b = = b = 0.6 % GPa 0.2% GPa -1-1

26 HIGH PRESSURE CELL Option #1 #2 #3 Pressure range, GPa Out er di amet er, mm Inner di amet er, mm Wor ki ng vol ume at max pr essur e, ccm Wei ght, kg Institute for High Pressure Physics Tel. ( 7-095) TROI TSK Moscow Reg. RUSSI A Fax. ( 7-095)

27 12 8 (a) TWO OR ONE PLANE Bi-2212 Bi mv (b) 2 mv GOTHENBURG UNIVERSITY CURRENT (ma) P = GPa T = 30 K VOLTAGE P = 0.8 GPa T = 4.2 K VOLTAGE 0.85 GPa No change in shape of I-V s 10/25/00 27 Tord Claeson

28 INTERLAYER COUPLING AND PRESSURE

29 Ic (ma) PRESSURE EFFECTS Bi P(GPa) GPa 0.04 GPa Bi PRESSURE (GPa) TEMPERATURE (K) (1-Tc/Tc0) (%) Bi-2201 Bi-2212 (b) The pressure affects the c-axis transport but not the superconducting transition

30 INTERLAYER COUPLING AND PRESSURE Bi2212 I c goes up with pressure, but T c remains about the same

31 CONCLUSIONS! Fabrication several methods! Pseudogap and the superconducting gap seem to coexist T, H, HgBr 2, pressure,...! No evidence for the interlayer coupling theory for HTS from experiments on Bi2212 and Bi2201! Intrinsic Josephson effect and vortex matter! Multiple valued critical current

32 REFERENCES AND FURTHER READING Yurgens, Intrinsic Josephson Junctions - Recent Developments Supercond. Sci. Technol. 13, R (2000). D. Winkler, Niklas Mros, August Yurgens, and Vladimir M. Krasnov, Edward J. Tarte, David T. Foord, Wilfred E. Booij, and Mark G. Blamire Intrinsic Josephson effects in submicrometer Bi2212 mesas fabricated by using focussed ion beam etching, Supercond. Sci. and Technol. 12, (1999). A. Yurgens, D. Winkler, T. Claeson, T. Murayama, and Y. Ando, Interlayer coupling and superconducting critical temperature of Bi 2 Sr 1.5 La 0.5 CuO 6+δ and Bi 2 Sr 2 CaCu 2 O 8+δ : Incommensurate effects of pressure scheduled for Phys. Rev. Lett. 82, (1999). V.M.Krasnov, A.Yurgens, D.Winkler, P.Delsing and T.Claeson, "Evidence for Coexistence of the Superconducting Gap and the Pseudogap in Bi-2212 from Intrinsic Tunneling Spectroscopy, Phys.Rev.Lett. 84, 5860 (2000) V.M.Krasnov, A.E.Kovalev, A.Yurgens, D.Winkler, "Discrimination between the superconducting gap and the pseudo-gap in Bi2212 from intrinsic tunneling spectroscopy in magnetic field" condmat/ (subm. to PRL, title "Magnetic field dependence of the superconducting gap and the pseudogap in Bi2212 studied by intrinsic tunneling spectroscopy") Microelectronics and Nanoscience, Chalmers University of Technology and Göteborg University