Search for conducting stripes in lightly hole doped YBCO

Transcription

1 Search for conducting stripes in lightly hole doped YBCO András Jánossy 1, Titusz Fehér 1,2 Kálmán Nagy 1 Andreas Erb 3 László Mihály 4 1 Budapest University of Technology and Economics, Institute of Physics and Solids in Magnetic Fields Research Group of the Hungarian Academy of Sciences, P.O.Box 91, H-1521 Budapest, Hungary 2 Institute of Physics of Complex Matter, EPFL, CH-1015 Lausanne, Switzerland 3 Walther Meissner Institut, Bayerische Akademie der Wissenschaften, D Garching, Germany 4 Stony Brook University New York USA

2 ESR spectrometer oscillator B detector sample υ L -1/2 hν L =gµ B B +1/2

3 ESR spectrometer oscillator B detector sample υ L linearly polarized ellipticaly polarized grid -1/2 hν L =gµ B B +1/2

4 ESR spectrometer MICROWCVAVE DETECTOR SOURCE grid LOCK-IN AMPLIFIER 9, 35, 75, 150, 225 GHz M s / / B M s / / B M s B u n d o p e d M A G N E T I C F I E L D [ m T ] MAGNET 0-9 T C a d o p e d M s B M A G N E T I C F I E L D [ m T ] SAMPLE

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8 High frequency ESR: - high resolution -magnetic field dependence

9 - high resolution ESR in C 59 N doped solid C 60 C 59 N:C 60 ESR 225 GHz, 276 K f13s (blue) and f17s(black) C 59 N conc. 100ppm 2000ppm molecule with hindered rotation freely rotating C 59 N MAGNETIC FIELD [T]

10 Outline cuprate phase diagram Gd 3+ ESR probe antiferromagnetic domains search for conducting stripes

11 Structure of Ca x Y 1-x Ba 2 Cu 3 O 6 hole doping hole doping Ca

12 YBCO undoped CuO 2 plane e -

13 Phase diagram of cuprates TEMPERATURE (K) 0% antiferromagnet THIS WORK insulator strange metal superconductor metal 5% 16% HOLE CONCENTRATION / CuO 2 plane

14 Charge- spin phase separation TEMPERATURE commensurate normal collateral, incommensurate Diagonal, incommensurate STRIPES Predictions: J. Zaanen, O. Gunnarsson, 1989 H.J. Schultz 1990 K. Machida 1989 First experiment: J. Tranquada, 1995 hole concentration Hubbard model. Mean field. K. Machida, M. Ichioka J. Phys. Soc. Jpn

15 charge poor charge rich charge poor charge rich collinear incommensurate spin and charge modulation π domain wall

16 diagonal incommensurate modulation

17 Neutron diffraction wavelength π/l diagonal collinear ESR

18 Search for anisotropic conductivity of stripes - D.C. conductivity (Y. Ando et al) - IR response (Lucarelli et al, Dumm et al) - Raman scattering (R. Hackl et al)

19 anisotropic conductivity E(t)

20 anisotropic conductivity E(t)

21 D.C. resistance in magnetic field H I Magneto resistance H // I magnetostriction?

22 Infrared conductivity LaSCO infrared conductivity twinned crystal conductivity cm -1?stripes Lucarrelli et al PRL (2003)

23 Raman scattering X = 0.02 X = 0.10 The response can only be observed if both incoming and outgoing photons have a finite projection on the direction of the stripes or perpendicular to them. R. Hackl, L. Tassini et al

24 Raman scattering, Ca x Y 1-x Ba 2 Cu 3 O 6 2 and 3% Ca Response in B 2g : diagonal stripes? R. Hackl, L. Tassini et al

25 Interactions: Zeeman + exchange + "crystal field" Gd 3+ ESR measures: spin susceptibility (ESR Knight shift) hole doping and lattice distortion or charge redistribution ( J=7/2 fine structure) in CuO 2 planes ESR probe: 1% Gd 3+ substituted for Y Gd

26 Gd 3+ Zeeman splitting ESR Knight shift spin susceptibility fine structure charge redistribution hν L free ion Gd 3+ - CuO 2 exchange crystal field S = 7/2 + second order exchange

27 Phase diagram of cuprates TEMPERATURE (K) 0% undoped antiferromagnet insulator strange metal superconductor metal 5% 16% HOLE CONCENTRATION / CuO 2 plane

28 ESR in Gd: YBa 2 Cu 3 O 6 B//c, 225 GHz experiment St 6 7 fit MAGNETIC FIELD (T)

29 - Antiferromagnetic domains - Orientation of spins hole doping 3+ Gd tetragonal structure

30 90 0 wall

31 domain wall magneto-striction can stabilize collateral spin structure

32 B B: magnetic field M s B χ large 90 0 wall M s // B χ small

33 undoped B antiferromagnetic domains in YBaCu 3 O 6 Gd 3+ ESR M s M s B MAGNETIC FIELD [T]

34 undoped B: magnetic field

35 undoped M s B M s M A G N E T I C F I E L D ( T )

36 Phase diagram of cuprates TEMPERATURE (K) 0% antiferromagnet THIS WORK insulator strange metal superconductor metal 5% 16% HOLE CONCENTRATION / CuO 2 plane

37 Reorientation of M s in Ca:YBCO 0.8% Ca [100] B [100] B [010] [010] [100] M s [010] a) 205 K 100 K B//[100] AFI(0) // B B b) 160 K 100 K B//[110] AFI(0) [100] M s 70 K 40 K 6 K AFI(π/4) [100] [110] [010] 70 K 40 K 6 K AFI(π/4) [100] [110] [010] [010] // B B MAGNETIC FIELD [T] MAGNETIC FIELD [T]

38 undoped AFI(0) AFI(π/4) all T Low T

39 magnetic reorientation in Ca doped YBa 2 Cu 3 O % Ca AFI(0) AFI(π/4) High T Low T

40 magnetic reorientation in Ca doped YBa 2 Cu 3 O 6 2 % Ca AFI(0) AFI(π/4)?? High T Low T

41 Phase diagram of cuprates TEMPERATURE (K) 0% antiferromagnet THIS WORK insulator strange metal superconductor metal 5% 16% HOLE CONCENTRATION / CuO 2 plane

42 TEMPERATURE [K] COLLATERAL FLUCTUATING? DIAGONAL Ca doped YBCO 6.0 HOLE CONCENTRATION %

43 Charge- spin phase separation TEMPERATURE commensurate normal collateral, incommensurate Diagonal, incommensurate HOLE CONCENTRATION Hubbard model. Mean field. K. Machida, M. Ichioka J. Phys. Soc. Jpn

44 Model: Low T: charge modulation network with weakly pinned AF magnetization High T: no charge modulation, spin magnetization fluctuating or pinned to lattice by defects or magneto-striction TEMPERATURE [K] COLLATERAL DIAGONAL FLUCTUATING? HOLE CONCENTRATION %

45 Localisation of holes Are holes localised around Ca 2+ ions at low T?

46 Ca doped YBa 2 Cu 3 O 6 phase diagram TEMPERATURE [K] antiferro This work strange metal hole localization HOLE CONCENTRATION supracond Ch. Niedermayer, C. Bernhard, T. Blasius, A. Golnik, A. Moodenbaugh, and J. I. Budnick Phys. Rev. Lett.80 (1998) 3843

47 High T: delocalized holes Gd 3+ distant Gd 3+ Ca 2+ 1 st neighbour

48 low T if holes were localized near Ca: Gd 3+ distant Gd 3+ Ca 2+ 1 st neighbour crystal field changes!

49 low T holes ordered in stripes: Gd 3+ Gd 3+ Ca 2+ 1 st neighbour no crystal field change!

50 ESR spectrum of Ca first neighbors and distant sites x1 distant I A 5 A * 1 I 3 M I (I 6 ) I I B x20 Ca 1 Ca 2 Ca 6 (Ca 7 ) 1 st neighbour MAGNETIC FIELD [T]

51 (T) 0.8% Ca, 17 K x10 Ca1 1 st neighbour distant sites x1 Reference 0% Ca, 20K Magnetic field (T)

52 Holes do not localize at the Ca 2+ sites Main line ZFS [mt] (T) lattice expansion Ca satellite - main line ZFS [mt] TEMPERATURE [K] 5/2> -3/2> and 3/2> 5/2> 75 GHz, B//c

53 Change of domain structure with magnetic field

54 Magnetic fields turn crystal into single domain zero magnetic field

55 Magnetic fields turn crystal into single domain M s B χ large M s // B χ small intermediate magnetic field

56 Magnetic fields turn crystal into single domain M s B χ large large magnetic field: magnetically single domain

57 a) T (9 GHz) b) T (75 GHz) c) 5.4 T (150 GHz) MAGNETIC FIELD (T)

58 Magnetic fields turn crystal into single domain Experiment: undoped 1.00 ESR INTENSITY M s B M s //B MAGNETIC FIELD ALONG a t (T)

59 2% Ca YBCO in 8 T field: magnetically single domain for all orientations

60 anisotropic conductivity E(t)

61 anisotropic conductivity E(t)

62 90 o domain wall 180 o wall stripe

63 180 o wall stripe E(ω) 90 o domain wall

64 B 180 o wall stripe 90 o domain wall

65 B 180 o wall stripe E(ω) 90 o domain wall

66 B 180 o wall stripe 90 o domain wall

67 IR transmission in magnetic field DETECTOR SYNCHROTRON FT-IR ESR spectrometer Brookhaven NSLS IR12 SPECTROMETER MAGNET 0-12 T SAMPLE rotate polarisation A. Janossy et al Phys.Rev.B 2007

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69 IR transmission in magnetic field

70 experiment: both 2 and 4-fold anisotropies, 4 fold stronger

71 Along a * Along b * YBa 2 Cu 3 O 6.85 YBa 2 Cu 3 O 6.6 untwinned T=10K Two-dimensional geometry of spin excitations in the high-transition-temperature superconductor YBa2Cu3O6+x V. Hinkov, S. Pailhès, P. Bourges, Y. Sidis, A. Ivanov, A. Kulakov, C. T. Lin, D. P. Chen, C. Bernhard and B. Keimer Nature 430, (5 August 2004)

72 Conclusions: In lightly hole doped Ca:YBCO at low temperatures: -Holes are not localized around Ca -AF magnetization is diagonal => stripes diagonal -AF domain structure is static AF magnetization is weakly pinned to stripes No anisotropy in σ(ω) below ~70 cm -1 => No sign of conducting stripes Charged "stripes" are strongly pinned to lattice