1. photons muons neutrons Tuning the static spin-stripe phase and superconductivity in La 2-x Ba x CuO 4 (x = 1/8) by hydrostatic pressure Zurab Guguchia Physik-Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland

2. Collaborators Alexander Maisuradze Hugo Keller Alexander Shengelaya Ekaterina Pomjakushina Kazimierz Conder Rustem Khasanov Tbilisi State University Universität Zürich UZH

3. Thank you! University of Zürich in collaboration with: Tbilisi State University, Georgia Paul Scherrer Institute (PSI), Switzerland Tbilisi State University

4. Superconductivity in La 2-x Ba x CuO 4 J. D. Axe et. al., Phys. Rev. Lett. 62, 2751 (1989). M. Hücker et. al., Phys. Rev. B 83, 104506 (2011). T LTO→LTT ≈ 50 K T HTT→LTO ≈ 200 K A. R. Moodenbaugh et. al., Phys. Rev. B 38, 4596 (1988). 1/8 problem LTO 0.11 < x ≤ 0.13

5. Stripe order in cuprate superconductors K.A. Moler, Nature 468, 643-644 (2010). J. Zaanen, PRB 40, 7391 (1989). La 1.48 Nd 0.4 Sr 0.12 CuO 4 J.M. Tranquada et. al., Nature (London) 375, 561 (1995).

6. La 2-x Ba x CuO 4 La 1.8-x Eu 0.2 Sr x CuO 4 G.M. Luke et. al., Physica C 185-189, 1175-1176 (1991). M. Hücker et. al., Physica C 460-462, 170(2007).

7. Stripe order in La 1.875 Ba 0.125 CuO 4 M. Hücker et. al., Phys. Rev. B 83, 104506 (2011). High-pressure studies on La 1.875 Ba 0.125 CuO 4 have suggested that T c of the system is restored under high pressure. T so vs hydrostatic pressure?

8. Superconducting properties of La 1.875 Ba 0.125 CuO 4 Diamond anvil cell for high-pressure measurements

9. Muon production/decay and parity violation The muon beam is 100 polarised with S µ antiparallel to P µ.

10. Muon-spin rotation (μSR) technique B μ = (2π/γ μ ) ν μ local B-field at the muon site

11. TRIUMF http://neutron.magnet.fsu.edu/muon_relax.html Muon-spin rotation (μSR) technique

13. Courtesy of H. Luetkens homogeneous amplitude → magnetic volume fraction frequency → average local magnetic field damping → magnetic field distribution / magnetic fluctuations time (  s) μSR in magnetic materials inhomogeneous

14. High pressure µSR experiments on La 1.875 Ba 0.125 CuO 4 D. Andreica, Ph.D. thesis, IPP/ETH-Zürich, (2001).

16. High pressure µSR experiments on La 1.875 Ba 0.125 CuO 4

17. Phase diagrams

18. Conclusions  The interplay between magnetism and superconductivity was studied in La 1.875 Ba 0.125 CuO 4 as a function of pressure up to p ≈ 2.25 GPa.  At p = 0 static spin-stripe order is stabilized below T s o = 32 K, occupies nearly the whole sample volume and superconductivity exists in a minor part of the sample only.  The ordered moment size and the magnetic ordering temperature does not change upon application of pressure. However, the volume fraction of spin-stripe order significantly decreases with increasing p.  At the same time by the application of pressure SC phase volume increases proportionally to the non-magnetic volume fraction.  These results indicate that in La 1.875 Ba 0.125 CuO 4 magnetism and superconductivity occur in mutually exclusive spatial regions.

19. Thank you very much for your attention! Thank you very much for your attention!

21. M. Hücker et. al., PRL 104, 057004 (2010).

22. B. Nachumi et. al., PRB 58, 8760 (1998).