1 / 20

CRITICAL OPALESCENCE IN SUPEROXYGENATED La 2 CuO 4+y

6th INTERNATIONAL CONFERENCE OF THE STRIPES SERIES STRIPES 08. Quantum Phenomena in Complex Matter. CRITICAL OPALESCENCE IN SUPEROXYGENATED La 2 CuO 4+y. Erice, July 26-August 1, 2008. Michela Fratini Dipartimento di Fisica Università degli studi di Roma “La Sapienza”. OUTLINE.

keaira
Download Presentation

CRITICAL OPALESCENCE IN SUPEROXYGENATED La 2 CuO 4+y

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 6th INTERNATIONAL CONFERENCE OF THE STRIPES SERIESSTRIPES 08 Quantum Phenomena in Complex Matter CRITICAL OPALESCENCEIN SUPEROXYGENATED La2CuO4+y Erice, July 26-August 1, 2008 Michela Fratini Dipartimento di Fisica Università degli studi di Roma “La Sapienza”

  2. OUTLINE • We have investigated the ordering of interstitial oxygen (iO) in superoxigenated La2CuO4 • Method:synchrotron x-ray micro-diffraction as a probe to detect microscopic phase separation giving self-organized electronic textures • Evidence for : • 1. The coexistence of ordered and disordered domains • 2. The order to disorder phase transition at 330K • 3. The statistical distribution of the size of ordered domains shows a power law distribution indicating critical opalescence near a critical point • These results open the way to control and manipulate the phase separation for new functional devices

  3. HIGH Tc SUPERCONDUCTORS:SHOW A COMMON STRUCTURE Cuprates ROFeAs MgB2 • The nanoscale architecture: The lamellar Structure

  4. PHASE DIAGRAM OF CUPRATES: 1 2 3 Critical point for structural phase transition from LTT to LTO

  5. Interstitial oxygen STRUCTURE OF La2CuO4+y • The cuprate perovskite La2CuO4 is formed by bcc CuO2 monolayers intercalated by fcc rocksalt LaO bilayers with a periodicity of 1.3 nanometers. • The oxygen dopants in the LaO planes are mobile above 200 K • Space group=Fmmm

  6. PHASE COEXISTING OF SUPERCONDUCTIVITY AND MAGNETIC ORDER (Savici et al. Phys. Lett. 95 157001 (2005)) The system shows a coexistence between superconducting and magnetic domains below 41K • High Tc superconductor Tc=41K Lee et al. Phys. Rev. B 60 3643 (1999)

  7. OXYGEN ORDERED PHASE The existence of an ordered phase of interstitial oxygen has been detected at room temperature q2=0.09 a* +0.25 b*+0.50 c* X-ray diffraction pattern with: higher harmonics and narrow lines indicates Domains of 3D commensurate ordered oxygen dopants

  8. CONTINUOUS FIRST ORDER PHASE TRANSITION Interstitial oxygen ordering T=300-350K Hysteresis cycle of Q2 phase using a photon flux of 1.5*1014 photons/cm2/s in the range from 300K to 350K. b) Hysteresis cycle of Q2 phase using a photon flux of 10*1014photons/cm2/s The result of the x.ray illumination is a reduction of the Hysteresis loop

  9. PHOTO-INDUCED ORDERING PROCESS AT DIFFERENT TEMPERATURES. • Under x-ray illumination the size of the ordered domains increases in the temperature range between 250 K and 300 K. • The photo-induced ordering process shows a threshold characteristic of cooperative phenomena.

  10. INHOMOGENEOUS phase with the COEXISTENCE of domains of ordered and disordered interstitial oxygen ions • Below 350K • bubbles of 3D ordered iO’s in a disordered medium What is the spatial distribution of the ordered domains?

  11. METHOD Space-resolved X-ray diffraction based upon a beam size of ~ 1 µm specialises in the delivery of the microfocused X-ray beam • Photon sources in the range 12/13 Kev • The focussed beam is defined by a pinhole of 5 micron diameter

  12. OXYGEN ORDERING PHASE We have done a mesh of the whole sample, with a beam size of about 1 micron, after locating q2, present in this oxide cuprate at room temperature around the bragg peak (0,0,6). q2= (0.09; 0; 0.50) The large orthorhombicity makes easy identify the twinning of the crystal domains and to index the superstructure peaks. q2 (0;0.25; 0.50) 006 peak in the diffraction pattern

  13. MICROMAPPING SUPEROXYGENATED SAMPLE Mean Intensity =1.7233 Tc=41 K • The colours dots show the intensity of the q2 superstructure due to interstitial oxygen ordering • The figure shows the intensity on 5000 diffraction superstructure spots due to charge ordered domains

  14. STATISTICAL DISTRIBUTION OF THE Q2 PHASE in SUPEROXYGENATED SAMPLE Mean Intensity =1.7233 γ= 1.7 ξ= 2.6

  15. MICROMAPPING SAMPLE withINTERMEDIATE OXYGEN CONTENT Mean Intensity =1.5752 Tc= 32 K and 41 K Y (1 pixel=4.9 micron) X (1 pixel=20.3 micron)

  16. STATISTICAL DISTRIBUTION OF THE Q2 PHASE in SAMPLEwithINTERMEDIATE OXYGEN CONTENT. Mean Intensity = 1.5752 RANK γ= 1.7 ξ= 1.5

  17. MICROMAPPING IN A SAMPLE withLOW OXYGEN CONTENT Mean Intensity =1.0954 Tc=12K and 36K Y (1 pixel=4.9 micron) X (1 pixel=20.3 micron)

  18. STATISTICAL DISTRIBUTION OF THE Q2 PHASEIN SAMPLE with LOW OXYGEN CONCENTRATION DOPING. Mean Intensity =1.0954 RANK γ= 1.7 ξ= 1.1

  19. CONCLUSIONS • The proximity to a quantum critical point determines the critical opalescence with a power law distribution of the size of oxygen ordered domains • This is supported by the scale invariance • This result is assigned to the criticality of the system being close to the tricritical point identified in the phase diagram (Tc, doping and chemical pressure) • This conclusion is supported by the photoinduced phase transition near the critical point.

  20. Alessandra Vittorini-Orgeas Nicola Poccia Ginestra Bianconi Luisa Barba (Elettra) Manfred Burghammer (ESRF) Gaetano Campi Finally I would like to thank my collaborators

More Related