1 / 24

A. Perucchi

Optical properties of (SrMnO 3 ) n /(LaMnO 3 ) 2n superlattices: an insulator-to-metal transition observed in the absence of disorder. A. Perucchi. SISSI, the IR beamline of the ELETTRA Storage Ring. Synchrotron Infrared Source for Spectroscopy and Imaging.

jeroen
Download Presentation

A. Perucchi

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. Optical properties of (SrMnO3)n/(LaMnO3)2n superlattices: an insulator-to-metal transition observed in the absence of disorder A. Perucchi

  2. SISSI, the IR beamline of the ELETTRA Storage Ring Synchrotron Infrared Source for Spectroscopy and Imaging

  3. SISSI - Solid State Physics activities Electrodynamics at High Pressures THz Superconducting Gaps (MgB2, V3Si, Ba(Fe,Co)2As2) Insulator to Metal Transitions (VO2, V2O3, V3O5, NiS2, etc.) Charge-Density-Waves (CeTe3, LaTe2) Superconductivity (BaFe2As2)

  4. Optical Properties of (LaMnO3)2n/(SrMnO3)n • L. Baldassarre • S. Lupi • P. Calvani • A. Nucara • L. Maritato • P. Orgiani • D.G. Schlom • C. Adamo

  5. Outline • Basic concepts on Manganites Double-Exchange, Jahn-Teller polarons, optical conductivity • (LMO)2n/(SMO)n SuperLattices (SL) • Optical properties of n=1 compound Understanding the role of disorder in LSMO alloys • Optical properties of large period SLs Appearance of novel “bulk” electronic states

  6. Colossal Magnetoresistance (CMR) manganites O Mn R,A R1-xAxMnO3 P. Schiffer, Phys. Rev. Lett. 75, 3336 (1995)

  7. Electronic Structure and Phase Diagram Mn3+ Jahn-Teller LaMnO3 (Mn3+) SrMnO3 (Mn4+) Y. Tokura, Rep. Prog. Phys 69, 797 (2006).

  8. CMR Models Double-Exchange model C Zener, Phys Rev 82, 403 (1951); PW Anderson and H Hasegawa, Phys Rev 100, 675 (1955) Phys Rev Lett 74, 5144 (1995) • DE explains the PI-FM transition, but fails in predicting • the right Curie temperature (TcDE~103 K vs TcExp~102 K) • the resistivity values (above Tc: DE~10-3.cm vs Exp~10-2.cm ) Double-Exchange + Jahn-Teller polarons

  9. CMR and Phase Separation Zhang et al., Science 298, 805 (2002) Phase Separation as an essential CMR ingredient Role of disorder as a source of nucleation centers see Poster from A. Pineiro on Tuesday Sarma et al., Phys Rev 93, 097202 (2004) Dagotto, New J Phys 7, 67 (2005)

  10. Optical conductivity NORMAL METAL “BAD” METAL (Strongly correlated metals, Polaronic metals, etc.) MIR bands indicate that a localization mechanism (mass enhancement) is at play MIR band

  11. LSMO optical properties La0.825Sr0.175MnO3 cleaved single crystal Takenaka et al., Phys. Rev B 60, 13011 (1999) 40 nm La2/3Sr1/3MnO3 on STO Haghiri-Gosnet et al., Phys. Rev B 78, 115118 (2008)

  12. Interfaces and Superlattices • Designing materials with novel electronic states at the interface between two different oxides as in (LAO/STO), (LTO/LAO), etc. • Addressing CMR and the physics of DE in the absence of substitutional disorder. • The (LMO)2n/(SMO)n SL series mimics the doping content of La2/3Sr1/3MnO3 alloys Smadici et al., 2007

  13. Tuning the MIT in (LaMnO3)2n/(SrMnO3)n A peak in the resistivity is always found at the Curie Temperature!!! Double-Exchange physics Adamo PRB 2009

  14. Optical reflectivity of 20 nm (LMO)2n/(SMO)n on STO IR I0 R=IR/I0

  15. Optical properties of the multilayer vacuum (n=1, k=0) sample (n, k) STO substrate (nSTO, kSTO) vacuum (n=1, k=0)

  16. The Lorentz-Drude model

  17. Data fitting

  18. Hartinger et al. (2004) (LMO)2/(SMO)1 parameters • 1 Drude term • 1 MIR band • 2 T-independent HOs with if

  19. Comparing n=1 SL with alloys AP et al., Nano Letters 10, 4819 (2010) dc conductivity ~ 104.cm Tcurie ~ 350 K m*/mb ~ 7 MIR band softening edge in1 at ~ 1000 cm-1 The electronic properties of (LMO)2/(SMO)1 SL are fully equivalent to those of the corresponding La2/3Sr1/3MnO3 Adamo PRB 2009 • The n=1 SL has homogeneous electronic density • Disorder probably plays a very limited role in the corresponding LSMO alloy

  20. Reflectivity of n=1,3,5 and 8 compounds AP et al., Nano Letters 10, 4819 (2010)

  21. Optical conductivity AP et al., Nano Letters 10, 4819 (2010)

  22. (LMO)2n/(SMO)n parameters The overall free carrier spectral weight diminishes with n The agreement between resistivity measurements and dc conductivity worsens with increasing n: Role of perpendicular paths in the resistivity Dong et al. (2008)

  23. Large period SLs, end-members, and alloys Adamo PRB 2009 SrMnO3 In site Mn4+ transitions: t2g-eg La1-xSrxMnO3 Mn3+ to Mn4+ transitions: 1/2 Jahn-Teller LaMnO3 In site Mn3+ transitions: eg-eg (Jahn-Teller) The presence of a mid-IR band signals mixed Mn valencies. Its sizable spectral weight can not be attributed to interfacial Mn3+-Mn4+ transitions alone AP et al., Nano Letters 10, 4819 (2010)

  24. Conclusions Homogeneous electronic state for short period SLs Similarities between n=1 SL and corresponding alloy (reduced role for disorder) Optical characterization of the Metal to Insulator transition with increasing n Novel “bulk” (not limited to interface) electronic states in large period SLs

More Related