Keimer's department > Groups > Optical spectroscopy > Methods

Spectral ellipsometry

Spectral ellipsometry allows measurements of the real and imaginary parts of the dielectric function of solids with significantly higher accuracy and reproducibility than regular reflection spectroscopy, because reference measurements and Kramers-Kronig transformations are not required (Fig. 1). Our group has used synchrotron radiation to extend the frequency range of this method into the far-infrared regime. A Fourier-transform infrared spectrometer and ellipsometer was implemented and commissioned at the ANKA synchrotron at the Forschungszentrum Karlsruhe, building on experience previously acquired using a prototype instrument at the Brookhaven National Laboratory (USA). The apparatus now operates routinely and has been instrumental for many of our projects. The photon energy range from ≈ 1meV to ≈ 5.6 eV is now continuously covered with ellipsometers available in our group.

Highlights of recent research with spectral ellipsometry include the determination of collective modes and spectral weight shifts in cuprate superconductors [1-4]; the discovery of magneto-polaron excitations in cobaltates [5]; a quantitative analysis of the interplay between the magnetic structure high-energy charge excitations in a Mott-Hubbard insulator [6]; the discovery of the enhancement of the “pseudogap” in a high-temperature superconductor by magnetic impurities [7]; phonon anomalies associated with charge ordering in iron oxides [8,9]; and the determination of the optical properties of oxide superlattices [10].

Current instrument development work is aimed at the use of coherent far-infrared radiation at ANKA, and at the development of infrared reflectance and ellipsometry methods in the presence of high magnetic fields. A high-field infrared reflectivity setup has just become operational in our laboratory.

References

  1. A. V. Boris, N. N. Kovaleva, O. V. Dolgov, T. Holden, C. T. Lin, B. Keimer, C. Bernhard. Science 304 (2004), 708
  2. A. V. Boris, D. Munzar, N. N. Kovaleva, B. Liang, C. T. Lin, A. Dubroka, A. V. Pimenov, T. Holden, B. Keimer, Y.-L. Mathis, C. Bernhard. Phys. Rev. Lett. 89 (2002), 277001
  3. D. Munzar, T. Holden, C. Bernhard. Phys. Rev. B 67 (2003), 020501(R)
  4. N. N. Kovaleva, A. V. Boris, T. Holden, C. Ulrich, B. Liang, C. T. Lin, B. Keimer, C. Bernhard, J. L. Tallon, D. Munzar, A. M. Stoneham. Phys. Rev. B 69 (2004), 054511
  5. C. Bernhard, A. V. Boris, N. N. Kovaleva, G. Khaliullin, A. Pimenov, L. Yu, D. P. Chen, C. T. Lin, B. Keimer. Phys. Rev. Lett. 93 (2004), 167003
  6. N. N. Kovaleva, A. V. Boris, C. Bernhard, A. Kulakov, A. Pimenov, A. M. Balbashov, G. Khaliullin, B. Keimer. Phys. Rev. Lett. 93 (2004), 147204
  7. A. V. Pimenov, A. V. Boris, Li Yu, V. Hinkov, Th. Wolf, J. L. Tallon, B. Keimer, C. Bernhard. Phys. Rev. Lett. 94 (2005), 227003
  8. A. Lebon, P. Adler, C. Bernhard, A. Boris, A. Pimenov, A. Maljuk, C. T. Lin, C. Ulrich, B. Keimer. Phys. Rev. Lett. 92 (2004), 037202
  9. P. Adler, A. Lebon, V. Damljanovic, C. Ulrich, C. Bernhard, A. V. Boris, A. Maljuk, C. T. Lin, B. Keimer. Phys. Rev. B 73 (2006), 094451
  10. T. Holden , H-U. Habermeier, G. Cristiani, A. Golnik, A. Boris, A. Pimenov, J. Humlícek, O. Lebedev, G. Van Tendeloo, B. Keimer, C. Bernhard. Phys. Rev. B 69 (2004), 064505
Figure
Fig. 1. Schematic diagram of a resonant x-ray diffraction experiment with polarization analysis.

Photos
Photo 1. Ellipsometry setup for low and high temperature applications in VIS / UV light range.

Photo 2. Standard ellipsometry configuration: light outlet, sample holder with reference wafer, VIS- and UV detector.
Pictures from the ANKA synchrotron.