N.C.S.R. "Demokritos"

Research

Department of Materials Science

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Strong Electron Correlations in transition metal oxides

The study of Strongly Correlated Electrons – within the area of Condensed Matter - is among the most active and exciting areas of research in physics, covering both theoretical and experimental aspects. In recent years, investigations in this context unveiled exotic phenomena such as superconductivity at high temperature, the fractional Hall Effect, and colossal magnetoresistivity (CMR) in manganese perovskites. The remarkable interplay of quantum mechanical oriented basic science and potential technological applications makes strongly correlated electron systems amongst the most interesting research areas in present day science.

In the NMR laboratory of IMS, studies in this field are focused primarily in the area of CMR manganites. Specifically, we have applied 139La and 55Mn NMR spectroscopy in the study of two of the most characteristic manganite families, La1-xCaxMnO3 and La1-xSrxMnO3. The investigations include the detection of phase separation, the nanoscale orbital texturing in the low doping regime, ferromagnetic to paramagnetic phase transitions etc. A characteristic example of the research conducted is shown in the figure at left, where the nature of the Jahn-Teller lattice distortions in the PM phase of optimally dopped La2/3Ca1/3MnO3 is investigated by using 139La NMR in field 9.4 Tesla and in the temperature range 300K – 900K. This is a crucial point in understanding the nature of the CMR effect, which is very promising for applications.












Relevant journal articles

  • Koumoulis, D., Panopoulos, N., Reyes, A., Fardis, M., Pissas, M., Douvalis, A., Bakas, T., Argyriou, D.N., and Papavassiliou, G. (2010) Direct NMR Evidence of Phase Solitons in the Spin Ground State of Overdoped Manganites, Physical Review Letters 104, 077204 1-4.
  • Panopoulos, N., Koumoulis, D., Diamantopoulos, G., Belesi, M., Fardis, M., Pissas, M., and Papavassiliou G. (2010) Spin order and lattice frustration in optimally doped manganites. A high temperature NMR study, Physical Review B (Editor's Suggestion) 82, 235102 1-9.
  • Papavassiliou, G., Pissas, M., Diamantopoulos, G., Belesi, M., Fardis, M., Stamopoulos, D., Kontos, A.G., Hennion, M., Dolinsek, J., Ansermet, J.-Ph., Dimitropoulos, C. (2006) Low temperature charge and orbital textures in La0.875Sr0.125MnO3, Physical Review Letters 96, 097201 1-4.
  • Pattabiraman, M., Venkatesh, R., Rangarajan, G., Murugaraj, P., Dimitropoulos, C., Ansermet, J.-Ph., Papavassiliou, G. (2006) The Nd-Mn exchange interaction in Nd0.7Sr0.3MnO3, Journal of Physics Condensed Matter 18, 11081-11088.
  • Pissas, M., Margiolaki, I., Papavassiliou, G., Stamopoulos, D., Argyriou, D. (2005) Crystal and magnetic structure of the La1-xCaxMnO3 compound (0.11 < x < 0.175), Physical Review B 72, 1-15.
  • Papavassiliou, G., Pissas, M., Belesi, M., Fardis, M., Karayanni, M., Ansermet, J.P., Carlier, D., Dimitropoulos, C., Dolinsek, J. (2004) Spin-polarized oxygen hole states in cation-deficient La1-xCaxMnO3+?, Europhysics Letters 68, 453-459.
  • G. Papavassiliou, G., Pissas, M., Belesi, M., Fardis, M., Dolinsek, J., Dimitropoulos, C., Ansermet, J.P., (2003) Orbital domain state and finite size scaling in ferromagnetic insulating manganites, Physical Review Letters 91, 147205 1- 4.
  • Pattabiraman, M., Murugaraj, P., Rangarajan, G., Dimitropoulos, C., Ansermet, J.-Ph., Papavassiliou, G., Balakrishnan, G., Paul, D.Mc.K., Lees, M.R. (2002) 55Mn NMR investigation of Nd1-xSrxMnO3 (0.1?x?0.5), Physical Review B - Condensed Matter and Materials Physics 66, 2244151-2244157.
  • Belesi, M., Papavassiliou, G., Fardis, M., Pissas, M., Wegrowe, J.E., Dimitropoulos, C. (2001) NMR as a local probe of magnetic anisotropy: The possibility of orbital ordering and orbital liquid states in colossal magnetoresistance manganites, Physical Review B - Condensed Matter and Materials Physics 63, 1804061-1804064.
  • Papavassiliou, G., Belesi, M., Fardis, M., Dimitropoulos, C. (2001) 139La NMR investigation of quasistatic orbital ordering in La1-xCaxMnO3, Physical Review Letters 87, 177204 1-4.
  • Papavassiliou, G., Fardis, M., Belesi, M., Maris, T.G., Kallias, G., Pissas, M., Niarchos, D., Dimitropoulos, C., Dolinsek, J. (2000) 55 Mn NMR Investigation of Electronic Phase Separation in La1-xCaxMnO3 for 0.2 <= x <= 0.5, Physical Review Letters 84, 761-764.
  • Papavassiliou, G., Fardis, M., Belesi, M., Pissas, M., Panagiotopoulos, I., Kallias, G., Niarchos, D., Dimitropoulos, C., Dolinsek, J. (1999) Polarons and phase separation in lanthanum-based manganese perovskites: A 139La and 55Mn NMR study, Physical Review B - Condensed Matter and Materials Physics 59, 6390-6394.
  • Department of Materials Science, N.C.S.R. "Demokritos", 153 10 Aghia Paraskevi, Attiki, phone: +30 210 6503381, fax: +30 210 6519430
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