Workshop "NMR, µSR, Mössbauer spectroscopies in the study of Fe-based and other unconventional high-Tc superconductors"
Local probing for structural phase transitions in doped lanthanum cuprates
Seung-Ho Baek, IFW Dresden, Germany
In this talk, I will present systematic nuclear magnetic resonance (NMR) studies of the structural aspects in lanthanum-based copper-oxide superconductors (cuprates). It is well known that, for hole concentration x above a certain value in lanthanum cuprates, a sequence of structural phase transitions (SPTs) occurs on lowering temperature: high temperature tetragonal (HTT) → low-temperature orthorhombic (LTO) → low temperature tetragonal (LTT) phase . Despite much debate, however, there has been an unsettled issue regarding the detailed nature of the SPTs. In this talk, I will demonstrate that the SPTs in both La2-xSrxCuO4 (LSCO)  and La2-xBaxCuO4 (LBCO)  are of the displacive type, i.e. each phases are described by different pattern of tilted CuO6 octahedra. On the contrary, Eu-codoping into LSCO alters the nature of the SPTs from displacive to order-disorder type .
 M. Hücker, Physica C 481, 3 (2012)
 S.-H. Baek et al., Phys. Rev. B 85, 184508 (2012)
 S.-H. Baek et al., (unpublished, in preparation)
 S.-H. Baek et al., Phys. Rev. B 87, 174505 (2013)