Direct evidence of non-Zhang-Rice Cu3+ centers in La2Li0.5Cu0.5O4

S. A. Moskvin (1) , A. A. Gippius (2) , A. V. Tkachev (2) , A. V. Mahajan (3) , T. Chakrabarty (4) , Igor A. Presniakov (5) , Alexey Sobolev (5) , Gérard Demazeau (6)

1 Department of Theoretical Physics
2 Low Temperature Physics and Superconductivity Department
3 Department of Physics
4 IIT Bombay - Indian Institute of Technology Bombay
5 MSU - Lomonosov Moscow State University
6 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux

A well-isolated Zhang-Rice (ZR) singlet as a ground state of the Cu3+ center in hole-doped cuprates is a leading paradigm in modern theories of high-temperature superconductivity. However, a dramatic temperature evolution of the 6,7Li NMR signal in La2Li0.5Cu0.5O4, a system with a regular lattice of well-isolated Cu3+ centers, reveals significant magnetic fluctuations and suggests a quasidegeneracy to be a generic property of their ground state at variance with the simple ZR model. We argue for a competition of the ZR state with nearby states formed by a "doped" hole occupying purely oxygen nonbonding a2g(π) and eu(π) orbitals rather than a conventional b1g(dx2−y2) Cu 3d-O 2p hybrid. The temperature variation of the 6,7Li NMR line shape and spin-lattice relaxation rate point to a gradual slowing down of some magnetic order parameter's fluctuations without distinct signatures of a phase transition down to T=2 K. This behavior agrees with a stripelike ferrodistortive fluctuating Ammm order in a two-dimensional structure of the (CuLi)O2 planes accompanied by unconventional oxygen orbital antiferromagnetic fluctuations.

Domaines: Supraconductivité [cond-mat.supr-con]

S. A. Moskvin, A. A. Gippius, A. V. Tkachev, A. V. Mahajan, T. Chakrabarty, et al.. Direct evidence of non-Zhang-Rice Cu3+ centers in La2Li0.5Cu0.5O4. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2012, 86 (24), pp.241107(R). ⟨10.1103/PhysRevB.86.241107⟩. ⟨hal-00772877⟩