FIZIKA A 10 (2001) 4 , 169-176

LETTER TO THE EDITOR

ELECTRONICALLY INDUCED ANOMALY IN LO PHONON DISPERSION OF HIGH-T_c SUPERCONDUCTORS

SLAVEN BARIŠIĆ, IVANA MRKONJIĆ^* and IVAN KUPČIĆ

Department of Physics, University of Zagreb, POB 331, 10002 Zagreb, Croatia
^*E-mail address: ivanam@phy.hr
Dedicated to Professor Kseno Ilakovac on the occasion of his 70^th birthday

Received 28 September 2001; revised manuscript received 21 December 2001
Accepted 7 January 2002        Online 6 April 2002

Strong, electronically-induced anomaly in the spectrum of the longitudinal optical (LO) phonons propagating along the main axes of the CuO₂ plane is tentatively attributed to the oxygen-oxygen charge transfer between two in-plane oxygen atoms. It is argued that this charge transfer can be large and that it is strongly coupled to the LO dimerization of the oxygens. The corresponding negative contribution to the free energy is quartic in the LO phonon amplitude, indicating the instability via the first-order phase transition, with a concomitant domain structure.

PACS numbers: 74.25.Kc, 74.72.Bk, 74.72.Bn
UDC 538.945

Keywords: superconductivity, high-T_c cuprates, La_2-xSr_xCuO₄, YBa₂Cu₃O_6+x, LO phonons, oxygen-oxygen charge susceptibility, first-order phase transitions

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