External vs. ``internal'' pressure effect on the anti-ferromagnetic superexchange energy, J, in LnBa2Cu3O6 (Ln=La,Nd,...,Lu)
Abstract
What causes the difference between the effect of ``internal'' pressure, as caused by ionic substitution, and external pressure on Tc^max in the cuprates [1]? Is it the density of states, the pairing boson energy scale (φB), condensation energy (which governs fluctuations), or ...? Many models of high temperature superconductivity put the energy scale of φB as the anti-ferromagnetic super-exchange energy, J, between adjacent Cu(2) ions in the CuO2 plane. We therefore investigated Raman B1g two-magnon scattering in high quality LnBa2Cu3O6 (Ln123) single crystals, Ln(=La, Nd, Sm, Eu, Gd, Dy, Yb, Lu), at ambient pressure to determine the effect of internal pressure on J. Comparing with measurements of J under external pressure reveals that internal and external pressure have quantitatively the same effect on J. However, and most surprisingly, we find an anticorrelation between J and Tc^max when ion size or internal pressure is the implicit variable. Given the opposite effects of internal and external pressure on Tc^max, this result suggests that some energy scale other than short range anti-ferromagnetic interactions has a more dominant effect on Tc^max.[4pt] [1] e.g. M. Marezio, Physica C, 341-348, 375 (2000)
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- February 2012
- Bibcode:
- 2012APS..MARV21007M