Fermi arc evolution and doping mechanism in high-temperature superconductors
Event details
| Date | 12.12.2014 |
| Hour | 14:15 |
| Speaker | Prof. Denis K. Sunko, Department of Physics, Faculty of Science, University of Zagreb, Croatia |
| Location | |
| Category | Conferences - Seminars |
We calculate realistic Fermi surface (FS) evolution of La2-x Srx CuO4 (LSCO) with Sr doping within an extensive ab-initio framework including advanced band-unfolding techniques. We show that ordinary Kohn-Sham DFT+U can reproduce the observed metal-insulator transition and arc growth, when not restricted to the paramagnetic solution space. We elucidate both arc protection and the inadequacy of therigid-band picture as consequences of a rapid change in orbital symmetry at the Fermi energy: the material undergoes a dimensional crossover along the Fermi surface, between the nodal (2D) and antinodal (3D) regions. In LSCO, this crossover accounts for FS arcs, the antinodal pseudogap, and insulating behavior in c-axis conductivity, all ubiquitous phenomena in high-Tc cuprates. The same calculation shows that the Sr hole stays localized in the vicinity of the dopand atom, indicating that metallization of the Cu-O plane is due to an orbital transition between Cu and O planar sites, originally proposed by Mazumdar in 1989. We can directly observe effects of the transition in charge transfers among in-plane atoms, which are different than predicted by non-interacting coherent models. This “ionic doping” mechanism has close parallels to modern views on the metallization of interfaces.
The orbital transition is experimentally confirmed by replacing 4% of planar Cu in nearly optimally doped YBa2Cu3O6.92 powder with isotopically pure 67 Zn, lowering Tc to 57 K. The pure nuclear quadrupole resonance (NQR) spectrum of 67 Zn, measured for the first time, shows that each Zn dopand surrounds itself with an AF insulating cluster. We conclude that Zn destroys the SC metal by a Coulombic “domino effect” which reverts the orbital transition locally and pushes a significant number of surrounding sites back towards the parent-compound configuration, as suggested by Mazumdar in 1990. An unexpected asymmetry of the NQR signal is traced to the same splitting of the planar oxygens as the LTT tilt in LSCO, also well known to lower Tc strongly. This elevates the intra-unit-cell oxygen splitting to a universal microscopic antagonist of SC in the cuprates, shedding an interesting light on the SC mechanism.
The orbital transition is experimentally confirmed by replacing 4% of planar Cu in nearly optimally doped YBa2Cu3O6.92 powder with isotopically pure 67 Zn, lowering Tc to 57 K. The pure nuclear quadrupole resonance (NQR) spectrum of 67 Zn, measured for the first time, shows that each Zn dopand surrounds itself with an AF insulating cluster. We conclude that Zn destroys the SC metal by a Coulombic “domino effect” which reverts the orbital transition locally and pushes a significant number of surrounding sites back towards the parent-compound configuration, as suggested by Mazumdar in 1990. An unexpected asymmetry of the NQR signal is traced to the same splitting of the planar oxygens as the LTT tilt in LSCO, also well known to lower Tc strongly. This elevates the intra-unit-cell oxygen splitting to a universal microscopic antagonist of SC in the cuprates, shedding an interesting light on the SC mechanism.
Practical information
- Informed public
- Free
Organizer
- ICMP (Arnaud Magrez and Raphaël Butté)