Berlin 2008 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 29: Superconductivity: Mechanisms, Phase Diagram, Competing Order

TT 29.4: Vortrag

Donnerstag, 28. Februar 2008, 10:15–10:30, H 3010

Variational cluster calculation of the magnetic resonance mode in high-T_c superconductors — •Sascha Brehm¹, Enrico Arrigoni², Michael Potthoff³, Markus Aichhorn¹, and Werner Hanke¹ — ¹Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Germany — ²Institut für Theoretische Physik, Technische Universität Graz, Austria — ³Institut für Theoretische Physik, Universität Hamburg, Germany

We present a new quantum-cluster scheme for calculating two-particle correlation functions within symmetry-broken, e.g. antiferromagnetic (AF) and d-wave superconducting (dSC) phases. This scheme, which we apply to the 2-D Hubbard model, is based on the variational cluster approach (VCA) from which we obtain the normal and anomalous one-particle Green’s functions in the thermodynamic limit from variationally optimized self-energies computed on finite clusters. In the spirit of this embedded cluster calculation, we also obtain the frequency and momentum dependent two-particle vertex from a calculation on an isolated cluster. It is specifically demonstrated that the new approach reproduces the magnetic resonance mode, which has been found in inelastic neutron scattering experiments in various underdoped high-T_c superconductors. Confirming a general belief, this resonance is indeed intimately related to the microscopic mechanism of superconductivity, i.e. it is a (S=1) magnetic exciton lying in the SC gap. In contrast to previous calculations, which are weak-coupling schemes (e.g. RPA), our scheme takes into account the strongly correlated physics of the high-T_c superconductors.