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Proposing Institution

Uni Bielefeld, Dept. of Physics
Project Manager

Prof. Dr. Jürgen Schnack
Universitätsstr. 25
33615 Bielefeld
In frustrated quantum spin lattices the competition of quantumand frustration effects promises rich physics. A reliable descriptionof such systems often constitutes a challenge for theory.A famous example is the kagome lattice antiferromagnet. Inspite of extensive studies over decades its ground stateproperties are not fully understood yet. Classically it has infinite continuous degeneracies. In the quantum case(s=1/2), the system is likely to be a spin liquid with a gapfor magnetic excitations and a huge number of singlet statesbelow the first triplet state. The numerical state of the art includes Density Matrix Renormalization Group (DMRG) studies,calculations with the Coupled Cluster Method (CCM) as well as Lanczos diagonalizations of lattice sizes up toN=42. All methods yield only the ground state and very few low-lying eigenstates. N=42 requires already a substantial numerical effort, and onlyvery advanced codes such as spinpack scale well enough toyield results in reasonable time. Nevertheless, all such calculations aim at the respective groundstates as a function of external field but are not able topredict the behavior at non-zero temperature. Since the kagomelattice is supposed to host very many low-lying states a quantumstatistical treatment is highly desirable. Otherwiseexperimental measurements might be confused by low-energyfluctuations of the density of states which easily introduceadditional low-temperature scales into the problem.Our aim is to evaluate the thermodynamic properties of thekagome lattice antiferromagnet with up to N=42 sites and single spinquantum number s=1/2 in the Heisenberg model using the Finite Temperature Lanczos Method (FTLM). In addition weare going to study the influence of both anisotropy as well asnext-nearest neighbor interactions in order to tune quantumfluctuations and frustration.

Impressum, Conny Wendler