University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Thursday, March 9th 2017
Speaker: Johannes Reuther, Freie Universitat Berlin
Subject: Functional renormalization group - a new approach to frustrated quantum magnetism

The experimental and theoretical investigation of quantum spin systems has
become one of the central disciplines of contemporary condensed matter
physics. From an experimental viewpoint, the field has been significantly
fueled by the recent synthesis of novel strongly correlated materials with
exotic magnetic or quantum paramagnetic ground states. From a theoretical
perspective, however, the numerical treatment of realistic models for
quantum magnetism in two and three spatial dimensions still constitutes a
serious challenge. This particularly applies to frustrated systems, which
complicate the employment of established methods. This talk gives an
introduction into the pseudofermion functional renormalization group
(PFFRG) technique which represents a novel approach to determine large
size ground state correlations of a wide class of spin Hamiltonians. Using
a diagrammatic pseudofermion representation for quantum spin models, the
PFFRG performs systematic summations in all two-particle fermionic
interaction channels, capturing the correct balance between classical
magnetic ordering and quantum fluctuations. We first apply the PFFRG
method to spin models on the 2D square and kagome lattices and benchmark
our results against other numerical methods. A particular focus is on the
recently synthesized compound Ca10Cr7O28 which in neutron scattering, muon
spin relaxation and thermodynamic susceptibility measurements shows all
signatures of a quantum spin liquid. Applying the PFFRG technique to a
bilayer kagome model we are able to reproduce the spin fluctuations
measured in neutron scattering and confirm the non-magnetic ground state
of this compound.

Faculty Host: Natalia Perkins

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