Johannes Reuther

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We develop a numerical technique based on the pseudofermion functional
renormalization group (PFFRG) to calculate hopping and pairing amplitudes
of emergent spinon quasiparticles in spin-1/2 quantum spin liquids. Within
this approach, we first formulate a self-consistent Fock-like equation for
these amplitudes where instead of the bare propagators and couplings we
use the fully renormalized ones from PFFRG. We solve these equations using
different ansätze for the hoppings and pairings which we take from a
projective symmetry group (PSG) classification. From the overall size of
these amplitudes we identify which of the PSGs are preferably realized in
the system. We apply this approach to the antiferromagnetic J1-J2
Heisenberg model on the square lattice and to the antiferromagnetic
nearest neighbor Heisenberg model on the kagome lattice. For the J1-J2
model, we find that in the regime of maximal frustration (J1~J2/2) the
largest amplitudes are obtained for a U(1) pi-flux state with a Dirac cone
spinon dispersion. In the case of the kagome model we identify a gapless
Z2 pi-flux state where the bands show a Dirac-cone-like structure at
finite energies but also feature a small circular Fermi surface at zero
energy. We discuss our findings and benchmark them against variational
Monte Carlo results.

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FU Berlin
Seminar Room 0.03, ETP
Contact: Simon Trebst