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Spins can be represented in terms of complex fermionic operators. This allows for a direct application of many-body techniques like the functional RG approach to frustrated quantum magnets. However, as the representation above introduces unphysical Hilbert space sectors, the applicability of this approach at finite temperatures is questionable. Here, I review an alternative Majorana fermion representation of spins which does not introduce any unphysical states. We develop a general functional RG formalism for Majoranas and apply it to the Pseudo-Majorana representation of Heisenberg models on small spin clusters as well as frustrated square and triangular lattices. We compute the finite temperature behavior of spin correlations and thermodynamic quantities and compare to exact diagonalization and the high-temperature series expansion.

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Bjoern Sbierski, UC Berkeley
Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 )
Contact: Simon Trebst