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arXiv · 1906.11553

Finite-temperature topological invariant for interacting systems

Razmik Unanyan·Maximilian Kiefer-Emmanouilidis·Michael Fleischhauer
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Abstract

We generalize the Ensemble Geometric Phase (EGP), recently introduced to classify the topology of density matrices, to finite-temperature states of interacting systems in one spatial dimension (1D). This includes cases where the gapped ground state has a fractional filling and is degenerate. At zero temperature the corresponding topological invariant agrees with the well-known invariant of Niu, Thouless and Wu. We show that its value at finite temperatures is identical to that of the ground state below some critical temperature $T_c$ larger than the many-body gap. We illustrate our result with numerical simulations of the 1D extended super-lattice Bose-Hubbard model at quarter filling. Here a cyclic change of parameters in the ground state leads to a topological charge pump with fractional winding $\nu=1/2$. The particle transport is no longer quantized when the temperature becomes comparable to the many-body gap, yet the winding of the generalized EGP is.

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Razmik Unanyan, Maximilian Kiefer-Emmanouilidis, Michael Fleischhauer. 2019-06-27. Finite-temperature topological invariant for interacting systems. https://doi.org/10.1103/physrevlett.125.215701

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