[Seminar] Mr. Markus Drescher "Dynamical signatures of emergent quantum phases in the triangular-lattice Heisenberg antiferromagnet"

Speaker

Mr. Markus Drescher / Technical University of Munich

Title

Dynamical signatures of emergent quantum phases in the triangular-lattice Heisenberg antiferromagnet

Abstract

We study an extended spin-1/2 antiferromagnetic Heisenberg model on the triangular lattice, including both nearest- and next-nearest-neighbour interactions, as well as a scalar chiral term. This leads to a rich phase diagram featuring several competing phases: candidate quantum spin-liquid regimes and magnetically ordered states, including coplanar 120° order, stripe order, and non-coplanar tetrahedral order.

We employ large-scale matrix product state simulations optimised for GPUs to obtain high-resolution dynamical responses. The computation of dynamical spin correlations provides access to spectral features across both ordered and liquid domains of the phase diagram. We identify unique signatures of the ordered phases in the form of gapless Goldstone modes at the ordering wave vectors. Our results in the – quantum spin-liquid regime are consistent with a U(1) Dirac spin liquid (DSL).

In the chiral spin-liquid phase, we find signatures of spinons as fractional excitations of the underlying theory, manifested by the onset of a two-spinon continuum that agrees with predictions from the Kalmeyer–Laughlin ansatz for the ground-state wave function, as well as collective modes that can be interpreted as spinon bound states.

As an alternative numerical probe, we compute the time-dependent dimer–dimer correlations of the system. This quantity provides a means to detect overlaps with spin-singlet excitations. We analyze the resulting dynamical dimer structure factor in comparison with predictions from linear spin-wave theory and the field-theoretical description of the DSL. Our findings indicate the presence of low-energy singlet monopole excitations at specific momenta, supporting the characterisation of the paramagnetic phase around  as a Dirac spin liquid.

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Meeting ID: 928 5915 4521
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