5 research outputs found
Magnetic excitations, phase diagram and order-by-disorder in the extended triangular-lattice Hubbard model
The dynamical structure factor is an important observable of quantum magnets
but due to numerical and theoretical limitations, it remains a challenge to
make predictions for Hubbard-like models beyond one dimension. In this work, we
study the magnetic excitations of the triangular lattice Hubbard model
including next-nearest neighbor hopping. Starting from the 120 and
stripe magnetic orders we compute the magnon spectra within a self-consistent
random phase approximation. In the stripe phase, we generically find accidental
zero modes related to a classical degeneracy known from the corresponding
- Heisenberg model. We extend the order-by-disorder mechanism to
Hubbard systems and show how quantum fluctuations stabilize the stripe order.
In addition, the frustration-induced condensation of magnon modes allows us to
map out the entire phase diagram which is in remarkable agreement with recent
numerical works. We discuss connections to experiments on triangular lattice
compounds and the relation of our results to the proposed chiral spin liquid
phase
Spin-Peierls instability of the U(1) Dirac spin liquid
Quantum spin liquids are tantalizing phases of frustrated quantum magnets. A
complicating factor in their realization and observation in materials is the
ubiquitous presence of other degrees of freedom, in particular lattice
distortion modes (phonons). These provide additional routes for relieving
magnetic frustration, thereby possibly destabilizing spin-liquid ground states.
In this work, we focus on triangular-lattice Heisenberg antiferromagnets, where
recent numerical evidence suggests the presence of an extended U(1) Dirac spin
liquid phase which is described by compact quantum electrodynamics in 2+1
dimensions (QED), featuring gapless spinons and monopoles as gauge
excitations. Its low energy theory is believed to flow to a strongly-coupled
fixed point with conformal symmetries. Using complementary perturbation theory
and scaling arguments, we show that a symmetry-allowed coupling between
(classical) finite-wavevector lattice distortions and monopole operators of the
U(1) Dirac spin liquid generally induces a spin-Peierls instability towards a
(confining) 12-site valence-bond solid state. We support our theoretical
analysis with state-of-the-art density matrix renormalization group
simulations. Away from the limit of static distortions, we demonstrate that the
phonon energy gap establishes a parameter regime where the spin liquid is
expected to be stable.Comment: 23 pages, 10 figure
Butterfly effect and spatial structure of information spreading in a chaotic cellular automaton
Inspired by recent developments in the study of chaos in many-body systems, we construct a measure of local information spreading for a stochastic cellular automaton in the form of a spatiotemporally resolved Hamming distance. This decorrelator is a classical version of an out-of-time-order correlator studied in the context of quantum many-body systems. Focusing on the one-dimensional Kauffman cellular automaton, we extract the scaling form of our decorrelator with an associated butterfly velocity vb and a velocity-dependent Lyapunov exponent λ(v). The existence of the latter is not a given in a discrete classical system. Second, we account for the behavior of the decorrelator in a framework based solely on the boundary of the information spreading, including an effective boundary random walk model yielding the full functional form of the decorrelator. In particular, we obtain analytic results for vb and the exponent β in the scaling ansatz λ(v) ~ μ (v−vb)ᵝ, which is usually only obtained numerically. Finally, a full scaling collapse establishes the decorrelator as a unifying diagnostic of information spreading.Physic
Spin-Peierls instability of the U(1) Dirac spin liquid
<p>We perform density matrix renormalization group (DMRG) simulations on cylinders for the J1-J2 Heisenberg model on the triangular lattice with spatial lattice deformations. This data set contains the results from the various simulations and the corresponding plotting scripts.</p>
Spin-Peierls instability of the U(1) Dirac spin liquid
<p>We perform density matrix renormalization group (DMRG) simulations on cylinders for the J1-J2 Heisenberg model on the triangular lattice with spatial lattice deformations. This data set contains the results from the various simulations and the corresponding plotting scripts.</p>