arXiv subjects

Dave Allen

Publications and source records attributed to Dave Allen.

3 recordsLinked to original sources

arXiv2001

Two leg quantum Ising ladder: A bosonization study of the ANNNI model

The quantum ANNNI chain in a transverse field is investigated by means of the bosonization approach in the limit of large next-nearest neighbor interaction. In this regime, this model can be viewed as a weakly coupled two-leg zigzag ladder which enables us to derive its low energy effective field theory. In particular, it is shown that the effect of frustration in the system is captured by the presence of a non zero conformal spin perturbation that accounts for the existence of all the incommensurate phases of the model.

cond-mat↗

arXiv2000

The fate of spinons in spontaneously dimerised spin-1/2 ladders

We study a weakly coupled, frustrated two-leg spin-1/2 Heisenberg ladder. For vanishing coupling between the chains, elementary excitations are deconfined, gapless spin-1/2 objects called spinons. We investigate the fate of spinons for the case of a weak interchain interaction. We show that despite a drastic change in ground state, which becomes spontaneously dimerised, spinons survive as elementary excitations but acquire a spectral gap. We furthermore determine the exact dynamical structure factor for several values of momentum transfer.

cond-mat.str-el↗

arXiv1996

Non-Abelian bosonization of the frustrated antiferromagnetic spin-1/2 chain

We study the spin-1/2 chain with nearest neighbor ($κ_1$) and next-nearest neighbor ($κ_2$) interactions in the regime $κ_2\gg κ_1$, which is equivalent to two chains with a `zig-zag' interaction. In the continuum limit, this system is described in term of two coupled level-1 WZW field theories. We illustrate its equivalence with four off-critical Ising models (Majorana fermions). This description is used to investigate the opening of a gap as a function of $κ_1$ and the associated spontaneous breakdown of parity. We calculate the dynamic spin structure factor near the wavevectors accessible to the continuum limit. We comment on the nonzero string order parameter and show the presence of a hidden ${\Bbb Z}_2\times{\Bbb Z}_2$ symmetry via a nonlocal transformation on the microscopic Hamiltonian. For a ferromagnetic interchain coupling, the model is conjectured to be critical, with different velocities for the spin singlet and spin triplet excitations.

cond-mat↗