Series expansion analysis of a frustrated four-spin tube

Abstract

We study the magnetism of a frustrated four-leg spin-1/2 ladder with transverse periodic boundary conditions: the frustrated four-spin tube (FFST). Using a combination of series expansion (SE), based on the continuous unitary transformation method and density-matrix renormalization group (DMRG) we analyze the ground-state, the one-, and the two-particle excitations in the regime of strong rung-coupling. We find several marked differences of the FFST with respect to standard two-leg ladders. First we show that frustration destabilizes the spin-gap phase of the FFST which is adiabatically connected to the limit of decoupled rung singlets, leading to a first order quantum phase transition at finite inter-rung coupling. Second, we show that apart from the well-know triplon branch of spin-ladders, the FFST sustains additional elementary excitations, including a singlon, and additional triplons. Finally we find, that in the two-particle sector the FFST exhibits collective (anti)bound states similar to two-leg ladders, however with a different ordering of the spin-quantum numbers. We show that frustration has significant impact on the FFST leading to a flattening of the ground-state energy landscape, a mass-enhancement of the excitations, and to a relative enhancement of the (anti)binding strength. Where possible we use DMRG to benchmark the findings from our SE calculations, showing excellent agreement.

Quantum phase diagram of a frustrated antiferromagnet on the bilayer honeycomb lattice

“…We refer for technical details about the calculation to ref. 62 . Note finally that the contribution of perturbation in the case V (j 1 , j 1 , 0) is zero, reflecting the invariance of original Hamiltonian under j 1 ↔ j x exchange.…”

Magnetization plateaus and jumps in a frustrated four-leg spin tube under a magnetic field

“…The critical lines, limiting integer plateaux, Luttinger liquid and half-integer plateaux phases, are determined by solving numerically the Eqs. (13) corresponding to the effective models around h 01 and h 02 . This calculation, together with the comparison with the other techniques (see Fig.…”

Nematic quantum phases in the bilayer honeycomb antiferromagnet

“…For SE we use the continuous unitary transformation (CUT) method [53,57,[73][74][75][76] starting from the limit of decoupled dimers. This method allows to obtain analytical expressions for the ground state energy and the dispersion of the elementary triplon excitations of the IDP versus J 1,2 /J ⊥ .…”