Topological Excitations in Doped Spin Ladders

TL;DR

This paper investigates the magnetic excitations in doped spin ladders, analyzing how doping influences spiral order, spin gaps, and magnetic properties, with results aligning with numerical studies.

Contribution

It introduces an effective Hamiltonian approach to study doped spin ladders, revealing doping-dependent spiral phases and spin gap formation, especially in odd-legged ladders.

Findings

Doping affects spiral order and antiferromagnetic correlations.

Spin gap formation is possible in odd-legged ladders at specific doping.

Results agree with existing numerical studies on doping ranges for gapped modes.

Abstract

We study low-energy magnetic excitations of doped spin-ladders, based on an effective Hamiltonian describing interactions of mobile spin and background spins. The helicity modulus against fluctuations in the ladder plane as well as out-of-the-plane are calculated in terms of the doping concentration, the leg number and interaction strengths in the ladder. The doping range for spiral phase is computed and its relation to spin gap structure is discussed. The spiral order can enhance existing antiferromagnetic order at certain doping or reduce it at very low density of holes. For odd-legged ladders, formation of spin gap at certain narrow doping range becomes possible via coupling of spirals and background spins. Our results of the doping range for gapped mode in odd-ladders agree well with those existing numerical studies.