Magnetic Phase Diagram of Spin-1/2 Two-Leg Ladder with Four-Spin Ring Exchange

TL;DR

This paper investigates the magnetic phase diagram of a spin-1/2 two-leg ladder with four-spin ring exchange interactions, revealing novel phases and dualities using numerical methods.

Contribution

It introduces an exact duality transformation extending previous spin-chirality duality, and maps out the phase diagram including a magnetization plateau, a nematic phase, and a Tomonaga-Luttinger liquid.

Findings

Identification of a magnetization plateau.

Discovery of a nematic phase with magnon pairing.

Demonstration of a self-dual surface in parameter space.

Abstract

We study the spin-1/2 two-leg Heisenberg ladder with four-spin ring exchanges under a magnetic field. We introduce an exact duality transformation which is an extension of the spin-chirality duality developed previously and yields a new self-dual surface in the parameter space. We then determine the magnetic phase diagram using the numerical approaches of the density-matrix renormalization-group and exact diagonalization methods. We demonstrate the appearance of a magnetization plateau and the Tomonaga-Luttinger liquid with dominant vector-chirality quasi-long-range order for a wide parameter regime of strong ring exchange. A "nematic" phase, in which magnons form bound pairs and the magnon-pairing correlation functions dominate, is also identified.