Surprises on the Way from One- to Two-Dimensional Quantum Magnets: The Ladder Materials

TLDR

Ladder structures bridge the gap between one‑dimensional spin chains and two‑dimensional magnetic order. Even‑leg ladders exhibit short‑range order and a finite spin gap. The crossover is abrupt, the predicted spin‑gap ground state has been experimentally confirmed, and doped holes may pair and lead to superconductivity.

Abstract

One way of making the transition between the quasi-long range order in a chain of S=1/2 spins coupled antiferromagnetically and the true long range order that occurs in a plane, is by assembling chains to make ladders of increasing width. Surprisingly this crossover between one and two dimensions is not at all smooth. Ladders with an even number of legs have purely short range magnetic order and a finite energy gap to all magnetic excitations. Predictions of this novel groundstate have now been verified experimentally. Holes doped into these ladders are predicted to pair, and possibly superconduct.