Spin operator matrix elements in the superintegrable chiral Potts quantum chain

TL;DR

This paper derives explicit formulas for spin operator matrix elements in the superintegrable chiral Potts quantum chain, connecting algebraic structures to physical order parameters and extending known results for the Ising case.

Contribution

It provides a new derivation of spin matrix elements using the extended Onsager algebra, including factorized forms and thermodynamic limit results for order parameters.

Findings

Derived spin matrix elements in factorized form

Obtained order parameters in the thermodynamic limit

Connected results to the Ising quantum chain case

Abstract

We derive spin operator matrix elements between general eigenstates of the superintegrable Z_N-symmetric chiral Potts quantum chain of finite length. Our starting point is the extended Onsager algebra recently proposed by R.Baxter. For each pair of spaces (Onsager sectors) of the irreducible representations of the Onsager algebra, we calculate the spin matrix elements between the eigenstates of the Hamiltonian of the quantum chain in factorized form, up to an overall scalar factor. This factor is known for the ground state Onsager sectors. For the matrix elements between the ground states of these sectors we perform the thermodynamic limit and obtain the formula for the order parameters. For the Ising quantum chain in a transverse field (N=2 case) the factorized form for the matrix elements coincides with the corresponding expressions obtained recently by the Separation of Variables Method.