A theorem on extensive ground state entropy, spin liquidity and some related models
Abstract
The physics of the paradigmatic onedimensional transverse field quantum Ising model $J \sum_{\langle i,j \rangle} \sigma^x_i \sigma^x_j + h \sum_i \sigma^z_i$ is wellknown. Instead, let us imagine "applying" the transverse field via a transverse Ising coupling of the spins to partner auxiliary spins, i.e. $H= J_x \sum_{\langle i,j \rangle} \sigma^x_i \sigma^x_j + J_z \sum_i \sigma^z_i \sigma^z_{\text{partner of }i}$. If each spin of the chain has a unique auxiliary partner, then the resultant eigenspectrum is still the same as that of the quantum Ising model with $\frac{h}{J} = \frac{J_z}{J_x}$ and the degeneracy of the entire spectrum is $2^{\text{number of auxiliary spins}}$. We can interpret this as the auxiliary spins remaining paramagnetic down to zero temperature and an extensive ground state entropy. This follows from the existence of extensively large and mutually « anticommuting»$\;$ sets of $local$ conserved quantities for $H$. Such a structure will be shown to be not unnatural in the class of bonddependent Hamiltonians. In the above quantum Ising model inspired example of $H$, this is lost upon the loss of the unique partner condition for the full spin chain. Other cases where such degeneracy survives or gets lost are also discussed. Thus this is more general and forms the basis for an exact statement on the existence of extensive ground state entropy in any dimension. Furthermore this structure can be used to prove spin liquidity nonperturbatively in the ground state manifold. Higherdimensional quantum spin liquid constructions based on this are given which may evade a quasiparticle description.
 Publication:

arXiv eprints
 Pub Date:
 July 2024
 DOI:
 10.48550/arXiv.2407.06236
 arXiv:
 arXiv:2407.06236
 Bibcode:
 2024arXiv240706236P
 Keywords:

 Condensed Matter  Statistical Mechanics;
 Condensed Matter  Strongly Correlated Electrons
 EPrint:
 11+ pages, 6 figures, 3 tables. No major changes compared to v4. Multispin correlations results sharpened and made complete. Additional discussion on global parity conservation in the twodimensional models added