# Bond particle theory for the pseudogap phase of underdoped cuprates

## TL;DR

This paper develops a bond particle theory for the lightly doped t-J model, revealing Fermi pockets and gapped excitations relevant to the pseudogap phase of underdoped cuprates.

## Contribution

It introduces an exact bond particle representation and an averaged translationally invariant Hamiltonian for the t-J model, providing new insights into the pseudogap phase.

## Key findings

- Fermi pockets near (pi/2, pi/2) with area proportional to hole doping
- Presence of a gapped spin-wave-like triplet band
- Theoretical framework applicable to underdoped cuprates

## Abstract

We present a theory for the lightly doped t-J model which is of possible relevance for the normal state of underdoped cuprates. Starting from an arbitrary dimer covering of the plane an exact representation of the t-J Hamiltonian in terms of bond bosons and fermions can be derived. Since all dimer coverings must give identical results for observable quantities we construct an approximate but translationally invariant Hamiltonian by averaging the bond particle Hamiltonian over all possible dimer coverings. Treating the resulting Hamiltonian in mean-field approximation we find fermi pockets centered near (pi/2,pi/2) with a total area of x/2 (with x the hole concentration) and a gapped spin-wave-like band of triplet excitations.