Gapless symmetry-protected topological phase of quantum antiferromagnets on anisotropic triangular strip

Understand

We study a three-leg spin-1/2 ladder with geometrically frustrated interleg interactions.

• We call this model an anisotropic triangular-strip (ATS) model.
• We numerically and field-theoretically show that its ground state belongs to a gapless symmetry-protected topological (SPT) phase.
• The numerical approach is based on density-matrix renormalization group analyses of the entanglement entropy and the entanglement spectrum.