Signatures of gapless fermionic spinons on a strip of the kagome Heisenberg antiferromagnet

Developing a complete understanding of the ground state properties of spin-1/2 Heisenberg antiferromagnets on the 2D kagome lattice remains a central challenge in the field of frustrated quantum magnetism. Here, we consider the narrowest possible quasi-1D incarnation of the kagome Heisenberg antiferromagnet which consists entirely of corner-sharing triangles. Using large-scale density matrix renormalization group calculations, we identify in this model an extended gapless quantum phase characterized by central charge $c=2$ and power-law decaying spin and bond-energy correlations which oscillate at tunably incommensurate wave vectors. We argue that this intriguing spin liquid phase can be understood as a marginal instability of a two-band spinon Fermi surface coupled to a U(1) gauge field, an interpretation which we substantiate via bosonization analysis and Monte Carlo calculations on model Gutzwiller variational wave functions. Our results represent one of the first numerical demonstrations of fermionic spinons in a simple SU(2) invariant nearest-neighbor Heisenberg model beyond the strictly 1D (Bethe chain) limit.