The emergence of gapless quantum spin liquid from deconfined quantum critical point

Abstract

A quantum spin liquid (QSL) is a novel phase of matter with long-range many-body quantum entanglement where localized spins are highly correlated with the vanishing of magnetic order. Such exotic quantum states typically host emergent gauge fields and fractional excitations. Here we show that a gapless QSL can naturally emerge from a deconfined quantum critical point (DQCP), which is originally proposed to describe Landau forbidden continuous phase transition between antiferromagnetic (AFM) and valence-bond solid (VBS) phases. Via large-scale tensor network simulations of a square-lattice spin-1/2 frustrated Heisenberg model, we find that a gapless QSL can gradually develop from a DQCP by tuning the couplings. Remarkably, along the phase boundaries of AFM-QSL and QSL-VBS transitions, we always observe the same correlation length exponents ν ≈ 1.0, which is intrinsically different from the one of the well known AFM-VBS DQCP transition, indicating new types of universality classes. Our results suggest a new scenario for understanding the emergence of gapless QSL from an underlying DQCP. The discovered QSL phase survives in a large region of tuning parameters and we expect its experimental realizations in solid state materials or cold atom systems.

Electronic spectra with paramagnon fractionalization in the single band Hubbard model

“…The resulting Fermi surfaces, shown in Fig. 7(a), are similar to that obtained for Bi2201: upon hybridization, the two large Fermi surfaces (red lines) split by the bilayer coupling, transform into gapless Z 2 spin liquid which has attracted significant recent interest [32][33][34][35][36][37][38][39][40][41][42][43][44][45], but the paramagnon fractionalization approach allows for a very wide range of possibilities on the second hidden layer.…”

“…One promising description of the spinons in the second hidden layer in a model without disorder is the gapless Z 2 spin liquid, which has received significant attention recently [32][33][34][35][36][37][38][39][40][41][42][43][44][45]. Appendix A presented results for the electronic self energy using this gapless Z 2 spin liquid, and showed that this liquid can yield significant damping of the fermions at the pseudogap energy in the antinodal region, and also improve correspondence with observations.…”

“…These self-energies are dependent upon the unknown spin susceptibility of the spin liquid on the second hidden layer. In Appendix A we will consider a realistic candidate gapless Z 2 spin liquid which has been the focus of significant recent interest [32][33][34][35][36][37][38][39][40][41][42][43][44][45]. The needed computations are numerically demanding, and we compute the f and c self energies for representative parameters.…”

“…We now discuss the behavior of the spectral function on the physical c-electron layer when the system on the second hidden layer is considered to be a gapless Z 2 spin liquid [32][33][34][35][36][37][38][39][40][41][42][43][44][45]. While the first two layers are coupled via J K coupling constant, the second and the third layers are perturbatively coupled via the J ⊥ and J K exchange interactions (see Fig.…”

Anisotropic deconfined criticality in Dirac spin liquids

“…Numerical evidence has since accumulated for the presence of a VBS phase in the J 1 -J 2 modelin particular, it was recently shown that a non-zero antiferromagnetic third-nearest-neighbor interaction J 3 stabilizes a clear VBS phase in a large parameter range of J 2 /J 1 [15], and this phase is argued to be stable down to J 3 = 0. The nature of the Néel-VBS transition in this model has remained a question of significant debate.…”