Gapless Symmetry Protected Topological Matter Proposed

by Tommy on 5/05/2017

After slugging through the previous paper, this was a breath of relief.

Gapless Symmetry Protected Topological Order, Thomas Scaffidi, Daniel E. Parker and Romain Vasseur (3 May 2017)

We introduce exactly solvable gapless quantum systems in d dimensions that support symmetry protected topological (SPT) edge modes. Our construction leads to long-range entangled, critical points or phases that can be interpreted as critical condensates of domain walls “decorated” with dimension (d−1) SPT systems. Using a combination of field theory and exact lattice results, we argue that such gapless SPT systems have symmetry-protected topological edge modes that can be either gapless or symmetry-broken, leading to unusual surface critical properties. Despite the absence of a bulk gap, these edge modes are robust against arbitrary symmetry-preserving local perturbations near the edges. In two dimensions, we construct wavefunctions that can also be interpreted as unusual quantum critical points with diffusive scaling in the bulk but ballistic edge dynamics.

Here, the method of their construction is useful. And the result is … interesting.

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