简介: |
Significant progress in the study of classical and
quantum phase transitions involving symmetry breaking has been
achieved over the past decades. Now, a new set of questions have
been thrown up by the ?discovery of symmetry protected topological
states (SPTs), that generalize the notion of topological insulators.
Here, symmetries and a bulk gap stabilize unusual modes at surfaces
or at topological defects. What is the fate of these protected modes
at a quantum critical point, when the protecting symmetries are on
the verge of being broken? This interplay of topology and
criticality is expected to be extremely rich, given that it
incorporates both the bulk dynamics of critical points described by
nontrivial conformal field theories and the intrinsically quantum
aspects of SPT physics. Combining these two disparate ingredients in
an analytically tractable framework is challenging. Here, we make
progress towards this goal by studying the simplest nontrivial model
- that of a 0+1 dimensional topological mode, coupled to a 2+1D
critical ?bulk - using the large-N technique. We introduce a series
of models that can be solved within the large-N approximation which,
as a consequence of topology, demonstrate intermediate coupling
fixed points. We compare our results to previous numerical
simulations and find good agreement. We also point out some
intriguing connections to the physics of Sachdev-Ye-Kitaev (SYK)
models, in particular we show that a Luttinger theorem derived for
the complex SYK models, that relates the charge density to
particle-hole asymmetry, also holds in our setting. These results
should help open up the analytical study of the rich interplay
between SPT physics and quantum criticality.?
|