  One of the most interesting predictions resulting from quantum physics, is
the violation of classical symmetries, collectively referred to as anomalies. A
remarkable class of anomalies occurs when the continuous scale symmetry of a
scale free quantum system is broken into a discrete scale symmetry for a
critical value of a control parameter. This is an example of a (zero
temperature) quantum phase transition. Such an anomaly takes place for the
quantum inverse square potential known to describe 'Efimov physics'. Broken
continuous scale symmetry into discrete scale symmetry also appears for a
charged and massless Dirac fermion in an attractive $1/r$ Coulomb potential.
The purpose of this article is to demonstrate the universality of this quantum
phase transition and to present convincing experimental evidence of its
existence for a charged and massless fermion in an attractive Coulomb potential
as realised in graphene.
