We explore an unconventional class of problems in the study of (quantum) critical
phenomena, termed “deep boundary criticality”. Traditionally, critical systems are analyzed
with two types of perturbations: those uniformly distributed throughout the bulk, which can
significantly alter the bulk criticality by triggering a nontrivial bulk renormalization group
flow, and those confined to a boundary or subdimensional defect, which affect only the
boundary or defect condition. Here, we go beyond this paradigm by studying quantum
critical systems with boundary perturbations that decay algebraically (following a power
law) into the bulk. By continuously varying the decay exponent, such perturbations can
transition between having no effect on the bulk and strongly influencing bulk behavior. We
investigate this regime using two prototypical models based on (1+1)D massless Dirac
fermions. Through a combination of analytical and numerical approaches, we uncover
exotic scaling laws in simple observables and observe qualitative changes in model behavior
as the decay exponent varies.
HK Institute of Quantum Science & Technology,
Room525, Chong Yuet Ming Physics Building, The University of Hong Kong
Phone: 3917 1108
