Deconfined Fermi liquid to Fermi liquid transition and superconducting instability
arxiv(2024)
摘要
Deconfined quantum critical points (DQCP) have attracted lots of attentions
in the past decades, but were mainly restricted to incompressible phases. On
the other hand, various experimental puzzles call for new theory of
unconventional quantum criticality between metals at a generic density. Here we
explore the possibility of a deconfined transition between two symmetric Fermi
liquids in a bilayer model tuned by inter-layer antiferromagnetic spin-spin
coupling J_⊥. Across the transition the Fermi surface volume per flavor
jumps by 1/2 of the Brillouin zone (BZ), similar to the small to large Fermi
surface transitions in heavy Fermion systems and maybe also in the high Tc
cuprates. But in the bilayer case the small Fermi surface phase (dubbed as sFL)
has neither symmetry breaking nor fractionalization, akin to the symmetric mass
generation (SMG) discussed in high energy physics. We formulate a deconfined
critical theory where the two Fermi liquids correspond to higgs and/or confined
phases of a U(1)× U(1) gauge theory. We show that this deconfined FL to
FL transition (DFFT) fixed point is unstable to pairing and thus a
superconductor dome is expected at low temperature. At finite temperature above
the pairing scale, microscopic electron is a three particle bound state of the
deconfined fractional fermions in the critical theory. We also introduce
another parameter which can suppress the pairing instability, leading to a
deconfined tri-critical point stable to zero temperature. We also provide
numerical results of the bilayer model in one dimension, with a Luther-Emery
liquid between two different Luttinger liquids, similar to the phase diagram
from the field theory in two dimension. Our work opens a new direction to
exploring deconfined metallic criticality and new pairing mechanism from
critical gauge field.
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