Dynamical signature of fractionalization at a deconfined quantum critical point

Abstract

Deconfined quantum critical points govern continuous quantum phase transitions at which fractionalized (deconfined) degrees of freedom emerge. Here we study dynamical signatures of the fractionalized excitations in a quantum magnet (the easy-plane J-Q model) that realize a deconfined quantum critical point with emergent O(4) symmetry. By means of large-scale quantum Monte Carlo simulations and stochastic analytic continuation of imaginary-time correlation functions, we obtain the dynamic spin structure factors in the S x and S z channels. In both channels, we observe broad continua that originate from the deconfined excitations. We further identify several distinct spectral features of the deconfined quantum critical point, including the lower edge of the continuum and its form factor on moving through the Brillouin Zone. We provide field-theoretical and lattice model calculations that explain the overall shapes of the computed spectra, which highlight the importance of interactions and gauge fluctuations to explaining the spectral-weight distribution. We make further comparisons with the conventional Landau O(2) transition in a different quantum magnet, at which no signatures of fractionalization are observed. The distinctive spectral signatures of the deconfined quantum critical point suggest the feasibility of its experimental detection in neutron scattering and nuclear magnetic resonance experiments.

Dynamics of compact quantum electrodynamics at large fermion flavor

“…3 (b), which reflects the expected deconfinement and fractionalization of spinons and their interactions mediated by the fluctuating U(1) gauge field. Similar S(q, ω), with gapless excitations at (0, 0), (π, 0) and (π, π) and pronounced continua upto high energy, have also been seen at the deconfined quantum critical point with emergent O(4) symmetry [33,55].…”

“…The resulting spectra will be collected as an ensemble average of the Metropolis process within the configurational space of {a i , ω i }, as explained in Refs. [33,[48][49][50][51][52].…”

“…The very recent breakthrough of quantum Monte Carlo (QMC) simulations of Z2 [23][24][25]27] and U(1) [1] gauge fields coupled to fermions provide the possibility of concrete investigations at the small N f , and the expected deconfinement-to-confinement phase transitions and special properties of these phases are discovered. In such settings, the interactions between fermions are mediated via the fluctuating gauge bosons, which resemble the situation of fractionalized particles and emergent gauge fields in several prototypical strongly correlated systems including, but not limited to, the low-energy description of the high-temperature superconductors [11,15,19], frustrated magnets [19,28,29] and deconfined quantum criticalities [30][31][32][33][34][35]. The quantum phases and phase transitions discovered are clearly beyond the Landau-Ginzburg-Wilson paradigm built upon the concepts of symmetry-breaking and local order parameters, and served as the building bulks of the new paradigm of quantum matter.…”

“…One first measures the imaginary time correlation functions with good statistics, then performs analytic continuation to convert the correlation from imaginary to real frequencies. The recent developments of stochastic analytic continuation (SAC) scheme [48] is proven to be more reliable and could reveal non-trivial results in both unfrustrated and frustrated magnetic systems in 2D and 3D [33,[49][50][51][52]. Therefore the techniques for investigating the dynamical properties of the QED 3 -GN transitions are available.…”

Spin excitation spectra of the two-dimensional S=12 Heisenberg model with a checkerboard structure

“…The long-range Néel order is destroyed at the quantum critical point while the spin-rotation symmetry [S U(2) symmetry] is restored [50]. For the disordered phase, i.e., the plaquette phase, the lattice symmetry is not spontaneously broken but is destroyed by the designed model, which is very similar to the so-called dimer phase (or named the coupled-dimer antiferromagnet) [12,51].…”