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arXiv:2304.12697 · Physical review. B./Physical review. B

Weakly damped bosons and precursor gap in the vicinity of an antiferromagnetic metallic transition

Ori Grossman, Erez Berg

Published Aug 28, 2023• 1 citation
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Abstract

We study the electronic spectral function of a metal in the vicinity of an antiferromagnetic (AFM) quantum critical point, focusing on a situation where the bare bandwidth of the spin fluctuations is significantly smaller than the Fermi energy. In this limit, we identify a range of energies where the fermionic quasiparticles near the ``hot spots'' on the Fermi surface are strongly scattered by the quantum critical fluctuations, whereas the damping of the AFM fluctuations by the electrons is negligible. Within a one-loop approximation, there is a parameter range where the $T=0$ spectral function at the hot spots has a ``precursor gap'' feature, with a local maximum at a finite frequency. However, we find that the ratio of the bare spin-wave velocity to the Fermi velocity required to obtain a precursor gap is smaller by about an order of magnitude than the value in the electron-doped cuprate superconductors. Hence, our results cannot easily account for the recent angle-resolved photoemission experiments in this system [He et al., Proc. Natl. Acad. Sci. USA 116, 3449 (2019)]. At lower frequencies, the Landau damping of the AFM fluctuations becomes important, and the electronic spectral function has the familiar ${\ensuremath{\omega}}^{\ensuremath{-}1/2}$ singularity. Our one-loop perturbative results are supported by a numerical Monte Carlo simulation of electrons coupled to an undamped, nearly critical AFM mode.

DOI
10.1103/physrevb.108.075165

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We study the electronic spectral function of a metal in the vicinity of an antiferromagnetic (AFM) quantum critical point, focusing on a situation where the bare bandwidth of the spin fluctuations is significantly smaller than the Fermi energy. In this limit, we identify a range of energies where the fermionic quasiparticles near the hot spots'' on the Fermi surface are strongly scattered by the quantum critical fluctuations, whereas the damping of the AFM fluctuations by the electrons is negligible. Within a one-loop approximation, there is a parameter range where the $T=0$ spectral function at the hot spots has a precursor gap'' feature, with a local maximum at a finite frequency. However, we find that the ratio of the bare spin-wave velocity to the Fermi velocity required to obtain a precursor gap is smaller by about an order of magnitude than the value in the electron-doped cuprate superconductors. Hence, our results cannot easily account for the recent angle-resolved photoemission experiments in this system [He et al., Proc. Natl. Acad. Sci. USA 116, 3449 (2019)]. At lower frequencies, the Landau damping of the AFM fluctuations becomes important, and the electronic spectral function has the familiar \ensuremathω\ensuremath−1/2{\ensuremath{\omega}}^{\ensuremath{-}1/2}\ensuremathω\ensuremath−1/2 singularity. Our one-loop perturbative results are supported by a numerical Monte Carlo simulation of electrons coupled to an undamped, nearly critical AFM mode.
We study the single-particle spectral properties of a model for coexisting antiferromagnetic and incommensurate charge-density-wave critical fluctuations coupled to electrons, which naturally arises in the context of the stripe-quantum-critical-point scenario for high-Tc{T}_{c}Tc​ superconducting materials. Within a perturbative approach, we show that the on-shell inverse scattering time deviates from the normal Fermi-liquid behavior near the points of the Fermi surface connected by the characteristic wave vectors of the critical fluctuations (hot spots). The anomalous behavior is stronger when the hot spots are located near singular points of the electronic spectrum. The violations to the normal Fermi-liquid behavior are associated with the transfer of spectral weight from the quasiparticle peak to incoherent shadow peaks, which produces an enhancement of incoherent spectral weight near the Fermi level. We use our results to discuss recent angle-resolved photoemission spectroscopy experiments on Bi2212 near optimal doping.
Near the antiferromagnetic quantum critical point (QCP) of electron-doped cuprate superconductors, angle-resolved photoemission experiments detect hot spots where the Fermi surface disappears. Here, we demonstrate, using the two-particle self-consistent theory, that in the antinodal region the Fermi liquid remains stable for a broad range of angles on the Fermi surface and for all dopings near the QCP. We show how the quasiparticle weight Z and effective mass m^{*} change and then abruptly become meaningless as the hot spots are approached. We propose a dimensionless number, easily accessible in ARPES experiments, that can be used to gauge the strength of correlations.
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Metallic quantum criticality is among the central themes in the understanding of correlated electronic systems, and converging results between analytical and numerical approaches are still under review. In this work, we develop a state-of-the-art large-scale quantum Monte Carlo simulation technique and systematically investigate the itinerant quantum critical point on a 2D square lattice with antiferromagnetic spin fluctuations at wavevector [Formula: see text]-a problem that resembles the Fermi surface setup and low-energy antiferromagnetic fluctuations in high-Tc cuprates and other critical metals, which might be relevant to their non-Fermi-liquid behaviors. System sizes of [Formula: see text] ([Formula: see text]) are comfortably accessed, and the quantum critical scaling behaviors are revealed with unprecedented high precision. We found that the antiferromagnetic spin fluctuations introduce effective interactions among fermions and the fermions in return render the bare bosonic critical point into a different universality, different from both the bare Ising universality class and the Hertz-Mills-Moriya RPA prediction. At the quantum critical point, a finite anomalous dimension [Formula: see text] is observed in the bosonic propagator, and fermions at hotspots evolve into a non-Fermi liquid. In the antiferromagnetically ordered metallic phase, fermion pockets are observed as the energy gap opens up at the hotspots. These results bridge the recent theoretical and numerical developments in metallic quantum criticality and can serve as the stepping stone toward final understanding of the 2D correlated fermions interacting with gapless critical excitations.
Angle-resolved photoemission spectroscopy (ARPES) has revealed peculiar properties of mobile dopants in correlated antiferromagnets (AFMs). But, describing them theoretically, even in simplified toy models, remains a challenge. Here, we study ARPES spectra of a single mobile hole in the $t\ensuremath{-}J$ model. Recent progress in the microscopic description of mobile dopants allows us to use a geometric decoupling of spin and charge fluctuations at strong couplings, from which we conjecture a one-to-one relation of the one-dopant spectral function and the spectrum of a constituting spinon in the undoped parent AFM. We thoroughly test this hypothesis for a single hole doped into a two-dimensional Heisenberg AFM by comparing our semianalytical predictions to previous quantum Monte Carlo results and our large-scale time-dependent matrix product state calculations of the spectral function. Our conclusion is supported by a microscopic trial wave function describing spinon-chargon bound states, which captures the momentum and t/Jt/Jt/J dependence of the quasiparticle residue. From our conjecture we speculate that ARPES measurements in the pseudogap phase of cuprates may directly reveal the Dirac-fermion nature of the constituting spinons. Specifically, we demonstrate that our trial wave function provides a microscopic explanation for the sudden drop of spectral weight around the nodal point associated with the formation of Fermi arcs, assuming that additional frustration suppresses long-range AFM ordering. We benchmark our results by studying the crossover from two to one dimension, where spinons and chargons are confined and deconfined, respectively.
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