Source capture
Authors Kaustubh Roy, Piers Coleman
arXiv / Publisher https://arxiv.org/abs/2610.35814
PDF https://arxiv.org/pdf/2610.35814
Relevance score 5.433
Primary category cond-mat.supr-con
Published 2026-10-27
Research paradigm Theoretical
Sample form Thin Film

Summary

This paper addresses the pairing-symmetry problem of high-temperature superconductivity in the bilayer nickelate La3Ni2O7; against the theoretical background of competition between s± and copper-oxide-like d-wave pairing, it constructs a mean-field fractionalization scheme that preserves the full SU(2) particle-hole symmetry of the half-filled t-J model and applies it to a simplified bilayer t-J model of La3Ni2O7. The authors note that the conventional U(1) treatment does not fully incorporate Coulomb repulsion and the constraint prohibiting double occupancy, whereas the fractionalization method introduces an additional Coulomb pseudopotential constraint. Calculations show that this pseudopotential suppresses s± pairing and favors d-wave pairing, theoretically indicating that interlayer coupling and the local no-double-occupancy condition can alter the pairing-symmetry competition in La3Ni2O7; this conclusion is a mean-field theoretical prediction, not an experimentally established pairing mechanism.

Materials

Methods

  • mean-field fractionalization treatment
  • SU(2) particle-hole-symmetric t-J model
  • Wen-Lee path-integral formulation
  • Hubbard-Stratonovich decoupling
  • Bogoliubov-de Gennes (BdG) mean-field theory
  • self-consistent mean-field calculations
  • free-energy minimization

Keywords

Highlights

  • The mean-field fractionalization captures the full SU(2) particle-hole symmetry of the t-J model at half-filling.
  • The additional Coulomb pseudopotential constraint on the superconducting order parameter is absent in conventional mean-field treatments.
  • The correction from the Coulomb pseudopotential is positive semidefinite and reduces the eigenvalues of the susceptibility matrix, lowering Tc for s± pairing.
  • Recent ARPES measurements on ambient-pressure (La,Pr,Sm)La3Ni2O7 films reveal nodeless gaps on the α and β Fermi-surface pockets, challenging the d-wave state favored by the calculations and motivating phase-sensitive tests.

Conclusions

  • A systematic treatment of the full SU(2) particle-hole symmetry of the half-filled t-J model leads to an added Coulomb pseudopotential constraint that is absent in the usual U(1) treatment.
  • Applying the fractionalization scheme to a simplified bilayer t-J model of La3Ni2O7 shows that the Coulomb pseudopotential suppresses the existence of s± symmetry in favor of d-wave pairing.
  • The Coulomb constraint does not prohibit superconductivity; strong interlayer exchange enhances interlayer pairing and can partially overcome the Coulomb suppression.
  • For the parameters studied, the constraint favors d-wave superconductivity over much of the phase diagram, including the nominal doping of La3Ni2O7.
  • The Coulomb pseudopotential creates a positive-semidefinite correction to the pairing susceptibility, reducing Tc for s± pairing while leaving the d-wave channel unaffected by symmetry.

Main claims

  • A mean-field fractionalization treatment capturing the full SU(2) particle-hole symmetry of the half-filled t-J model leads to an added Coulomb pseudopotential constraint that is absent in the usual U(1) treatment.
    • Evidence: The abstract states that the proposed fractionalization treatment captures the full SU(2) particle-hole symmetry and leads to an added Coulomb pseudopotential constraint absent in the usual U(1) treatment.,Section I.2 states that the transverse constraints eliminate an on-site spinon pair amplitude and that their Lagrange multiplier acts as a self-consistent Coulomb pseudopotential.
  • In the simplified bilayer t-J model of La3Ni2O7, the Coulomb pseudopotential suppresses s± symmetry in favor of d-wave pairing.
    • Evidence: The abstract states that applying the scheme to a simplified bilayer t-J model shows the Coulomb pseudopotential suppresses s± symmetry in favor of d-wave pairing.,Section V reports that once the Coulomb pseudopotential constraint is added, s± pairing is suppressed significantly.
  • The d-wave channel is unaffected by the Coulomb pseudopotential by symmetry, while the s± pairing susceptibility is reduced by a positive-semidefinite correction.
    • Evidence: Section V states that the Coulomb pseudopotential creates an effective susceptibility with a positive semidefinite correction that reduces eigenvalues and Tc for pairing.,Section V and VI state that for d-wave pairing the correction is zero because d-wave symmetry is orthogonal to the Coulomb pseudopotential.
  • Strong interlayer exchange can enhance interlayer pairing and partially overcome Coulomb suppression, but the constraint still favors d-wave over much of the phase diagram, including the nominal doping of La3Ni2O7.
    • Evidence: Section VI states that strong interlayer exchange enhances interlayer pairing and can partially overcome Coulomb suppression.,Section VI states that for the parameters studied the constraint favors d-wave superconductivity over much of the phase diagram, including the nominal doping of La3Ni2O7.
  • The result is a mean-field theoretical prediction rather than an experimentally established pairing mechanism, and ARPES data on ambient-pressure films may challenge the favored d-wave state.
    • Evidence: The summaryen states that the conclusion is a mean-field theoretical prediction, not an experimentally established pairing mechanism.,Section VI notes that recent ARPES measurements reveal nodeless gaps that challenge the d-wave state favored by the calculations.

Workflow

  • model_construction — A minimal bilayer t-J model captures the relevant low-energy bilayer nickelate physics for studying pairing competition.
    • Materials: simplified bilayer t-J model of La3Ni2O7; projected bilayer t-J model; Hubbard operators on the local three-state space
    • Methods: derive interlayer superexchange from Hund's coupling to orbitals; Fourier transform projected hopping to a Bloch Hamiltonian
    • Observations: the model qualitatively reproduces the Fermi-surface pocket features seen in ARPES
  • strong_coupling_fractionalization — A mean-field fractionalization treatment preserving full SU(2) particle-hole symmetry introduces an additional Coulomb pseudopotential constraint absent in the usual U(1) treatment.
    • Materials: fermionic spinon; two-component charge boson; Wen-Lee SU(2) gauge formulation
    • Methods: slave-boson fractionalization; impose local charge and transverse constraints; symplectic Hubbard-Stratonovich decoupling
    • Observations: the constraints produce longitudinal and on-site pair Lagrange multipliers
  • mean_field_saddle_point — The mean-field saddle-point equations yield a pairing instability and critical temperature for competing d-wave and s± states.
    • Materials: bilayer Bogoliubov-de Gennes Hamiltonian; intralayer and interlayer link fields
    • Methods: momentum-space link fields; Bogoliubov-de Gennes spectrum; free-energy extremization; coupled self-consistency equations
    • Observations: the pairing instability is determined by a sign change in the susceptibility determinant
  • numerical_solution — The Coulomb pseudopotential suppresses s± pairing in favor of d-wave pairing over much of the studied phase diagram.
    • Materials: coupled self-consistency equations; doping sweep
    • Methods: numerically minimize the free energy; solve the coupled self-consistency equations; calculate critical temperatures
    • Observations: without the Coulomb constraint s± can exceed d-wave at larger doping; with the Coulomb constraint s± is suppressed and forced to change sign between Fermi surfaces
  • interpretation — The local no-double-occupancy condition alters the competition between interlayer s± and intralayer d-wave pairing, favoring d-wave for the parameters studied.
    • Materials: pairing-symmetry phase diagram; comparison with ARPES literature
    • Methods: compare symmetry sectors; analyze the positive-semidefinite correction to the susceptibility
    • Observations: the d-wave channel is orthogonal to the Coulomb pseudopotential; the s± pairing susceptibility is reduced by the constraint; strong interlayer exchange can enhance interlayer pairing but does not eliminate the constraint