Unified description of cuprate superconductors by fractionalized electrons emerging from integrated analyses of photoemission spectra and quasiparticle interference

Electronic structure of high-temperature superconducting cuprates is studied by analyzing experimental data independently obtained from two complementary spectroscopies, one, quasiparticle interference (QPI) measured by scanning-tunneling microscopy and the other, angle-resolved photoemission spectroscopy (ARPES) and by combining these two sets of data in a unified theoretical analysis. Through explicit calculations of experimentally measurable quantities, we show that a simple two-component fermion model (TCFM) representing electron fractionalization succeeds in reproducing various detailed features of these experimental data: ARPES and QPI data are concomitantly reproduced by the TCFM in full energy and momentum spaces. The measured QPI pattern reveals a signature characteristic of the TCFM, distinct from the conventional single-component prediction, supporting the validity of the electron fractionalization in the cuprate. The integrated analysis also solves the puzzles of ARPES and QPI data that are seemingly inconsistent with each other. The overall success of the TCFM offers a comprehensive understanding of the electronic structure of the cuprates. We further predict that a characteristic QPI pattern should appear in the unoccupied high-energy part if the fractionalization is at work. We propose that integrated-spectroscopy analyses offer a promising way to explore challenging issues of strongly correlated electron systems.

💡 Research Summary

The paper presents a unified theoretical framework that simultaneously accounts for angle‑resolved photoemission spectroscopy (ARPES) and quasiparticle interference (QPI) data obtained from scanning‑tunneling microscopy on the high‑temperature cuprate superconductor Bi₂Sr₂CaCu₂O₈₊δ (Bi2212). The authors argue that previous analyses treated these spectroscopies independently, leading to apparent contradictions such as the dispersion of the QPI “q7” feature, which seemed incompatible with the d‑wave superconducting gap observed by ARPES. To resolve these discrepancies, they adopt the two‑component fermion model (TCFM), a minimal Hamiltonian that embodies electron fractionalization: an electron is represented as a superposition of a conventional quasiparticle (c) and a hidden fermion (d) that hybridize via a momentum‑dependent term Vₖ.

The TCFM Hamiltonian reads
H = Σₖ,σ ε_c(k) c†{kσ}c{kσ} + ε_d(k) d†{kσ}d{kσ} + Vₖ (d†{kσ}c{kσ}+c†{kσ}d{kσ}) – Σₖ