Plasmarons in high-temperature cuprate superconductors
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2023-07-08 |
| Journal | Communications Physics |
| Authors | Hiroyuki Yamase, MatĆas Bejas, A. Greco |
| Institutions | Institute of Physics Rosario, National Institute for Materials Science |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled āExecutive SummaryāThis study provides theoretical evidence for the existence and mechanism of plasmarons (electron-plasmon coupled quasiparticles) in strongly correlated high-temperature cuprate superconductors.
- Emergent Quasiparticles: Plasmons generate an emergent, incoherent replica bandādubbed plasmaronsāin the one-particle excitation spectrum, rather than the characteristic ākinkā structure caused by phonons or magnetic fluctuations.
- Correlation-Driven Mechanism: Plasmarons in cuprates are uniquely driven by bosonic fluctuations associated with the local constraint (prohibition of double electron occupancy), a direct consequence of strong correlation effects, distinguishing them from plasmarons in weakly correlated metals.
- Dispersion Relation: The plasmaron band exhibits a dispersive feature that closely follows the renormalized quasiparticle dispersion (e.g., 0.98Īµk - 1.33t), confirming its nature as a replica band.
- Energy and Location: The plasmaron band is realized near the optical plasmon energy (typically ~1 eV), appearing below the quasiparticle band in electron-doped cuprates (e.g., LCCO) and above it in hole-doped cuprates.
- Critical Role of Optical Plasmon: Numerical analysis confirms that the optical plasmon is the crucial bosonic fluctuation responsible for generating the plasmarons; acoustic-like plasmons are far less effective.
- General Concept Established: The findings establish a general concept of plasmarons in metallic systems, linking strongly correlated cuprates to weakly correlated materials like alkali metals, graphene, and SrIrO3 films.
Technical Specifications
Section titled āTechnical SpecificationsāThe following parameters were used in the large-N theoretical framework of the layered t-J model to model electron-doped cuprates (La1.825Ce0.175CuO4, LCCO).
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Hopping Integral Scale (t/2) | 0.5 | eV | Energy normalization scale (t is the in-plane nearest-neighbor hopping). |
| Exchange Interaction (J/t) | 0.3 | Dimensionless | Ratio of in-plane exchange to hopping. |
| Second Neighbor Hopping (tā/t) | 0.3 | Dimensionless | Ratio of second neighbor to hopping. |
| Interlayer Hopping (tz/t) | 0.03 | Dimensionless | Ratio of interlayer to hopping. |
| Doping Rate (Ī“) | 0.175 | Dimensionless | Electron doping concentration (e.g., in LCCO). |
| Coulomb Interaction (V0/t) | 18 | Dimensionless | Long-range Coulomb interaction strength. |
| Anisotropy Factor (Ī±) | 2.9 | Dimensionless | Anisotropy ratio (Īµ||/Īµā„) of dielectric constants. |
| Number of Layers (Nz) | 10 | Dimensionless | Used for 3D layered structure calculation. |
| Quasiparticle Renormalization (Z) | 0.29 | Dimensionless | Reduction factor of spectral weight due to charge fluctuations. |
| Optical Plasmon Energy (v) | ~1.15 | t | Energy scale of the optical plasmon, controlling plasmaron position. |
| Plasmaron Dispersion Fit | 0.98Īµk - 1.33t | Energy | Empirical fit for the plasmaron band dispersion. |
| Energy Window Studied | -2 ā¤ Ļ/t ā¤ -1 | Dimensionless | Focus region for plasmaron detection in electron-doped systems. |
Key Methodologies
Section titled āKey MethodologiesāThe study employed a sophisticated theoretical approach based on the layered t-J model to compute the electron self-energy and spectral function.
- Model Selection: The layered t-J model, derived from the Hubbard model, was used to describe doped Mott insulators, explicitly incorporating the strong correlation constraint (no double occupancy) and the layered 3D structure necessary for plasmon analysis.
- Theoretical Framework: A large-N technique, utilizing a path integral representation in terms of Hubbard operators, was employed to systematically treat strong correlation effects and charge excitations.
- Charge Fluctuation Analysis: The theory focuses on two types of charge fluctuations (on-site and bond-charge), finding that the on-site fluctuations, described by a 2 x 2 matrix Dab(q, iĪ½n), are responsible for plasmaron formation.
- Self-Energy Calculation: The electron self-energy (Ī£(k, Ļ)) was computed at the order of 1/N, incorporating the bosonic propagator Dab(q, iĪ½n) and the long-range Coulomb interaction (Vq).
- Spectral Function Determination: The one-particle spectral function A(k, Ļ) was calculated using the Greenās function G(k, Ļ) = [Ļ + iĪ“sf - Īµk - Ī£(k, Ļ)]-1, where poles in A(k, Ļ) reveal the quasiparticle and plasmaron dispersions.
- Mechanism Verification: An auxiliary parameter (r) was introduced into the self-energy calculation (ImĪ£(k, Ļ; r)) to isolate the contribution of the local constraint fluctuations (D22 and D12 components), confirming their necessity for plasmaron emergence.
- Plasmon Role Confirmation: The calculation was repeated while excluding the contribution of the optical plasmon (by removing the qz ā¤ 2Ļ/10 region in the momentum summation), confirming that the optical plasmon is essential for the plasmaron peak structure.
Commercial Applications
Section titled āCommercial ApplicationsāThe fundamental understanding of quasiparticle dynamics in strongly correlated materials has direct implications for the development and optimization of next-generation electronic and energy technologies.
- High-Tc Superconductor Optimization: Provides critical insight into the electronic structure near the superconducting gap and pseudogap, guiding material synthesis to maximize Tc in cuprate systems.
- Correlated Electronics Design: Applicable to designing novel electronic components based on Mott physics, where strong correlations and local constraints dictate charge transport (e.g., Mott transistors or switches).
- Advanced Spectroscopic Calibration: The predicted plasmaron dispersion and energy scale (~1 eV) provide targets for experimental techniques like ARPES, RIXS, and X-ray photoemission spectroscopy, improving the accuracy of electronic structure measurements in complex oxides.
- Plasmonic Device Engineering: The generalized concept of plasmarons is relevant for engineering plasmon-enhanced devices in materials like graphene, transition-metal dichalcogenides, and SrIrO3 films, potentially leading to faster optical modulators or sensors.
- Energy Storage and Conversion: Understanding charge dynamics in layered oxides (like cuprates) is foundational for developing high-efficiency cathode materials and solid-state electrolytes.
View Original Abstract
Abstract Metallic systems exhibit plasmons as elementary charge excitations. This fundamental concept was reinforced also in high-temperature cuprate superconductors recently, although cuprates are not only layered systems but also strongly correlated electron systems. Here, we study how such ubiquitous plasmons leave their marks on the electron dispersion in cuprates. In contrast to phonons and magnetic fluctuations, plasmons do not yield a kink in the electron dispersion. Instead, we find that the optical plasmon accounts for an emergent bandāplasmaronsāin the one-particle excitation spectrum; acoustic-like plasmons typical to a layered system are far less effective. Because of strong electron correlations, the plasmarons are generated by bosonic fluctuations associated with the local constraint, not by the usual charge-density fluctuations. Apart from this physical mechanism, the plasmarons are similar to those discussed in alkali metals, Bi, graphene, monolayer transition-metal dichalcogenides, semiconductors, diamond, two-dimensional electron systems, and SrIrO 3 films, establishing a concept of plasmarons in metallic systems in general. Plasmarons are realized below (above) the quasiparticle band in electron-doped (hole-doped) cuprates, including a region around ( Ļ , 0) and (0, Ļ ) where the superconducting gap and the pseudogap are most enhanced.