Graphene’s Plasmons Enable Precise Hydrodynamic Transport with 205127 Contributions

The behaviour of collective electronic excitations, known as plasmons, fundamentally influences how electrons transport through materials, and understanding these excitations in graphene is crucial for developing advanced electronic devices. Maksim Ulybyshev, Adrien Reingruber, and Kitinan Pongsangangan, from the Universität Würzburg and Mahidol University, investigate plasmons in a specific form of graphene, half-filled graphene, using a highly accurate computational technique. Their work addresses a significant gap in current understanding, as previous studies often rely on approximations that neglect important factors like the finite size of the material and strong interactions between electrons. By employing Quantum Monte Carlo calculations, the team reveals how these neglected effects substantially alter the properties of plasmons, demonstrating a clear need to incorporate them into theoretical models of electronic transport in free-standing graphene and paving the way for more accurate predictions of material behaviour.

Graphene Plasmons and Strong Correlation Accuracy

Transport properties of strongly correlated materials arise from both individual particle excitations and collective modes like plasmons, which are oscillations of electrons responding to external stimuli and significantly influence material behaviour. The research establishes the accuracy of RPA in describing plasmon properties in strongly correlated systems, benchmarking it against the highly accurate, but computationally demanding, QMC method. The team investigates the plasmon dispersion relation, describing the relationship between plasmon frequency and wavevector, and calculates the spectral function, revealing the energy and momentum of electronic excitations. Results demonstrate that RPA provides a surprisingly accurate description of the plasmon dispersion in half-filled graphene, even with relatively strong electron correlations, offering a computationally efficient alternative to QMC for similar systems. The simulations go beyond the limitations of traditional theoretical approaches, revealing a more complex plasmon structure influenced by many-body effects and vertex corrections. Accurate knowledge of plasmon excitations is vital for applications in plasmonics, optoelectronics, and sensing. Stochastic Analytic Continuation (SAC) extracts the frequency-dependent information, a crucial but challenging step. These simulations require significant computing resources and were performed using high-performance computing facilities. The paper delves into key concepts including plasmons, the dynamic structure factor, and Random Phase Approximation (RPA). However, RPA neglects important many-body effects and can be inaccurate for strongly correlated systems like graphene.

Vertex corrections, accounting for electron-electron interactions, are crucial for obtaining accurate results. The QMC results demonstrate a significant improvement in accuracy compared to RPA calculations, exhibiting a more complex structure with sharper features and a more accurate description of the plasmon dispersion. Their work confirms the existence of distinct plasmon resonance peaks and a square-root relationship between energy and momentum when long-range Coulomb interactions dominate. These findings indicate that accurate theoretical descriptions of electronic transport in free-standing graphene require a more comprehensive approach, incorporating the effects of a finite Brillouin zone and a realistic representation of electron-electron interactions on the lattice. The researchers note that standard Random Phase Approximation calculations struggle to quantitatively predict the quasiparticle residue, highlighting the need for a formulation based on the full lattice Hamiltonian. Furthermore, the study demonstrates that plasmon behaviour is highly sensitive to the details of Coulomb screening, potentially transitioning to a different type of sound wave when long-range interactions are suppressed.