Observation of Plasmarons in Quasi-Freestanding Doped Graphene

Abstract

A hallmark of graphene is its unusual conical band structure that leads to a zero-energy band gap at a singleElectrons in metals and semiconductors undergo many complex interactions, and most theoretical treatments make use of the quasiparticle approximation, in which independent electrons are replaced by electron-and holelike quasiparticles interacting through a dynamically screened Coulomb force. The details of the screening are determined by the valence band structure, but the band energies are modified by the screened interactions. A complex self-energy function describes the energy and lifetime renormalization of the band structure resulting from this interplay.Bohm and Pines (1) accounted for the short-range interactions between quasiparticles through the creation of a polarization cloud formed of virtual electron-hole pairs around each charge carrier, screening each from its neighbors. The long-range interactions manifest themselves through plasmons, collective charge density oscillations of the electron gas that can propagate through the medium with their own band-dispersion relation.These plasmons can in turn interact with the charges, leading to strong self-energy effects. Lundqvist predicted the presence of new composite particles called plasmarons formed by the coupling of the elementary charges with plasmons (2). Their distinct energy bands should be observable using angle-resolved photoemission spectroscopy (ARPES), but so far have only been observed by optical (3, 4) and tunneling spectroscopies (5), which probe the altered density of states.Understanding the coupling between electrons and plasmons is important because of new "plasmonic" devices proposed to merge photonics and electronics. Graphene in particular has been proposed as a promising candidate for such devices (6-8). Plasmarons have been predicted to occur in graphene and to be observable in ARPES (9, 10), yet their detailed dispersion and interaction with defects remain unknown. Here we present a

Studies of Li intercalation of hydrogenated graphene on SiC(0001)

“…For the as grown monolayer graphene, the Dirac crossing point of the π band is located around 0.4 eV below the Fermi level indicating n-type doping due to the charge transfer from SiC substrate [25]. However, after hydrogenation hydrogenated SiC(0001) [26][27] has demonstrated that there is no gap opening at the K point which is consistent to our Li case. Instead they observed a plasmaronic dispersion,…”

“…a diamond-like shape, near the Dirac energy. A shadow band next to the main band was also detected and suggested to be a plasmaron band [26][27]. We observe no pronounced deformation of the π-band around the Dirac point after Li deposition.…”

“…We observe no pronounced deformation of the π-band around the Dirac point after Li deposition. This can be due to the high doping concentration obtained which reduces the strength of the plasmaron band [27]. After heating the sample to 300 ºC two π-bands are clearly visible as seen in Fig 6d).…”

Plasmonics of 2D Nanomaterials: Properties and Applications

“…It has been theoretically predicted that those composite quasiparticles named plasmarons, which consist of the carrier charges and plasmons in the material. The energy band of plasmarons can be observed by high‐resolution ARPES, which exist in the graphene sheet on SiC substrate 63. As shown in Figure 2e, the Dirac energy spectrum of quasi‐freestanding graphene is shown on the left panel, and it is in a non‐interacting picture, the momentum has two components as k x and k y , while E D presents the energy of the Dirac point.…”

Plasmas meet plasmonics

“…Whilst graphene and its derivatives [143][144][145][146][147] have been used in combination with metallic nanostructures for plasmonic-based sensing [148], it is also useful by itself. In fact, a quasiparticle termed a 'plasmaron' (combination of a plasmon and an electron) was recently observed in free standing graphene [149]. For graphene, plasmons are excited in the near infrared (or THz range) [150,151].…”