Long-living carriers in a strong electron–phonon interacting two-dimensional doped semiconductor

Abstract

Carrier doping by the electric field effect has emerged recently as an ideal route for monitoring many-body physics in two-dimensional (2D) materials where the Fermi level is tuned in a way that -indirectly-the strength of the interactions can also be scanned 1, 2 . The possibility of systematic doping in combination with high resolution photoemission has allowed to uncover a genuinely many-body electron spectrum in single-layer MoS 2 transition metal dichalcogenide, resolving three clear quasi-particle states, where only one state should be expected if the electron-phonon interaction vanished 3 . Our analysis combines first-principles and consistent complex plane analytic approaches and brings into light the presence and the physical origin of two gaps and the three quasi-particle bands which are unambiguously present in the photoemission spectrum. One of these states, though being strongly interacting with the accompanying virtual phonon cloud, presents a notably long lifetime which is an appealing property when trying to understand and take advantage of many-body interactions to modulate the transport properties 4-7 .The effective velocity and the lifetime of electron states close to the Fermi level determine most of the transport properties of metals, and the interactions with collective excitactions e.g. phonons, magnons or plasmons, are responsible for modifying or renormalizing these properties 8 .Specifically, phonons are the low energy excitations that more strongly couple to electron states in normal metals 9 . The interaction of electrons and phonons has a many-body character primarily because the Pauli exclusion principle prohibits the scattering to occupied states and because quantum mechanics allows the virtual excitation of phonons even in the absence of available energy for low energy electrons. All this physics is already contained in the most drastically simplified Einstein model, where one single optical phonon mode with energy ω 0 interacts with a single electron band with a parabolic dispersion in absence of coupling (Fig. 1a) 10 . The many-body coupling divides the spectrum in two regions, below and above ω 0 . On the one hand, for energies below ω 0 , elec-1 arXiv:1905.05168v1 [cond-mat.mes-hall]

Emergence of large nonadiabatic effects induced by the electron-phonon interaction on the complex vibrational quasiparticle spectrum of doped monolayer MoS2

“…This directly results from the enrichment of the FS topology, which gives rise to additional spin-conserving scattering channels connecting electron and hole states at the K(K ) and/or Q(Q ) valleys (see Supplemental Material of Ref. [31]), screening the lattice vibrations themselves through the electron-phonon coupling. Finally, within the large doping regime, the inplane acoustic Kohn anomalies develop instabilities at the q = K(K ) and M points, and also at q = Q(Q ) as doping increases (see Fig.…”

Strong band-filling-dependence of the scattering lifetime in gated MoS2 nanolayers induced by the opening of intervalley scattering channels

“…This is consistent with the stronger Fermi surface nesting associated with the simultaneous filling of all the available sub-bands in both the K/K and Q/Q valleys 34,69 . Moreover, both the sharp increasing part of the SC dome of gated MoS 2 34,66,67 -which develops as a function of doping from a quantum-critical point in the same doping range where the Q 2 Lifshitz transition is observed 2,34,61,67,73 -and the polaronic reconstruction of the Fermi sea in the K/K valleys revealed by high-resolution angle-resolved photoemission spectroscopy 71,74 , have been explicitly attributed to the strong increase in the EPC induced by the Lifhitz transition which allows the opening of additional intervalley scattering channels. Upon further increasing the electron doping, the related Fermi surface nesting has also been predicted to become so efficient as to destabilize the 2H crystal structure of pristine MoS 2 69 , thus potentially triggering the onset of a charge-density wave 60,75 and/or a structural transition towards the 1T /1T polytypes 60,[76][77][78][79] and thus suppressing the SC state.…”

Symmetric Helmholtz Fermi-surface harmonics for an optimal representation of anisotropic quantities on the Fermi surface: Application to the electron-phonon problem

“…Phonon properties have been computed within density functional perturbation theory [6] on a 8 3 q-point grid. Electron-phonon matrix elements have been computed on a coarse (8 3 , 8 3 ) k and q-point grid, and the Wannier interpolation method [7,8,[29][30][31] has been used to interpolate the matrix elements to the triangular vertices [8,13,16,[39][40][41]. As a last remark, we note that the high-quality triangulated Fermi surface as obtained by the method presented in Sec.…”

“…The main obstacle to overcome has been the ability to compute, at a reasonable cost, the electron-phonon matrix elements on dense meshes sampling the Brillouin Zone (BZ), which is necessary to capture the fine details of the FS anisotropy. Several efficient numerical techniques have been developed during the last years for this purpose [6][7][8], which have boosted tremendously the accuracy of theoretical studies on electron-phonon driven phenomena, such as temperature-dependent charge transport [9,10], non-adiabatic corrections to phonon dispersions [11][12][13], quasiparticle renormalization signatures in angle resolved photoemission spectra [14][15][16], or gap anisotropy in phonon-mediated superconductors [17].…”