Crossover from lattice to plasmonic polarons of a spin-polarised electron gas in ferromagnetic EuO

Abstract

Strong many-body interactions in solids yield a host of fascinating and potentially useful physical properties. Here, from angle-resolved photoemission experiments and ab initio many-body calculations, we demonstrate how a strong coupling of conduction electrons with collective plasmon excitations of their own Fermi sea leads to the formation of plasmonic polarons in the doped ferromagnetic semiconductor EuO. We observe how these exhibit a significant tunability with charge carrier doping, leading to a polaronic liquid that is qualitatively distinct from its more conventional lattice-dominated analogue. Our study thus suggests powerful opportunities for tailoring quantum many-body interactions in solids via dilute charge carrier doping.

Many-Body Calculations of Plasmon and Phonon Satellites in Angle-Resolved Photoelectron Spectra Using the Cumulant Expansion Approach

“…(7) and (14)] is included in the calculation of the spectral function, which can thus contain both plasmon and polaron satellite features. This concurrence of plasmon and polaron satellites has been observed experimentally in the case of the ferromagnetic semiconductor EuO, and confirmed by first principles calcula-tions [60]. Experimental ARPES spectra for Gd-doped EuO are reported in Fig.…”

Exploring the intrinsic limit of the charge-carrier-induced increase of the Curie temperature of Lu- and La-doped EuO thin films

“…It is challenging to grow stoichiometric EuO thin films, mainly because of their tendency to form higher oxides such as Eu 3 O 4 and Eu 2 O 3 . This problem could be solved for many applications by using adsorption-controlled growth at substrate temperatures >400 • C. Previous work showed that using this method it is possible to reproducibly grow close-to-stoichiometric EuO films with excellent crystalline quality according to XRD [20,[23][24][25][26]. Reaching a similar film quality with lower-temperature growth is much more challenging.…”

“…Importantly, not all dopant atoms contribute an electron to the conduction band. The only published measurements quantifying the relationship between the doping concentration x and free carrier density n (allowing calculation of the fractions of active and inactive dopants), and T C of doped EuO, are on Gd-doped EuO films [22][23][24]. These experiments show a roughly logarithmic increase of T C up to 129 K when plotted as a function of n. For high doping concentrations x 10% the mobile carrier density saturates around 1 × 10 21 cm −3 .…”

SternheimerGW: A program for calculating GW quasiparticle band structures and spectral functions without unoccupied states

“…These features were originally examined for the homogeneous electron gas, 9,[27][28][29][30] but have recently been investigated both experimentally and theoretically for charge carriers in semiconductors coupling to plasmons, 1,[31][32][33][34][35][36][37][38][39][40][41][42][43] Fröhlich polarons [44][45][46][47][48][49][50][51][52][53][54][55] or hybridizations of these excitations. 56,57 While the GW approximation does produce satellite features in the spectral function, their strength is overestimated and their energy is blue-shifted. [27][28][29]32,58 This mismatch is intrinsic to the GW approximation and cannot be overcome by self-consistency.…”