Spin and charge excitations in artificial hole- and electron-doped infinite layer cuprate superconductors

Abstract

The asymmetry between electron-and hole-doping in high critical-temperature superconducting (HTS) cuprates is key information for the understanding of Cooper pairs formation mechanisms.Despite intensive studies on different cuprates, a comprehensive description of related magnetic and charge excitations is still fragmentary. In the present work, artificial cuprates were used to cover the entire phase diagram within the same HTS family. In particular, Cu L 3 -edge resonant inelastic x-ray scattering (RIXS) measurements were performed on artificial n-and p-type infinite layers (IL) epitaxial films. Beside several similarities, RIXS spectra show noticeable differences in the evolution, with doping level, of magnetic and charge intensity and damping. Compatible trends can be found in spectra measured on bulk cuprates, as well as in theoretical calculations of the spin dynamical structure factor S(q, ω). The findings give a deeper insight about the evolution of collective excitations across the cuprate phase diagram, and on underlying general features, only connected to the doping type. Moreover they pave the way to the exploration of general properties of HTS physics over a broad range of conditions, by means of artificial compounds not constrained by the thermodynamic limitations governing the chemical stability of bulk materials.

Doping evolution of the charge excitations and electron correlations in electron-doped superconducting La2−xCexCuO4

“…Bimagnon excitations, however, were suggested to disperse weakly near BZ center and appear as tails of the ∆m J = 1 paramagnon excitations [29,30]. Therefore, the higher energy feature is most likely to be charge excitations, consistent with previous interpretations [11][12][13][14].…”

“…The excitation at lower energy with stronger intensity can be assigned as spin fluctuations, following previous studies of holedoped cuprates [15][16][17][18][19]. The other excitation with higher energy and weaker intensity was absent in RIXS measurements of hole-doped systems, and appears to be unique to electron-doped cuprates [11][12][13][14]. This feature disperses much more steeply, and merges into the high energy dd excitations above ∼ 1.3 eV with in-plane wavevector q ≥ 0.2 reciprocal space units (r.l.u).…”

“…Here we report RIXS measurements on electron doped LCCO [25] at the Cu L 3 -edge, focusing on charge excitations around the two dimensional BZ center with various c-direction momentum transfer. By using dopingconcentration-gradient (combi) films [26], we are able to provide much finer doping dependence than measured previously covering the optimal superconducting state to the non-superconducting metallic phase [11][12][13][14]. We find that the charge excitations have mostly collective arXiv:1906.11354v1 [cond-mat.supr-con] 26 Jun 2019 nature, and exhibit out-of-plane momentum transfer dependence.…”

Electron self-energy from quantum charge fluctuations in the layered t−J model with long-range Coulomb interaction

“…For electron-doped cuprates (e-cuprates), charge excitations were reported in both a low-energy region [6,9] with a scale of the superexchange interaction J (≈150 meV) and a high-energy region [2,7,8,[10][11][12] with a scale larger than J. These features were captured in the layered t-J model with the long-range Coulomb interaction as a dual structure of the charge excitations [13].…”

“…The origin of high-energy charge excitations in h-cuprates [27] is also highly controversial. High-energy excitations can be (i) specific to e-cuprates [7,10], (ii) present as a broad peak of the particle-hole excitation spectrum [27], (iii) present as plasmons similar to the e-cuprates [11,12,17,28,29], and (iv) related to strange metal physics [30,31], not to plasmons.…”