Effect of epitaxial strain on the electronic structure and magnetic correlations in infinite-layer (Nd,Sr)NiO$_2$

Abstract

We present a theoretical study of the effect of electron-electron interactions and Sr doping on the electronic structure of infinite-layer (Nd,Sr)NiO2 using the density functional+dynamical mean-field theory approach. In particular, we explore the impact of epitaxial compressive strain that experience (Nd,Sr)NiO2 films on the electronic properties, magnetic correlations, and exchange couplings. Our results reveal the crucial importance of orbital-dependent correlation effects in the Ni 3d shell of Sr-doped NdNiO2. Upon doping with Sr, it undergoes a Lifshitz transition which is accompanied by a reconstruction of magnetic correlations: For Sr x < 0.2 (Nd,Sr)NiO2 adopts the Néel ( 111) antiferromagnetic (AFM) order, while for x > 0.2 the C-type (110) AFM sets in the unstrained (Nd,Sr)NiO2, with a highly frustrated region at x 0.2, all within DFT+DMFT at T = 290 K. Our results for the Néel AFM at Sr x = 0 suggest that AFM NdNiO2 appears at the verge of a Mott-Hubbard transition, providing a plausible explanation for the experimentally observed weakly insulating behavior of NdNiO2 for Sr x < 0.1. We observe that the Lifshitz transition makes a change of the band structure character from electron-to hole-like with Sr x, in agreement with recent experiments. Our results for magnetic couplings demonstrate an unanticipated frustration of the Ni 3d magnetic moments, which suppresses magnetic order near Sr x = 0.2. We find that the effect of frustration is maximal for Sr doping x 0.1 − 0.2 that nearly corresponds to the experimentally observed doping value. We conclude that the in-plane strain adjusts a bandwidth of the Ni x 2 − y 2 band, i.e., controls the effect of electron correlations in the Ni x 2 − y 2 orbitals. It suppresses the static C-type (110) ordering in (Nd,Sr)NiO2 for Sr x > 0.2. Moreover, the in-plane strain affects the character of the Fermi surface of Sr-doped NdNiO2 near the Brillouin zone A point, adjusting the crossover from electron-to hole-like behavior at high Sr x. The electronic structure and magnetic correlations of (Nd,Sr)NiO2 reveal an anomalous sensitivity upon a change of the crystal structure parameters.

Universal spin-glass behaviour in bulk LaNiO2, PrNiO2 and NdNiO2

“…Off-stoichiometry defects or chemical inhomogeneity in bulk samples are likely suspects to hamper superconductivity, while the role of the SrTiO 3 substrate has also been considered [6]. Strain effects may play an important role in the superconductivity of thin films, where a 3% larger c-axis lattice constant affects the Ni d z 2 orbital which may be crucial for nickelate superconductivity [7,8].…”

Nickelate superconductors: an ongoing dialog between theory and experiments

“…DFT+DMFT (dynamical mean-field theory) calculations according to the model interaction Hamiltonian (1) have been performed to further scrutinize the correlated nature of the different orbitals and clarify the multiband nature in RNiO 2 [47,49,[52][53][54][55][56][57][58][59][60]. In addition, DMFT has also been applied in combination with the quasiparticle self-consistent GW approximation in a parameter-free fashion [44,51].…”

Characterizing the superconducting instability in a two-orbital $d$-$s$ model: insights to infinite-layer nickelate superconductors

“…Undoubtedly, the most important question is the pairing symmetry and mechanism in this new family of superconductors and furthermore its similarity and difference from other transition metal based superconductors like Cuand Fe-based compounds. For example, given that the parent compound of infinite-layer NdNiO 2 is discovered not to host the long-range magnetic order [7][8][9][10][11][12][13][14][15] in spite of magnetic correlations [16][17][18][19][20] , whether the debated spin-fluctuation scenario for cuprate superconductors also applies for the infinite-layer nickelates is an intriguing question.…”

“…Physically, the minimal microscopic model to capture the essential physics of infinite-layer nickelates is a demanding task. Previous numerous electronic structure calculations based on DFT 7,[9][10][11][21][22][23][24][25][26][27][28][29] and/or DFT+DMFT [12][13][14][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] methodologies have provided fruitful understanding of the electronic structure of infinite-layer nickelates including R n+1 Ni n O 2n+2 with R = La, Nd, Pr for varying n 3,31,32 , whose calculated properties have been partly confirmed by recent experiments for n = 5 6 . One distinct feature associated with infinite-layer nickelates lies in the presence of the Nd-derived bands, whose self-doping effect on the magnetic and superconducting properties is highly debated, which is manifested by the opposite arguments supporting the single Ni-d x 2 −y 2 band description 23,29,33,46 versus the multi-orbital scenarios 8 , e.g.…”