Nickelate superconductors: an ongoing dialog between theory and experiments

Abstract

After decades of fundamental research, unconventional superconductivity has recently been demonstrated in rare-earth infinite-layer nickelates. The current view depicts these systems as a new category of superconducting materials, as they appear to be correlated metals with distinct multiband features in their phase diagram. Here, we provide an overview of the state of the art in this rapidly evolving topic.

Geometric effects in the infinite-layer nickelates

“…The infinite-layer nickelates RNiO 2 (R = rare-earth element) have long been discussed as candidate materials for cuprate-like high-T c superconductivity [1][2][3][4]. Thus, the recent discovery of unconventional superconductivity in these systems has generated a substantial research attention [5][6][7]. Initially, superconductivity was observed in Sr-doped thin films for R = Nd but not for R = La [8].…”

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

“…The realization of the superconductivity (SC) in Srdoped NdNiO 2 films grown on a SrTiO 3 substrate 1 is the breakthrough in the decade-long pursuit of rare-earth nickelates 2,3 .…”

“…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.…”

Single-layer T'-type nickelates: Ni$^{1+}$ is Ni$^{1+}$

“…The reduced Ruddlesen-Popper series R n+1 Ni n O 2n+2 (R = rare-earth element) provides a special class of nickelates. These compounds are of particular interest both as a chemistry challenge and as a new arena for quantum materials [1][2][3]. Infinite-layer (n = ∞) nickelates are known since the early 1980s [4][5][6][7], while the synthesis of the n = 2 and 3 phases are more recent achievements [8][9][10][11].…”

“…The latest discovery of unconventional superconductivity in the infinite-layer case has sparked a renewed interest on these systems [15][16][17][18][19]. This long-sought finding has motivated a flurry of studies on the normal and superconducting-state properties of these systems [1], as well as the search for additional d 9 materials [20][21][22].…”