Absence of superconductivity in bulk Nd1−xSrxNiO2

Abstract

Recently superconductivity at 9 -15 K was discovered in an infinite-layer nickelate (Nd0.8Sr0.2NiO2 films), which has received enormous attention.Since the Ni 1+ ionic state in NdNiO2 may have the 3d 9 outer-shell electronic orbit which resembles that of the cuprates, it is very curious to know whether superconductivity discovered here has similar mechanism as that in the cuprates. By using a three-step method, we successfully synthesize the bulk samples of Nd1-xSrxNiO2 (x = 0, 0.2, 0.4). The X-ray diffractions reveal that all the samples contain mainly the infinite layer phase of 112 with some amount of segregated Ni. This has also been well proved by the SEM image and the EDS composition analysis. The resistive measurements on the Sr doped samples show insulating behavior without the presence of superconductivity. Temperature dependence of the magnetic moment under high magnetic fields exhibits a Curie-Weiss law feature with the paramagnetic moment of about 2B/f.u.. By applying pressure on Nd0.8Sr0.2NiO2 up to about 50.2 GPa, we find that the strong insulating behavior at ambient pressure is significantly suppressed, but superconductivity has not been observed either. Since the lattice constants derived from our XRD data are very close to those of the reported superconducting films, we argue that the superconductivity in the reported film may not originate from the expected Nd0.8Sr0.2NiO2, but arise from the interface or the stress effect.Since the discovery of high critical temperature superconductivity (HTS) in cuprates in 1986 [1] , there are plenty of experimental and theoretical studies to explore the intrinsic mechanism for superconductivity [2][3][4][5] . There is a general agreement that the parent compound of cuprates like La2CuO4 is a Mott insulator with a charge transfer gap and long-range antiferromagnetic (AF) order [6] . With chemical doping, the long-range AF order will be suppressed at a hole doping level (p  0.02) and d-wave superconductivity emerges at a higher doping level (p  0.05) [7][8][9] . After the efforts more than three decades, some common features have been observed, although the intrinsic pairing mechanism of HTS remains unresolved yet. These include two-dimensional electronic structure and coexistence with an AF order or spin fluctuations, all these also occur in most iron-based [10] and heavy fermion superconductors [11] .Moreover, in cuprates, it is also important that the spin S = 1/2 magnetic moment from 3d 9 electrons form the basic structure of the AF order. One intuitive way to explore the pairing mechanism of cuprates is to find additional high-TC superconductors with different transition metals but similar crystal and

Absence of superconductivity in Nd0.8Sr0.2NiOx thin films without chemical reduction

“…2(b). It exhibits insulating behavior with room-temperature resistivity ~0.48 cm, and is in good agreement with the transport properties and the absence of superconductivity in synthesized bulk Nd0.8Sr0.2NiO2 crystals [8]. Figure 3 plots the X-ray diffraction spectra of the NSNO films deposited on STO at different oxygen pressures that were measured by a four-circle Bruker D8 Discover thin-film X-ray diffractometer.…”

“…a) Powder X-ray diffraction spectrum. Red solid circles mark the peaks of the Nd0.8Sr0.2NiO2 phase and black solid circles indicate the diffraction peaks of the Nd0.8Sr0.2NiO3 phase[8]. b) Temperature-dependent resistivity of the bulk NSNO target.…”

Role of 4f states in infinite-layer NdNiO2

“…A dynamical mean field approximation treatment of Ni 3d fluctuations [11] in LaNiO 2 found little shifting and broadening of bands around E F , and no mechanism for the high resistivity. The large residual resistivity may be the result of the topotactic synthesis technique, with indications to be learned between the similarities and the distinctions between the doped thin films and doped bulk materials, [35] which also have similarly high residual resistivity.…”

Effective Hamiltonian for nickelate oxides Nd1−xSrxNiO2

“…Due to the similar crystal and electronic structure, LaNiO 2 has been theoretical studies as the possible analogs to the cuprates 5,6 . Recently, the superconductivity with the critical temperature up to T c ∼ 15 K is indeed discovered in Nd 0.8 Sr 0.2 NiO 2 thin film 7 , albeit the presence of the superconductivity remains debated 8,9 . Similar to copper oxides, perovskite nickelates (RNiO 3 , where R is rare earth or heavy metal such as Tl or Bi) display lots of strongly correlated physics properties, such as the sharp metal-insulator transitions, particular magnetic order, and charge order [10][11][12][13] .…”