Electronic structure of cuprate-nickelate infinite-layer heterostructure

The discovery of superconductivity in Sr/Ca-doped infinite-layer nickelates Nd(La)NiO_(2)thin films inspired extensive experimental and theoretical research.However,research on the possibilities of enhanced critical temperature by interface heterostructure is still lacking.Due to the similarities of the crystal structure and band structure of infinite-layer nickelate La NiO_(2)and cuprate CaCuO_(2),we investigate the crystal,electronic and magnetic properties of La NiO_(2):CaCuO_(2)heterostructure using density functional theory and dynamical mean-field theory.Our theoretical results demonstrate that,even a very weak inter-layer z-direction bond is formed,an intrinsic charge transfer between Cu-3d_(x^(2)-y^(2))and Ni-3d_((x^(2)-y^(2)))orbitals is obtained.The weak interlayer hopping between Cu and Ni leaves a parallel band contributed by Ni/Cu-3d_((x^(2)-y^(2)))orbitals near the Fermi energy.Such an infinite-layer heterostructure with negligible interlayer interaction and robust charge transfer opens a new way for interface engineering and nickelate superconductors.

SYNTHESIS AND STRUCTURE OF A NOVEL INFINITE-LAYER COPPER(Ⅱ)COMPLEX BRIDGED BY OXAMIDE AND PYRIMIDINE

The complex polymer[Cu_2(oxap)(pyr)_2]_n(ClO_4)_(2n),where oxap^(2-)stands for N,N' -bis(2—aminopropyl)oxamide,have been synthesized.It crystallizes in monoclinic system, space group P2_1/C,with a=8.721(2),b=8.679(2),c=16.741(2),β=98.59(0),Z=4.The least-square refinement coverged at R=0.054,R_w=0.055 with 1869 unique reflections.The whole structure of the complcx consists of layers of two-dimensional network arraying along a-axis with perchlorate ions interspersed in the gap between layers.Inside the layer. trans-oxamide-bridged copper(Ⅱ)dimers connected by pyrimidine in an asymmetric fashion spread out along be plane to form an infinite two-dimensional network.

Structural stability of infinite-layer CaCuO_2 under high pressure

In situ high-pressure energy dispersive X-ray diffraction measurements on polycrystalline powder Ca-CuO2 with an infinite layer structure (IL CaCuO2) have been performed by using diamond anvil cell (DAC) instrument with synchrotron radiation. The results suggest that the crystal structure of IL CaCuO2 is stable under pressure up to 30 GPa at room temperature. According to Birch-Murn- aghan equation of state, assuming pressure derivative 4,=0Bthe bulk modulus B0=181 ?9 GPa is obtained.

Optimization for epitaxial fabrication of infinite-layer nickelate superconductors

The discovery of nickelates superconductor creates exciting opportunities to unconventional superconductivity. However, its synthesis is challenging and only a few groups worldwide can obtain samples with zero-resistance. This problem becomes the major barrier for this field. From plume dynamics perspective, we found the synthesis of superconducting nickelates is a complex process and the challenge is twofold, i.e., how to stabilize an ideal infinite-layer structure Nd_(0.8)Sr_(0.2)NiO_(2), and then how to make Nd_(0.8)Sr_(0.2)NiO_(2) superconducting? The competition between perovskite Nd_(0.8)Sr_(0.2)NiO_(3) and Ruddlesden−Popper defect phase is crucial for obtaining infinite-layer structure. Due to inequivalent angular distributions of condensate during laser ablation, the laser energy density is critical to obtain phase-pure Nd_(0.8)Sr_(0.2)NiO_(3). However, for obtaining superconductivity, both laser energy density and substrate temperature are very important. We also demonstrate the superconducting Nd_(0.8)Sr_(0.2)NiO_(2) epitaxial film is very stable in ambient conditions up to 512 days. Our results provide important insights for fabrication of superconducting infinite-layer nickelates towards future device applications.

Relevance of 3d multiplet structure in nickelate and cuprate superconductors

The recent discovery of superconductivity in doped rare-earth infinite-layer nickelates RNiO_(2),R=Nd,Pr as a new family of unconventional superconductors has inspired extensive research on their intriguing properties.One of the major motivation to explore the nickelate superconductors originated from their similarities with and differences from the cuprate superconductors,which have been extensively studied over the last decades but are still lack of the thorough understanding.In this short review,we summarized our recent investigation of the relevance of Ni/Cu-3d multiplet structure on the hole doped spin states in cuprate and recently discovered nickelate superconductors via an impurity model incorporating all the 3d orbitals.Further plausible explorations to be conducted are outlined as well.Our presented work provides an insightful framework for the investigation of the strongly correlated electronic systems in terms of the multiplet structure of transition metal compounds.