La2CuO4

La2CuO4
Name	Lanthanum cuprate
Formula	La2CuO4
Crystal system	Orthorhombic / Tetragonal

La2CuO4 is a layered transition metal oxide notable as the parent compound of the high-temperature high‑Tc superconductors discovered in the late 20th century. It occupies a central place in research linking Bardeen–Cooper–Schrieffer theory debates, materials discovered by teams associated with IBM, Bell Laboratories, and groups around Chu, Müller, and Bednorz. La2CuO4 provides a prototypical platform for studies involving quantum correlated electrons, Wigner lattice concepts, and competing orders investigated at institutions such as MIT, Stanford, and Cambridge.

Introduction

La2CuO4 is a ceramic oxide composed of Lanthanum and Copper with oxygen in a perovskite‑related framework studied intensively after the 1986 report by Bednorz and Müller that linked copper oxides to superconductivity. As an antiferromagnetic insulator at stoichiometry, it forms the undoped end member of families examined by research groups at Tokyo, Geneva, and Zurich. Its relevance spans experimental programs at Los Alamos, Argonne, and synchrotron facilities like ESRF for spectroscopic probes.

Crystal Structure and Chemical Properties

The crystal structure of La2CuO4 adopts a layered perovskite motif related to the K2NiF4 structure and shows a low‑temperature orthorhombic distortion from a high‑temperature tetragonal phase. Copper atoms occupy square‑planar coordination sites forming CuO2 sheets separated by La–O blocks, a motif shared with materials synthesized in groups at Bell Labs and IBM Research. Substitutions on the La site with Strontium or Barium were pioneered by teams at Houston and Alabama to introduce holes, paralleling chemical strategies used by Wollan and Penny in oxide chemistry. Oxygen nonstoichiometry and interstitial oxygen, topics explored at Oak Ridge and NIST, influence lattice parameters and tilt patterns studied by crystallographers at Royal Institution and Max Planck.

Electronic Structure and Magnetism

Electronically, La2CuO4 is a charge‑transfer insulator within the Zaanen–Sawatzky–Allen scheme and exhibits strong on‑site Coulomb repulsion described in model Hamiltonians promoted by Anderson and Zaanen. The single Cu 3d x2–y2 band hybridizes with O 2p orbitals producing an antiferromagnetic Néel ground state observed by neutron groups at ILL and Oak Ridge. Spin dynamics and magnon dispersions were mapped by researchers connected to Harvard, Princeton, and Columbia using inelastic neutron scattering and resonant probes developed at SLAC and Brookhaven.

Superconductivity and Phase Diagram

Upon hole doping via substitution (e.g., La1.85Sr0.15CuO4) or oxygen intercalation, insulating La2CuO4 evolves to a superconducting dome, an observation that catalyzed work at University of Houston, University of Tokyo, and University of Geneva. The phase diagram shows competing antiferromagnetic, superconducting, and pseudogap phases debated in publications involving Thomas and theorists from Caltech, Chicago, and Cambridge. Key experimental milestones involved groups at Bell Labs, IBM Research, and Los Alamos that traced doping dependence, critical temperatures, and vortex physics connecting to studies by Abrikosov and Ginzburg in superconductivity theory.

Synthesis and Materials Processing

Synthesis techniques for La2CuO4 include solid‑state sintering, sol–gel routes, molecular beam epitaxy (MBE), and pulsed laser deposition (PLD) used by thin‑film groups at Berkeley, UIUC, and Penn. High‑pressure and floating‑zone growth methods were developed in facilities at Tohoku, Max Planck, and Oak Ridge, enabling single crystals for spectroscopy used by Columbia and Princeton teams. Processing challenges such as controlling La/Cu stoichiometry, oxygen content, and defect chemistry have been addressed by materials science programs at MIT, Imperial College, and ETH.

Experimental Characterization Techniques

Characterization employs X‑ray diffraction at synchrotrons like ESRF and APS, neutron scattering at ILL and Oak Ridge, angle‑resolved photoemission spectroscopy (ARPES) at SLAC and MAX IV, and scanning tunneling microscopy (STM) performed in groups at IBM Research and Stanford. Nuclear magnetic resonance (NMR) and muon spin rotation (μSR) experiments conducted at PSI and TRIUMF probe local magnetism; Raman and infrared spectroscopies at Columbia and Harvard track phonons and electron–phonon interactions relevant to pairing mechanisms discussed by theorists affiliated with University of Illinois and University of Cambridge.

Applications and Technological Relevance

While pristine La2CuO4 is insulating, its doped derivatives underpin technologies and concepts explored by industrial and academic labs including IBM Research, Hitachi, and Sony in superconducting electronics, Josephson junction research, and magnetic sensor prototypes linked to programs at NIST and CERN. Research on heterostructures combining La2CuO4 layers with oxides studied by teams at MIT and Harvard informs oxide electronics, neuromorphic devices, and spintronics initiatives pursued at University of Tokyo and KAIST.

Category:Copper oxides