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Related Concept Videos

Valence Bond Theory02:42

Valence Bond Theory

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Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
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Metallic solids such as crystals of copper, aluminum, and iron are formed by metal atoms. The structure of metallic crystals is often described as a uniform distribution of atomic nuclei within a “sea” of delocalized electrons. The atoms within such a metallic solid are held together by a unique force known as metallic bonding that gives rise to many useful and varied bulk properties.
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Crystal Field Theory - Octahedral Complexes02:58

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Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
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Ionic crystals consist of two or more different kinds of ions that usually have different sizes. The packing of these ions into a crystal structure is more complex than the packing of metal atoms that are the same size.
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Tetrahedral Complexes
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Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom,...
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Probe Type II Band Alignment in One-Dimensional Van Der Waals Heterostructures Using First-Principles Calculations
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Three-dimensional flat bands in pyrochlore metal CaNi2.

Joshua P Wakefield1, Mingu Kang1,2, Paul M Neves1

  • 1Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.

Nature
|November 8, 2023
PubMed
Summary

Researchers discovered three-dimensional (3D) flat bands in CaNi2, a material with a nickel pyrochlore lattice. Chemical tuning of these bands to the Fermi level induced superconductivity and enhanced electron correlations.

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Quantum Materials

Background:

  • Flat-band materials exhibit quenched kinetic energy, fostering electron correlation and emergent quantum phenomena.
  • Recent advances have realized flat bands in 2D systems, but their existence in 3D networks remains an open experimental question.

Purpose of the Study:

  • To investigate the existence and properties of three-dimensional (3D) flat bands in the C15 Laves phase metal CaNi2.
  • To explore the potential for realizing novel quantum phenomena in 3D flat-band systems.

Main Methods:

  • Utilized angle-resolved photoemission spectroscopy (ARPES) to probe electronic band structure.
  • Employed chemical tuning to modify the electronic properties of CaNi2.
  • Investigated electronic correlations and superconductivity through experimental measurements.

Main Results:

  • Observed a dispersionless band across the 3D Brillouin zone, identified as the predicted pyrochlore flat band.
  • Discovered two additional flat bands resulting from multi-orbital interference of Ni d-electrons.
  • Demonstrated that tuning the flat-band manifold to the Fermi level enhances electronic correlations and induces superconductivity.

Conclusions:

  • CaNi2 hosts a unique 3D topological flat band and additional multi-orbital flat bands.
  • Chemical tuning provides a pathway to engineer correlated states and superconductivity in 3D flat-band systems.
  • This work extends the concept of intrinsic band flatness to 3D, opening avenues for higher-dimensional quantum phenomena.