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Related Concept Videos

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There is variation in the electrical conductivity of materials - metals, semiconductors, and insulators that are showcased with the help of the energy band diagrams.
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A superconductor is a substance that offers zero resistance to the electric current when it drops below a critical temperature. Zero resistance is not the only interesting phenomenon as materials reach their transition temperatures. A second effect is the exclusion of magnetic fields. This is known as the Meissner effect. A light, permanent magnet placed over a superconducting sample will levitate in a stable position above the superconductor. High-speed trains that levitate on strong...
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Intrinsic semiconductors are highly pure materials with no impurities. At absolute zero, these semiconductors behave as perfect insulators because all the valence electrons are bound, and the conduction band is empty, disallowing electrical conduction. The Fermi level is a concept used to describe the probability of occupancy of energy levels by electrons at thermal equilibrium. In intrinsic semiconductors, the Fermi level is positioned at the midpoint of the energy gap at absolute zero. When...
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When two or more atoms come together to form a molecule, their atomic orbitals combine and molecular orbitals of distinct energies result. In a solid, there are a large number of atoms, and therefore a large number of atomic orbitals that may be combined into molecular orbitals. These groups of molecular orbitals are so closely placed together to form continuous regions of energies, known as the bands.
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Network covalent solids contain a three-dimensional network of covalently bonded atoms as found in the crystal structures of nonmetals like diamond, graphite, silicon, and some covalent compounds, such as silicon dioxide (sand) and silicon carbide (carborundum, the abrasive on sandpaper). Many minerals have networks of covalent bonds.
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Granular topological insulators.

Abhishek Banerjee1, Oindrila Deb, Kunjalata Majhi

  • 1Department of Physics, Indian Institute of Science, Bengaluru 560 012, India. anil@physics.iisc.ernet.in.

Nanoscale
|May 10, 2017
PubMed
Summary
This summary is machine-generated.

Researchers created a macroscopic topological insulator (TI) phase using tiny TI nanocrystals. This granular material offers tunable properties and behaves like an ideal TI, opening new avenues for topological insulator research.

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Nanotechnology

Background:

  • Topological insulators (TIs) are materials with unique electronic properties, hosting conducting surface states while the bulk remains insulating.
  • Existing TI materials often suffer from defects and surface imperfections, limiting their ideal performance.
  • Nanocrystalline materials offer potential for novel quantum phenomena and tunable properties.

Purpose of the Study:

  • To experimentally demonstrate the emergence of a macroscopic topological insulator phase in a granular conductor.
  • To investigate the properties of topological surface states in nanocrystalline topological insulators.
  • To explore the tunability of topological and non-topological phases in designer materials.

Main Methods:

  • Fabrication of thin films from Bi2Se3 nanocrystals (approx. 10 nm x 10 nm x 2 nm).
  • Electrical transport measurements to probe surface and bulk conductivity.
  • Analysis of surface state penetration depth and tunability via nanocrystal size and coupling.

Main Results:

  • Demonstrated a macroscopic topological insulator phase in a granular conductor of coupled TI nanocrystals.
  • Observed decoupled top and bottom topological surface states with significant penetration depth (approx. 30 nm at 2 K).
  • Showcased the ability to tune the material between topological and non-topological phases by altering nanocrystal size and coupling.

Conclusions:

  • Granular/nanocrystalline topological insulators present a promising platform for realizing ideal TI properties.
  • This 'dirty' system exhibits superior TI characteristics compared to many single-crystal systems.
  • The tunable nature of these materials allows for the design of novel topological phases for future research and applications.