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Related Concept Videos

Semiconductors01:22

Semiconductors

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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.
Metals such as copper (Cu), zinc (Zn), or lead (Pb) have low resistivity and feature conduction bands that are either not fully occupied or overlap with the valence band, making a bandgap non-existent. This allows electrons in the highest energy levels of the valence band to easily transition to the conduction band upon gaining...
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Metal-Semiconductor Junctions01:24

Metal-Semiconductor Junctions

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The contact of metal and semiconductor can lead to the formation of a junction with either Schottky or Ohmic behavior.
Schottky Barriers
Schottky barriers arise when a metal with a work function (Φm) contacts a semiconductor with a different work function (Φs). Initially, electrons transfer until the Fermi levels of the metal and semiconductor align at equilibrium. For instance, if Φm > Φs, the semiconductor Fermi level is higher than the metal's before contact. The...
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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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Band Theory02:35

Band Theory

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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.
The energy difference between these bands is known as the band gap.
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Fermi Level Dynamics01:12

Fermi Level Dynamics

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The vacuum level denotes the energy threshold required for an electron to escape from a material surface. It is usually positioned above the conduction band of a semiconductor and acts as a benchmark for comparing electron energies within various materials.
Electron affinity in semiconductors refers to the energy gap between the minimum of its conduction band and the vacuum level and it is a critical parameter in determining how easily a semiconductor can accept additional electrons.
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Fermi Level01:18

Fermi Level

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The Fermi-Dirac function is represented by an S-shaped curve indicating the probability of an energy state being occupied by an electron at a given temperature. The Fermi level is the energy level at which there is a fifty percent chance of finding an electron, and it is positioned between the lower-energy valence band and the higher-energy conduction band.
At absolute zero temperature, electrons fill all energy states up to the Fermi level, leaving upper states empty. As the temperature rises,...
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Dirac Semimetals in Two Dimensions.

Steve M Young1, Charles L Kane2

  • 1Center for Computational Materials Science, U.S. Naval Research Laboratory, Washington, D.C. 20375, USA.

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PubMed
Summary
This summary is machine-generated.

Researchers discovered new 2D Dirac semimetals protected by symmetry. These materials exhibit unique Dirac cones, distinct from graphene, and are crucial for understanding topological and trivial insulators.

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Area of Science:

  • Condensed matter physics
  • Materials science
  • Solid-state physics

Background:

  • Graphene hosts 2D Dirac fermions but is gapped by spin-orbit coupling, classifying it as a quantum spin Hall insulator.
  • Existing 2D materials lack robust Dirac cones due to spin-orbit interactions.

Purpose of the Study:

  • To introduce and characterize novel symmetry-protected 2D Dirac semimetals.
  • To explore their distinct electronic properties compared to graphene and 3D Dirac semimetals.
  • To investigate the role of symmetry in creating and protecting Dirac points.

Main Methods:

  • Utilized a two-site tight-binding model to construct and analyze 2D Dirac semimetal phases.
  • Investigated the impact of nonsymmorphic space group symmetries on electronic band structures.
  • Examined phase transitions by breaking specific symmetries.

Main Results:

  • Demonstrated that single symmetry-protected Dirac points are not possible in 2D systems.
  • Identified three distinct 2D Dirac semimetal phases.
  • Showcased the critical role of nonsymmorphic symmetries in stabilizing Dirac points at the boundary of topological and trivial insulators.
  • Observed access to trivial insulators, topological insulators, and Weyl semimetal phases upon symmetry breaking.

Conclusions:

  • Symmetry-protected 2D Dirac semimetals offer a new platform for exploring exotic electronic phenomena.
  • Nonsymmorphic symmetries are essential for realizing these unique semimetal phases in two dimensions.
  • These findings provide a pathway to engineer topological and trivial insulating phases and Weyl semimetals.