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Related Concept Videos

Types Of Superconductors01:28

Types Of Superconductors

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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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Theory of Metallic Conduction01:17

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The conduction of free electrons inside a conductor is best described by quantum mechanics. However, a classical model makes predictions close to the results of quantum mechanics. It is called the theory of metallic conduction.
In this theory, Newton's second law of motion is used to determine the acceleration of an electron in the presence of an applied electric field. Then, its velocity is expressed via this acceleration.
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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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Types of Semiconductors01:20

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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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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.
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Properties of Transition Metals02:58

Properties of Transition Metals

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Transition metals are defined as those elements that have partially filled d orbitals. As shown in Figure 1, the d-block elements in groups 3–12 are transition elements. The f-block elements, also called inner transition metals (the lanthanides and actinides), also meet this criterion because the d orbital is partially occupied before the f orbitals.
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Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating
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Type-II Weyl semimetals.

Alexey A Soluyanov1, Dominik Gresch1, Zhijun Wang2

  • 1Theoretische Physik and Station Q Zurich, ETH Zurich, 8093 Zurich, Switzerland.

Nature
|November 27, 2015
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Summary

Researchers discovered a new type of Weyl fermion, a fundamental particle, in a novel phase of matter. This type-II Weyl fermion, found in topological semimetals like WTe2, differs from conventional types due to broken Lorentz symmetry.

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Area of Science:

  • Condensed Matter Physics
  • High-Energy Physics
  • Quantum Mechanics

Background:

  • Fermions, including electrons, are fundamental particles classified as Dirac, Majorana, or Weyl.
  • Experimental observation of Majorana and Weyl fermions was limited until recent discoveries in condensed matter systems like topological superconductors and semimetals.

Purpose of the Study:

  • To propose the existence of a novel type of Weyl fermion.
  • To identify this new particle in a previously unrecognized phase of matter.
  • To differentiate this new fermion from existing classifications.

Main Methods:

  • Generalizing the Dirac equation within the framework of condensed matter physics.
  • Analyzing the boundary between electron and hole pockets in material systems.
  • Identifying topological semimetals hosting these excitations.

Main Results:

  • Discovery of a type-II Weyl fermion, characterized by its emergence at the contact of electron and hole pockets.
  • This type-II Weyl fermion breaks Lorentz symmetry, a condition not strictly enforced in condensed matter physics.
  • Prediction of WTe2 as a material exhibiting type-II Weyl fermions as low-energy excitations around type-II Weyl points.

Conclusions:

  • The existence of type-II Weyl points in materials like WTe2 signifies a new class of topological semimetals.
  • These materials possess distinct physical properties compared to conventional Weyl semimetals with point-like Fermi surfaces.
  • This finding expands our understanding of fermion classification and their manifestations in exotic quantum materials.