Graphene is a material with outstanding electronic characteristics. Many of them arise from the cone-like dispersion of charge carriers near the Fermi level (at which the occupation probability of energy levels is 0.5), where electrons behave as relativistic Dirac fermions, i.e., as if they had no mass. This excellent video from toutestquantique.fr summarizes them very […]
Superconductors are a particularly strange kind of metal. What makes them different is their behavior at very low temperatures – extremely low, that is, close to absolute zero. Basic thermodynamics dictates that in this regime we should expect all motion to cease, the constituents of the material being frozen at fixed positions. And with no […]
The exotic properties of layered materials have become a major focus of scientific research. The most famous member of this group is graphene which serves as a building block for few layered graphene and graphite as well as for single- and multi-walled carbon nanotubes. Here, each layer is an one-atom thick hexagonal sheet of sp […]
In an electromagnetic wave, the direction of the electric field is perpendicular to the direction of propagation of the wave. We say the wave is circularly polarized if the tip of the vector that represents the electric field describes a circular helix (thus circular polarization is sometimes called helicity) about the direction of propagation. Waves […]
An electric current can be visualized as a flow of electrons through a conducting piece of material. The less the resistance the material structure opposes to the flow of electrons the better a conductor it is. A part of this resistance appears at the surface of the material, where the electrons first encounter it; as […]
One of the main features of a F1 car is aerodynamics. How the car minimizes the drag imposed by the fact it is moving through a fluid, air, and how it takes advantage of the forces this movement generates to keep it stuck to the track, are most important for its performance. Even though the […]
Imagine that you enter a room full of a poisonous gas wearing a mask that is not good enough to prevent the gas reaching your lungs and killing you. The mask is not good enough because it would allow the gas to diffuse through the fabric it is made of, eventually reaching your nose and […]
Condensed matter • Materials • Physics • Quantum physics • Theoretical physics
At low temperatures, the resistivity of a metal (the inverse of its conductivity) is nearly constant. As the temperature of a material is lowered and as we approach absolute zero the resistivity should approach a constant value. Many metals, known as normal metals, behave in this way. The behaviour of another class of metals and […]
Condensed matter • Materials • Physics • Theoretical physics
Achieving room temperature superconductivity is among the most pursued but elusive goals of scientists. A paper uploaded to the arXiv in December 2014 claims to have observed superconductivity as high as 190 K in hydrogen sulfide at high pressure, breaking all the records thus far. If this observation is confirmed, cuprates will be knocked from […]
There are some concepts in physics difficult to grasp. Mainly because we have no direct evidence of them and, in orther to get some understanding, we rely on analogies that are not strictly correct. One of these difficult concepts is the spin of the electron. The analogy for the spin usually goes this way: Imagine […]