The band theory of metals has been subjected to experimental tests many times and is now the accepted model of the behaviour of conductors and insulators. But it has to be modified when it comes to superconductivity. Electrical resistance is due to collisions of the electrons (whether treated as particles or waves) with impurities, imperfections […]
In the early days of organic chemistry, the word aromatic was used to describe fragrant substances such as benzene (from coal distillate), benzaldehyde (from cherries, peaches, and almonds), and toluene (from tolu balsam). It was soon realized, however, that substances classed as aromatic differed from most other organic compounds in their chemical behaviour. Today, the […]
At a fundamental level the term “quantum computing” implies de use of quantum effects that have no classical analogue to process information. In a “classical computer” information is held in bits, which can have two alternative values (0 and 1). quantum computer the values 0 and 1 are held simultaneously in an entangled state. This […]
In 1928, just two years after the formulation of quantum mechanics, the German physicist Arnold Sommerfeld modified the classical free-electron model by treating the electrons according to quantum mechanics. But the new theory still contained the unrealistic assumption that the electrons do not interact with the charged lattice ions except to collide with them. As […]
Electrical energy is now the dominant form of energy consumption in industrialized countries and is an essential element in the operation of many of the devices we use every day. For decades, one of the most poorly understood yet most practical properties of a piece of solid matter was its ability, or lack of ability […]
One of the first recognized successes of the early quantum theory arose, not from the study of radiation, but from the theory of solids. Once again in the physics of the first half of the 20th century Albert Einstein was at the forefront; but this time the story is seldom told. After presenting the hypothesis […]
Newton suggested that the apparent colours of natural objects depend on which colour is most strongly reflected or scattered to the viewer by the object. In general, there is no simple way of predicting from the surface structure, chemical composition, etc., what colours a substance will reflect or scatter. However, the blue colour of the […]
We know that incident light can provoke a strong optical response in metallic nanostructures due to the excitation of resonant plasmonic modes, i.e, the electrons in the metal become excited by the photons in the incident light and oscillate collectively. One of the most interesting properties of plasmon resonances is their associated enhancement and confinement […]
In nature, light harvesting organisms make extensive use of energy and electron transfer between adjacent molecules. Thus, in the photosynthetic cell of an algae, bacterium, or plant, there are light-sensitive molecules called chromophores, which contain a π-conjugated system (a system with alternate single and double bonds), arranged in an antenna-shaped structure named a photocomplex. When […]
With “many-body problem” we usually make reference to one that is very difficult to obtain exact solutions for, because the system involves interactions between more than two bodies. This kind of problem appears both in classical and quantum systems. In order to understand the physics of many-body systems, it is necessary to make use of […]