According to how the electronic band theory is usually explained, solids can be classified as insulators, semiconductors, or metals. But, actually, there is another kind of solid between semiconductors and metals, the semimetals. In insulators and semiconductors the filled valence band is separated from an empty conduction band by a band gap, in metals there […]
In 1882, Heinrich Hertz devoted himself to the study of electromagnetism, including the recent and still generally unappreciated work of Maxwell. Two years later he began his famous series of experiments with electromagnetic waves. During the course of this work, Hertz discovered the photoelectric effect, which has had a profound influence on modern physics. The […]
Major technological revolutions have occurred when the humankind has been able to harness natural resources, such as fire, electricity or nuclear energy. We are now in the verge of the so called second quantum revolution, that aims to harness two of the weirdest natural resources, coherence and entanglement. This is a tall order that calls […]
Interfacial electron transfer constitutes the key step in the conversion of solar energy into electricity and fuels. Required for fast and efficient charge separation, strong donor−acceptor interaction is typically achieved through covalent chemical bonding…or not. Experiences with donor−acceptor molecular diads and triads, conjugated polymers, and DNA, leads to the expectation that a covalent bonding is […]
Extended and refined by Bloch and others during the 1930s, Bloch’s theory, known as the band theory of solids, accounts very well for the conducting behaviour of materials. When atoms are joined together into a crystal, each of the individual quantum states of the atoms joins with the corresponding states in other (identical) atoms in […]
Topological insulators are electronic materials that have a bulk band gap like an ordinary insulator but have conducting states on their edge or surface. The conducting surface is not what makes topological insulators unique, but the fact that it is protected due to the combination of spin-orbit interactions and time-reversal symmetry. Researchers are chasing efficient […]
For centuries, metals were employed in optical applications only as mirrors and gratings. New vistas opened up in the late 1970s and early 1980s with the discovery of surface-enhanced Raman scattering and the use of surface plasmon (collective electronic oscillations at the surface of metals) resonances for sensing. However, it was not until the 1990s […]
There are compounds, called isomers, that have the same molecular formulae but different molecular structures or different arrangements of atoms in space. In the so-called cis-trans isomerism, isomers have different positions of groups or specific atoms with respect to a double bond, a ring or a central atom. For example, the numbers in the name […]
Condensed matter • Materials • Nanotechnology • Quantum physics • Theoretical physics
So-called “valleytronics” is a new type of electronics that could lead to faster and more efficient computer logic systems and data storage chips in next-generation devices. Valley electrons are so named because they carry a valley “degree of freedom.” This is a new way to harness electrons for information processing that’s in addition to utilizing […]
We have considered in some previous articles the importance of the spin-orbit interaction. But it is interesting to go through some basic concepts we have seen elsewhere once again in order to grasp the surprising discovery we will be talking about below. The analogy for the spin usually goes this way: Imagine that the electron […]