Parts Of An Electron

Credit: pixabay.com

Studying basics of matter all around us leads our understanding to its fundamental building block called atom.  Atom is made up of electrons revolving in orbits around a nucleus containing protons and neutrons.  Protons and neutrons are well understood not to be the fundamental particles and are having sub-fundamental particles like quarks. Until now, electrons have been regarded as an elementary particle—which means that scientists thought they had no component parts or substructure. But now, electrons have been observed decaying into two separate parts—causing physicists to rethink what they know about the particles.

Electron having charge exhibiting spin and orbital motions, until now, standard physics generally accepted that an electron was a fundamental particle – that it was not made of smaller components. However, as early as 1980 theorists had predicted an electron could be made of three smaller pieces: A “Spinon” (providing spin), an “Orbiton” (providing the orbit) and a “Holon” (carrying the charge). In 1996, physicists seemed to split an electron into a holon and spinon. American physicists made a theoretical prediction that if we confine electrons to individual atomic chains, the Wiedemann-Franz law could be strongly violated. In this one-dimensional world, the electrons split into two distinct components or excitations, one carrying spin but not charge (the spinon), the other carrying charge but not spin (the holon). Recently, Swiss and German researchers led by experimenter Thorsten Schmitt fired a tightly focused X-ray beam at a copper-oxide compound called “strontium cuprate,” special because particles in it can only move in one-dimension, one degree of freedom – forward or backwards. They observed an electron split into two of the three predicted parts – a Spinon and an Orbitron. What solidified their observation is finding distinct properties for the two parts. According to researchers “these quasiparticles can move with different speeds and even in different directions in the material. Thus, researchers have separated an electron into two smaller quasi-particles – a “Spinon” and an “Orbiton;” meaning they have physically separated the spin and the orbit properties of an electron.

Electrons in atoms behave like waves, and when researchers excite them to higher orbits, those waves can split up, revealing the constituent characteristics of the electron. The electrons split into two separate parts, each carrying a particular property of the electron. The first, called a "spinon" carries its spin—which causes electrons to behave a bit like compass point. The second, called an "orbiton" carries its orbital moment—that's what keeps electrons moving around the nucleus of atoms.  It had been known for some time that, in particular materials, an electron can in principle be split, but until now the empirical evidence for this separation into independent spinons and orbitons was lacking. The observations were made in the copper-oxide compound Sr2CuO3, a material peculiar because the particles in it are constrained to move only in one direction, either forwards or backwards. The electron-splitting was measured using X-rays to measure the energy and momentum of particles in the material. The beam excited the electron to a higher orbital, causing the beam to lose a fraction of its energy in the process, then rebounded. The team measured the number of scattered photons in the rebounding beam, along with their energy and momentum, and compared this with computer simulations of the beam's properties. The researchers found that when the photons' energy loss was between about 1.5 and 3.5 electron volts, the beam's spectrum matched their predictions for the case in which an orbiton and spinon had been created and were moving in opposite directions through the material. Now that we know where exactly to look for them, we are bound to find these new particles in many more materials. These quasi-particles can move with different speeds and even in different directions in the material. Atomic electrons have this ability because they behave like waves when confined within a material. When excited, that wave splits into multiple waves, each carrying different characteristics of the electron; but they cannot exist independently outside the material.

In order for electrons to fractionalize, many of them must be tightly confined so that they repel each other. In trying to stay apart, the electrons modify how they behave so that their magnetism (which is associated with spin) and charge separate into the two new quasi-particles. In condensed matter physics, quasi-particles are phenomena of groups of particles that behave as if they were particles. Physicists first observed spinons and holons in 2009 by confining electrons in a quantum wire and detecting how electrons in a nearby metal could tunnel into the quantum wire by splitting into the two quasi-particles. One unsolved part of electron fractionalization involves figuring out what happens to an electron’s Fermi statistics after spin-charge separation. Fermi statistics describe the properties of all particles that obey the Pauli Exclusion Principle, which says that no two of these particles can occupy the same quantum state. In the Standard Model, these particles include all the fermions, one of which is the electron. The question that physicists ask is, when the electron fractionalizes into its spin and charge, where do its Fermi statistics go? The Fermi statistics have previously been proposed to be either with the spin or with the charge. But now scientists suggest that these seemingly divergent possibilities can be unified into one picture. The physicists suggest that the electron fractionalizes into not just two, but three components that carry the electron’s spin, charge, and Fermi statistics. While spinons and chargons (or holons) are the first two carriers, the Fermi statistics are carried by a Majorana fermion. The physicists also illustrated these ideas on a honeycomb lattice to demonstrate how the proposal works.

Overall, a better understanding of electron fractionalization could have useful applications, such as in designing quantum computers and achieving quantum entanglement at long scales. The findings of electron parts will lead to a deeper understanding of the different types of quantum entanglement in many-electron states at very low temperatures. Quantum computers manipulate the entanglement in a complex manner. Though the electrons can split, the resulting two parts can't escape the material in which they are produced. Regardless of that, the finding should transform our understanding of superconductivity—and could even eventually make high-temperature superconductivity a real possibility.  Orbitons could also aid the quest to build a quantum computer — which would use the quantum properties of particles to perform calculations more quickly than its classical counterpart.  A major stumbling block for quantum computing has been that quantum effects are typically destroyed before calculations can be performed. The advantage here is that orbital transitions are extremely fast, taking just femtoseconds. That’s so fast that it may create a better chance for making a realistic quantum computer. That seems be the direction this will go in the future — encoding and manipulating information in both spinons and orbitons.

Current Issue

NEWSLETTER