#quasiparticles

The twisted nanotubes that tell a story: Geometry-based approach can transmit magnon-based data

In collaboration with scientists in Germany, EPFL researchers have demonstrated that the spiral geometry of tiny, twisted magnetic tubes can be leveraged to transmit data based on quasiparticles called magnons, rather than electrons. Magnonics is an emerging engineering subfield that targets high-speed, high-efficiency information encoding without the energy loss that burdens electronics. This energy loss occurs when electrons flowing through a circuit generate heat, but magnonic systems don't involve any electron flow at all. Instead, an external magnetic field is applied to a magnet, upsetting the magnetic orientation (or "spin") of the magnet's electrons. This upset enables a tailored collective excitation called a spin wave (magnon), which travels through the magnet—like a ripple travels across a pond—while the electrons themselves stay put.

Proton - Positive vibes, pretty quarky. A classic.

Neutron - Like the proton, but neutral. Sometimes simplicity is best.

Electron - Less than 1/1000th the mass of our first 2 particles. Less mass means more quantum weirdness, which means more fun. At this point, wave-like behavior is becoming pretty significant.

Atom - A particle created from the combination of a nucleus of protons and neutrons and orbiting electrons, atoms are a chemist’s bread and butter. Otherwise, these are pretty straightforward. For simplicity, I’ll be excluding ions from this list, as they’re just atoms either with more or less electrons than they’re supposed to have.

Molecules - Created from several atoms bonded together by shared electrons, molecules are like atoms, but a little more complicated. They can rotate, vibrate, and much more. Molecules can have anywhere from 2 atoms to millions, and it’s molecules that describe most chemical systems.

Photon - The particle form of light. Photons are massless packets of energy that can be freely created or destroyed. This is about the point where things are really getting weird. Let’s see how.

Phonon* - The particle form of lattice vibrations. In a solid, vibrations of individual molecules are not independent of each other; however, these collective vibrations can be separated into a series of fixed patterns with their own energies. Those patterns can then be treated as particles in their own right, creating a “gas” of phonons. At this point, the particle definition is getting stretched quite a bit, but to deal with a system like this, this particle treatment works quite well to simplify the math and make it reasonable to deal with the system.

Hole* - One of the few of these that doesn’t end in “-on”, the hole represents an empty space where an electron should be on a material’s surface. The remaining particles on this list, much like the phonon, are designed to deal with solids in a convenient way. In this case, because the surface is made up of positively charged nuclei with negatively charged electrons on top, removing the electron leaves a positively charged space behind. Turns out, we can say this hole behaves like a particle itself, which moves as electrons shift across the surface. It should also be noted that electrons on a surface are treated differently than in free space, so one could argue that a surface electron is also its own kind of particle*.

Exciton* - We’ve seen that pairing a nucleus and electrons creates an atom, but what if we try to create the surface equivalent? Normally, putting an electron where a hole is would just move the hole, but what if we were to excite the electron so that it orbits around the hole? These are excitons. Excited, neutrally charged hydrogen-like particles on the surface of a solid. This is what my research focuses on.

Plasmon* - As our final particle, we’ll briefly talk about plasmons. I don’t know these particles too well, but from discussion with some colleagues who work with them, a plasmon is the particle form of oscillating electrons either on a surface or in a plasma. These are notably rather similar to phonons, in that we’re just treating the movement of many electrons by dividing them into collective states that we can treat as particles. At this point, the definition of a particle has been stretched pretty well beyond the typical limit, but for these kinds of system, mathematical convenience is beyond just desirable. It’s essential.

This list is not a list of every possible particle or quasiparticle. I’ve omitted antimatter, quarks, and many elementary particles in the standard model on one end, and on the quasiparticle end, I’ve omitted things like polarons (excitons + phonons) and polaritons (excitons/plasmons/phonons + photons). Maybe I’ll discuss these at another point, but there is still much I would like to learn about these kinds of systems. Either way, until next time, byyyyyyeeeeeee.

Physicists have captured their first clear glimpse of the tangled web woven by particles called anyons.

The observed effect, known as braiding, is the most striking evidence yet for the existence of anyons — a class of particle that can occur only in two dimensions. When anyons are braided, one anyon is looped around another, altering the anyons’ quantum states. That braiding effect was spotted within a complex layer cake of materials, researchers report in a paper posted June 25 at arXiv.org.

“It’s absolutely convincing,” says theoretical physicist Frank Wilczek of MIT, who coined the term “anyon” in the 1980s. Theoretical physicists have long thought that anyons exist, but “to see it in reality takes it to another level.”

Fundamental particles found in nature fall into one of two classes: fermions or bosons. Electrons, for example, are fermions, whereas photons, particles of light, are bosons. Anyons are a third class, but they wouldn’t appear as fundamental particles in our 3-D universe. “It’s not something you see in standard everyday life,” says physicist Michael Manfra of Purdue University in West Lafayette, Ind., a coauthor of the study. But anyons can show up as disturbances within two-dimensional sheets of material. Technically “quasiparticles,” anyons are the result of collective movements of many electrons, which together behave like one particle.

A key way anyons differ from fermions and bosons is in how they braid. If you were to drag one boson or one fermion around another of its own kind, there would be no record of that looping. But for anyons, such braiding alters the particles’ wave function, the mathematical expression that describes the quantum state of the particles. The process inserts an additional factor, called a phase, into the wave function.

In the new study, the researchers created a device in which anyons traveled within a 2-D layer along a path that split into two. One path looped around other anyons at the device’s center — like a child playing duck, duck, goose with friends — while the other took a direct route. The  two paths were reunited, and the researchers measured the resulting electric current.

The extra phase acquired in the trek around the device would alter how the anyons interfere when the paths reunited and thereby affect the current. So the researchers tweaked the voltage and magnetic field on the device, which changed the number of anyons in the center of the loop — like duck, duck, goose with a larger or smaller group of playmates. As anyons were removed or added, that altered the phase, producing distinct jumps in the current.

Seeing the effect required a finely tuned stack of layered materials to screen out other effects that would overshadow the anyons. “It is definitely one of the more complex and complicated things that have been done in experimental physics,” says theoretical physicist Chetan Nayak of Microsoft Quantum and the University of California, Santa Barbara.

Previous work had already revealed strong signs of anyons. For example, physicist Gwendal Fève and colleagues looked at what happened when quasiparticles collide with one another (SN: 4/9/20). Together, the two studies make “a very, very robust proof of the existence of anyons,” says Fève, of the Laboratoire de Physique de l’Ecole Normale Supérieure in Paris.

Visualizing a Hypothetical Planck Scale Substructure of Reality 

Geometer, animator and QGR research scientist Dugan Hammock displays some of his work visualizing the quasicrystalline point space on which our framework of emergence theory is built upon. This 3D point space which we call the QSN (Quasicrystalline Spin Network) is derived from a 4D quasicrystalline point space called the Elser-Sloane quasicrystal, which is a projection to 4D of the E8 lattice at a particular angle.

Observing exotic quasiparticle states in kagome superconductor CsV₃Sb₅

A research team led by Prof. Hao Ning of the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, in collaboration with Anhui University and the University of Science and Technology of China, has identified two distinct types of unusual low-energy quasiparticle states in the kagome superconductor CsV3Sb5 using single-atom impurities as local "quantum probes" combined with scanning tunneling spectroscopy. The study was recently published in Nature Physics. CsV3Sb5 has attracted growing interest for its unusual crystal structure and complex quantum phenomena. Evidence for time-reversal symmetry breaking remains under debate, and the mechanism of its superconductivity is still not fully understood. Studying its response to single-atom impurities provides a promising way to address these questions.

New method uses spin motion to control heat flow in magnetic materials

NIMS, in joint research with the University of Tokyo, AIST, the University of Osaka, and Tohoku University, have proposed a novel method for actively controlling heat flow in solids by utilizing the transport of magnons—quasiparticles corresponding to the collective motion of spins in a magnetic material—and demonstrated that magnons contribute to heat conduction in a ferromagnetic metal and its junction more significantly than previously believed. The creation of new principles "magnon engineering" for modulating thermal transport using magnetic materials is expected to lead to the development of thermal management technologies. This research result is published in Advanced Functional Materials. Thermal conductivity is a fundamental parameter characterizing heat conduction in a solid. The primary heat carriers are known to be electrons and phonons, quasiparticles corresponding to lattice vibrations. In current thermal engineering, efforts are underway to modulate thermal conductivity and interfacial thermal resistance by elucidating and controlling the transport properties of heat carriers. In particular, heat conduction modulation focusing on the transport and scattering of phonons has been actively studied over the past decades as "phonon engineering."

An earth-abundant mineral for sustainable spintronics

In 2023, EPFL researchers succeeded in sending and storing data using charge-free magnetic waves called spin waves, rather than traditional electron flows. The team from the Lab of Nanoscale Magnetic Materials and Magnonics, led by Dirk Grundler, in the School of Engineering, used radiofrequency signals to excite spin waves enough to reverse the magnetization state of tiny nanomagnets. When switched from 0 to 1, for example, this allows the nanomagnets to store digital information, a process used in computer memory, and more broadly, in information and communication technologies. This work was a big step toward sustainable computing, because encoding data via spin waves (whose quasiparticles are called magnons) could eliminate the energy loss, or Joule heating, associated with electron-based devices. But at the time, the spin wave signals could not be used to reset the magnetic bits to overwrite existing data.

Looking for elusive quantum particles? Try a bad metal, researchers suggest

Metals, as most know them, are good conductors of electricity. That's because the countless electrons in a metal like gold or silver move more or less freely from one atom to the next, their motion impeded only by occasional collisions with defects in the material. There are, however, metallic materials at odds with our conventional understanding of what it means to be a metal. In so-called "bad metals"—a technical term, explains Columbia physicist Dmitri Basov—electrons hit unexpected resistance: each other. Instead of the electrons behaving like individual balls bouncing about, they become correlated with one another, clumping up so that their need to move more collectively impedes the flow of an electrical current. Bad metals may make for poor electrical conductors, but it turns out that they make good quantum materials. In work published on February 13 in the journal Science, Basov's group unexpectedly observed unusual optical properties in the bad metal molybdenum oxide dichloride (MoOCl2).