Iron screws and other ferromagnetic materials consist of atoms with electrons that behave as miniature magnets. Typically, the magnets’ orientations are aligned within a specific region of the material, but they vary between different regions. Imagine groups of tourists in Times Square, eagerly gesturing towards the various billboards that surround them. However, with the application of a magnetic field, the spins of the magnets in the various regions align, resulting in the material becoming completely magnetized. It’s as if all the tourists suddenly synchronized their movements to point at the same sign.

The alignment of spins, however, does not occur instantaneously. Instead, when a magnetic field is present, neighboring regions, known as domains, interact with each other, causing changes to propagate unevenly throughout the material. Scientists often draw parallels between this phenomenon and the cascading of snow in an avalanche, where a single piece of snow initiates the movement, exerting force on neighboring pieces until the entire mountainside of snow is in motion, all heading in the same direction.

In 1919, Heinrich Barkhausen showcased the avalanche effect in magnets, providing a groundbreaking demonstration. Through the clever use of a coil and a magnetic material connected to a loudspeaker, it was demonstrated that these fluctuations in magnetism produce an audible crackling sound, now referred to as Barkhausen noise.

A recent study published in the journal Proceedings of the National Academy of Sciences reveals that Barkhausen noise can be generated not just by conventional methods but also by quantum mechanical phenomena.

Experimental detection of quantum Barkhausen noise is a groundbreaking achievement. This research signifies a significant breakthrough in the field of physics and holds potential for future applications in the development of quantum sensors and electronic devices.

“Barkhausen noise is the result of the small magnets flipping together,” explains Christopher Simon, the lead author of the paper and a postdoctoral scholar in the lab of Thomas F. Rosenbaum, a professor of physics at Caltech, the president of the Institute, and the Sonja and William Davidow Presidential Chair.

“We are conducting a familiar experiment, but with a twist—in a quantum material.” We are observing that quantum effects can result in significant changes at a macroscopic level.

Typically, magnetic flips occur in a classical manner, through thermal activation. In this process, particles must temporarily acquire sufficient energy to overcome an energy barrier. However, the new study reveals that these flips can also happen through a process called quantum tunneling, which operates on a quantum level.

In the phenomenon of tunneling, particles have the ability to traverse an energy barrier by seemingly bypassing it altogether. If this effect could be applied to everyday objects, such as golf balls, it would be as if the golf ball effortlessly passed through a hill instead of having to ascend it to reach the other side.

“In the quantum realm, the ball doesn’t need to traverse a hill as it transforms into a wave-like particle, with a portion already present beyond the hill,” explains Simon.

Furthermore, the latest research reveals a fascinating co-tunneling phenomenon, where clusters of tunneling electrons interact and coordinate to induce simultaneous flips in the direction of their spins.

“Traditionally, every individual mini avalanche, where clusters of spins flip, would occur independently,” explains co-author Daniel Silevitch, a research professor of physics at Caltech. “However, it has been discovered that, by means of quantum tunneling, two avalanches occur simultaneously.” This phenomenon arises from the interaction between two extensive collections of electrons, which communicate with each other and, as a consequence of their interactions, bring about these alterations. This unexpected co-tunneling effect quite surprised me.

Members of the team utilized a pink crystalline material known as lithium holmium yttrium fluoride, which was cooled to temperatures close to absolute zero (-273.15°C) for their experiments. They placed a coil around it, applied a magnetic field, and then observed small changes in voltage, similar to Barkhausen’s experiment in 1919.

The voltage spikes that are observed indicate the moments when clusters of electron spins change their magnetic orientations. When the groups of spins flip, one after the other, we can observe a series of voltage spikes known as the Barkhausen noise.

Through careful analysis of the noise, the researchers demonstrated the occurrence of a magnetic avalanche, even in the absence of classical effects. They demonstrated that these effects remained unaffected by variations in the material’s temperature. Through careful analysis, they reached the conclusion that quantum effects were the underlying cause of the significant transformations.

Scientists have found that these regions can hold an astonishing number of spins, far more than the rest of the crystal.

“We are observing this quantum behavior in materials containing an incredibly large number of spins.” Ensemblies of microscopic objects are all behaving in a coherent manner,” Rosenbaum says. “This work exemplifies the core focus of our lab: isolating and comprehending quantum mechanical effects.”

Researchers in Rosenbaum’s lab recently published another paper in PNAS that examines the fascinating connection between minute quantum effects and their influence on larger-scale phenomena. In the earlier study, scientists looked at the element chromium and showed how two different types of charge modulation—one involving ions and the other involving electrons—interact with each other at different length scales using quantum mechanics.

“Chromium has been a subject of study for quite some time,” remarks Rosenbaum, “yet only recently have we come to fully grasp this particular facet of quantum mechanics.” This is yet another instance of designing uncomplicated systems to uncover quantum phenomena that can be observed on a larger scale.

Researchers have identified the initial non-traditional superconductor that has a chemical composition with natural substances. The mineral under consideration is known as miassite, a remarkably distinctive material. Three further natural superconductors exist, all of which adhere to the principles outlined in the Bardeen-Cooper-Schrieffer hypothesis, which is recognized as the initial microscopic theory of superconductivity. The presence of lab-grown miassite is distinct.

Superconductivity refers to the property of a substance to exhibit zero electrical resistance, allowing it to transfer electricity without any energy loss while simultaneously generating magnetic fields outside the material. This phenomenon occurs at temperatures below a specific critical threshold. The production of electron pair bonding in a state is responsible for this phenomenon in typical superconductors. They are commonly referred to as cooperating pairs. Unconventional superconductors have similar macroscopic properties, but their state is attributed to a distinct factor.

Conventional and unusual superconductors exhibit a distinct disparity. The former has a critical temperature that is significantly closer to absolute zero, whereas the latter demonstrates the ability to exhibit high-temperature superconductence. High temperature refers to temperatures exceeding 77 Kelvin, which is still distant from achieving room-temperature superconductivity but is progressing towards it.

Miassite is the solution for this situation. Despite possessing a very low critical temperature of -267.75°C (-449.95°F), this material exhibits the characteristic features of superconductors with higher critical temperatures. Consequently, researchers aim to utilize this material in order to get a deeper comprehension of the underlying mechanisms responsible for unconventional superconductivity. The compound exhibits a sophisticated chemical formula consisting of 17 rhodium atoms and 15 sulfur atoms (Rh17S15).

Senior author Ruslan Prozorov from the Ames National Laboratory stated that it is improbable for this phenomenon to occur naturally and that it is intuitively believed to be the result of deliberate creation by a focused investigation. However, it is evident that it does.

Miassite was observed in the vicinity of the Miass River inside the Chelyabinsk Oblast of Russia. The ingredients responsible for its reactivity with oxygen contribute to its relatively low occurrence. Furthermore, due to its inability to form well-defined crystals, the evaluation of its qualities can only be conducted through laboratory growth.

Scientists were investigating rhodium-sulfur systems as a potential location for the presence of intriguing superconductors. Prozorov’s group maintained the material at a temperature just above absolute zero (-273.1°C/-460°F), and after achieving superconductivity, they conducted tests to determine its typical behavior.

A test known as the “London penetration depth” is conducted. Within a typical superconductor, a feeble magnetic field has the ability to permeate the entirety of the material at a consistent distance. In an atypical manner, this phenomenon varies in accordance with the temperature.

An alternative methodology involved subjecting the material to high-energy electrons, resulting in the formation of flaws. These flaws have a significant impact on unconventional superconductors. Miassite exhibited characteristics akin to those of an unusual superconductor.

“It is akin to uncovering a concealed fishing hole that is teeming with large, fatty fish.” Three novel superconductors were identified in the Rh-S system. According to Professor Paul Canfield, affiliated with Iowa State University and Ames Lab, it was determined through Ruslan’s meticulous measurements that miassite exhibits characteristics of an unusual superconductor. Canfield created miassite specifically for this endeavor.

The findings have been documented in a scholarly article published in the journal Communications Materials.

Earlier this month, researchers published an article outlining new evidence from an excavation in Jebel Irhoud (Morocco) that provides the earliest date yet for the presence of Homo sapiens. A variety of dating methods provide an age of about 315,000 years ago (kya). Prior to this, the earliest securely dated evidence for Homo sapiens were the bones from the Omo Kibish site in Ethiopia dating to about 195 kya.

The decades-long excavation at Jebel Irhoud has uncovered various types of palaeo archaeological data. The skeletal material (e.g. skull, mandible, teeth, humerus, hip bone) shows that there were at least five individuals. The assemblage of stone tools includes examples of the Mousterian industry and the Levallois napping technique. Both of these are closely associated with Neanderthals (Homo neanderthalensis), though are not exclusive to the species. Also, the majority of the tools were made from stone not native to the Jebed Irhoud area. Other recovered evidence includes examples of fire use and animal bones (primarily gazelle) showing signs of hunting and butchering.

Dating Methods

A variety of dating techniques helped establish the age of the new assemblage at 315 kya. The research team measured sediment from the different stratigraphic levels for the quantity of radiation present. They used electron spin resonance on bone samples. Finally, the researchers applied thermoluminescence to the stone tools that were in direct association with the bones. Unfortunately, the research team was unable to extract DNA from the bones.

Samples of stone tools recovered from Jebel Irhoud (Morocco).

Importance of Evidence

The importance of the evidence is twofold. First, it secures a mature development of Homo sapiens over 100,000 years earlier than previous evidence indicated. The date does not remove the firm placement of Homo sapiens within the Middle Pleistocene and during the Middle Palaeolithic. However, a date of 315 kya does provide overlap with the existence of Homo heidelbergensis. Previous evidence indicated that Homo sapiens developed from Homo heidelbergensis between 300 – 200 kya. The Jebel Irhoud data do not exclude this hypothesis but it means that Homo sapiens must have developed much earlier, probably closer to the nadir of Homo antecessor. It also means that Homo sapiens had much longer contemporaneity with Homo erectus than previously known.

The second important aspect is the location of the finds. Morocco is around 3,400 miles from Ethiopia. The prevailing models of human evolution place the development of Homo sapiens in Ethiopia. This makes sense based on the quantity and age of data recovered from sites in Ethiopia and in East Africa. The location of the new finds, and the fact that the fossils represent developed Homo sapiens, indicate that our ancestors had already moved across the continent in viable population sizes so the broad evolutionary changes that resulted in our species had already occurred.

The Jebel Irhoud evidence does not lessen the importance of East Africa in understanding the development of our species. Rather, it contributes data to provide a richer, more robust picture of hominid development and migrations across Africa and the world. It is quite exciting to imagine what else the excavation will recover to further elucidate the history of hominids and Homo sapiens. What are your thoughts?

Nature