The world of modern physics has been revolutionized by the emergence of twisted materials, also known as moiré structures. These remarkable systems have been hailed as today’s “alchemy” due to their ability to create entirely new phases of matter through simple geometric manipulation. By carefully controlling the twist angle, physicists can engineer entirely new quantum states, opening doors previously closed to experimental science.

One striking example of this effect is twisted bilayer graphene, where superconductivity unexpectedly emerges, even though graphene layers individually cannot become superconducting. This phenomenon has fascinated scientists and engineers alike, as it holds promise for a wide range of technological applications, from quantum simulators to ultrasensitive terahertz sensors and single-photon detectors.

However, until now, the focus has predominantly been on hexagonal lattices twisted around what are known as K-points – special points of electronic momentum symmetric under 120-degree rotations. Only a handful of materials such as graphene, MoTe2, MoSe2, and WSe2 have been explored experimentally.

In a groundbreaking new research published in Nature, an international team of researchers introduces an entirely new twisting paradigm based on the M-point of the electron momentum, significantly expanding the moiré landscape. This breakthrough has opened up a completely new class of twisted quantum materials with entirely new quantum behavior.

The position of the electronic band minimum is key,” explains Dumitru Călugăru, a Leverhulme-Peierls fellow at the University of Oxford. “By shifting our focus to the M points, we unlock a completely new class of twisted quantum materials with entirely new quantum behavior.”

The research team began by identifying hundreds of candidate materials suitable for this novel type of twisting. These materials were systematically classified based on the position of their electronic band minimum, a critical feature controlling the resulting quantum properties of the twisted layers.

Out of these materials, two (SnSe2 and ZrS2) – with band minimum at the M point — were chosen for the in-depth current study. “Unlike K-point twisting, where moiré bands typically exhibit topological characteristics, we found the M-point twisted bands to be topologically trivial yet remarkably flat,” explained Haoyu Hu, a postdoctoral researcher at Princeton.

Through extensive microscopic ab initio calculations – requiring over six months of computational effort – Yi Jiang and Hanqi Pi (Donostia International Physics Center) demonstrated that the electron bands become significantly flattened at low twist angles of about three degrees. Flattening electron bands effectively slows down electrons, enhancing their mutual interactions, and giving rise to novel quantum phenomena.

“This flattening can localize electrons in either a hexagonal lattice or a kagome lattice arrangement,” Jiang noted. Pi further elaborated, “Such localization means we can now experimentally realize diverse quantum states, potentially including quantum spin liquids.”

Quantum spin liquids, elusive states that have fascinated physicists, promise exciting applications including possible pathways to high-temperature superconductivity. However, they have never been conclusively observed experimentally in bulk materials, largely because of extreme difficulties in precisely controlling doping (adding or removing electrons) and other essential material properties.

Twisted materials, however, offer greater experimental controllability due to their tunable structure and the possibility of electrostatic gating – a technique which allows the doping of electrons without degrading the material, overcoming many of these historical hurdles.

The team’s theoretical predictions and detailed electronic models represent a major step toward observing these states in realistic materials. Other phases of matter identified, such as unidirectional spin liquids and orthonormal dimer valence bond phases, are entirely new and unique to the M-point system.

Yet, this research transcends theory. Collaborators in quantum materials chemistry – Leslie Schoop (Princeton University) and Claudia Felser (Max Planck Institute, Dresden) – have already successfully synthesized bulk crystals of several predicted candidate materials, providing the critical first step toward practical realization.

World-leading experts in 2D materials – including Dmitri Efetov (Ludwig Maximilian University of Munich), Jie Shan, and Kin Fai Mak (both at Cornell University) – then are exfoliating these bulk crystals into single-layer sheets, clearly to demonstrate the experimental feasibility of the proposed platform.

“The experimental realization of these materials is critical. Once twisted, gated, and measured, these new quantum states may become tangible realities,” said B. Andrei Bernevig, Professor of Physics at Princeton University. Every new twist we perform seems to yield surprises. Fundamentally, these materials offer a gateway to quantum states of matter nobody has envisioned.

Because they are so experimentally controllable, the possibilities truly are limitless.”

The study by scientists at UCL (University College London) and the University of Cambridge has revealed that “space ice” is not as disordered as previously assumed. The most common form of ice in the Universe, low-density amorphous ice, contains tiny crystals (about three nanometers wide) embedded within its disordered structures.

For decades, scientists have believed that ice in space is completely amorphous, with colder temperatures meaning it does not have enough energy to form crystals when it freezes. However, the researchers used computer simulations and experimental work to show that this is not entirely true.

They found that low-density amorphous ice contains a mixture of crystalline and amorphous regions, rather than being completely disordered. This has significant implications for our understanding of water and life in the Universe.

The findings also have implications for one speculative theory about how life on Earth began, known as Panspermia. According to this theory, the building blocks of life were carried here on an ice comet. However, the researchers’ discovery suggests that this ice would be a less good transport material for these origin of life molecules.

Lead author Dr Michael B. Davies said: “We now have a good idea of what the most common form of ice in the Universe looks like at an atomic level.” The study’s results raise many additional questions about the nature of amorphous ices, and its findings may hold the key to explaining some of water’s many anomalies.

Co-author Professor Christoph Salzmann said: “Ice on Earth is a cosmological curiosity due to our warm temperatures. Ice in the rest of the Universe has long been considered a snapshot of liquid water.” However, this study shows that this is not entirely true, and that ice can take on different forms depending on its origin.

The research team’s findings also raise questions about amorphous materials in general, which have important uses in advanced technology. For instance, glass fibers that transport data long distances need to be amorphous for their function. If they do contain tiny crystals and we can remove them, this will improve their performance.

In conclusion, the study has revealed that cosmic ice is more complex than previously thought, with tiny crystals hidden within its disordered structures. This has significant implications for our understanding of water and life in the Universe, and raises many additional questions about the nature of amorphous ices.

The discovery of hidden stars known as dark dwarfs has sent shockwaves throughout the scientific community. These enigmatic objects have been linked to dark matter, one of the most debated topics in modern cosmology and astrophysics research. Dark matter is estimated to comprise approximately 25% of the universe’s mass-energy density, yet it remains invisible to our telescopes due to its non-emission of light.

“We think that 25% of the universe is composed of a type of matter that doesn’t emit light, making it invisible to our eyes and telescopes. We only detect it through its gravitational effects. That’s why we call it dark matter,” explains Jeremy Sakstein, Professor of Physics at the University of Hawai’i and one of the study’s authors.

The most well-known dark matter candidates are Weakly Interacting Massive Particles (WIMPs), which interact very weakly with ordinary matter and reveal themselves only through their gravitational effects. This type of dark matter would be necessary for dark dwarfs to exist, as it could be captured by stars and accumulate inside them.

Dark dwarfs emit light, but not due to nuclear fusion processes like ordinary stars. Instead, they shine faintly due to the energy produced by their relatively small gravitational contraction. However, if brown dwarfs are located in regions with abundant dark matter, they can transform into something else – dark dwarfs.

This entire hypothesis relies on a specific type of dark matter, where heavy particles interact strongly with each other and annihilate into visible energy. Sakstein and colleagues propose a distinctive marker for identifying dark dwarfs: the presence of Lithium-7. This element burns easily and is quickly consumed in ordinary stars, making it a unique effect that can be used to distinguish between brown dwarfs and dark dwarfs.

Tools like the James Webb Space Telescope might already be able to detect extremely cold celestial objects like dark dwarfs. However, Sakstein suggests another possibility: looking at a whole population of objects and asking, statistically, if it is better described by having a sub-population of dark dwarfs or not.

If in the coming years we manage to identify one or more dark dwarfs, how strong would that clue be in support of the hypothesis that dark matter is made of WIMPs? Reasonably strong. With light dark matter candidates, something like an axion, I don’t think you’d be able to get something like a dark dwarf. They don’t accumulate inside stars. If we manage to find a dark dwarf, it would provide compelling evidence that dark matter is heavy, interacts strongly with itself, but only weakly with the Standard Model. This includes classes of WIMPs, but it would include some other more exotic models as well.