The Hefei Institutes of Physical Science of the Chinese Academy of Sciences has made a groundbreaking discovery in the field of nanotechnology. A research team led by Prof. Mingtai Wang has developed a revolutionary method for creating titanium dioxide nanorod arrays (TiO2-NA) with precise control over rod spacing, without affecting individual rod size. This breakthrough has significant implications for high-performance solar cells and other applications.

The researchers used a carefully tuned process to grow TiO2 nanorods, which excel at harvesting light and conducting charge. Traditional methods, however, often result in linked parameters – adjusting one aspect affects others, potentially compromising device efficiency. The team’s innovative approach separates rod density from diameter and length, allowing for precise control over the former.

Their strategy involves extending the hydrolysis stage of a precursor film to create longer “gel chains,” which assemble into smaller anatase nanoparticles. These nanoparticles then convert in situ into rutile ones, serving as seeds for nanorod growth. By controlling this process, the team successfully produced TiO2-NA films with constant rod diameter and height, despite varying rod density.

When integrated into low-temperature-processed CuInS2 solar cells, these films achieved remarkable results – power conversion efficiencies exceeding 10%, peaking at 10.44%. To explain why spacing matters so profoundly, the researchers introduced a Volume-Surface-Density model, illustrating how rod density influences light trapping, charge separation, and carrier collection.

This research marks a significant step forward in regulating nanostructures and optimizing device performance. By establishing a complete system linking process regulation, microstructure evolution, and device optimization, this breakthrough has far-reaching implications for clean energy and optoelectronics applications.

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.”

Researchers from the University of Rochester and University of California, Santa Barbara, have made a groundbreaking discovery that could change the game for various industries. By engineering a laser device smaller than a penny, they’ve created a tool that can power LiDAR systems in self-driving vehicles to gravitational wave detection – one of the most delicate experiments in existence.

The new chip-scale laser is a marvel of miniaturization, capable of conducting extremely fast and accurate measurements by precisely changing its color across a broad spectrum of light at rates of about 10 quintillion times per second. Unlike traditional silicon photonics, this laser is made with synthetic material lithium niobate, leveraging the Pockels effect to change the refractive index of a material when an electric field is present.

This tiny powerhouse has numerous applications that can already benefit from its designs. For instance, it can drive a LiDAR system on a spinning disc and identify objects at highway speeds and distances. The researchers demonstrated this capability by using their laser to spot toy building blocks forming the letters U and R.

Another significant application is the Pound-Drever-Hall (PDH) laser frequency locking technique, essential for optical clocks that can measure time with extreme precision. A typical setup would require instruments the size of a desktop computer, but the chip-scale laser can integrate all these components into a single tiny chip that can be tuned electrically.

The research was supported in part by the Defense Advanced Research Projects Agency (DARPA) and the National Science Foundation, showcasing the potential of this miniature marvel to revolutionize metrology and beyond.