A discovery six years ago took the condensed-matter physics world by storm: Ultra-thin carbon stacked in two slightly askew layers became a superconductor, and changing the twist angle between layers could toggle their electrical properties. The landmark 2018 paper describing “magic-angle graphene superlattices” launched a new field called “twistronics,” and the first author was then-MIT graduate student and recent Harvard Junior Fellow Yuan Cao.

Together with Harvard physicists Amir Yacoby, Eric Mazur, and others, Cao and colleagues have built on that foundational work, smoothing a path for more twistronics science by inventing an easier way to twist and study many types of materials.

A new paper in Nature describes the team’s fingernail-sized machine that can twist thin materials at will, replacing the need to fabricate twisted devices one by one. Thin, 2D materials with properties that can be studied and manipulated easily have immense implications for higher-performance transistors, optical devices such as solar cells, and quantum computers, among other things.

“This development makes twisting as easy as controlling the electron density of 2D materials,” said Yacoby, Harvard professor of physics and applied physics. “Controlling density has been the primary knob for discovering new phases of matter in low-dimensional matter, and now, we can control both density and twist angle, opening endless possibilities for discovery.”

Cao first made twisted bilayer graphene as a graduate student in the lab of MIT’s Pablo Jarillo-Herrero. Exciting as it was, the achievement was tempered by challenges with replicating the actual twisting.

At the time, each twisted device was hard to produce, and as a result, unique and time-consuming, Cao explained. To do science with these devices, they needed tens or even hundreds of them. They wondered if they could make “one device to twist them all,” Cao said—a micromachine that could twist two layers of material at will, eliminating the need for hundreds of unique samples. They call their new device a MEMS (micro-electromechanical system)-based generic actuation platform for 2D materials, or MEGA2D for short.

The Yacoby and Mazur labs collaborated on the design of this new tool kit, which is generalizable to graphene and other materials.

“By having this new ‘knob’ via our MEGA2D technology, we envision that many underlying puzzles in twisted graphene and other materials could be resolved in a breeze,” said Cao, now an assistant professor at University of California Berkeley. “It will certainly also bring other new discoveries along the way.”

In the paper, the researchers demonstrated the utility of their device with two pieces of hexagonal boron nitride, a close relative of graphene. They were able to study the bilayer device’s optical properties, finding evidence of quasiparticles with coveted topological properties.

The ease of their new system opens several scientific roadways, for example, employing hexagonal boron nitride twistronics to produce light sources that can be used for low-loss optical communication.

“We hope that our approach will be adopted by many other researchers in this prosperous field, and all can benefit from these new capabilities,” Cao said.

The paper’s first author is nanoscience and optics expert Haoning Tang, a postdoctoral researcher in Mazur’s lab and a Harvard Quantum Initiative fellow, who noted that developing the MEGA2D technology was a long process of trial and error.

“We didn’t know much about how to control the interfaces of 2D materials in real time, and the existing methods just weren’t cutting it,” she said. “After spending countless hours in the cleanroom and refining the MEMS design—despite many failed attempts—we finally found the working solution after about a year of experiments.” All nanofabrication took place at Harvard’s Center for Nanoscale Systems, where staff provided invaluable technical support, Tang added.

“The nanofabrication of a device combining MEMS technology with a bilayer structure is a veritable tour de force,” said Mazur, the Balkanski Professor of Physics and Applied Physics. “Being able to tune the nonlinear response of the resulting device opens the door to a whole new class of devices in optics and photonics.”

This story is published courtesy of the Harvard Gazette, Harvard University’s official newspaper. For additional university news, visit Harvard.edu.

Female and male primates often form close bonds, but not purely out of affection. Close relationships usually evolve when there is a clear benefit for both parties, with protection and reproductive control playing key roles.

A new study, led by primatologists Liesbeth Sterck from Utrecht University and Julia Ostner from the University of Göttingen, provides theoretical insights into how these bonds are formed. The study, published in Evolution and Human Behavior, underlines the decisive role that females play.

Why do some female and male primates hit it off and form strong bonds, while others don’t? Science has long offered various theories to explain these connections, ranging from sheer physical attraction to deep-rooted evolutionary processes.

While these ideas are compelling, most studies on primate bonding have traditionally focused on males as the key players, often overlooking the crucial role that females might play in these relationships.

Benefits for both

Mapping hundreds of primate observations from the past decades, an international team of primatologists suggests that these ‘friendships with benefits’ between male and female primates usually evolve when both can gain something. For females, it’s about choosing whom they mate with. For males, it’s about caring for and protecting their young.

These dynamics are especially important in groups where males cannot just dominate females and where offspring need looking after. These bonds are also most likely to form in groups where males aren’t the boss and where male care is crucial. The primatologists mapped hundreds of earlier observations of chimpanzees, lemurs, macaques, and other species.

“Our findings show that these bonds aren’t just about attraction and affection,” says Sterck.

“They are also strategic. Both male and female primates unconsciously seek out these friendships that provide benefits. The benefits can be protection, better access to resources, or securing the survival of their offspring. For evolution to shape these behaviors, it is not needed that they know when or how the bonds pay off.”

Changing bonds and breaking up

The study also shows that the nature of these bonds can change over time. Initially, males tend to groom females more often during the mating season, but this dynamic can shift. Females might look for male support to protect their infants during nursing. A male may bond with a female initially to secure mating rights, and after the female gives birth, she may rely on the male for protection.

Once the offspring become independent, these bonds often dissolve, and both the male and female may move on to other partners.

However, in cases where females give males the opportunity to father multiple subsequent offspring, long-term bonds are more likely to form. These stable relationships are common in species like macaques, baboons and chimpanzees, where females repeatedly prefer the same male and males provide ongoing care. Such long-lasting bonds are often supported by mutual benefits, making continued investment worthwhile for both sides.

Human relationships

When it comes to human relationships, the dynamics might be more complex. Moreover, humans typically form exclusive pairs, while both female and male primates maintain a practice with multiple mating partners. But some of the same underlying principles from primate bonds apply, according to Sterck’s team.

“Just like our primate relatives, human bonds often involve a mix of affection and strategic partnership,” says Sterck. “While love and emotional connection are vital, unconsciously there’s also an element of mutual benefit, whether it’s support, protection, or shared resources.”

Love and affection still play a crucial role in primate bonding, says Sterck, even if the evolutionary foundation of these relationships is built on long-term benefits. “While the drive to form strong bonds may stem from evolutionary advantages, emotions like love and affection kick-start these connections. These feelings act as the lubricant, smoothing the way for the actions and behaviors necessary to maintain and deepen these bonds over time.”

Future research

To further investigate how widespread their bonding theory can be in the animal kingdom, Sterck’s team calls for additional research. They specifically call for additional research in great apes (such as gorillas and bonobos) and so-called New World primates, including tamarins and capuchins—or even further to non-primate species living in permanent social groups, such as wolfs and lions.

They also envision that this approach can shed new light on the evolution and dynamics of human pair bonding.