January 2024

Superconductors have intrigued physicists for decades. But these materials, which allow the perfect, lossless flow of electrons, usually only exhibit this quantum-mechanical peculiarity at temperatures so low — a few degrees above absolute zero — as to render them impractical.

A research team led by Professor of Physics and Applied Physics Philip Kim has demonstrated a new strategy for making and manipulating a widely studied class of higher-temperature superconductors, called cuprates, clearing a path to engineering new, unusual forms of superconductivity in previously unattainable materials.

Using a uniquely low-temperature device fabrication method, Kim and his team report in the journal Science a promising candidate for the world’s first high-temperature, superconducting diode — essentially, a switch that makes current flow in one direction — made out of thin cuprate crystals. Such a device could theoretically fuel fledging industries like quantum computing, which rely on fleeting mechanical phenomena that are difficult to sustain.

“High-temperature superconducting diodes are, in fact, possible, without application of magnetic fields, and opens new doors of inquiry toward exotic materials study,” Kim said.

Cuprates are copper oxides that, decades ago, upended the physics world by showing they become superconducting at much higher temperatures than theorists had thought possible, “higher” being a relative term (the current record for a cuprate superconductor is minus 225 Fahrenheit). But handling these materials without destroying their superconducting phases is extremely complex due to their intricate electronic and structural features.

The team’s experiments were led by S.Y. Frank Zhao, a former student in the Griffin Graduate School of Arts and Sciences and now a postdoctoral researcher at MIT. Using an air-free, cryogenic crystal manipulation method in ultrapure argon, Zhao engineered a clean interface between two extremely thin layers of the cuprate bismuth strontium calcium copper oxide, nicknamed BSCCO (“bisco”). BSCCO is considered a “high-temperature” superconductor because it starts superconducting at about minus 288 Fahrenheit — very cold by practical standards, but astonishingly high among superconductors, which typically must be cooled to about minus 400.

Zhao first split the BSCCO into two layers, each one-thousandth the width of a human hair. Then, at minus 130, he stacked the two layers at a 45-degree twist, like an ice cream sandwich with askew wafers, retaining superconductivity at the fragile interface.

The team discovered that the maximum supercurrent that can pass without resistance through the interface is different depending on the current’s direction. Crucially, the team also demonstrated electronic control over the interfacial quantum state by reversing this polarity. This control was what effectively allowed them to make a switchable, high-temperature superconducting diode — a demonstration of foundational physics that could one day be incorporated into a piece of computing technology, such as a quantum bit.

“This is a starting point in investigating topological phases, featuring quantum states protected from imperfections,” Zhao said.

The Harvard team worked with colleagues Marcel Franz at University of British Columbia and Jed Pixley at Rutgers University, whose teams previously performed theoretical calculations that accurately predicted the behavior of the cuprate superconductor in a wide range of twist angles. Reconciling the experimental observations also required new theory developments, performed by University of Connecticut’s Pavel A. Volkov.

The research was supported, in part, by the National Science Foundation, the Department of Defense, and the Department of Energy.

 

 



Freezing is one of the most common and debilitating symptoms of Parkinson’s disease, a neurodegenerative disorder that affects more than 9 million people worldwide. When individuals with Parkinson’s disease freeze, they suddenly lose the ability to move their feet, often mid-stride, resulting in a series of staccato stutter steps that get shorter until the person stops altogether. These episodes are one of the biggest contributors to falls among people living with Parkinson’s disease.

Today, freezing is treated with a range of pharmacological, surgical, or behavioral therapies, none of which are particularly effective.

What if there was a way to stop freezing altogether?

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Boston University Sargent College of Health & Rehabilitation Sciences have used a soft, wearable robot to help a person living with Parkinson’s walk without freezing. The robotic garment, worn around the hips and thighs, gives a gentle push to the hips as the leg swings, helping the patient achieve a longer stride.

The device completely eliminated the participant’s freezing while walking indoors, allowing them to walk faster and further than they could without the garment’s help.

“We found that just a small amount of mechanical assistance from our soft robotic apparel delivered instantaneous effects and consistently improved walking across a range of conditions for the individual in our study,” said Conor Walsh, the Paul A. Maeder Professor of Engineering and Applied Sciences at SEAS and co-corresponding author of the study.

The research demonstrates the potential of soft robotics to treat this frustrating and potentially dangerous symptom of Parkinson’s disease and could allow people living with the disease to regain not only their mobility but their independence.

The research is published in Nature Medicine.

For over a decade, Walsh’s Biodesign Lab at SEAS has been developing assistive and rehabilitative robotic technologies to improve mobility for individuals’ post-stroke and those living with ALS or other diseases that impact mobility. Some of that technology, specifically an exosuit for post-stroke gait retraining, received support from the Wyss Institute for Biologically Inspired Engineering, and was licensed and commercialized by ReWalk Robotics.

In 2022, SEAS and Sargent College received a grant from the Massachusetts Technology Collaborative to support the development and translation of next-generation robotics and wearable technologies. The research is centered at the Move Lab, whose mission is to support advances in human performance enhancement with the collaborative space, funding, R&D infrastructure, and experience necessary to turn promising research into mature technologies that can be translated through collaboration with industry partners.

This research emerged from that partnership.

“Leveraging soft wearable robots to prevent freezing of gait in patients with Parkinson’s required a collaboration between engineers, rehabilitation scientists, physical therapists, biomechanists, and apparel designers,” said Walsh, whose team collaborated closely with that of Terry Ellis,  professor and Physical Therapy Department chair and director of the Center for Neurorehabilitation at Boston University.

The team spent six months working with a 73-year-old man with Parkinson’s disease, who — despite using both surgical and pharmacologic treatments — endured substantial and incapacitating freezing episodes more than 10 times a day, causing him to fall frequently. These episodes prevented him from walking around his community and forced him to rely on a scooter to get around outside.

In previous research, Walsh and his team leveraged human-in-the-loop optimization to demonstrate that a soft, wearable device could be used to augment hip flexion and assist in swinging the leg forward to provide an efficient approach to reduce energy expenditure during walking in healthy individuals.

Here, the researchers used the same approach but to address freezing. The wearable device uses cable-driven actuators and sensors worn around the waist and thighs. Using motion data collected by the sensors, algorithms estimate the phase of the gait and generate assistive forces in tandem with muscle movement.

The effect was instantaneous. Without any special training, the patient was able to walk without any freezing indoors and with only occasional episodes outdoors. He was also able to walk and talk without freezing, a rarity without the device.

“Our team was really excited to see the impact of the technology on the participant’s walking,” said Jinsoo Kim, former Ph.D. student at SEAS and co-lead author on the study.

During the study visits, the participant told researchers: “The suit helps me take longer steps and when it is not active, I notice I drag my feet much more. It has really helped me, and I feel it is a positive step forward. It could help me to walk longer and maintain the quality of my life.”

“Our study participants who volunteer their time are real partners,” said Walsh. “Because mobility is difficult, it was a real challenge for this individual to even come into the lab, but we benefited so much from his perspective and feedback.”

The device could also be used to better understand the mechanisms of gait freezing, which is poorly understood.

“Because we don’t really understand freezing, we don’t really know why this approach works so well,” said Ellis. “But this work suggests the potential benefits of a ‘bottom-up’ rather than ‘top-down’ solution to treating gait freezing. We see that restoring almost-normal biomechanics alters the peripheral dynamics of gait and may influence the central processing of gait control.”

The research was co-authored by Jinsoo Kim, Franchino Porciuncula, Hee Doo Yang, Nicholas Wendel, Teresa Baker, and Andrew Chin. Asa Eckert-Erdheim and Dorothy Orzel also contributed to the design of the technology, as well as Ada Huang, and Sarah Sullivan managed the clinical research.

It was supported by the National Science Foundation under grant CMMI-1925085; the National Institutes of Health under grant NIH U01 TR002775; and the Massachusetts Technology Collaborative, Collaborative Research and Development Matching Grant.



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