Paving the Way in Twistronics: Exploring New Horizons with Graphene Ribbons

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Graphene ribbons, depicted in grey, can be laid flat on another graphene sheet, allowing continuous change in twist angle between them. In some regions, the atomic structures align at 0°, while in others, they twist by up to 5°. Image credit: Cory Dean, Columbia University.

A unique method created at Columbia provides a systematic examination of twist angle and strain in two-dimensional (2D) materials.

Twistronics is a burgeoning field that’s redefining our comprehension of 2D substances like graphene by modifying their characteristics through alterations in twist angles. Columbia University’s team has innovated a technique with graphene ribbons for more nuanced control of these angles. This could open doors to new applications in condensed matter physics by facilitating a precise investigation of the properties of twisted layers.

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Twistronics

Do you think you know all there is about a material? Try twisting it, literally. Twistronics, an emerging area in condensed matter physics, involves substantial changes to 2D materials, like graphene, through subtle angle adjustments between stacked layers.

Twisted graphene layers, for example, have revealed behaviors not found in single sheets, such as magnetic, superconductive, or insulative properties, all thanks to minor alterations in twist angles.

Theoretical Possibilities and Difficulties

While it’s theoretically possible to fine-tune any property by adjusting the twist angle, the practical aspect is more complex, says Columbia physicist Cory Dean. Understanding why and how different properties emerge in twisted graphene layers is still elusive, and complete control remains a challenge.

New Approach to Graphene Manufacturing

Dean and his colleagues have conceived a straightforward new technique that could aid in systematically and consistently exploring the foundational properties of twisted graphene and other 2D materials. According to an article in Science, they used long graphene ribbons (rather than square flakes) to build devices that offer unprecedented control over twist angle and strain.

Instead of creating ten devices with different angles, the team now has more control over strain. This brings more predictability and smoother layering.

Ribbon Technology Advantages

The research demonstrates that ribbons can make layering more uniform. By applying a gentle force with an atomic force microscope, they can create a stable arc in a graphene ribbon that lies flat on another layer, resulting in a steady twist angle variation between 0° and 5° across the device.

“We can now systematically explore how materials are transformed into something else, much like quantum alchemy,” says Columbia postdoc Bjarke Jessen.

Looking Forward: Quantum Alchemy

The initial paper mainly investigated the behavior and attributes of graphene ribbons and other similar materials. Columbia’s lab is set to probe how quantum materials’ core properties evolve with changes in twist angle and strain. However, certain mysteries, such as the origins of superconductivity at “magic angles,” remain to be elucidated.

The ribbon devices, encompassing angles from 0° to 5°, allow the team to delve into these phenomena with greater accuracy.

“What we are doing resembles quantum alchemy. We have a system to systematically investigate how this transformation occurs,” Jessen remarked.

Reference: “Programming twist angle and strain profiles in 2D materials” by Kapfer et al., 10 August 2023, Science.
DOI: 10.1126/science.ade9995

The Department of Energy’s Energy Frontier Research Center (EFRC) on Programmable Quantum Materials (Pro-QM) primarily backed this research.

Frequently Asked Questions (FAQs) about Twistronics

What is twistronics?

Twistronics is an emerging field in condensed matter physics that involves altering the properties of 2D materials like graphene by adjusting the twist angles between their stacked layers.

How does twist angle affect 2D materials?

Tiny changes in the twist angle between stacked layers of 2D materials, even as small as from 1.1° to 1.2°, can lead to significant changes in their properties, such as magnetic behavior, superconductivity, and insulation.

What is the significance of graphene ribbons?

Graphene ribbons offer better control over twist angles and strain in layered materials. They allow for systematic exploration of the properties of twisted layers, potentially unlocking new applications in condensed matter physics.

What challenges are associated with controlling twist angles?

While theoretically possible to control material properties through twist angles, the complex interactions between layers and the origins of new behaviors are not yet fully understood, making precise control a challenge.

How do ribbons improve control over twist angles?

Graphene ribbons, compared to square flakes, provide more predictable and controllable variation in twist angles between layers. This enhances the ability to explore and understand the effects of different angles on material properties.

What’s the goal of the new graphene fabrication technique?

The new technique developed by Columbia University aims to allow physicists to systematically investigate the properties of twisted layers of graphene and other 2D materials. It offers a higher level of predictability and control over both twist angle and strain.

How do ribbons eliminate random bubbles and wrinkles?

Using graphene ribbons, researchers can create a stable arc that lies flat on another layer, resulting in a controlled variation in twist angle across the device. This eliminates random variations like bubbles and wrinkles, providing more uniform results.

What future directions does the research take?

The research intends to explore how fundamental properties of quantum materials change with variations in twist angle and strain. This could help unravel phenomena like superconductivity at different “magic angles” and provide insights into quantum transformations.

How does this research contribute to understanding materials?

The research allows scientists to delve into the transformation of materials, resembling “quantum alchemy.” By systematically exploring the effects of twist angles, researchers can better understand how materials evolve and exhibit unique properties.