Twisted Science: New Quantum Ruler to Explore Exotic Matter

Graphene, a single-atom-thick sheet of carbon, boasts remarkable properties. However, when multiple layers of graphene are stacked with slight misalignments, they give rise to intriguing behaviors. These moiré quantum materials can generate magnetic fields, become superconductors with zero resistance, or transform into perfect insulators, depending on the twist angle between layers.

Introducing the Quantum Ruler

Researchers, led by Joseph A. Stroscio from the National Institute of Standards and Technology (NIST) in collaboration with international scientists, have developed a “quantum ruler.” This innovative tool aims to measure and explore the peculiar properties of twisted graphene layers. Additionally, it holds the potential to establish a miniaturized standard for electrical resistance, enabling on-site calibration of electronic devices.

Creating Moiré Quantum Matter

Physicist Fereshte Ghahari, working at George Mason University, crafted a moiré quantum matter device by twisting two layers of graphene (bilayer graphene) with precision. This device, approximately 20 micrometers across, was produced using NIST’s nanofabrication facility. The researchers, Marlou Slot and Yulia Maximenko from NIST, then lowered the device’s temperature to nearly absolute zero, reducing atomic and electron motion and enhancing electron interactions within the material.

The Quantum Ruler in Action

To measure energy levels, the team employed a versatile scanning tunneling microscope designed by Stroscio. When a voltage was applied to the graphene bilayers within a magnetic field, the microscope detected the minuscule current produced as electrons “tunneled” from the material to the probe tip.

Uncovering Quantum Ruler Deviations

In a magnetic field, electrons follow circular paths, typically adhering to a fixed relationship between the area enclosed by their orbits and the applied field. This relationship, a fundamental quantum characteristic, serves as a ruler for measuring a material’s electronic and magnetic properties. The researchers observed a deviation from this pattern when altering the magnetic field applied to the moiré graphene bilayers, indicating the presence of a new quantum ruler. This shift in energy level tick marks reflects the unique magnetic properties arising from electrons confined to twisted graphene layers.

Exploring Moiré Quantum Materials

The quantum ruler’s application promises to shed light on the magnetic properties of moiré quantum materials. These materials feature a range of electron energies, forming “valleys” within their electric field. The substantial spacing between these valleys, found in bilayers with larger intervals than single or untwisted multiple graphene layers, contributes to their distinctive magnetic characteristics.

Potential Applications

The ability to select specific twist angles and layer configurations in moiré quantum materials offers a deeper understanding of tailoring and optimizing their magnetic and electronic properties. These insights hold promise for applications in microelectronics and related fields, including ultrathin superconductors.

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A New Standard for Electrical Resistance

Additionally, researchers envision a novel application for moiré quantum matter: a portable standard for electrical resistance. Unlike the current standard, which relies on strong magnetic fields and can only be conducted at specialized facilities, moiré quantum materials could potentially exhibit magnetization even without an external field. This innovation could lead to a more accessible and cost-effective method for calibrating electronic devices directly at manufacturing sites, potentially saving substantial resources.

In summary, the development of the “quantum ruler” and the exploration of moiré quantum materials offer exciting prospects for both understanding fundamental quantum phenomena and revolutionizing practical applications in the realm of electronics.