hexagonal synthetic diamond hardness record

Hexagonal Synthetic Diamond Sets New Record for Hardness, Surpassing Natural Diamonds

Breakthrough in Diamond Synthesis by International Team

An international team of physicists, materials scientists and engineers, collaborating with Umeå University in Sweden, has successfully grown a synthetic diamond that surpasses natural diamonds in hardness. Their groundbreaking work, published in Nature Materials, involves a process that heats and compresses graphite to produce the advanced material.

Diamonds: From Aesthetic to Industrial Use

Renowned for their brilliance, diamonds have been highly valued throughout human history. Beyond their aesthetic appeal, their exceptional hardness has made them indispensable in industrial applications such as drilling. These unique properties sustain their high market value, prompting scientists to develop synthetic alternatives. Today, a wide range of lab-grown diamonds is commercially available.

The Quest for Harder Diamonds with Hexagonal Lattice Structures

Scientists have long sought to create harder diamonds by engineering hexagonal lattice structures instead of the conventional cubic formations found in both natural and synthetic diamonds. However, previous efforts have yielded hexagonal diamonds that were either too smaller or lacked the necessary purity for practical applications.

New Method for Growing Synthetic Hexagonal Diamonds

In an effort to refine diamond synthesis, the research team devised a process that subjected graphene to extreme heat within a high-pressure chamber. By optimizing the experimental settings, they successfully grew synthetic diamonds with a hexagonal lattice.

Extraordinary Properties of the New Hexagonal Diamond

Exceptional Durability and Thermal Stability

The group's initial synthesized diamond, measuring in the millimeter range, exhibited remarkable durability under 155 GPa of pressure and maintained thermal stability up to 1,100°C—significantly surpassing natural diamonds, which typically endure pressures between 70 and 100 GPa and temperatures up to 700°C.

Potential Industrial Applications for Hexagonal Synthetic Diamonds

According to the researchers, diamonds produced through this technique are not intended for ornamental use but rather for industrial applications such as drilling and machining. Additionally, they highlight potential uses in data storage and thermal regulation.

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Physics Experiment Reveals Order in Quantum Chaos

Breakthrough Discovery in Quantum Research

UC Santa Cruz physicist Jairo Velasco, Jr., and a global team of researchers have confirmed the existence of order within chaos in the quantum domain. Their findings, published in Nature on November 27, verify a 40-year-old theory that electrons confined to quantum space adhere to predictable trajectories rather than displaying chaotic behavior.

The Nature of Electrons: Particle and Wave Characteristics

Electrons demonstrate both particle and wave-like characteristics, defying simple behavior such as rolling like a ball. Their counterintuitive nature becomes evident as their wave properties, under specific conditions, interact to form concentrated movement patterns. Physicists refer to these shared trajectories as "unique closed orbits."

The Role of Graphene in Quantum Experiments

In Velasco's lab, achieving this breakthrough necessitated an elaborate blend of sophisticated imaging techniques and meticulous control of electron behavior within graphene. This material, renowned for its unique properties and two-dimensional nature, is frequently used in research to observe quantum phenomena.

Using Advanced Imaging Techniques to Study Electron Movement

Velasco's team employed the sharp-tipped probe of a scanning tunneling microscope in their experiment to initially create an electron trap and then positioned it near a graphene surface to observe electron movements without causing physical disruption.

Implications for Electronics: Efficient Electron Movement

According to Velasco, one major advantage of electrons following closed orbits within a confined space is that their intrinsic properties are better maintained as they move between points. This could have significant implications for electronics, as information encoded in electron properties could be transferred without loss, potentially leading to low-power, highly efficient transistors.

"One of the most exciting possibilities of this discovery lies in its use for information processing." Velasco explained. "With slight disturbances, or 'nudges' to these orbits, electrons could travel in a predictable manner across a device, conveying information from one side to the other."

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[A numerical simulation depicting the quantum dynamics achieved in the team's experiment. Credit: Anton Graf, Harvard University.]

Understanding Quantum Scars: The Imprint of Electron Trajectories

The Origins of Quantum Scarring

In the field of physics, these distinct electron trajectories are referred to as "quantum scars." This concept was first introduced in a 1984 theoretical study by Eric Heller, a physicist at Harvard University, who used computer simulations to demonstrate that electrons confined in a space would trace high-density paths due to the constructive interference of their wave motions.

"Quantum scarring is more than just an intriguing phenomenon; it provides insight into the peculiar nature of the quantum realm," said Heller, who also co-authored the paper. "Scarring represents a form of localization around orbits that retrace their paths. In the classical world, such returns have no lasting impact and are quickly forgotten. However, in the quantum world, they are perpetually retained."

Potential Applications of Quantum Scars in Technology

With Heller's theory now validated, researchers have the empirical basis to investigate practical applications. Current transistors, already operating at the nanoelectronic level, could achieve greater efficiency through quantum scar-based designs, potentially improving devices such as computers, smartphones, and tablets that depend on compact, high-performance transistors to enhance processing ca pabilities.

"Looking ahead, we aim to expand our work on visualizing quantum scars to create techniques for controlling and manipulating scar states," said Velasco. "Harnessing chaotic quantum phenomena could lead to new, precise methods for the selective and adaptable delivery of electrons at the nanoscale, opening the door to innovative quantum control approaches."

A Comparative Analysis of Classical and Quantum Chaos

Visualizing Chaos: The 'Billiard' Model

Velasco's team uses a visual representation known as a 'billiard' to demonstrate the classical mechanics of linear and chaotic systems. This model involves a confined area that shows the movement of particles, with the 'stadium' shape being a common example characterized by curved ends and straight sides. In the realm of classical chaos, particles exhibit erratic, unpredictable motion, eventually covering the entire area.

Observing Quantum Chaos in Action

The experiment involved creating a stadium billiard on atom-thin graphene, measuring approximately 400 nanometers in length. With the aid of a scanning tunneling microscope, the team successfully observed quantum chaos, revealing the intricate pattern of electron orbits within the stadium billiard built in Velasco's lab.

"I'm thrilled that we managed to capture images of quantum scars in an actual quantum system," said Zhehao Ge, a UC Santa Cruz graduate student and first co-corresponding author of the study. "We hope that these findings will contribute to a more profound understanding of chaotic quantum systems."

Acknowledgments and Collaborations

The paper, titled "Direct Visualization of Relativistic Quantum Scars in Graphene Quantum Dots," includes co-authors:

• UC Santa Cruz: Peter Polizogopoulos, Ryan Van Haren, and David Lederman
• Harvard University: Anton Graf and Joonas Keski-Rahkonen
• University of Manchester: Sergey Slizovskiy and Vladimir Fal'ko
• Japan's National Institute for Materials Science: Takashi Taniguchi and Kenji Watanabe

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Twisted Light Spins Electrons: A Breakthrough in Quantum Interaction Control

The Profound Power of Light

Enjoying a sunny day at the beach might make light seem gentle and serene, but its power is profound. A beam of light not only transmits energy but also carries momentum. This includes linear momentum, the force that challenges braking a moving train, and orbital angular momentum, fundamental to Earth's solar revolution.

The Experiment: Advancing Quantum Science

The Role of Orbital Angular Momentum in Light

On November 26, 2024, Nature Photonics published a paper detailing a novel experiment in quantum science. Researchers showcased how a beam of light could impart orbital angular momentum to electrons in graphene, advancing the understanding of light-matter quantum interactions.

The Importance of Light-Matter Interaction

Why Manipulating Light-Matter Interaction Matters

Precise manipulation of light-matter interactions is critical for advancing technologies such as quantum computing and quantum sensing. Researchers have particularly focused on encouraging electrons to respond to the unique and exotic patterns of light beams.

The Nature of Orbital Angular Momentum in Light

What is Orbital Angular Momentum?

A beam of light carrying orbital angular momentum rotates around its axis as it moves forward. Viewed directly, it features a dark center—a vortex shaped by its helical nature.

Theoretical Background and Challenges

"The interaction between light carrying orbital angular momentum and matter has been theorized since the 1990s," notes Deric Session, a postdoctoral researcher at JQI and the University of Maryland (UMD), who led the study. "But only a handful of experiments have demonstrated this phenomenon."

The Scale Mismatch Problem

The challenge arises from a mismatch in scale. For electrons to interact with a light beam carrying momentum, they must detect its changing characteristics as it propagates. Unfortunately, the spatial extent of these changes typically exceeds the dimensions of the material being studied, making electron targeting particularly arduous.

Addressing the Challenge: Expanding Electron Space

The Limitations of Traditional Approaches

For example, atoms and their orbiting electrons—fundamental to quantum physics research and prime candidates for precise control—are approximately 1,000 times smaller than the light beams used to interact with them.

The Problem with Photons and Atom Interaction

Light propagates as oscillating waves of electric and magnetic fields, and the distance it covers before repeating itself is known as the wavelength.

Beyond being a fundamental characteristic, the wavelength of light also dictates the energy carried by its individual particles, known as photons. Only photons with specific energy levels can interact with atoms, and these photons typically have wavelengths much larger than the atoms they engage with.

Although atoms as a whole can absorb energy and momentum from photons, the wavelength of these photons is too large for the atom's internal components—the nucleus and electrons—to detect any significant difference. This poses a challenge for transferring orbital angular momentum directly to the electrons.

Potential Solutions and Innovations

One potential solution to this challenges is to reduce the wavelength of light. However, doing so increases the energy carried by each photon, making atoms impractical as reliable targets. In their latest experiment, researchers, including JQI Fellows Mohammad Hafezi and Nathan Schine, JQI Co-Director Jay Sau, and JQI Adjunct Fellow Glenn Solomon, took a different approach: rather than shortening the light's wavelength, they expanded the electrons to occupy a larger space.

The Role of Graphene in the Ex periment

Why Graphene Was Chosen

Electrons that are bound to an atom's nucleus can only move within a limited a range before being freed from the atom, making them unsuitable for experimental use. In contrast, conductive materials allow electrons greater freedom to travel over longer distance while still being kept under control. To explore how to expand the electrons' spatial distribution, the researchers chose graphene—a highly efficient electrical conductor.

Experimental Setup and Findings

When a sample of graphene is cooled to 4 degrees above absolute zero and exposed to a powerful magnetic field, the electrons that typically move freely become ensnared in loop-like structures called cyclotron orbits. As the field strength increases, these orbits tighten further, packing more and more electrons until no additional ones can fit. Though compact, these orbits remain much larger than electron orbitals in atoms, providing an ideal setup for them to interact with light that carries orbital angular momentum.

Methodology and Results

Setting Up the Experiment

The experiment involved a graphene sample equipped with electrodes. One electrode was situated in the center, while another was arranged in a ring surrounding the edges of the sample.

Theoretical Predictions and Observations

Theoretical studies from 2021, led by Bin Cao, a former graduate student at JQI and UMD, and three other authors of the present paper, indicated that electrons circulating in this type of sample might gain angular momentum in distinct increments from incoming light, which would enlarge their orbits and ultimately result in their absorption by the electrodes.

Key Experimental Findings

"The principle is to modify the size fo the cyclotron orbits by transferring orbital angular momentum to or from the electrons, which in turn moves them throughout the sample and creates a current," says Session.

In their latest paper, the research team reported observing a stable current that persisted across a broad range of experimental conditions. They directed light with orbital angular momentum rotating clockwise at their graphene sample and detected the current moving in a single direction.

The research team then illuminated the sample with light carrying counterclockwise orbital angular momentum and noted that the direction of the current flipped. When they reversed the applied magnetic field, they observed the same directional change in the current—an anticipated finding since reversing the magnetic field direction also reverses the electron flow in cyclotron orbits. Changing the voltage across the inner and outer electrodes still resulted in the same difference between currents generated by clockwise and counterclockwise vortex light.

The researchers also exposed the sample to circularly polarized light, which possesses intrinsic angular momentum, and observed that it generated only a negligible current. The data consistently showed that a current was only detected when the light carried orbital angular momentum, with its direction directly related to whether the light's momentum was clockwise or counterclockwise.

Overcoming Technical Challenges

Sample Fabrication and Alignment Difficulties

This outcome was the result of years of dedicated effort, which included initial challenges with sample fabrication and difficulties in gathering sufficient reliable data for the experiment.

"I spent more than a year trying to fabricate graphene samples with this precise geometry," says Session. Ultimately, Session and the research team connected with a group they had previously worked with, headed by Roman Sordan, a physicist from the Polytechnic University of Milan with extensive experience in graphene sample fabrication.

According to Session, "They delivered and created the samples that we ultimately used."

Beam Alignment and Data Collection

Once they achieved samples that worked as expected, they still encountered difficulties aligning their twisted light with the sample to observe the current.

"The signal we were analyzing wasn't entirely consistent," says Mahmoud Jalali Mehrabad, a postdoctoral researcher at JQI and UMD and co-author of the paper. "Then one day, with Deric, we decided to do a spatial sweep. We essentially mapped the sample with exceptional precision. Once we identified the optimal  position for the beam, everything fell into place."

Within a week, they  had amassed all the data needed and were able to isolate the signals that demonstrated the current's relationship with the beam's orbital angular momentum.

Implications and Future Prospects

Significance of the Findings

Mehrabad states that, in addition to offering a new method for light-based control of matter, this technique could enable unprecedented electron measurements in quantum materials. Specially engineered light beams, when combined with interference techniques, could serve as a microscope to visualize the electron's spatial extent, providing a direct assessment of their quantum properties.

Potential for Future Quantum Research

"Measuring these spatial degrees of freedom in free electrons is vital for evaluating their coherence properties in a controlled way and for manipulating them," Mehrabad says. "It's not just detection; it's about control. That's what makes this achievement so significant."

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