Wednesday, September 11, 2024

The Graphene Legacy


Graphene was first discovered around 2004, and since then it's changed the world of science in ways far greater than most materials ever discovered. But we're at the point now where it's time to move on. Seeing the word "graphene" in a headline is no longer enough to make you want to see what it's doing. 

There's graphene but made of gold (goldene), there's something better than graphene (made of boron nitride), and there's the moiré lattice phenomena, which seems about as mindblowing as graphene itself was twenty years ago. 

Here are a few examples of how we're going ahead into the post-graphene world, and from now on, news about graphene will be limited to make for other things:

Researchers put a new twist on graphite
Jul 2023, phys.org

Didn't see this one coming!

They placed a single layer of graphene on top of a thin, bulk graphite crystal, and then introduced a twist angle of around 1 degree between graphite and graphene. They detected novel and unexpected electrical properties not just at the twisted interface, but deep in the bulk graphite as well. The electrical properties of the whole material differed markedly from typical graphite.

"Though we were generating the moiré pattern only at the surface of the graphite, the resulting properties were bleeding across the whole crystal."

Also: "Interdimensional" means mixed dimensional materials, like embedding 2D graphene into 3D graphite.

via University of Washington, Osaka University and the National Institute for Materials Science in Japan: Matthew Yankowitz, Mixed-dimensional moiré systems of twisted graphitic thin films, Nature (2023). DOI: 10.1038/s41586-023-06290-3.


Navigating moiré physics and photonics with band offset tuning
Oct 2023, phys.org

They started with a mismatched silicon-based bilayer moiré superlattice and adjusted the band offset by varying the thickness of one layer of the superlattices, to find that the offset effectively controls the moiré flatbands.

via SPIE Society of Photo-Optical Instrumentation Engineers, University of Electronic Science and Technology of China, Anqing Normal University, Guangxi University, and Nankai University: Peilong Hong et al, Robust moiré flatbands within a broad band-offset range, Advanced Photonics Nexus (2023). DOI: 10.1117/1.APN.2.6.066001


Researchers create first functional semiconductor made from graphene
Jan 2024, phys.org

Where you been - world's first functional semiconductor made from graphene

via Georgia Institute of Technology: Walt de Heer, Ultrahigh-mobility semiconducting epitaxial graphene on silicon carbide, Nature (2024). DOI: 10.1038/s41586-023-06811-0. 


Unlocking exotic physics: Exploring graphene's topological bands in super-moiré structures
Apr 2024, phys.org

Super-Moiré all day 

They're sandwiching monolayer graphene between two bulk boron nitride layers to create a new structure known as a super-moiré structure (whereas regular moiré is just two graphene layers).

via National University of Singapore:  Mohammed M. Al Ezzi et al, Topological Flat Bands in Graphene Super-Moiré Lattices, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.132.126401.


A single atom layer of gold—researchers create goldene
Apr 2024, phys.org
https://phys.org/news/2024-04-atom-layer-gold-goldene.html

Goldene - a sheet of gold only a single atom layer thick

via Linköping University: Synthesis of goldene comprising single-atom layer gold, Nature Synthesis (2024). DOI: 10.1038/s44160-024-00518-4

Wednesday, September 4, 2024

Quantum Surprise


You can't escape quantum this and quantum that while perusing science headlines, but these articles in particular are examples of moments when quantum experiments produced surprising results, or even better, results that look really cool but we don't even know what to do with them yet. That's the best kind of surprise. 

Promising quantum state found during error correction research
Sep 2023, phys.org

A team of Cornell researchers unexpectedly discovered the presence of "spin-glass" quantum state while conducting a research project designed to learn more about quantum algorithms and, relatedly, new strategies for error correction in quantum computing.

The researchers emphasized that they weren't simply trying to generate a better error protection scheme when they began this research. Rather, they were studying random algorithms to learn general properties of all such algorithms.

"Interestingly, we found nontrivial structure," Mueller said. "The most dramatic was the existence of this spin-glass order, which points toward there being some extra hidden information floating around, which should be useable in some way for computing, though we don't know how yet."

via Cornell's Laboratory of Atomic and Solid State Physics: Vaibhav Sharma et al, Subsystem symmetry, spin-glass order, and criticality from random measurements in a two-dimensional Bacon-Shor circuit, Physical Review B (2023). DOI: 10.1103/PhysRevB.108.024205



Redefining quantum machine learning
Mar 2024, phys.org

The team has discovered that neuronal quantum networks can not only learn but also memorize seemingly random data. 

"Our experiments show that these quantum neural networks are incredibly adept at fitting random data and labels, challenging the very foundations of how we understand learning and generalization."

via Free University of Berlin: Elies Gil-Fuster et al, Understanding quantum machine learning also requires rethinking generalization, Nature Communications (2024). DOI: 10.1038/s41467-024-45882-z


Research demonstrates a new mechanism of order formation in quantum systems
Apr 2024, phys.org

This means something for materials science which is already leaping past us. Also RIKEN:

Active matter agents change from a disordered to an ordered state in what is called a "phase transition." As a result, they move together in an organized fashion without an external controller.

They created a theoretical model in which spins of subatomic particles align in one direction just like how flocking birds face the same direction while flying. They found that the ordering can appear without elaborate interactions between the agents in the quantum model.

"It was different from what was expected based on biophysical models."

via University of Tokyo and RIKEN: Activity-induced ferromagnetism in one-dimensional quantum many-body systems, Physical Review Research (2024). dx.doi.org/10.1103/PhysRevResearch.6.023096