How Dirac and Weyl Fermions Revolutionize Our Electronics
Explore the DiscoveryIn the quest to understand the fundamental building blocks of our universe, physicists have long pursued elusive particles that defy conventional matter. Imagine discovering that these exotic entities aren't just floating in deep space but are hiding inside crystals that can fit in the palm of your hand.
This isn't science fiction—it's the fascinating world of topological semimetals, where collective electron behavior creates quasiparticles that mimic long-theorized fundamental particles. Recently, scientists have made stunning breakthroughs, observing massless particles that could enable revolutionary technologies from dissipationless electronics to quantum computing.
The detection of these strange entities—particularly Dirac and Weyl fermions—in solid materials represents one of the most exciting frontiers in modern physics, blurring the line between the cosmic and the crystalline.
Potential for dissipationless electronics that waste minimal energy as heat.
Robust topological states ideal for stable qubits in quantum computers.
In particle physics, Dirac and Weyl fermions represent solutions to quantum equations that describe how matter behaves at relativistic speeds. British physicist Paul Dirac's 1928 equation famously predicted the existence of antimatter, while Hermann Weyl's subsequent work identified a possible massless particle with a definite "handedness" or chirality.
For decades, these were considered purely theoretical concepts—until scientists realized that inside certain crystalline materials, electrons can collectively behave as if they were these exotic particles. These aren't fundamental particles but emergent quasiparticles that arise from the complex interplay of countless electrons within a crystal structure.
These quasiparticles exhibit a linear energy-momentum relationship and are protected by specific crystal symmetries. They appear as fourfold degenerate points (where bands cross) in the electronic structure and can be thought of as two Weyl fermions of opposite chirality merged together6 .
The term "topological" refers to mathematical properties that remain unchanged under continuous deformation—like how a coffee mug and a donut are topologically equivalent because both have one hole. In topological materials, the electronic band structure contains similar robust characteristics that can't be easily destroyed, leading to extraordinary properties like conducting surfaces that remain perfect even when the material contains imperfections1 .
This robustness stems from the unique arrangement of electronic states, where Weyl points act as sources (monopoles) and sinks (anti-monopoles) of Berry curvature—an abstract mathematical property that influences how electrons move through crystals. The topological protection ensures that these points can only be eliminated by annihilating them with their counterparts of opposite charge5 .
| Fermion Type | Mass Characteristics | Degeneracy | Key Features | Example Materials |
|---|---|---|---|---|
| Dirac | Massive or massless | Fourfold | Merged Weyl pairs, protected by symmetry | Cd₃As₂, Na₃Bi6 |
| Weyl | Massless | Twofold | Definite chirality, separated in momentum space | TaAs, PrAlSi2 |
| Semi-Dirac | Direction-dependent | Twofold | Massless in one direction, massive in another | ZrSiS3 |
| High-fold Chiral | Varies | Three-, four-, or sixfold | Large Chern numbers, long Fermi arcs | CoSi family, Mn₂Al₃5 |
In 2024, scientists reported a breakthrough—the creation of the first two-dimensional Weyl semimetal using bismuthene (a single atomic layer of bismuth) grown on SnS(Se) substrates. Through sophisticated techniques including spin- and angle-resolved photoemission spectroscopy, the team observed spin-polarized Weyl cones and the elusive Fermi string edge states that serve as the 2D equivalent of Fermi arcs in 3D systems4 .
This discovery was particularly significant because dimension reduction creates unconventional physical properties not found in 3D materials, including parity anomaly and potential charge fractionalization. The bismuthene system provided an ideal platform thanks to its unique crystal structure and the symmetry-breaking effect of its substrate, which generated the necessary spin splitting to create Weyl states4 .
Perhaps one of the most bizarre discoveries came in late 2024 when researchers accidentally observed "semi-Dirac fermions"—quasiparticles that only have mass when moving in one direction but remain massless when moving in another. This strange behavior was detected inside crystals of ZrSiS using magneto-optical spectroscopy at the National High Magnetic Field Laboratory3 .
Imagine a tiny train that races at light speed along straight tracks but suddenly develops mass and experiences resistance when switching to perpendicular tracks. This directional dependence creates extraordinary electronic properties that could be harnessed for future technologies3 .
| Discovery | Material System | Experimental Method | Significance |
|---|---|---|---|
| 2D Weyl Semimetal | Bismuthene on SnS(Se) | Spin-ARPES, STS | First realization of Weyl fermions in 2D4 |
| Semi-Dirac Fermions | ZrSiS | Magneto-optical spectroscopy | Directional mass behavior first theorized 16 years prior3 |
| Isotropic Dirac Fermions | LaAlSi | Landau level spectroscopy | Ideal Dirac fermions unaffected by direction6 |
| Chiral Magnetic Effect | WP₂₊δ | Transport measurements | Giant effect enabling "negative" resistance |
The accidental discovery of semi-Dirac fermions followed a meticulous experimental approach that combined extreme conditions with precise measurement techniques3 :
Researchers began with high-quality single crystals of the semi-metal ZrSiS, carefully grown to ensure atomic-level perfection in the crystal structure.
The team cooled the ZrSiS crystal to a breathtaking -452 degrees Fahrenheit—just a few degrees above absolute zero—to freeze out ordinary thermal vibrations that could mask quantum behaviors. They then placed it in the world's most powerful sustained magnetic field, approximately 900,000 times stronger than Earth's magnetic field, generated by the National High Magnetic Field Laboratory's hybrid magnet.
The researchers shone infrared light on the supercooled, magnetized crystal and meticulously analyzed the light reflected from the material. This technique, called magneto-optical spectroscopy, reveals how electrons inside materials respond to light under extreme magnetic conditions.
When the experimental data revealed puzzling patterns, the experimental physicists partnered with theoretical teams to develop models that could explain the bizarre electronic behavior they were witnessing.
The experiment yielded extraordinary results that defied conventional electronic behavior3 :
Researchers observed that electron energy levels followed a completely unexpected pattern called the "B^(2/3) power law"—the key theoretical signature of semi-Dirac fermions.
Analysis revealed that these quasiparticles appeared massless when moving along linear paths but suddenly acquired mass when changing to perpendicular directions.
The discovery was particularly valuable because ZrSiS is a layered material similar to graphite, suggesting potential for exfoliation into atomically thin sheets.
The observation of semi-Dirac fermions represents more than just the discovery of another exotic quasiparticle. It demonstrates that matter can exist in previously unimagined states with potentially revolutionary properties for electronics and quantum technologies. As lead researcher Yinming Shao noted, "There are many unsolved mysteries in what we observed," suggesting that semi-Dirac fermions may lead to even more surprising discoveries in the future3 .
Exploring the frontier of topological quantum materials requires specialized tools and approaches. Below are key "research reagent solutions" essential for discovering and characterizing Dirac and Weyl fermions in topological semimetals.
| Tool/Material | Function/Role | Examples/Notes |
|---|---|---|
| Synchrotron Light Sources | High-resolution angle-resolved photoemission spectroscopy (ARPES) | Maps electronic band structure with extreme precision4 |
| Hybrid Magnets | Generate ultra-strong sustained magnetic fields | National High Magnetic Field Laboratory (900,000× Earth's field)3 |
| Molecular Beam Epitaxy (MBE) | Grow atomically-perfect 2D materials | Used to create bismuthene monolayers4 |
| Crystal Structure Databases | Provide training data for AI discovery | Materials Project, Topological Materials Database1 |
| Deep Generative Models | Inverse design of new topological materials | CDVAE algorithm discovers new topological crystals1 |
| Magneto-optical Spectroscopy | Probe quantum oscillations and Landau levels | Reveals semi-Dirac fermions through B^(2/3) power law3 6 |
The field is rapidly evolving beyond serendipitous discovery toward systematic design of new topological materials. Recent breakthroughs in deep generative machine learning models are enabling researchers to inverse-design topological crystals with specific properties. The CTMT method combines crystal generation, heuristic screening, stability estimation, and topology diagnosis to discover new topological insulators and semimetals that don't exist in nature1 .
This approach has already proven remarkably successful, identifying 4 new topological insulators and 16 new topological semimetals, including several chiral materials whose topology was previously considered too challenging to discern. The integration of AI with traditional computational methods promises to dramatically accelerate the discovery of topological materials with customized properties1 .
The unique properties of Dirac and Weyl fermions enable extraordinary applications that could transform technology:
Topological surface states remain perfectly conducting even when the material contains defects, potentially enabling electronics that waste minimal energy as heat1 .
The robustness of topological states against local disturbances makes them ideal candidates for stable qubits in quantum computers.
Chiral semimetals with extremely long Fermi arcs provide enhanced electron mobility that could dramatically improve catalytic efficiency5 .
The extreme sensitivity of topological states to external fields enables ultra-sensitive detectors for magnetic fields and rotations.
The recent observation of giant chiral magnetic effect in WP₂₊δ crystals demonstrates "negative" resistance phenomena that could enable novel circuit elements.
Deep generative models are enabling the inverse design of topological crystals with customized properties1 .
The discovery of Dirac and Weyl fermions in crystalline materials represents a remarkable convergence of fundamental physics and materials science. What began as abstract mathematical solutions to quantum equations now exists as measurable entities in laboratory crystals, bringing the exotic world of relativistic quantum physics into tangible reality.
These discoveries do more than just satisfy scientific curiosity—they open pathways to technological capabilities that could transform our relationship with electronics, energy, and information.
As research advances, particularly through the integration of artificial intelligence with traditional experimental approaches, we stand at the threshold of a new era in materials design. The ability to create "designer quantum materials" with customized topological properties promises not only deeper understanding of our universe's fundamental workings but also revolutionary technologies that today exist only in imagination. The ghosts of quantum theory have found homes in crystals, and they're just beginning to reveal their secrets.