The “Higgs Mode,” otherwise known as the Higgs amplitude mode, is seen as a close relative to the Higgs boson. Since the Higgs boson was first theorized in the 1960s, the first physical discovery came in 2012, and new quantum phenomena have since been detected. In this article, we look at the new quantum state known as the Higgs mode, the materials that the Higgs mode is found in and the Higgs Boson itself.
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What is the Higgs Boson?
The Higgs boson is an elementary particle that was predicted by the standard model of particle physics. The standard physics model involves three of the four known fundamental forces (apart from gravity) and classifies all known (and theoretically predicted) elementary particles – i.e., a subatomic particle that is not made up of any smaller particles. The standard model helps to predict and explain many of the phenomenon seen in the physics world, from expanding universes to particle interactions and can be used as a basis for more elaborate models such as supersymmetry.
The standard Higgs boson is a type of scalar boson predicted by the standard model, but other types of Higgs boson quasiparticle are often outside of the realm of the standard model. A Higgs boson is fundamentally seen as a quantum excitation of the Higgs field – the energy field in which all particles interact. The Higgs field is also the reason why particles have a mass. The Higgs boson carries the Higgs field and is made up of W and Z bosons that provide a weak nuclear force, and a gluon that provides a strong nuclear force. Higgs bosons have now been proven to exist, but they quickly decay into more stable particles after one septillionth of a second.
The Higgs Mode
The Higgs amplitude mode is a quantum phenomenon seen in materials and occurs when the magnetic field of its electrons fluctuate in a way similar to that of a Higgs boson. The materials that exhibit this phenomenon can do so because the crystal structure of the material enables the electrons to behave in such a way. When the Higgs mode presents itself in these materials, the material is often undergoing a quantum phase transition. It is at this point where researchers can understand more about the quantum properties of a material.
Where the Higgs Mode Has Been Detected
The Higgs mode has been detected in many different systems, including in ultracold atomic gases, disordered superconductors, and dimerized quantum magnets. However, in many cases, the Higgs mode is unstable and decays. As such, it has only been reported in a handful of publications.
However, some systems can support these quantum effects without decaying. The earliest experimental observation was seen in the Raman scattering of a superconducting charge-density wave compound. The Raman spectra found an unexpected peak that was later characterized as the presence of a Higgs mode.
The Higgs mode has been detected in various 2-dimensional and 3-dimensional materials. Copper bromide materials have been studied because the copper ion is ideal for studying quantum effects, but these materials have only shown promise at temperatures close to absolute zero. Two-dimensional superfluids are a general class of material that have been known to exhibit a Higgs mode, and it is often seen in superfluids composed of Mott-insulator materials.
One of the most recent observations has arisen from a two-dimensional Ca2RuO4 antiferromagnet. This was determined by inelastic neutron scattering measurements to detect the Higgs mode and its subsequent decay into pairs of photons, W and Z bosons, and leptons. These antiferromagnets have been found to have a well-defined and dispersive Higgs mode, although its intensity does diminish relatively quickly.
It is certain that more materials exhibiting Higgs mode will arise in the future, be it in 2 or 3-dimensional form. These Higgs modes should provide useful insights into the quantum properties of a material, including whether they are a topological insulator, superconductor, charge-density wave system, ultracold bosonic system, an antiferromagnet, or another quantum system.
- “Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point”- Hong T., Nature Physics, 2017, DOI: 10.1038/nphys4182
- “Higgs mode and its decay in a two-dimensional antiferromagnet”- Jain A., Nature Physics, 2017, DOI: 10.1038/nphys4077
- “Amplitude / Higgs Modes in Condensed Matter Physics”- Pekker D. and Varma C. M., Annual Reviews of Condensed Matter Physics, 2015, DOI: 10.1146/annurev-conmatphys-031214-014350
- “Higgs Mode in a Two-Dimensional Superfluid”- Pollet L. and Prokof’ev N., Physical Review Letters, 2012, DOI: 10.1103/PhysRevLett.109.010401
- “The ‘Higgs’ amplitude mode at the two-dimensional superfluid/Mott insulator transition”- Endres M., et al., Nature, 2012, DOI: 10.1038/nature11255
- CERN: https://home.cern/topics/higgs-boson
- Quanta Magazine: https://www.quantamagazine.org/elusive-higgs-mode-created-in-exotic-materials-20180228/