May 1, 2017 ThALES. Credit: R. Cubitt, ILL <\/p>\n
In modern physics of the past century, understanding the electronic properties and interactions between electrons inside matter has been a major challenge. Electrons are responsible for the chemical link between atoms and almost all factors that characterise a piece of matter, such as colour, heat transport, conductivity and magnetism. An elementary property of electrons is the spin, and the combination of electronic spins on the atomic level can induce a magnetic moment on certain atoms, which constitute the material. These moments can add up to macroscopic magnetic forces. <\/p>\n
As magnetism is the footprint of the interactive behaviour of electrons, studying it on the atomic level informs us about the collective electronic behaviour in the atomic environment. This can explain macroscopically observed electronic properties, like the temperature dependence of the conductivity. <\/p>\n
On the atomic level, magnetic ions are closely packed and thus mutually influence each other, resulting in the adoption of a common magnetic order to minimise their energy balance. A slight perturbation leads to a spin wave, whereby an oscillation of one magnetic moment around its central axis induces oscillating perturbations with a slight phase shift on the atomic neighbours. Spin waves are routinely observed in ordered magnetic materials by inelastic neutron scattering (INS) on spectrometers at the Institut Laue-Langevin (ILL). <\/p>\n
Transitioning from a classical to a quantum magnetic world <\/p>\n
The magnetic moment is characterised by its spin number. The larger the spin number, the more appropriate it is to compare the atomic magnetic moment with a classical magnet. Lowering the spin means accentuating its quantum properties; exploring the transition into the quantum world, which is fundamentally different from the daily, macroscopic world, is one of the most exciting challenges in solid state physics. <\/p>\n
The most cited example is the spin -1\/2 moments placed in the corner of an equidistant triangle. Due to its quantum nature, one spin can only point upwards or downwards with respect to its local axis. A magnetic exchange between the spin moments, that is antiferromagnetic in nature, forces them to align antiparallel to each other. As a quantum magnet cannot order, rather than adopting one ground state, several states are equally likely (6 in the case of the triangle), and the spins are in a super-positioned state pointing in several directions at once. <\/p>\n
Combining equidistant triangles leads to a two-dimensional network of spins. Its ground state, i.e. the spin arrangement with the lowest possible energy cost, has challenged theorists for decades. In 1973, noble laureate P.W. Anderson proposed a so-called 'quantum spin liquid state,' which is conceptually completely different to ordered magnetic phases. Anderson argued that for a triangular system, it is energetically more favourable for spins to organise into bonds. In these valence bonds, electrons are quantum mechanically 'entangled,' a purely quantum mechanical state. A superposition of a manifold of bond pattern exists in parallel and bonds fluctuate due to a quantum mechanical principle, which imposes zero point motions on the particles. This state is called a Resonant Valence Bond (RVB) state. <\/p>\n
Neutron scattering provides experimental proof for the RVB state <\/p>\n
Here at ILL, two cold three-axis spectrometers, IN14 and IN12, contributed over decades to the discovery and unravelling of magnetic correlations in classical and non-conventional superconductors, multiferroic crystals and a wide range of low-dimensional, frustrated and quantum magnetic systems. As both instruments dated from the 1980s, they were in need of a complete refurbishment to be able to continue contributing to the scientific progress in these fields. The new IN12 spectrometer's relocation and refurbishment was completed in 2012, and by the end of 2014, the IN14 spectrometer was replaced by its successor, ThALES. <\/p>\n
ThALES, Three-Axis instrument for Low Energy Spectroscopy, is a next generation cold neutron three-axis spectrometer that builds on the strengths of its predecessor, IN14, but uses state-of-the-art neutron optics. The ThALES project is a collaboration between ILL and Charles University, Prague, and is financed by the Czech Ministry of Science and Education. <\/p>\n
After replacing the IN14, ThALES became the new reference for cold single crystal neutron spectroscopy at a steady state neutron source like the ILL reactor. ThALES has been fully optimised to address the physics of highly correlated electron systems and scientific problems in the field of quantum magnetism. Moreover, the flexibility of the spectrometer has been enhanced through the implementation of various optical elements. <\/p>\n
The key aims of ThALES are: <\/p>\n
ThALES was used to carry out INS measurements in a recent study conducted by a collaboration of scientists, including ILL's Martin Boehm, current co-ordinator of the EU-funded neutron network SINE2020. The study published in Nature, titled 'Evidence for a spinon Fermi surface in a triangular lattice quantum-spin-liquid candidate,' argued that the triangular-lattice antiferromagnet YbMgGaO4 has the long sought quantum spin liquid RVB ground state. This study was the first to use neutron scattering as a means of providing experimental proof for the RVB state. <\/p>\n
The experimental effort to discover the RVB ground state has considerably increased since P.W. Anderson suggested that it might explain the phenomenon of superconductivity in a class of materials that show particularly high transition temperatures between a normal conducting and superconducting state. However, providing experimental proof for the existence of the RVB state is very challenging, because while a magnetically ordered system has a clear experimental response, the RVB state is characterised by the absence of a measurable quantity. <\/p>\n
Due to the lack of a measurable quantity, the experimental approach of this study, using ThALES, selected indirect experimental proof by deliberately exciting the ground state with neutrons and measuring the dynamic response. According to theoretical expectations, the excited spin liquid behaves 'exotically,' meaning the excited state is explained by spinons with very unusual properties. Spinons can rearrange the distribution of valence bonds and travel throughout the triangular plane with a minimum amount of energy. <\/p>\n
In a scattering process between the neutron and the spin liquid, the law of conservation of total momentum imposes the creation of two spin-1\/2 spinons in the liquid. This pair of spinons travel in opposite directions with a total amount of energy equalling the loss of neutron energy in the scattering process. Using the ThALES spectrometer, it is possible to trace the direction and energies of the spinons by measuring the direction and energy of the neutron that created the spinon pair. In this way, this study traced a complete dynamical landscape of the spin quantum liquid in the triangular plane, and compared the measurements with theoretical predictions, which gave strong evidence for the existence of the spin liquid phase in YbMgGaO4. <\/p>\n
This research is important as a quantum spin liquid state of matter is potentially relevant for applications of quantum information. Moreover, experimental identification of a quantum spin liquid state contributes greatly to our understanding of quantum matter. <\/p>\n
Explore further: Novel state of matter: Observation of a quantum spin liquid <\/p>\n
More information: Yao Shen et al. Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate, Nature (2016). DOI: 10.1038\/nature20614<\/p>\n
Journal reference: Nature <\/p>\n
Provided by: Institut Laue-Langevin <\/p>\n
A novel and rare state of matter known as a quantum spin liquid has been empirically demonstrated in a monocrystal of the compound calcium-chromium oxide by team at HZB. According to conventional understanding, a quantum ... <\/p>\n
Magnetism is one of the oldest recognised material properties. Known since antiquity, records from the 3rd century BC describe how lodestone, a naturally occurring magnetised ore of iron, was used in primitive magnetic compasses. ... <\/p>\n
An international team of researchers have found evidence of a mysterious new state of matter, first predicted 40 years ago, in a real material. This state, known as a quantum spin liquid, causes electrons - thought to be ... <\/p>\n
A little frustration can make life interesting. This is certainly the case in physics, where the presence of competing forces that cannot be satisfied at the same time known as frustration can lead to rare material ... <\/p>\n
Fermions are ubiquitous elementary particles. They span from electrons in metals, to protons and neutrons in nuclei and to quarks at the sub-nuclear level. Further, they possess an intrinsic degree of freedom called spin ... <\/p>\n
Antiferromagnets are materials that lose their apparent magnetic properties when cooled down close to absolute zero temperature. Different to conventional magnets, which can be described with classical physics even at the ... <\/p>\n
Researchers at Sandia National Laboratories have developed new mathematical techniques to advance the study of molecules at the quantum level. <\/p>\n
The first experimental result has been published from the newly upgraded Continuous Electron Beam Accelerator Facility (CEBAF) at the U.S. Department of Energy's Thomas Jefferson National Accelerator Facility. The result ... <\/p>\n
Sudden cardiac death resulting from fibrillation - erratic heartbeat due to electrical instability - is one of the leading causes of death in the United States. Now, researchers have discovered a fundamentally new source ... <\/p>\n
(Phys.org)A team of researchers at Sandia Labs in the U.S. has developed a type of atom interferometer that does not require super-cooled temperatures. In their paper published the journal Physical Review Letters, the ... <\/p>\n
(Phys.org)A team of researchers working on the CERN Axion Solar Telescope (CAST) project report passing an important milestone in their search for the axionthey have moved below established astrophysical constraints ... <\/p>\n
When spacecraft and satellites travel through space they encounter tiny, fast moving particles of space dust and debris. If the particle travels fast enough, its impact appears to create electromagnetic radiation (in the ... <\/p>\n
Adjust slider to filter visible comments by rank <\/p>\n
Display comments: newest first <\/p>\n
Electrons are repelled by other electrons (Coulomb's Law). This is the opposite of a \"bond\". Electrons are attracted by protons. The most simple atom is Hydrogen. This is a very engaging subject, which I have studied since 1989. Max Planck's original quantum theory was based on the hydrogen atom as an electronic system, and there were no conflicts. My book (\"The Secret of Gravity\", 1997) presents proof that gravity is an electronic force. The dynamic forces of hydrogen atoms can be analyzed using special computer programs (\"Analyzing Atoms Using the SPICE Computer Program\", Computing in Science and Engineering, Vol. 14, No. 3, May\/June 2012). An electronic model of the hydrogen atom is presented and analyzed. <\/p>\n
Please sign in to add a comment. Registration is free, and takes less than a minute. Read more <\/p>\n
<\/p>\n
See the rest here:<\/p>\n
The application of three-axis low energy spectroscopy in quantum physics research - Phys.Org<\/a><\/p>\n","protected":false},"excerpt":{"rendered":" May 1, 2017 ThALES. Credit: R. Continue reading