NPC, CAS issued a paper Science! Important breakthroughs in the de-confinement quantum critical point
The deconfined quantum critical point (DQCP) is a precedent for a new paradigm in quantum matter science that goes beyond the traditional Landau-Ginzburg-Wilson (LGW) theoretical framework of phase transition and state of matter classification, which is based on sequential parameter and symmetry breaking. The LGW framework embodies the basic ideas of the new paradigm of quantum matter science such as fractionalization, matter-field and norm-field coupling, and evolutionary continuum symmetry.
In 2007, Professor Anders Sandvik of Boston University devised the J-Q model of quantum magnetism and used quantum Monte Carlo simulations to study its properties, which gradually brought this possibility into reality and attracted a lot of attention in the fields of many-body theory calculations and quantum magnetism experiments. The possibility of using quantum Monte Carlo simulations to study the properties of
However, even if numerical calculations are possible, the difficulty and breadth of the de-confined quantum critical behavior itself remains daunting. More than a decade later, several fundamental questions still plague the entire field of theory-numerical-experiment, including:
1) Does the deconfined quantum critical point, as a continuous phase transition, actually exist in the J-Q model or in other artificially designed models?
2) Is there an evolutionary continuum symmetry at this critical point, as predicted by the theory?
3) What spectroscopic signal should be sought to observe the deconfined quantum criticality phenomenon in neutron scattering experiments in quantum magnetic materials?
The first two questions have been theoretically fundamental and have been intensely debated for more than a decade with no sign of stopping for a while.
The paper, titled "Proximate deconfined quantum critical point in SrCu2(BO3)2", was published in the journal Science.
On May 25, Yi Cui, Huihang Lin, Rong Yu, and Weiqiang Yu of Renmin University of China, Lu Liu and Anders W. Sandvik of the Institute of Physics, Chinese Academy of Sciences, and others, published a paper in Science, demonstrating by high-pressure NMR measurements of the quantum magnet SrCu2(BO3)2 at 1.8 GPa above low temperature (Tc ≃ 0.07 K), the magnetic field induces a transition from the plaquette-singlet-monoclinic state of the tetramer to the antiferromagnetic state. The first-order leap characteristics weaken with increasing pressure, and a quantum critical scale is observed at the highest pressure of 2.4 GPa.
Overview of the experiment. Figure a shows the atomic structure of the SrCu2(BO3)2 plane.
Schematic phase diagram and quantum critical point (DQCP) scenario.
NMR mapping and line shifts. aFM conversion The NMR centerline splitting with increasing H at T = 0.07 K is shown in a and b for P = 2.1 GPa and 2.4 GPa, respectively.
Spin lattice relaxation.
Spin gap and emergent symmetry.
In this experiment, the team's high-pressure NMR experiments on SrCu2(BO3)2 in a magnetic field established the first case of a quantum magnet realizing the DQCP phenomenon: until then, this existed only in the field of field theory and modeling studies.
In the paper, the team states: "We believe that the apparent suppression of Tc and the absence of significant PS gap discontinuities are consequences of the emerging O(3) symmetry produced by the nearby DQCP. At the highest pressure (2.4 GPa), 1/T1 at T between 0.2 and 2K exhibits critical scaling, indicating close enough to the DQCP (which may be of the multicritical type) to achieve the characteristic quantum criticality on the gap PS side of the transition. The strong 3D AFM ordering effect (AFM ordering effect) on the gapless side of the transition masks the putative quantum criticality of 1/T1, but the AFM ordering temperature TN vanishes in a manner very similar to the PS ordering TP, again supporting the emergent symmetry of the order parameter."
[2]https://mp.weixin.qq.com/s/LYDTl9pd03JKLQgt23bGPQ
[3]https://www.science.org/doi/10.1126/science.adc9487
