Ovdat O, Mao Jinhai, Jiang Yuhang, Andrei E Y, Akkermans E
Department of Physics, Technion, Israel Institute of Technology, Haifa, 3200003, Israel.
Department of Physics and Astronomy, Rutgers University, Piscataway, NJ, 08854, USA.
Nat Commun. 2017 Sep 11;8(1):507. doi: 10.1038/s41467-017-00591-8.
One of the most interesting predictions resulting from quantum physics, is the violation of classical symmetries, collectively referred to as anomalies. A remarkable class of anomalies occurs when the continuous scale symmetry of a scale-free quantum system is broken into a discrete scale symmetry for a critical value of a control parameter. This is an example of a (zero temperature) quantum phase transition. Such an anomaly takes place for the quantum inverse square potential known to describe 'Efimov physics'. Broken continuous scale symmetry into discrete scale symmetry also appears for a charged and massless Dirac fermion in an attractive 1/r Coulomb potential. The purpose of this article is to demonstrate the universality of this quantum phase transition and to present convincing experimental evidence of its existence for a charged and massless fermion in an attractive Coulomb potential as realized in graphene.When the continuous scale symmetry of a quantum system is broken, anomalies occur which may lead to quantum phase transitions. Here, the authors provide evidence for such a quantum phase transition in the attractive Coulomb potential of vacancies in graphene, and further envision its universality for diverse physical systems.
量子物理学产生的最有趣的预测之一是经典对称性的破缺，统称为反常。当一个无标度量子系统的连续标度对称性对于控制参数的临界值破缺为离散标度对称性时，就会出现一类显著的反常。这是一个（零温度）量子相变的例子。对于已知描述“埃菲莫夫物理”的量子平方反比势，就会发生这样的反常。在吸引性的1/r库仑势中的带电无质量狄拉克费米子，也会出现从连续标度对称性破缺为离散标度对称性的情况。本文的目的是证明这种量子相变的普遍性，并为石墨烯中实现的吸引性库仑势中的带电无质量费米子提供其存在的令人信服的实验证据。当量子系统的连续标度对称性破缺时，就会出现反常，这可能导致量子相变。在这里，作者们为石墨烯中空位的吸引性库仑势中的这种量子相变提供了证据，并进一步设想了其在各种物理系统中的普遍性。
