ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Av. Carl Friedrich Gauss 3, 08860, Castelldefels, (Barcelona), Spain.
University of Lyon, Ens de Lyon, University Claude Bernard, CNRS, Laboratoire de Physique, F-69342, Lyon, France.
Nat Commun. 2019 Feb 4;10(1):577. doi: 10.1038/s41467-019-08324-9.
Albeit occurring at zero temperature, quantum critical phenomena have a huge impact on the finite-temperature phase diagram of strongly correlated systems, giving experimental access to their observation. Indeed, the existence of a gapless, zero-temperature quantum critical point induces the existence of an extended region in parameter space-the quantum critical fan (QCF)-characterized by power-law temperature dependences of all observables. Identifying experimentally the QCF and its crossovers to other regimes (renormalized classical, quantum disordered) remains nonetheless challenging. Focusing on paradigmatic models of quantum phase transitions, here we show that quantum correlations-captured by the quantum variance of the order parameter-exhibit the temperature scaling associated with the QCF over a parameter region much broader than that revealed by ordinary correlations. The link existing between the quantum variance and the dynamical susceptibility paves the way to an experimental reconstruction of the QCF using spectroscopic techniques.
尽管量子临界点发生在零温度下，但它们对强关联系统的有限温度相图有着巨大的影响，使实验能够观察到它们。事实上，零温无能隙量子临界点的存在导致了参量空间中存在一个扩展区域——量子临界点扇区（QCF）——所有可观测量的温度依赖性都是幂律的。然而，实验上确定 QCF 及其与其他状态（重整化经典状态、量子无序状态）的交叉仍然具有挑战性。在这里，我们关注量子相变的典型模型，结果表明，量子关联——由序参量的量子方差来描述——表现出与 QCF 相关的温度标度，其参量范围比普通关联所揭示的范围宽得多。量子方差与动态磁化率之间的联系为使用光谱技术重建 QCF 铺平了道路。
