有限温度下纳米多孔介质中$^4$ He的4D XY量子临界性证据
Evidence for 4D XY Quantum Criticality in $^4$He Confined in Nanoporous Media at Finite Temperatures
摘要：
$^4$ He被限制在纳米多孔介质中是一个模型玻色系统，通过改变压力表现出量子相变（QPT）。我们用Helmholtz共振器技术精确地测定了$^4$ He在孔径为3.0 nm的多孔Gelsil玻璃中的超流密度临界指数。当压力为0.1 < P < 2.4 MPa时，超流密度的临界指数$ζ$ = 1.0 $\pm$ 0.1。这个值提供了决定性的证据，证明有限温度超流转变属于四维（4D）XY普适类，而在体相液体4He中，它是经典的3D XY，其中$ζ$ = 0.67。有限温度下的量子临界行为可以通过超流转变温度以上局部玻色-爱因斯坦凝聚体中强的相位涨落来理解。纳米多孔介质中的$^4$ He是一个独特的例子，其中量子临界性不仅出现在0 K，而且出现在有限的温度下。
英文摘要：
$^4$He confined in nanoporous media is a model Bose system that exhibits quantum phase transition (QPT) by varying pressure. We have precisely determined the critical exponent of the superfluid density of $^4$He in porous Gelsil glasses with pore size of 3.0 nm using the Helmholtz resonator technique. The critical exponent $ζ$ of the superfluid density was found to be 1.0 $\pm$ 0.1 for the pressure range 0.1 < P < 2.4 MPa. This value provides decisive evidence that the finite-temperature superfluid transition belongs to the four-dimensional (4D) XY universality class, in contrast to the classical 3D XY one in bulk liquid 4He, in which $ζ$ = 0.67. The quantum critical behavior at a finite temperature is understood by strong phase fluctuation in local Bose-Einstein condensates above the superfluid transition temperature. $^4$He in nanoporous media is a unique example in which quantum criticality emerges not only at 0 K but at finite temperatures.
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