Study of Novel Quantum Phenomena in Helium Confined in Nano-Structures

本研究计划旨在研究和寻找限制在纳米多孔结构中的氦（^4He）中的各种新量子现象。该项目主要涉及五个主题。研究结果如下：1.纳米多孔玻璃中的^4He：（A）通过等容压力测量确定液-固相边界。我们发现，在比超流转变温度高得多的温度下，受限^4 He的热容会出现峰值。热容量峰明确地显示了在纳米孔中局部玻色-爱因斯坦凝聚体的形成。(B)提出了一种扭振子与超声同时测量的新方法。通过这种技术，我们发现超流转变温度与频率无关，但有很强的多孔样品依赖性。(C)我们已经成功地控制纳米多孔玻璃的孔径通过预镀氪原子的几个原子层。预镀后超流转变温度降低 ...更多信息 g，表明有效孔径的减小抑制了超流性.纳米多孔玻璃中氢的量子效应研究：为了研究分子氢中的BEC和超流性，我们采用等容压测量方法研究了氢过冷度与孔径的关系。发现过冷H_2在9 K左右凝固。然而，少量的H_2，可能被限制在最窄的孔中，在2.5-nm多孔玻璃中保持液态直到约7 K。这表明，通过将H_2限制在小于2.5 nm的均匀孔隙中，可以观察到BEC。一维纳米孔中^4He的超流性：FSM-16中一维纳米孔中^4He的扭振研究表明，超流性被加压液体显著抑制，Tc在2 Mpa左右达到0 K。这是受限^4He的量子超流跃迁的第二个例子。规则三维孔隙结构中的^4He：扭振和压力实验正在进行中。^4He的超固体研究：我们对大块固体^4He和纳米多孔玻璃中的固体进行了扭振实验。前者揭示了超固态行为对样品历史的强烈依赖性。少

This research project was planned to study and search for various novel quantum phenomena in helium (^4He) confined in nanoporous structures. The project involves mainly five subjects. The outcome are as follows:1. ^4He in nano-porous glass : (A) The liquid-solid phase boundary was determined by isochoric pressure measurements. We have discovered a peak in heat capacity of confined ^4He at much higher temperatures than the superfluid transition temperature. The heat capacity peak definitely shows the formation of localized Bose-Einstein condensates in nanopores. (B) We developed a new simultaneous measurement technique of torsional oscillator and ultrasound. By this technique we have found that the superfluid transition temperature is independent of frequency, but has a strong porous sample dependence. (C) We have succeeded to control the pore size of the nanoporous glass by preplating a few atomic layers of Krypton atoms. The superfluid transition temperature decreases after preplatin … More g, indicating that the decrease of the effective pore size suppress superfluidity.2. Search for quantum effects in hydrogen (H_2) in nanoporous glasses : Aiming at searching for BEC and superfluidity in molecular hydrogen, we have studied the pore size dependence of supercooling of liquid H_2 by isochoric pressure measurements. We have found that the majority of supercooled H_2 solidify at around 9 K. However, a small amount of H_2, probably confined in narrowest pores, remains liquid down to about 7 K in 2.5-nm porous glass. This indicates that BEC can be observed by confining H_2 in uniform pores narrower than 2.5 nm.3. Superfluidity of ^4He in one-dimensional nanopores: Torsional oscillator studies for ^4He in 1D nanopores in FSM-16 revealed that superfluidity is dramatically suppressed by pressurizing liquid, with Tc reaching 0 K at around 2 Mpa. This is second example of quantum superfluid transition of confined ^4He.4. ^4He in regular 3D pore structure : Torsional oscillator and pressure experiments are underway.5. Supersolid studies of ^4He : We have conducted torsional oscillator experiments for bulk solid ^4He and solid in nano porous glasses. The former study revealed strong dependence of supersolid behaviors on sample history. Less