Quantum Phase Transitions and Quantum Criticality in Helium Films

氦薄膜中的量子相变和量子临界性

• 批准号: EP/H048375/1
• 负责人: John Saunders
• 金额: $ 143.46万
• 依托单位: Royal Holloway University of London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FH048375%2F1
• 关键词: Quantum; Phase; Transitions; Criticality; Helium

Historically quantum fluids, the helium liquids near absolute zero, have provided simple model systems which have played a crucial role in the development of key concepts in condensed matter physics. The understanding of superfluidity and broken gauge symmetry; the development of the standard model of correlated fermions; the first unconventional superfluid/superconductor; the central role of topological excitations in two dimensional physics: all these discoveries and insights arose from the study of helium. The study of quantum fluids has also fuelled developments in techniques for producing and measuring low temperatures, high magnetic fields, and a host of novel measurement techniques and instrumentation. We propose to study a variety of low dimensional helium model systems to address fundamental issues in the understanding of strongly correlated quantum matter. We will study helium-3 (fermion) films and helium-4 (boson) films. These films grow as atomic layers on the atomically flat surface of graphite, and the lattice potential experienced by a helium layer can give rise to a triangular superlattice structure. The density of these layers can be varied essentially continuously to tune between different quantum mechanical ground states. These may include ground states theoretically proposed but yet to be unambiguously realized. We will study the quantum phase transitions between different ground states in some detail. We will study the Mott transition between a 2D helium-3 Fermi liquid and a 2D quantum spin liquid and the properties of the hole-doped spin liquid on a triangular lattice. We will attempt to stabilise a Mott insulator on a square lattice and perform a comparable experiment. In the corresponding helium-4 film we will study the superfluid-insulator transition, and investigate possible 2D supersolid behaviour. We will develop a highly ordered graphite substrate with a view to optimising conditions under which to search for the holy grail of unconventional superfluidity in a helium-3 fluid monolayer. We will investigate quantum criticality in the helium-3 bilayer heavy fermion system recently discovered by us. And we will study helium-3 in nano-channels as a one dimensional fermion system, and a possible realization of a Luttinger liquid. These experiments on fermionic and bosonic cold atoms are performed on uniform low dimensional systems in thermodynamic equilibrium at precisely measured temperatures in the range 200 microKelvin to 4K. The lowest temperatures will be produced by nuclear adiabatic demagnetization cryostats in our laboratory. A range of high precision experimental probes will be employed to study these systems. Sensitive NMR techniques developed in our laboratory, based on the detection of the precessing magnetic signal by SQUIDs (Superconducting Quantum Interference Devices), will be used to measure magnetic susceptibility, magnetization and spin dynamics. We will extend measurements of the heat capacity to the lowest temperatures in order to access system entropy and probe the elementary excitations. The superfluid density, and any dissipative component of the response, will be measured by high quality torsional mechanical resonators. We will collaborate on developing graphene based nano-mechanical resonators with wide-bandwidth SQUID amplifier detection. The project is expected to lead to fundamental insights into some of the most central issues in the physics of strongly correlated matter, and impact on the understanding of more complex materials of potential technological relevance. The project will drive innovation of new instrumentation and measurement techniques at an important scientific frontier; the low temperature frontier. As in any frontier science we may encounter the unexpected.

历史上，量子流体，即接近绝对零度的氦液体，提供了简单的模型系统，在凝聚态物理学的关键概念的发展中发挥了至关重要的作用。对超流性和破缺规范对称性的理解;关联费米子标准模型的发展;第一个非常规超流体/超导体;拓扑激发在二维物理学中的核心作用：所有这些发现和见解都源于对氦的研究。量子流体的研究也推动了低温、高磁场的产生和测量技术的发展，以及一系列新的测量技术和仪器的发展。我们建议研究各种低维氦模型系统，以解决理解强关联量子物质的基本问题。我们将研究氦-3（费米子）薄膜和氦-4（玻色子）薄膜。这些薄膜在石墨的原子级平坦表面上作为原子层生长，并且氦层所经历的晶格势可以产生三角形超晶格结构。这些层的密度可以基本上连续地变化，以在不同的量子力学基态之间进行调谐。这些可能包括理论上提出但尚未明确实现的基态。我们将详细研究不同基态之间的量子相变。我们将研究二维氦-3费米液体和二维量子自旋液体之间的Mott跃迁以及三角晶格上空穴掺杂自旋液体的性质。我们将尝试稳定一个莫特绝缘体在一个正方形晶格，并执行一个类似的实验。在相应的氦-4膜中，我们将研究超流-绝缘体转变，并研究可能的二维超固体行为。我们将开发一种高度有序的石墨衬底，以期优化条件下，寻找圣杯的非常规超流性的氦-3流体单层。我们将研究最近发现的氦-3双层重费米子系统的量子临界性。我们将研究氦-3在纳米通道中作为一个一维费米子系统，以及Luttinger液体的可能实现。这些实验的费米子和玻色子冷原子进行均匀的低维系统在热力学平衡，精确测量的温度范围在200微开尔文到4K。本实验室的核绝热退磁低温恒温器将产生最低温度。一系列高精度的实验探针将被用来研究这些系统。我们实验室开发的灵敏NMR技术，基于SQUID（超导量子干涉器件）检测旋进磁信号，将用于测量磁化率，磁化强度和自旋动力学。我们将扩展测量的热容的最低温度，以访问系统熵和探测的基本激发。超流密度和响应的任何耗散分量将由高质量扭转机械谐振器测量。我们将合作开发具有宽带SQUID放大器检测的石墨烯基纳米机械谐振器。该项目预计将导致对强相关物质物理学中一些最核心问题的基本见解，并影响对具有潜在技术相关性的更复杂材料的理解。该项目将在一个重要的科学前沿--低温前沿--推动新仪器和测量技术的创新。就像在任何前沿科学中一样，我们可能会遇到意想不到的事情。

项目成果

Charge density waves in graphite; towards the magnetic ultra-quantum limit

石墨中的电荷密度波；

• DOI: 10.48550/arxiv.1411.3323
• 发表时间: 2014
• 作者: Arnold F

Spear-anvil point-contact spectroscopy in pulsed magnetic fields.

脉冲磁场中的矛砧点接触光谱。

• DOI: 10.1063/1.4828657
• 发表时间: 2013
• 期刊: The Review of scientific instruments
• 作者: Arnold F

Intertwined superfluid and density wave order in two-dimensional 4He

• DOI: 10.1038/nphys4023
• 发表时间: 2017-02
• 期刊: Nature Physics
• 影响因子: 19.6
• 作者: J. Nyéki;A. Phillis;A. Ho;Derek Lee;P. Coleman;J. Parpia;B. Cowan;J. Saunders

On the 'Supersolid' Response of the Second Layer of 4 He on Graphite.

关于石墨上第二层 4 He 的“超固体”响应。

• DOI: 10.1007/s10909-017-1779-x
• 发表时间: 2017
• 期刊: Journal of low temperature physics
• 影响因子: 2
• 作者: Nyéki J

Two-dimensional ferromagnetism of a 3He film: influence of weak frustration.

3He 薄膜的二维铁磁性：弱挫败的影响。

• DOI: 10.1103/physrevlett.111.125302
• 发表时间: 2013
• 期刊: Physical review letters
• 影响因子: 8.6
• 作者: Casey A