Superconductor-(Metal)-Insulator Transitions: Understanding the Emergence of Anomalous Metallic States

超导体-（金属）-绝缘体转变：了解反常金属态的出现

基本信息

批准号：
1808385
负责人：
Aharon Kapitulnik
金额：
$ 64.85万
依托单位：
Stanford University
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-06-01 至 2022-05-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1808385&HistoricalAwards=false
关键词：
Superconductor Metal Insulator Transitions Understanding

项目摘要

Non-Technical Abstract:Conductivity of metals is determined by impurity scattering, and is given by a simple expression known as Drude Formula. As explained by Bardeen-Cooper-Schriefer in their celebrated "BCS" theory, at low temperatures electrons in such metals may also form an exotic state known as a condensate of bosonic Cooper pairs. However, despite the vast experimental data supporting the above "standard paradigm", anomalies in experimental data, particularly in the limit of two-dimensions (2D), have been accumulating. It became clear that there exists a new class of metallic states at low temperatures, where the electronic properties cannot be understood on the basis of existing theories. The project focuses on the investigations of novel metallic states that emerge at low temperature, primarily in proximity to superconducting states. The project includes training of graduate students, and a post-doctoral scholar. The project will also seek to continue this tradition by actively recruiting women graduate students and post-docs to the group, while also maintaining strong international collaborations.Technical Abstract:A metallic state is defined as a state in which the conductivity remains finite as the temperature tends to zero. There is an extraordinarily successful "Fermi liquid theory" of clean 3D metals with long mean free path and relatively weak interactions. In this theory fermionic excitations (quasiparticles) have a finite density of states at the Fermi level, while bosonic excitations (e.g. zero sound) have lesser role at low temperatures, since their contribution to the current is negligible due to their vanishing density of states. The low-T conductivity of relatively pure 3D metals is determined by impurity scattering, and is given by the Drude formula. Another well-established paradigm is the BCS theory of superconductivity, which is based on the idea that under some circumstances electron attraction can dominate the electron repulsion so that at low temperatures electrons form a condensate of bosonic Cooper pairs. It is this condensate that carries the supercurrent. As parameters controlling the electronic environment change, the system may exhibit a superconductor to metal transition, which at zero temperature is a quantum transition. The conventional theory of metals also predict that as the system approaches the BCS superconducting state from the metallic side, its properties in no way reflect the proximity of the superconducting phase, and the conductivity of the system is controlled by the fermionic excitations everywhere in the metallic phase. Despite the vast experimental data supporting the above "standard paradigm", especially on bulk superconductors, anomalies in experimental data, particularly in the limit of two dimensions, have been accumulating. It became clear that there exists a new class of metallic states in the zero-temperature limit, where the electronic properties cannot remotely be understood on the basis of Fermi liquid and Drude theories. This observation by itself is astonishing because it points to a new paradigm for the electronic properties of metals. Exploring the properties of such anomalous metallic states is the focus of this project. This will be done by fabricating a variety of thin-films superconductors, and study their transport properties. While in the past such studies focused solely on longitudinal conductivity measurements, this project will emphasize transverse transport, and will include thermal transport, which can further shed light on the nature of the metallic state. The application of electromagnetic perturbations such as magnetic and RF electric fields will be used to tune through these metallic states, or in some circumstances promote them. The project trains one or two graduate students, one post-doctoral scholar. The project will also seek to continue this tradition by actively recruiting women graduate students and post-docs to the group, while also maintaining strong international collaborations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术摘要：金属的电导率取决于杂质散射，并由称为Drude公式的简单表达式给出。正如Bardeen-Cooper-Schriefer在其著名的“ BCS”理论中所解释的那样，在这种金属中的低温电子中，电子也可能形成一种外来的状态，称为Bosonic Cooper Pairs的冷凝物。但是，尽管有大量的实验数据支持上述“标准范式”，但实验数据中的异常情况，尤其是在二维（2D）的限制中，已经积累了。很明显，在低温下存在一类新的金属状态，在这些金属状态下，基于现有理论无法理解电子特性。该项目的重点是对低温下出现的新金属状态的研究，主要是靠近超导状态。该项目包括对研究生的培训和博士后学者。该项目还将寻求通过积极招募女性研究生和邮政为小组的妇女研究生，同时还要维持强大的国际合作。技术摘要：金属状态定义为电导率仍然有限的状态，因为温度趋于零。有一个非常成功的“费米液体液体理论”的清洁3D金属具有较长的自由路径和相对较弱的相互作用。在该理论中，费米子激发（准粒子）在费米水平上具有有限的状态密度，而在低温下，骨气激发（例如，零声音）的作用较小，因为由于它们的消失状态，它们对电流的贡献可忽略不计。相对纯的3D金属的低T电导率取决于杂质散射，并由Drude公式给出。另一个完善的范式是BCS超导性理论，它基于这样的观念：在某些情况下，电子吸引力可以主导电子排斥，因此在低温下电子在低温上形成骨库珀对的冷凝物。正是这种冷凝物带有超流。随着控制电子环境变化的参数，系统可能会表现出对金属过渡的超导体，该电源在零温度下是量子过渡。金属的常规理论还预测，随着系统接近金属侧BCS超导状态，其特性绝不反映超导阶段的接近性，并且系统的电导率受到金属阶段各地的典型激励的控制。尽管有大量的实验数据支持上述“标准范式”，尤其是在散装超导体方面，但实验数据中的异常，尤其是在二维极限的情况下，仍在积累。很明显，在零温度的极限中存在一类新的金属状态，在零温度的极限中，无法根据费米液体和drude理论对电子性质进行远程理解。这种观察本身令人惊讶，因为它指出了金属电子特性的新范式。探索这种异常金属状态的特性是该项目的重点。这将通过制造各种薄膜超导体并研究其运输特性来完成。过去，这种研究仅集中在纵向电导率测量上，但该项目将强调横向运输，并包括热运输，这可以进一步阐明金属状态的性质。电磁扰动（例如磁性和RF电场）的应用将用于通过这些金属状态进行调整，或者在某些情况下促进它们。该项目训练一两个研究生，一名博士后学者。该项目还将寻求通过积极招募女性研究生和邮政为小组的妇女研究生，同时还保持着强大的国际合作。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子评估来获得支持的，并具有更广泛的影响。

项目成果

期刊论文数量（5）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Universal Bound to the Amplitude of the Vortex Nernst Signal in Superconductors

超导体中涡旋能斯特信号振幅的普遍束缚

DOI：
10.1103/physrevlett.126.077001
发表时间：
2021
期刊：
Physical Review Letters
影响因子：
8.6
作者：
Rischau, Carl Willem;Li, Yuke;Fauqué, Benoît;Inoue, Hisashi;Kim, Minu;Bell, Christopher;Hwang, Harold Y.;Kapitulnik, Aharon;Behnia, Kamran
通讯作者：
Behnia, Kamran

Robust anomalous metallic states and vestiges of self-duality in two-dimensional granular In-InOx composites