A study of unconventional transport in electron-doped oxide superconductors

电子掺杂氧化物超导体的非常规输运研究

• 批准号: 1708334
• 负责人: richard greene
• 金额: $ 45万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-01 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1708334&HistoricalAwards=false
• 关键词: study; unconventional; transport; electron; doped

Non-Technical Abstract:Superconductivity, the complete absence of electrical resistance, is an amazing low temperature property of some elements and compounds. This quantum property of solids was discovered in 1911 and was believed to be fully understood in 1957 by the Bardeen, Cooper, Schrieffer (BCS) theory. In 1987 some copper oxide compounds (cuprates) were discovered with unexpectedly high superconducting transition temperatures (up to 140 Kelvin). This high-temperature superconductivity cannot be explained by the conventional BCS mechanism and it is not presently understood. A complete understanding of high-temperature superconductivity is one of the major unsolved problems of condensed matter physics. The solution to this problem could lead to the discovery of room temperature (300 Kelvin) superconductors, a development with very significant practical applications. This project focuses on experimental transport studies on one class of cuprate compounds where the superconductivity can be completely suppressed by the application of a small magnetic field. This enables the normal metallic state to be studied over a full range of temperature from 300 K to well below 1K. An understanding of the normal metal state is believed to be crucial for a full understanding of the origin of the superconductivity. The transport experiments are planned on specially prepared thin films with variation of the magnetic field, the temperature and electron doping, all of which change the normal state properties in ways that are expected to give deep insight into the nature of the superconductivity. This project supports the education of PhD and undergraduate students at the University of Maryland---an urban university with a diverse population---in advanced vacuum deposition and electronic characterization techniques. These techniques have proven to be excellent training for productive scientific careers in academic and technology settings.Technical Abstract:Understanding the mechanism of superconductivity and the non-Fermi liquid normal state in strongly correlated copper oxides (cuprates) is one of the most significant unsolved problems of condensed matter physics. Much progress has been made, but there are still many puzzles to be solved. In the last few years some dramatic new experimental results have been found that give new insights into the physics of the hole-doped cuprates. Since hole- and electron-doped cuprates should obey the same fundamental physics, the goal of this project is to gain a more detailed understanding of the normal state and superconducting properties of the electron-doped (n-doped) cuprate superconductors. This new information should allow the mechanism of the unconventional superconductivity in all cuprates to be determined. A comprehensive set of experiments helps understand the nature of the normal state when superconductivity is suppressed by a magnetic field. The n-doped cuprates are particularly advantageous for this because the low temperature normal state (0 T Tc) can be reached with a modest dc magnetic field (H 10 T). An understanding of the nature of the normal state of the cuprates is believed to be crucial for understanding the cause of high-Tc superconductivity in both n- and p-type cuprates. The experimental techniques to be used are: resistivity, Hall Effect, magnetoresistance, Nernst effect, thermopower, and tunneling. Some transport experiments are performed at very high magnetic field at the NSF supported high magnetic field labs in Tallahassee and Los Alamos. A study of the superconducting state in the over doped region of the electron-doped phase diagram is also to be done, since anomalous behavior recently found there is suggestive of fundamentally new physics. With outside collaborators, penetration depth, high-field Nernst and thermal diffusivity experiments are attempted. This project incorporates the training of high-school students, undergraduate science majors, graduate students, and postdoctoral scientists in various experimental aspects of condensed matter physics research. As in the past, the principal investigator encourages women and underrepresented groups to participate in this project. The external collaborations in this project provide a unique vehicle for students to experience research in different laboratory environments, i.e., university, industry, and government. An ongoing participation in the Graduate Resources Advancing Diversity (GRADMAP) program at the University of Maryland involves undergraduates in research exposure programs designed to attract a broader audience to graduate studies. Efforts to encourage a broader education in science via existing Physics department outreach programs with predominately minority public-school students near the University of Maryland are continued. These include, Physics is Phun, Physics Discovery Days, and the Summer School Girl's Program.

非技术摘要：超导电性，即完全没有电阻，是某些元素和化合物惊人的低温特性。固体的这一量子特性于1911年被发现，并被认为在1957年被Bardeen，Cooper，Schrieffer(BCS)理论完全理解。1987年，一些铜氧化物(铜酸盐)被发现具有出人意料的高超导转变温度(高达140开尔文)。这种高温超导性不能用传统的BCS机制来解释，目前还不清楚。对高温超导电性的全面认识是凝聚态物理尚未解决的主要问题之一。这个问题的解决可能导致室温(300Kelvin)超导体的发现，这是一项具有非常重要的实际应用的发展。本项目致力于一类铜酸盐化合物的输运实验研究，在这种化合物中，超导电性可以通过施加一个小磁场来完全抑制。这使得可以在从300K到远低于1K的整个温度范围内研究正常的金属状态。对正常金属状态的理解被认为是全面理解超导起源的关键。输运实验计划在特殊制备的薄膜上进行，随着磁场、温度和电子掺杂的变化，所有这些都会改变正常态的性质，有望深入了解超导的本质。该项目支持马里兰大学的博士和本科生的教育-这是一所人口多样化的城市大学-先进的真空沉积和电子表征技术。这些技术已被证明是对学术和技术环境中富有成效的科学生涯的极好培训。技术摘要：了解强关联铜氧化物(铜酸盐)中超导和非费米液体正常态的机制是凝聚态物理学中最重要的悬而未决的问题之一。已经取得了很大进展，但仍有许多谜团有待解决。在过去的几年里，一些戏剧性的新实验结果被发现，这给了人们对空穴掺杂铜酸盐物理的新见解。由于空穴和电子掺杂的铜酸盐应该遵循相同的基本物理，本项目的目标是更详细地了解电子掺杂(n掺杂)铜酸盐超导体的正常态和超导性质。这一新信息应该可以确定所有铜酸盐中非传统超导电性的机制。一套全面的实验有助于理解当超导电性被磁场抑制时正常状态的性质。N掺杂的铜酸盐对此特别有利，因为在适度的直流磁场(H10T)下就可以达到低温正常态(0TTC)。了解铜酸盐正常态的性质对于理解n型和p型铜酸盐高T_c超导电性的原因至关重要。将使用的实验技术有：电阻率、霍尔效应、磁阻、能斯特效应、热电势和隧道效应。一些输运实验是在美国国家科学基金会支持的塔拉哈西和洛斯阿拉莫斯的高磁场实验室中进行的。还需要研究电子掺杂相图中过掺杂区的超导态，因为最近发现的反常行为暗示着根本上的新物理。与外部合作者一起，尝试了穿透深度、高场能级和热扩散率实验。该项目包括对高中生、理科专业本科生、研究生和博士后科学家在凝聚态物理研究的各个实验方面的培训。同以往一样，首席调查员鼓励妇女和代表性不足的群体参与这一项目。该项目的外部合作为学生在不同的实验室环境中体验研究提供了一个独特的工具，即大学、行业和政府。马里兰大学研究生资源促进多样性计划(GRADMAP)的持续参与让本科生参加旨在吸引更广泛受众进行研究生学习的研究暴露计划。继续努力通过现有的物理系外展计划鼓励更广泛的科学教育，这些计划主要针对马里兰大学附近的少数族裔公立学校的学生。这些活动包括，物理是芬，物理发现日，和暑期学校女孩计划。

项目成果

Ferromagnetic order beyond the superconducting dome in a cuprate superconductor

• DOI: 10.1126/science.aax1581
• 发表时间: 2020-05-01
• 期刊: SCIENCE
• 影响因子: 56.9
• 作者: Sarkar, Tarapada;Wei, D. S.;Greene, Richard L.
• 通讯作者: Greene, Richard L.

Correlation between scale-invariant normal-state resistivity and superconductivity in an electron-doped cuprate

• DOI: 10.1126/sciadv.aav6753
• 发表时间: 2019-05-01
• 期刊: SCIENCE ADVANCES
• 影响因子: 13.6
• 作者: Sarkar, Tarapada;Mandal, P. R.;Greene, Richard L.
• 通讯作者: Greene, Richard L.

Quantum oscillations from the reconstructed Fermi surface in electron-doped cuprate superconductors

电子掺杂铜酸盐超导体中重建费米表面的量子振荡

• DOI: 10.1088/1367-2630/aab7e7
• 发表时间: 2018
• 期刊: New Journal of Physics
• 影响因子: 3.3
• 作者: Higgins, J S;Chan, M K;Sarkar, Tarapada;McDonald, R D;Greene, R L;Butch, N P
• 通讯作者: Butch, N P

Three-dimensional collective charge excitations in electron-doped copper oxide superconductors

• DOI: 10.1038/s41586-018-0648-3
• 发表时间: 2018-11-15
• 期刊: NATURE
• 影响因子: 64.8
• 作者: Hepting, M.;Chaix, L.;Lee, W. S.
• 通讯作者: Lee, W. S.

Anomalous normal-state resistivity in superconducting La2−xCexCuO4 : Fermi liquid or strange metal?

超导 La2·xCexCuO4 中的反常常态电阻率：费米液体还是奇怪的金属？

• DOI: 10.1103/physrevb.98.224503
• 发表时间: 2018
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Sarkar, Tarapada;Greene, Richard L.;Das Sarma, S.
• 通讯作者: Das Sarma, S.