[论文解读] Evolution of high-temperature superconductivity from low-Tc phase tuned by carrier concentration in FeSe thin flakes

Bin Lei, Jianhua Cui+8 more|arXiv (Cornell University)|Sep 2, 2015

Iron-based superconductors research被引用 25

一句话总结

本研究证明，通过FeSe薄片的液体栅控实现电子掺杂，可诱导其从低Tc超导相转变为Tc高达48 K的高Tc相——且无需外加压力或外延界面。该转变与Lifshitz转变同时发生，表明仅通过载流子浓度调控即可在本征FeSe中稳定高温超导态，为铁基超导体配对机制提供了关键见解。

ABSTRACT

In contrast to bulk FeSe superconductor, heavily electron-doped FeSe-derived superconductors show relatively high Tc without hole Fermi surfaces and nodal superconducting gap structure, which pose great challenges on pairing theories in the iron-based superconductors. In the heavily electron-doped FeSe-based superconductors, the dominant factors and the exact working mechanism that is responsible for the high Tc need to be clarified. In particular, a clean control of carrier concentration remains to be a challenge for revealing how superconductivity and Fermi surface topology evolves with carrier concentration in bulk FeSe. Here, we report the evolution of superconductivity in the FeSe thin flake with systematically regulated carrier concentrations by liquid-gating technique. High-temperature superconductivity at 48 K can be achieved only with electron doping tuned by gate voltage in FeSe thin flake with Tc less than 10 K. This is the first time to achieve such a high temperature superconductivity in FeSe without either epitaxial interface or external pressure. It definitely proves that the simple electron-doping process is able to induce high-temperature superconductivity with Tc as high as 48 K in bulk FeSe. Intriguingly, our data also indicates that the superconductivity is suddenly changed from low-Tc phase to high-Tc phase with a Lifshitz transition at certain carrier concentration. These results help us to build a unified picture to understand the high-temperature superconductivity among all FeSe-derived superconductors and shed light on further pursuit of higher Tc in these materials.

研究动机与目标

• 阐明载流子浓度在调控FeSe中超导转变温度（Tc）中的作用。
• 研究在受控电子掺杂下，本征FeSe中超导性和费米面拓扑结构的演化。
• 确定FeSe中的高Tc超导性是否可在无外延界面或外加压力的情况下实现。
• 确定电子掺杂FeSe中高Tc超导性出现的微观机制。
• 通过系统的载流子浓度调控，建立对FeSe基材料中超导性的统一理解。

提出的方法

• 采用液体栅控技术精确调控机械剥离的FeSe薄片中的电子载流子浓度。
• 通过电阻率和霍尔效应测量，监测载流子密度和超导转变温度（Tc）。
• 系统性地调节栅压，实现连续电子掺杂，并探测超导性和电子性质的演化。
• 从霍尔测量推断费米面拓扑结构，并与超导相变相关联。
• 通过在临界掺杂水平处载流子密度和电子结构的非连续变化，识别出Lifshitz转变的存在。
• 通过与理论模型对比Tc的演化，识别出主导的配对机制。

实验结果

研究问题

• RQ1 是否仅通过电子掺杂即可在FeSe中实现高Tc超导性，而无需外加压力或人工界面？
• RQ2 随着FeSe薄片中电子载流子浓度的增加，超导转变温度（Tc）如何演化？
• RQ3 是否存在一个临界载流子浓度，使超导相从低Tc行为突然转变为高Tc行为？
• RQ4 费米面拓扑结构变化（Lifshitz转变）在触发FeSe中高Tc超导性方面起什么作用？
• RQ5 在电子掺杂FeSe中，导致高Tc超导性出现的主导配对机制是什么？

主要发现

• 通过液体栅控诱导的电子掺杂，在FeSe薄片中实现了高达48 K的高温超导性，且无需外加压力或外延界面。
• 在临界电子载流子浓度处，从低Tc超导相（Tc < 10 K）到高Tc相（Tc = 48 K）发生了明显的相变。
• 该相变与Lifshitz转变同时发生，表现为载流子密度和费米面拓扑结构的非连续变化。
• 超导性的演化与载流子浓度直接相关，表明仅通过电子掺杂即可在本征FeSe中稳定高Tc超导态。
• 结果表明，FeSe基超导体中的配对机制强烈受Lifshitz点附近电子结构变化的影响。
• 研究结果为FeSe基材料中超导性的统一图像提供了强有力的实验支持，强调了电子拓扑结构和掺杂的关键作用。