基于转角样品杆的脉冲强磁场电输运测量系统

Electrical transport measurement system in pulsed high magnetic field based on rotation sample rod

测量物质在不同外加磁场方向下的电输运性质是近年来研究拓扑量子材料的一种重要实验方法,为探索物质的新奇特性提供了独特的视角和手段.研究表明,在超高强度的脉冲强磁场下,材料的电输运研究可能扩展至量子极限区域,将观察到更加丰富的物理现象.而现有的电输运测量系统中,稳态场下的样品测量杆受限于尺寸和材料,难以适应脉冲场测量要求;脉冲场下的传统样品测量杆的角度分辨率和空间利用率较低,亟需研制更高性能的转角测量系统.为此,本文提出一种拉杆式转角样品杆,基于该转角样品杆的脉冲强磁场电输运测量系统,能够在极低温、强磁场的极端环境下,于脉冲磁体中心通孔的微型样品腔内开展磁场方向190°范围内任意变化的电输运性质测量实验,其旋转结构稳定性良好,转角控制精度达到0.1°;通过合理设计集成电路布局、前置补偿放大和数字锁相提取等信号处理环节,电输运测量结果的精确度优于0.1 m W.本文详细阐述了该测量系统的组成、转角测量杆的设计与研制、校准原理与信号处理过程,并简要介绍了该测量系统在费米面重构、拓扑绝缘体表面态、量子极限输运、超导电性等前沿研究领域的应用.

In recent years, measuring the electrical transport properties of materials in different directions of applied magnetic field has become an important experimental study of topological quantum materials. With the development of condensed matter physics, scientific research has shown that under the ultra-high intensity pulsed magnetic field, the electrical transport study of materials may extend to the quantum limit region, and more abundant physical phenomena will be observed. However, in the existing electric transport measurement system, the rotation sample rod under the action of steady-state field presents a large size and significant eddy current effect, which makes it difficult to meet the requirements for pulsed field measurement, and the current commercial physical property measurement system(PPMS) can only operate under ±16 T steady magnetic field. In addition, the conventional rotation sample rod encounters the problems of insufficient angular resolution and space utilization when used in pulsed high magnetic environment. So there is an urgent need to develop a higher performance rotation measurement system. In view of the above background, in this paper we present a kind of electrical transport measurement system designed by Wuhan National High Magnetic Field Center(WHMFC), which consists of five modules: pulse power supply, pulse magnet, control center, cryogenic system, and signal measurement. The key component is the sample measuring rod with rotation function, which restricts the movement of the drawbar through a double-groove structure to achieve an angular change in a range from –5° to 185°. An angle calibration coil is mounted on the back of the sample stage. Based on the double-calibration method, the angle control accuracy of 0.1° is achieved. The temperature, magnetoresistance and Hall resistance signal are collected by the integrated circuit on sample stage and extracted by compensation circuit and virtual digital lock-in amplifier, and the accuracy of electric transport measurement is better than0.1 m W. Furthermore, the effect of eddycurrent and material deformation at low temperatures are completely eliminated by using polyetheretherketone material, which effectively improves the stability and reliability of the rotation sample rod. Using this measuring rod, we complete a series of experiments in the 8 mm sample cavity in the center of the pulse magnet: the minimum ambient temperature reaches 1.3 K, the maximum magnetic field strength arrives at 65 T, and the direction angle of the magnetic field is able to change in a 190° range.Thus the universally applicable measurement system of electric transport experiment in pulsed high magnetic field is successfully established. In this paper, we elaborate the principle and device components of the measurement system, the design and fabrication of the angle measuring rod, and the calibration principle and measurement process. Relevant experimental results show that the system has important application value in the research of 3 D Fermi surface, topological insulator surface state, quantum limit transport, superconductivity analysis, etc. Based on this system, the electrical transport experimental system at WHMFC provides an effective means for the relevant research teams(home and abroad) engaged in the exploration of the intrinsic physical characteristics of quantum materials in extremely pulsed high magnetic field and low temperature environment.