基于小型脉冲管制冷机的高温超导体混频器

文中介绍在小型脉冲管制冷机的基础上设计制作的混频系统 ,利用高温超导双晶结作为混频元件 ,实现了毫米波段的谐波混频 ,并对小型脉冲管制冷机作为高温超导体微波器件的冷源做了一定的研究。说明小型脉冲管制冷机在高温超导器件走向实用方面大有潜力。     

高温超导混频器在锁相稳频源中的应用

基于小型脉冲管制冷机,设计并改善了与其配套的锁相混频系统,用约瑟夫森颗粒边界结实现了高温超导3mm波段96次谐波混频,完成了60次谐波下压控振荡器的锁相稳频实验。首次实现了基于小型脉冲管制冷机的实用高温超导混频器3mm锁相稳频源。     

实用高温超导混频器3mm锁相稳频源

基于小型脉冲管制冷机,设计并改善了与其配套的锁相混频系统,用约瑟夫森颗粒边界结实现了高温超导3mm波段96次谐波混频,完成了60次谐波下压控振荡器的锁相稳频实验.首次实现了基于小型脉冲管制冷机的实用高温超导混频器3mm锁相稳频源.     

使用脉冲管制冷机的高温超导电子学子系统的初步研究

利用微型制冷技术的最新成果，设计和制作了一台适用于高温超导微波子系统的脉冲管制冷机．制冷机冷头微振动精密测量表明，这台脉冲管制冷机冷头的最大振动比商品化的传统制冷机要小１～２个数量级左右．首次成功地将特殊设计的高温超导谐振腔与上述制冷机组成实用电子学子系统．实验表明，在同样条件下器件在传统制冷机（斯特林机）内出现的噪声，在脉冲管制冷机中完全消失，充分表明了脉冲管制冷的优越性，显示了由脉冲管制冷机与高温超导器件组成的实用电子学子系统的潜在应用前景．     

基于制冷机的高温超导谐波混频

我们分别选用了小型脉冲管制冷机以及小型G-M制冷机设计了高温超导混频测量系统,对亚毫米波段谐波混频进行了实验研究.采取了一些抑制系统噪声的措施后,在脉冲管制冷机上我们成功实现了100GHz混频,最高谐波次数达60次,在G-M制冷机上我们实现了300GHz混频,最高谐波次数达100次.     

热端温度对高频微型同轴脉冲管制冷机性能的影响及其在空间技术中的应用研究

本文用数值方法对热端温度对微型高频同轴脉冲管制冷机性能的影响进行了分析,并将其与实验结果进行了比较,随着热端温度的升高,制冷机的最低制冷温度单调升高,制冷量单调减少,试验结果与数值计算结果定性相符。在此基础上,探讨了高频微型同轴脉冲管制冷机和辐射制冷器相结合在空间飞行器中的应用,提出了两种应用模式,用数值方法对之进行了分析。     

热端温度对高频微型非金属脉冲管制冷机性能影响的实验研究

热端温度对小制冷量的微型脉冲管制冷机的性能有着较为显著的影响.本文针对所设计的两台高频微型同轴非金属脉冲管制冷机,实验研究了制冷机冷端无负荷最低温度和轴向导热损失随热端温度的变化规律.实验对其影响幅度进行了量化分析,并发现通过降低热端温度的方法可以对样机制冷机性能起到很好的促进作用.     

16．1K的高频两级脉冲管制冷机的实验研究

单级高频脉冲管制冷机直接降低到20 K以下温区存在很大困难,采用多级方案是高频脉冲管制冷机获得更低温度的主要方法.本文介绍了一套高频气耦合型两级脉冲管制冷机的性能特性,该脉冲管制冷机可以达到16.1 K的最低温度,是目前有报道高频气耦合型两级脉冲管制冷机的最低温度.文中给出了双向进气、频率和输入功率对最低温度的影响.     

脉冲管制冷机调相机构的研究 第三部分 惯性管调相能力的研究

惯性管作为脉冲管制冷机的主要调相机构,可以为制冷机获得合适的相位关系。但是有的制冷机仅仅使用惯性管作为调相机构,有的同时还采用双向进气作为调相机构,这引起了人们对二者使用的混乱认识。为了深入了解惯性管在脉冲管制冷机中的调相作用,对惯性管的调相能力进行了研究,发现惯性管并不能为所有的脉冲管制冷机实现所需的阻抗,因此双向进气模式在有的制冷机中仍然能够发挥积极的作用。     

高效同轴脉冲管制冷机性能的实验研究

同轴式脉冲管制冷机具有结构紧凑、与器件耦合简单的优点,在实际应用中得到了越来越广泛的采用.本文对一台经理论优化设计的高频同轴脉冲管制冷机进行了实验研究,采用自制的直线压缩机驱动,惯性管/气库作为调相机构,在输入电功150 W、冷端温度为77 K时得到了9.86 W的制冷量,相对卡诺效率达到18.4%,这是目前同轴脉冲管...     

Effects of edge boundaries on Josephson vortices in finite-size layered high-Tc superconductors

In order to systematically explain the in-plane size effects for the periodical dependence of the Josephson-vortex-flow resistance on the magnetic field, we numerically explore static lattice structures of Josephson vortices in layered high-Tc superconductors with finite in-plane sizes from sub-microm to more than 10 microm by simulating slow quenching processes from high temperature under the magnetic field. The numerical results reveal that in sub-microm size the rectangular lattice is a widely spread major structure in H-T diagram and the triangular lattice is a minor one which emerges only around the specific magnetic field supplying n(phi)0 per one junction area. These results suggest that sub-microm size layered high-Tc superconductors are promising for future device applications.     

Simple high-temperature superconducting yttrium cuprate-based device for measuring weak magnetic fields

The earlier data for the magnetic properties of YBa₂Cu₃O_{7 ? x} polycrystals are used to design a highly sensitive device measuring weak magnetic fields. The sensitivity of the device is close to that of SQUIDs and much higher than the sensitivity of flux-gate meters. At the same time, the device is simpler in design and more reliable in operation than SQUIDs. Unlike SQUIDs, the device makes it possible to directly measure the magnetic field strength, has a wide measuring range, and exhibits a well-defined directional pattern.     

Chimera states and synchronization in magnetically driven SQUID metamaterials

One-dimensional arrays of Superconducting QUantum Interference Devices (SQUIDs) form magnetic metamaterials exhibiting extraordinary properties, including tunability, dynamic multistability, negative magnetic permeability, and broadband transparency. The SQUIDs in a metamaterial interact through non-local, magnetic dipole-dipole forces, that makes it possible for multiheaded chimera states and coexisting patterns, including solitary states, to appear. The spontaneous emergence of chimera states and the role of multistability is demonstrated numerically for a SQUID metamaterial driven by an alternating magnetic field. The spatial synchronization and temporal complexity are discussed and the parameter space for the global synchronization reveals the areas of coherence-incoherence transition. Given that both one- and two-dimensional SQUID metamaterials have been already fabricated and investigated in the lab, the presence of a chimera state could in principle be detected with presently available experimental set-ups.     

Peculiarities of rf SQUID response in finite magnetic fields

Single-layer washer-type high-T_c YBa₂Cu₃O_7−x rf SQUIDs with grain-boundary Josephson junctions, as well as low-T_c Nb rf SQUIDs with Nb–Al₂O₃–Nb tunnel junctions, have been investigated in finite magnetic fields. It was shown experimentally that the suppression of the critical current of the Josephson junction due to the magnetic field leads to a modulation of the amplitude of the SQUID output signal. The role of the “unwanted” junction in high-T_c rf SQUIDs, which is formed by the grain boundary running through the washer of the SQUIDs on bicrystal substrates, has also been clarified. The drop of the SQUID signal at a finite magnetic field is originated by the penetration of the magnetic field into the unwanted junction. Based on these results, a direct radio-frequency method for the determination of the first critical field H_c1 for long Josephson junctions has been developed.     

Wide-band tuneability,nonlinear transmission,and dynamic multistability in SQUID metamaterials

Superconducting metamaterials comprising rf Superconducting QUantum Interference Devices (SQUIDs) have been recently realized and investigated with respect to their tuneability, permeability, and dynamic multistability properties. These properties are a consequence of intrinsic nonlinearities due to the sensitivity of the superconducting state to external stimuli. SQUIDs, made of a superconducting ring interrupted by a Josephson junction, possess yet another source of nonlinearity, which makes them widely tuneable with an applied dc dlux. A model SQUID metamaterial, based on electric equivalent circuits, is used in the weak coupling approximation to demonstrate the dc flux tuneability, dynamic multistability, and nonlinear transmission in SQUID metamaterials comprising non-hysteretic SQUIDs. The model equations reproduce the experimentally observed tuneability patterns and predict tuneability with the power of an applied ac magnetic field. Moreover, the results indicate the opening of nonlinear frequency bands for energy transmission through SQUID metamaterials, for sufficiently strong ac fields.     

A synthetic optically pumped gradiometer for magnetocardiography measurements

Magnetocardiography(MCG)measurement is important for investigating the cardiac biological activities.Traditionally,the extremely weak MCG signal was detected by using superconducting quantum interference devices(SQUIDs).As a room-temperature magnetic-field sensor,optically pumped magnetometer(OPM)has shown to have comparable sensitivity to that of SQUIDs,which is very suitable for biomagnetic measurements.In this paper,a synthetic gradiometer was constructed by using two OPMs under spin-exchange relaxation-free(SERF)conditions within a moderate magnetically shielded room(MSR).The magnetic noise of the OPM was measured to less than 70 fT/Hz1/2.Under a baseline of 100 mm,noise cancellation of about 30 dB was achieved.MCG was successfully measured with a signal to noise ratio(SNR)of about 37 dB.The synthetic gradiometer technique was very effective to suppress the residual environmental fields,demonstrating the OPM gradiometer technique for highly cost-effective biomagnetic measurements.     

YBaCuO BICRYSTAL JUNCTIONS AND DC SUPERCONDUCTING QUANTUM INTERFERENCE DEVICES

We have prepared yttria-stabilized-zirconia bicrystal substrates using a simple hot-pressing method. The grain-boundary junctions have been fabricated with YBa₂Cu₃O₇ thin films grown epitaxially on the bicrystals. The patterns are defined by conventional photolithography, The dc and microwave characteristics of the junctiorts and the dc superconducting quantum interference devices (SQUIDs) have been intensively studied. The current-voltage curves are bridge-typed with noise rounding near the critical current. Resistive tail has been observed in the resistance versus temperature curves. The results are compared with the theoretical prediction for classical Josephson junctions. It is found that the behavior of bicrystal junctions can be described in the frame of classical theory. The deviations are attributed to the nonuniformity of the junctions. The small loop dc SQUIDs demonstrate diffraction and interference effects with regard to the applied magnetic field. A large square-washer with a new configuration has been designed to enhance the effective area of dc SQUID as a magnetometer. It has achieved a magnetic field resolution down to 1 pT/(Hz)^1/2(at 10Hz) at 77K.     

Weak magnetic order in the normal state of the high-Tc superconductor La2-xSrxCuO4

We report magnetization measurements in the normal state of the high transition temperature (high-Tc) superconductor La2-xSrxCuO4. A magnetic order in the form of hysteresis in the low-field magnetization is observed at temperatures well above Tc. The doping (x) dependence of the onset and strength of this order follows Tc(x) and falls within the pseudogap regime.     

Nuclear magnetic resonance measurement station in SECUF using hybrid superconducting magnets

Nuclear magnetic resonance(NMR) is one of the most powerful tools to explore new quantum states of condensed matter induced by high magnetic fields at a microscopic level. High magnetic field enhances the intensity of the NMR signal, and more importantly, can induce novel phenomena. In this article, examples are given on the field-induced charge density wave(CDW) in high-Tc superconductors and on the studies of quantum spin liquids. We provide a brief introduction to the high magnetic field NMR platform, the station 4 of the Synergetic Extreme Condition User Facility(SECUF), being built at Huairou, Beijing.     

高温超导体组合薄膜和相图表征高通量方法

铜氧化物超导体和铁基高温超导体是已知的两类高温超导体,研究高温超导机理是如今超导领域最具有挑战性的前沿课题.构建高温超导的高维精确相图、寻找决定超导转变温度的关键物理量可以为高温超导机理做好实验铺垫.对于铜氧化物高温超导体,多种自由度的相互关联与耦合使其相图呈现出复杂性与多样性.现有的研究方法在构建高维“全息”相图及获取定量化物理规律等方面面临着难以克服的困难,而材料的高通量制备与表征技术可以在相图空间实现参量的线扫描甚至面扫描,有望快速建立可靠的高温超导高维相图和高温超导关键参量数据库,并从中提取重要的统计物理规律.本文从阳离子掺杂、母体氧掺杂、双电层晶体管(静电场/电化学)、磁场等几个调控维度,回顾了主要基于输运手段获得的铜氧化物电子态相图,介绍了基于脉冲激光沉积技术和分子束外延技术的组合薄膜生长方法以及与之匹配的跨尺度选区输运测量技术,展示了高通量技术在高温超导研究中的初步应用.高通量实验技术与超导研究结合,逐步形成了新兴的高通量超导研究范式,将在构建高维精确相图、突破高温超导机理、推进超导材料实用化等方面发挥不可替代的作用.