Artzi Yaron, Yishay Yakir, Fanciulli Marco, Jbara Moamen, Blank Aharon
Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa 3200003, Israel.
Department of Materials Science, University of Milano - Bicocca, Italy.
J Magn Reson. 2022 Jan;334:107102. doi: 10.1016/j.jmr.2021.107102. Epub 2021 Nov 2.
The field of electron spin resonance (ESR) is in constant need of improving its capabilities. Among other things, this means having better resonators to reach improved spin sensitivity and enable larger microwave-power-to-microwave-magnetic-field conversion factors. Surface micro-resonators, made of small metallic patches on a dielectric substrate, provide very good absolute spin sensitivity and high conversion factors due to their very small mode volume. However, such resonators suffer from relatively low spin concentration sensitivity and a low-quality factor, a fact that offsets some of their significant potential advantages. The use of superconducting patches to replace the metallic layer seems a reasonable and straightforward solution to the quality factor issue, at least for measurements carried out at cryogenic temperatures. Nevertheless, superconducting materials, especially those that can operate at moderate cryogenic temperatures, are not easily incorporated into setups requiring high magnetic fields due to the electric current vortices generated in the latter's surface. This makes the transition from normal conducting materials to superconductors highly nontrivial. Here we present the design, fabrication, and testing results of surface micro-resonators made of yttrium barium copper oxide (YBCO), a superconducting material that operates also at high magnetic fields and makes it possible to pursue ESR at moderate cryogenic temperatures (up to ∼ 80 K). We show that with a unique experimental setup, these resonators can be made to operate well even at high fields of ∼ 1.2 T. Furthermore, we analyze the effect of current vortices on the ESR signal and the spins' coherence times. Finally, we provide a head-to-head comparison of YBCO vs copper resonators of the same dimensions, which clearly shows their pros and cons and directs us to future potential developments and improvements in this field.
电子自旋共振（ESR）领域一直需要不断提升其性能。这尤其意味着要拥有更好的谐振器，以实现更高的自旋灵敏度，并获得更大的微波功率与微波磁场转换因子。由介电基片上的小金属贴片制成的表面微谐振器，由于其非常小的模式体积，具有非常好的绝对自旋灵敏度和高转换因子。然而，这种谐振器的自旋浓度灵敏度相对较低，品质因数也较低，这一事实抵消了它们一些显著的潜在优势。使用超导贴片来替代金属层似乎是解决品质因数问题的一种合理且直接的方案，至少对于在低温下进行的测量而言是如此。然而，超导材料，尤其是那些能够在中等低温下工作的材料，由于在高磁场表面会产生电流涡旋，不容易被纳入需要高磁场的装置中。这使得从常规导电材料向超导体的转变极具挑战性。在此，我们展示了由钇钡铜氧化物（YBCO）制成的表面微谐振器的设计、制造和测试结果，YBCO是一种超导材料，它也能在高磁场下工作，并使得在中等低温（高达约80 K）下进行电子自旋共振成为可能。我们表明，通过独特的实验装置，即使在约1.2 T的高磁场下，这些谐振器也能良好运行。此外，我们分析了电流涡旋对电子自旋共振信号和自旋相干时间的影响。最后，我们对相同尺寸的YBCO谐振器和铜谐振器进行了直接比较，清楚地展示了它们的优缺点，并为该领域未来的潜在发展和改进指明了方向。
