2-7、高通量超导研究新进展

金魁

中国科学院物理研究所

摘要：In this talk, I will demonstrate the high efficiency of high throughput experimental methods in accelerating superconductivity research. A combination of high throughput and traditional experimentations opens a promising avenue to elucidate the key ingredient to the superconducting transition temperature (T_c).

First, a high throughput research on FeSe to establish the lattice-T_c library is initiated. We were able to fabricate film sample with gradient T_c from < 2 K to 12 K on a centimeter substrate by single pulsed laser deposition, using two sliding laser beams to create a gentle distribution of the beam density across a focused laser spot on a FeSe target. The T_c gradient films display ~ 1% continuous stretch and compression in the out-of-plane and in-plane lattice constants respectively, tracking the continuous enhancement of superconductivity. In stark contrast, a collection of data on more than 1000 standard uniform FeSe samples failed to give us a clear relation between the lattice constants and the T_c due to the statistic uncertainty from different substrates and batches. Following the same trend of T_c, the electron carrier density increases by ~ 6 times at low temperature, which gradually approaches and then surpasses the roughly constant hole carrier density, confirmed by both transport measurements and angular-resolved photoemission. Thanks to the combination of high throughput and traditional experimentations, we arrive at the conclusion that more conduction electrons benefit T_c, attributed to a modification of d_xy orbital bands through the lattice modulation.

Secondly, we employed laser MBE technique with programmed-motion mask to deposit the so-called combinatorial films, e.g. La_2-xCe_xCuO₄ with x from 0.10 to 0.19 on a single substrate of 1 cm in length. That is, one sample can cover the regime from the optimally doped superconducting state to the heavily overdoped Fermi liquid state. The key process is that two targets La_2-xCe_xCuO₄ (x=0.1) and La_2-xCe_xCuO₄ (x=0.19) should be alternatively shot by single laser beam, with a mask moving forward and back in front of the heated substrate. After eighty periods, a 100 nm thick combinatorial film is achieved after the in-situ reduction process. Previously, we spent several years in getting a series of doped samples. However, such combinatorial sample provides us a continuous doping just in one batch, greatly saving the fabrication time. Then we characterized the doping level by wavelength dispersive X-ray spectroscopy and the crystal structure by scanning X-ray diffraction as well as synchrotron diffraction with high-spatial resolution (10 μm), which indeed display the right doping trend and an epitaxial growth. Later, the combinatorial sample was patterned into Hall-bar array (>300 channels/1cm) for simultaneous resistivity measurements in our homemade probe station. On the basis of high-efficiency screening techniques, a quantitative relation between the doping level and T_c was able to be identified for the first time in the electron-doped cuprates.

  Finally, I will briefly introduce the Center for Materials Genome Initiative (MGI) at Huairou in Beijing. We are eager to see more high-throughput materials research in the near future.

关键词： high throughput experimentations，superconducting materials，combinatorial thin films, MGI center

DOI:10.12110/secondfmge.20181014.207