Applications of MGI Techniques in Quantum Materials Research

Kui Jin*

Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China

ABSTRACT: In this talk, I will briefly review the history of high-throughput research and then focus on some recent applications in superconductivity research.

I will first show a high-throughput process from sample preparation to data library on La_2-xCe_xCuO₄ (LCCO) superconductor, to demonstrate the concept of experimental data matching over multiscale space. We succeeded in growing epitaxial LCCO film on 1 cm (00l)-SrTiO₃ substrate by the combinatorial laser MBE technique, with a composition gradient from optimal superconducting phase (x = 0.10) to Fermi liquid state (x = 0.19). Such high quality combinatorial films are suitable for multiscale fast screening, and therefore i) a lattice-doping library is set up assisted by high-throughput in-lab XRD and synchrotron XRD facilities, with the space resolution reduced from millimeter down to micrometer; ii) the electrical transport database, obtained in several weeks on a single chip, contains hundreds of resistivity data sets and helps to verify the relation between the doping level and the superconducting transition temperature (T_c) quantitatively; iii) information on magnetization is also collected by two-coil mutual inductance[4] and scanning SQUID techniques, displaying a textbook behavior of penetration depth. These combinatorial films are being used for pump-probe, XAS, RIXS measurements, to explore the systematical behavior without missing subtle feature.

In the second part, I will introduce a new fabrication method to obtain high-throughput samples, based on lattice structure modulation that is distinct from conventional composition combinatorial methods. The core idea is the construction of a dual-beam pulsed laser deposition (PLD) technique, which has been successfully applied on FeSe and BaTiO₃ systems. The binary compound FeSe, simple in structure, displays complex physics properties. After 10 years of intensive research, the relation between Tc and crystal lattice remains elusive. It is encouraging that the new method can assist in growing FeSe film with a gradient Tc, e.g. from 0 to 12 K, of high single crystallinity. Moreover, we extracted a Tc-lattice library on such FeSe chip and find unambiguous relation within several weeks, which sharply contrasts the failure to obtain such rules by fabricating more than 1000 uniform films in 3 years with the traditional single beam PLD process. Once obtaining a reference library, we can choose the right uniform samples for a comprehensive study, and finally verify that the T_c evolution is caused by local lattice distortions, rather than off-stoichiometric defects or doping effect. This is a key in understanding the nature of FeSe superconductor. Moreover, the material aging effect as a function of time due to the evolvement of lattice dislocations is projected to the real space axis.  

Finally, I will exhibit our homemade combi laser MBE integrated with an in-situ low temperature STM system, a gem of 4-year effort of the team, and introduce the Beijing Materials Genome Initiative Center and its design principles. The high-throughput paradigm will undoubtedly become an indispensable tool in superconductivity research in the near future.

Keywords: Combinatorial films; High-Tc superconductors; MGI center

* Corresponding author: kuijin@iphy.ac.cn