The Institute of Physics studies the universal physical laws of exotic metals and high-temperature superconductivity

Recently, the Institute of Physics, Chinese Academy of Sciences/Beijing National Research Center for Condensed Matter Physics has obtained a combination of exotic metal scattering (linear resistance slope A ₁ ) and high temperature superconductivity using materials genetic engineering "Continuous component epitaxial thin film and matching cross-scale characterization techniques" Universal physical law (A ₁ ^0.
5 ~ T _c ) between transition temperatures (T _c ) .
This law reveals the common driving mechanism of the two century-old problems of unconventional superconductivity and exotic metal states, and takes a key step in the "quantitative change leading to qualitative change" of high-temperature superconductivity .
The related results were published in the journal Nature on February 17th [Nature 602, 431, 2022] .

_{1 c 1} 0.

5
_c

Superconductivity has been researched for 110 years since its birth.

Early research on superconductivity focused on traditional metals and alloys, whose superconducting transition temperatures are usually low (less than 30 K)

The superconducting family of copper oxides discovered in 1986 has a superconducting transition temperature that breaks through the McMillan limit, reaching a maximum of 135K under normal pressure
.

Existing experimental results have confirmed that electron pairing also exists in high-temperature superconductors, but different from the electron-phonon pairing mechanism, high-temperature superconductors are widely believed to originate from the correlation interaction between electrons, and are called unconventional superconductors

With the deepening of research, more and more evidence shows that the mystery of high-temperature superconductivity may exist in the normal state that produces superconductivity
.

For cuprate superconductors, when the temperature rises above the superconducting transition temperature, the resistivity ρ exhibits a linear dependence (ie, Δρ = A ₁ T ) "strange metal" behavior with temperature T, which is similar to the square of the Fermi liquid of conventional metals.
The relationship (Δρ=A ₂ T ² ) contradicts and becomes the most “abnormal” characteristic in the normal state of high temperature superconductors

_{1 2} ²

Jin Kui, a researcher at the Institute of Physics, Chinese Academy of Sciences, led the team to give full play to the technical characteristics of superconducting single crystal thin films and superconducting composite thin films, and have long-term in-depth research on a key high-temperature superconducting system La _{2-x C x} CuO ₄ ( LCCO , the only one covering full superconducting doping electronic high-temperature superconducting system in the region, but can only exist stably in the form of a single crystal film)
.

In 2011, based on a series of high-quality single-component LCCO superconducting single-crystal thin films obtained by several years of hard work, Jin Kui and his collaborators obtained the complete phase diagram of the electron-doped copper oxide over-doped region for the first time, and found that the system is different from The second quantum critical point of antiferromagnetic spin fluctuations

_{2-x x 4}

By studying the normal state transport properties of LCCO films as low as 20 mK, they found that the strange metal scattering rate A ₁ is positively correlated with the superconducting transition temperature T _c
, suggesting that there is some intrinsic connection between the strange metal state and high-temperature superconductivity .

However, limited by the precision of composition control, it is difficult to obtain a sufficient amount of high-precision data using the traditional single-point research mode, which makes it a very challenging task to obtain the quantitative law between the two

_{1 c}

The team has creatively introduced the concept and core technology of material genetic engineering into superconductivity research for many years, and continuously developed high-throughput preparation and cross-scale rapid characterization technology according to the characteristics of high-temperature superconducting materials, and promoted the deep cross between the material genetic project and superconductivity research.
The fusion has created a unique high-throughput superconductivity research paradigm
.

_{In 2017, the team successfully fabricated single-oriented La 2-x C x} CuO with a continuous chemical composition gradient ( 0.
10≤x≤0.
19 ) along one direction on a 1 cm2 single crystal substrate using combined laser molecular beam epitaxy for the first time.
₄ High-flux thin films whose end components correspond to optimal superconducting doping (x = 0.
10) and Fermi liquid metal (x = 0.
19), respectively
.

_{2-x x 4}

On this basis, combined with the cross-scale structure and transport characterization techniques developed by the team from millimeters to micrometers, the physical property resolution was improved by two orders of magnitude (to 1/10,000), thereby accurately determining the quantum critical component x _c
.

Micron-scale X-ray structural analysis was completed at the Synchrotron Radiation Light Source of Lawrence Berkeley National Laboratory in the United States through international cooperation

_c

The traditional experimental method only has individual data points in three years, but based on the new generation of full-process high-throughput experiments, the team successfully accumulated a sufficient amount of reliable data in a few months, and observed the superconducting transition temperature T _c , relative doping group for the first time.
The quantification rule T _c ~ (xx _c ) ^0.
5 ~ A ₁ ^0.
5 between the three points (xx _c ) and the strange metal scattering rate A ₁ .
More importantly, the T _c ~ A ₁ ^0.
5 law obtained from LCCO can be extended to unconventional superconducting systems such as hole-type cuprates, iron-based superconductors, organic superconductors, etc.
Unconventional superconducting states share common drivers .

_{c c 1 c c} 0.

5
₁ ^0.
5
_{c 1} 0.

The work was proposed by Zhao Zhongxian, an academician of the Chinese Academy of Sciences, and was conceived by Jin Kui and led the team to tackle key problems.
Specially-appointed researcher Jiang Kun, researcher Yang Yifeng, Hu Jiangping, and Xiangtao provided theoretical support.
Distinguished researcher Cheng Zhigang assisted in low-temperature testing and the Lawrence Berkeley National Experiment in the United States.
Laboratory researcher Tamura and University of Maryland professor Takeuchi helped with synchrotron radiation structure characterization
.

Yuan Jie, chief engineer of the Jinkui team, and Chen Qihong, a specially-appointed researcher, are the co-first authors
.
Hu Jiangping, Takeuchi and Jin Kui are the co-corresponding authors
.

The above work is supported by the National Key Research and Development Program, the National Natural Science Foundation of China, the Beijing Natural Science Foundation, the Guangdong Provincial Key Field R&D Program, the Chinese Academy of Sciences' Strategic Pilot Science and Technology Project (Type B), cutting-edge key projects and innovative cross-team support
.