Studying the complexity of the electronic phase diagram is at the heart of understanding strongly correlated system in general, with high Tc superconductors as the most known examples. High temperature superconductivity has a wide range of application potentials in power transmission, nuclear magnetic resonance, magnetic levitation transportation, aerospace, information and communication technologies, etc. Understanding its mechanism remains a long-standing challenge, due to its complex material structures and interlays among different phases such as charge density wave, antiferromagnetic and superconducting phases. As a result, this has greatly hindered its further development.
Deviated from the traditional trial-and-error approach, combinatorial material synthesis and characterization techniques (now known as Material Genome Engineering techniques) have been used in the past to greatly shorten the material R&D cycle of the high-temperature superconductors and related materials [
1–
8]. Owing to strong correlation among multiple degrees of freedom in copper-based superconductors, a slight change of carrier concentration in a very narrow chemical doping range would trigger abrupt changes in the electronic phases, resulting in the famous “superconducting domes” and “complex quantum criticality” in its electronic phase diagram [
9–
12]. The compositional control accuracy in previous experiments was fairly coarse, roughly 1% to 0.1%. A higher compositional regulation accuracy around quantum critical point of copper-based superconductors is highly desired for reliable detailed study.
Recently, an international research team studied the quantitative correlation between the superconducting transition temperature and temperature dependence of resistivity precisely in “strange metal” regime [
13]. Their successful implementation is based on the breakthrough of both synthesis and characterization techniques: in synthesis, they, for the first time, used the laser molecular beam epitaxy to create a single crystal film of La
2−xCe
xCuO
4 continuous binary phase diagram with a linear distribution [
14]; in characterization, they used photolithographic technique to create a set of cross-scale 4-probe electrodes with a spatial resolution of micron level for transport measurement [
13], together achieved a compositional accuracy on the order of ∼10
−4.
As a result, a universal scaling behaves between “strange metal” and superconducting order parameters near quantum critical region is clearly unveilied [
13]. This founding is especially important since it has been proposed that “strange metal” state is necessary for high-
Tc superconductivity [
15], while the superconducting pseudogap is ruled by several competing ordering with strong collective fluctuations [
16], such as “smectic phase” [
17,
18] near quantum critical region.
Inspired by this work, novel topological materials could also be studied with similar approach, since the evolution of different topological phases is also very sensitive to the shift of Fermi surface with charge carrier density change.
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