A novel method for determining the resistivity of compressed superconducting materials Free

The superconductivity of materials always emerges from their normal state, and is closely related to the resistivity of that normal state.^1,2 However, measuring the resistivity of a material under high pressure has long presented a significant technical challenge, owing to the difficulty of measuring the pressure-induced changes in the crystallographic directions, especially for samples with anisotropic layered structures, such as high-T_c superconductors and other intriguing quantum materials. Here, we propose a novel and effective method for determining high-pressure resistivity. The validity of the method has been confirmed through our investigations of pressurized copper-oxide superconductors.³ This successful application of the proposed method provides encouraging evidence that it can provide an effective approach for quantitatively investigating the connections between normal-state and ground-state properties in various other quantum materials under high pressure, which has been becoming an increasingly fruitful research direction in condensed matter physics and materials science.

Apart from chemical doping, pressure is the most important way to tune the transport properties of materials. Applying pressure to superconductors or other quantum materials not only reveals numerous novel physical phenomena,^4–17 thereby providing vital insights for the exploration of new superconductors,^18,19 but also can effectively assist in uncovering the underlying physics.^20,21

It is evident that there are two sources of error in high-pressure resistivity measurements. One is associated with the lattice parameters a_i, b_i, and c_i, leading to errors typically around 5%.¹⁷ The other is associated the numbers of the unit cell of the measured sample in the three crystallographic directions (n, m, and l). The error attributed to these is about 5%–10%. Hence, in the most extreme scenario, the errors are around 10%.

It is important to note that when employing the proposed method, the sample must meet the following criteria:

1. The measured sample should be a bulk single crystal, and its ambient-pressure dimensions S and L, lattice parameters a₀, b₀, and c₀, and resistivity, as well as its high-pressure lattice parameters a_i, b_i, and c_i, and the resistance R_i, should be known.

2. Samples with cubic, tetragonal, and orthorhombic structures are suitable for obtaining more accurate ρ_i(P_i).

3. No pressure-induced structural phase transition should occur within the pressure range investigated.

4. When studying the low-temperature properties of materials, the use of low-temperature XRD to measure the lattice parameters at both ambient pressure and high pressure should yield more precise results than room-temperature XRD. This is because the values of a₀, b₀, and c₀, as well as those of a_i, b_i, and c_i, collected at low temperature may differ to some extent from those measured at room temperature.

The proposed method provides a viable way to overcome the technical challenges associated with determining the resistivities of compressed materials. It not only introduces researchers to a new means of obtaining the resistivities of pressurized samples, but also contributes to understand the underlying superconducting mechanism by generating a substantial amount of high-pressure data regarding the correlation of the superconducting transition temperature with superfluid density and resistivity. We have demonstrated the effectiveness of this approach by examining the pressure-induced coevolution of superconductivity with resistivity and superfluid density in bismuth-based cuprate superconductors.³ It is anticipated that this method can also be utilized in high-pressure studies on other quantum materials, thereby providing a basis for further advances in condensed matter physics and materials science.

This work was supported by the National Key Research and Development Program of China (Grant Nos. 2022YFA1403900 and 2021YFA1401800) and the NSF of China (Grant Nos. U2032214 and 12104487).

Liling Sun: Formal analysis (equal); Investigation (equal); Methodology (equal); Validation (equal); Writing – original draft (equal); Writing – review & editing (equal). Qi Wu: Formal analysis (equal); Investigation (equal); Methodology (equal); Validation (equal); Writing – original draft (equal); Writing – review & editing (equal). Shu Cai: Validation (equal); Writing – review & editing (equal). Yang Ding: Validation (equal); Writing – review & editing (equal). Ho-kwang Mao: Validation (equal); Writing – review & editing (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.