New light studies of Bi2212 superconductors reveal important information about high-temperature superconductivity, advancing research into room temperature applications. copper oxide (CuO₂) superconductorsIncluding₂Sir₂CaCu₂HE_8+delta (Bi2212) is characterized by extremely high critical temperatures. Previous studies using optical reflectance measurements have shown that Bi2212 exhibits strong optical anisotropy, meaning that its optical properties vary depending on the direction of incident light. However, its optical anisotropy has not been fully investigated using optical transmission measurements, which provide a more direct insight into the material’s internal structure.

Recently, using UV and visible light transmission techniques on lead-doped Bi2212 single crystals, researchers uncovered the source of this anisotropy, paving the way for a deeper understanding of superconductivity mechanisms.

High temperature superconductors

Superconductors are materials that can conduct electricity with zero resistance when cooled below a certain critical temperature. This unique feature makes them indispensable for advanced technologies such as electric motors, power generators, high-speed maglev trains and magnetic resonance imaging (MRI).

Among superconductors, copper oxide-based materials such as Bi2212 are particularly noteworthy because they operate at relatively high temperatures and exceed the theoretical limit of superconductivity set by the Bardeen-Cooper-Schrieffer (BCS) theory. Despite decades of research, the mechanism underlying superconductivity in these high-temperature materials remains one of the most intriguing mysteries in physics.

Investigation of optical anisotropy in superconductors

The key piece of the puzzle is the two-dimensional crystal plane of CuO.₂ These materials have been widely investigated using various experiments. Optical reflectance measurements, which analyze how light of different wavelengths reflect from the crystal plane from different directions, show that Bi2212 exhibits significant optical anisotropy in both crystal planes.eu” And “hungry”.

Optical anisotropy describes the change in optical properties of a material depending on the direction in which light passes through it. Now, while reflectance measurements provide valuable information, studying how light travels through the crystal at different wavelengths using optical “transmission” measurements of Bi2212’s optical anisotropy can offer a more direct insight into bulk properties. However, such studies have rarely been done before.

Innovative approaches to superconductivity research

To address this gap, Professor Dr. Toru Asahi, researcher Dr. A Japanese research team led by Kenta Nakagawa and Keigo Tokita, a graduate student from the Comprehensive Research Organization of Waseda University’s Faculty of Science and Engineering, investigated the origin of lead’s strong optical anisotropy. doped Bi2212 single crystals using ultraviolet transmission measurements and visible light.

Elaborating on the subject further, Prof. Dr. “Achieving room-temperature superconductivity has long been a dream, requiring an understanding of the mechanisms of superconductivity in high-temperature superconductors,” says Asahi. “Our unique approach to using UV-visible transmission measurements as a probe allows us to elucidate these mechanisms in Bi2212, bringing us one step closer to this goal.”

Professor Dr. from Tohoku University Materials Research Institute. The study, which included Masaki Fujita, was recently published in the magazine. Scientific Reports.

Advances in understanding optical anisotropy

In their previous work, the researchers examined the wavelength dependence of the optical anisotropy of Bi2212 along the crystal “c” axis at room temperature using a generalized high-precision universal polarimeter. This powerful tool allows simultaneous measurement of the transmission of optical anisotropy markers (linear birefringence (LB) and linear dichroism (LD)) along with optical activity (OA) and circular dichroism (CD) in the UV-visible region. Their preliminary findings showed significant peaks in the LB and LD spectra, which they hypothesized to be due to disproportionate modulation of the crystal structure of Bi2212; characterized by periodic variations that are not proportional to the regular structure of the atomic arrangement.

To understand whether this is truly the case, in this study the team investigated the optical anisotropy of lead-doped Bi2212 crystals. “Previous studies have shown that partial replacement of Bi with Pb in Bi2212 crystals suppresses disproportionate modulation,” explains Mr. Tokita. To this end, the team produced monocylindrical Bi2212 crystals with variable lead content using the sliding zone method. Ultrathin sheet samples that transmit ultraviolet and visible light were obtained from these crystals by exfoliation with water-soluble tape.

Experiments have shown that the large peaks in the LB and LD spectra decrease significantly with increasing lead content, corresponding to the suppression of disproportionate modulation. This reduction is crucial because it allows more accurate measurements of OA and CD in future experiments.

Commenting on these findings, Prof. Dr. “This discovery allows us to investigate the presence or absence of symmetry breaking in pseudo-vacancy and superconducting phases, which is a critical issue for understanding the mechanism of high-temperature superconductivity,” says Asahi. “This contributes to the development of new high-temperature superconductors.” The research marks an important step in the search for room-temperature superconductivity, a breakthrough that could revolutionize a variety of technologies, from energy transfer to medical imaging and transportation.