Introduction
Topological insulators (TIs) are a unique class of materials that conduct electricity along their surfaces while remaining insulative in their bulk, or interior. This property arises from their distinct electronic structure, which allows for surface conduction without energy loss due to resistance, even in the presence of impurities. These properties have significant implications for energy-efficient electronics and quantum computing, where minimizing energy loss and enhancing stability are crucial. As demand for high-performance and sustainable technologies grows, understanding TIs’ conductive and quantum behaviors has become essential for future technological innovations. This review explores current research on the key conductive properties of TIs, their role in quantum phenomena, and their potential for technological applications. First, it will examine studies on TI conductivity, mainly the effects of environmental and material-specific factors. Next, the review will focus on the role of TIs in exhibiting the quantum Hall effect, a phenomenon that is fundamental to understanding TIs’ potential in quantum devices. Finally, it will highlight recent research on the potential for future innovations in TIs. Together, these studies provide a foundation for understanding how TIs operate and how they may transform future technology.
Factors Influencing Conductivity
The conductive properties of TIs are a central area of study, as these define their technological applications. Huang, Skinner, and Shklovskii (2022) explored how Coulomb impurities, which are areas of charged defects in a material, affect the conductivity of two-dimensional TIs. Their study used theoretical models to analyze how electron puddles created by impurities in the material facilitate metallic-like behavior, thereby increasing surface conductivity. Their findings indicate that Coulomb impurities play a significant role in determining electron flow on the TI surface, suggesting that these impurities, while typically a limitation in semiconductors, may enhance conductivity in TIs. By modeling interactions between impurities and electrons, this research provides insights into how real-world applications can control TI conductivity through management of impurities.
Similarly, Nguyen, Hoi, and Yarmohammadi (2020) examined the electrical conductivity of topological crystalline insulators, specifically focusing on SnTe (001). They applied the KuboGreenwood formalism, a model used to calculate conductivity, and evaluated the material’s response to electric and magnetic fields, as well as the impact of external fields on conductivity. The researchers concluded that external fields could be used to manipulate conductivity, enhancing it under electric fields while reducing it under magnetic fields due to band gap formation. These studies collectively illustrate the adaptability of TIs, showing that their conductive properties can be fine-tuned through environmental and structural factors.
Comparing these studies, both emphasize how environmental conditions can optimize TI performance. Huang et al. focused on the effects of intrinsic impurities within the material, while Nguyen et al. investigated external influences on the material. The strengths of Huang et al.’s study lie in its detailed analysis of impurity-driven conductivity, while Nguyen et al.’s study offers a versatile approach for controlling conductivity via external fields. However, both studies are limited because of their reliance on theoretical models. There is a need for empirical data from physical experiments to further validate these predictions. Understanding these various conductivity influences would be useful in designing TIs for specific electronic purposes.
Quantum Hall Effect
The quantum Hall effect (QHE) is a phenomenon where Hall conductivity has “quantized”, or fixed, values instead of a range of many values. This effect typically occurs in low-temperature environments. Xu et al. (2014) studied the QHE in three-dimensional topological insulators by examining the quantum surface states that arise in these materials. Using experimental setups involving high magnetic fields, they observed that TIs strongly demonstrate the QHE. This observation is crucial, as it provides direct evidence of TIs’ ability to maintain quantum states at the surface while also insulating their bulk.
Xu et al.’s study highlights the broader implications of TIs for quantum computing and high-performance electronics. TIs are able to support the QHE without losing much energy, which could potentially help stabilize quantum information. However, although the study’s results are promising, they are not completely realistic. The implications of these findings are limited by practical challenges, as high magnetic fields and low temperatures aren’t easy to maintain outside of controlled environments. Additionally, the findings highlight the need to shield topological insulators from environmental noise to keep them stable, suggesting that future research could focus on making these materials more resilient to outside disturbances.
The comparison of Xu et al. with studies focused on conductivity reveals the multidimensional potential of TIs. While the QHE highlights their quantum capabilities, conductivity studies showcase their practicality for conventional electronics. Together, these findings suggest that TIs could bridge traditional electronics and quantum computing.
Potential for Future Innovations
Advancing the applicability of TIs under real-world conditions remains a central research goal. Zhao et al. (2024) investigated modified three-dimensional TIs with high-temperature insulating behavior, specifically Sn-doped Bi1.1Sb0.9STe2 (BSST), and assessed its performance under room temperature. The setup of the experiment was similar to that of Xu et al.’s study. Magnetic fields were applied to BSST, and conductivity data was recorded. The study found that the material retains its surface-conducting properties even in high-temperature conditions, which shows promise for real-world applications without the extreme cooling that TIs traditionally require. The study’s strength is in demonstrating the TI’s resilience to temperature fluctuations, marking a significant step toward widespread adoption in electronics.
However, the study is also limited, as it does not address other environmental factors, such as pressure or impurity interference, which could impact performance in varied settings. Factors like pressure changes may alter the electronic structure of the material, potentially affecting its conductive properties. Similarly, the presence of impurities in non-laboratory settings could disrupt the unique surface conductivity of BSST, reducing its effectiveness as a topological insulator. More research has to be done on BSST to fully determine its usefulness as a TI.
Conclusion
This review examined recent progress in understanding the conductive properties, quantum effects, and high-temperature capabilities of topological insulators, showcasing both their potential and ongoing challenges. Studies on TI conductivity suggest they could lead to flexible, impurity-resistant devices, while research into the quantum Hall effect highlights their promise for quantum technology. High-temperature studies on TIs indicate that these materials might soon move from theory to real-world use.
While recent findings offer important insights, there are still many limitations, particularly in testing theoretical models and managing challenges like temperature sensitivity and external interference. Future research should focus on experiments to confirm predictions, explore stability with impurities and environmental factors, and extend TIs’ effective temperature range. Addressing these gaps will help move TIs toward practical applications that need both quantum stability and energy efficiency, setting the stage for next-generation materials.
References
Huang, Y., Skinner, B., & Shklovskii, B. I. (2022). Conductivity of Two-Dimensional Small Gap Semiconductors and Topological Insulators in Strong Coulomb Disorder. Journal of Experimental and Theoretical Physics, 135(4), 409–425. https://doi.org/10.1134/s1063776122100065
Nguyen, V. C., Hoi, B. D., & Yarmohammadi, M. (2020). Electrical conductivity of statically perturbed topological crystalline insulators. Journal of Physics D: Applied Physics, 53(42), 425301. https://doi.org/10.1088/1361-6463/ab9d9c
Xu, Y., Miotkowski, I., Liu, C., Tian, J., Nam, H., Alidoust, N., Hu, J., Shih, C.-K., Hasan, M. Z., & Chen, Y. P. (2014). Observation of topological surface state quantum Hall effect in an intrinsic three-dimensional topological insulator. Nature Physics, 10(12), 956–963. https://doi.org/10.1038/nphys3140
Zhao, W., Xing, K., Chen, L., Vu, T., Akhgar, G., He, Y., Bake, A., Wang, X., & Karel, J. (2024). Quantum interference effects in a 3D topological insulator with high-temperature bulk-insulating behavior. Applied Physics Review, 11(1), 011419. https://doi-org.ccny-proxy1.libr.ccny.cuny.edu/10.1063/5.0168129
Yue, C., Jiang, S., Zhu, H., Chen, L., Sun, Q., & Zhang, D. (2018). Device Applications of Synthetic Topological Insulator Nanostructures. Electronics, 7(10), 225. https://doi.org/10.3390/electronics7100225
Tian, W., Yu, W., Shi, J., & Wang, Y. (2017). The Property, Preparation and Application of Topological Insulators: A Review. Materials, 10(7), 814. https://doi.org/10.3390/ma10070814
