Annotated Bibliography 1
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
In this study, the authors examine how Coulomb impurities affect the conductivity of semiconductors and topological insulators. It is discovered that a large concentration of Coulomb impurities results in the creation of puddles, which then leads to metallic-like behavior in materials. When many puddles form and overlap, electrons are able to move more freely throughout the material by hopping from one puddle to the next. This claim is supported by data collected from various theoretical models and simulations that illustrate the effect of impurities on conductivity. The findings of this study are crucial in understanding electron flow in semiconductors and topological insulators, which are frequently used in electronics. Thus, the authors provide insights that can inform the development of more efficient electronic devices.
This text is useful for my research on topological insulators, as it explains one of the biggest factors that influence conductivity in real-world conditions. Since impurities are inevitable in nature, it is important to understand the effect they have on materials. I plan to use this study to discuss the structure of topological insulators and potential challenges that arise when using topological insulators to design electronics, specifically regarding their conductivity when exposed to impurities. Additionally, this study will help illustrate electron movement in topological insulators.
Quotes and Terms:
“At lower temperatures the conductivity is due to hopping between nearest neighbor puddles (NNH). At even smaller temperatures it is due to variable range hopping (VRH) between puddles.” (Huang et al., 2022, p. 1)
Coulomb impurities: Areas of charged defects, such as charged atoms that differ from regular atom structure, in a material.
Puddles: Areas around impurities that temporarily trap electrons because of the attractive force between electrons and the charge.
Annotated Bibliography 2
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
This text discusses how external influences, such as electric fields, on-site energy differences, and exchange fields, influence the conductivity of topological crystalline insulators, specifically SnTe (001). The authors used theoretical frameworks, such as the continuum model and the Kubo-Greenwood formalism to analyze and model the properties of materials. The results illustrate how conductivity changes in response to these external influences. Electric fields and on-site energy differences tend to increase conductivity by shifting key energy points, while the exchange field, associated with magnetic properties, opens a band gap that decreases conductivity. Furthermore, the study highlights that by applying these external influences, it’s possible for topological crystalline insulators to conduct electricity even at zero temperature, where there’s normally no energy available for electrons to move. This finding is important for applications in quantum technology, where precise control of conductivity at low energy is often needed.
One key strength of this study is that it explores a wide range of variables that affect topological insulators. The paper helps describe how electron movement and energy level shifts occur, as well as how various environmental changes can affect electron flow. In addition, the key finding about conductivity at zero temperature is significant due to its practical applications, and I plan to discuss the importance of this discovery in my paper. I will also use this study to explain the structural properties of topological insulators in greater detail.
Quotes and Terms:
“Non-zero EC at very low-temperatures results directly from the shifted Fermi level in the band structure. This implies that the system transits to the metallic phase.” (Nguyen et al., 2020, p. 5)
“Furthermore, we found that the EC is increased with the electric field and on-site energy difference, while it is decreased with the exchange field.” (Nguyen et al., 2020, p. 6)
Continuum model: A model that simplifies complex atomic structure in order to describe a material’s properties on a larger scale.
Kubo-Greenwood formalism: A model used to calculate conductivity.
Annotated Bibliography 3
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
This paper focuses on investigating various properties of BiSbTeSe₂, a 3D topological insulator with a resistance-free conductive surface and an insulating interior. For this experiment, the authors applied a magnetic field to the topological insulator while measuring its Hall conductivity. When a strong magnetic field was applied, distinct step-like “spikes” of Hall conductivity were observed, a sign of the quantum Hall effect. The presence of the quantum Hall effect means that electrons on the surface of BiSbTeSe₂ can move without losing energy. Another notable finding was that the conductivity of the surface was mostly unaffected by high temperatures, which indicates that BiSbTeSe₂ is resilient to environmental conditions. This study highlights the unique conducting properties of this particular topological insulator that make it a potential choice for use in quantum computing devices.
The strong observation of the quantum Hall effect that was documented in this study makes this source valuable in understanding the unique conductivity of topological insulators. Additionally, this paper effectively explains the connection between the quantum Hall effect and the surface properties of topological insulators. I intend on using data from this source to showcase and explain the quantum Hall effect in relation to my topic.
Quotes and Terms:
“The intrinsic TI studied in this work, exhibiting surface dominated conduction at temperatures as high as room temperature and a surface Dirac fermion QHE at temperatures as high as 35K, demonstrates some of the most salient hallmarks of TSS transport free from contamination or the complications of bulk conduction. This system could provide an excellent clean experimental platform to pursue the plethora of exciting physics and applications proposed for ideal TIs.” (Xu et al., 2014, p. 7)
Hall conductivity: A measure of conductivity in a magnetic field.
Quantum Hall effect: A phenomenon where Hall conductivity has “quantized”, or fixed, values instead of a range of many values.
Annotated Bibliography 4
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
This text explores the properties and transport behavior of a modified 3D topological insulator called Sn-doped Bi1.1Sb0.9STe2 (BSST). The authors aimed to assess how well BSST functions at room temperature, examining how temperature affects the insulating and conducting properties. The experiment involved measuring the electrical behavior of BSST under an applied magnetic field. From this, a high Hall mobility was observed, suggesting that conduction was highly efficient. The authors also discovered that the transport behavior was mainly influenced by the surface and not the interior, even at high temperatures. Therefore, the unique surface-conducting properties of topological insulators are strong in BSST, making it a viable option for research involving 3D topological insulators.
The findings of this study are significant because they showcase the potential for developing new 3D topological insulators, advancing the field of materials science. The focus on room-temperature performance of BSST is particularly important, as it opens the door for practical implementations of the material in technology. I will use this study to speculate on potential future innovations in my research topic and prove the viability of engineered topological insulators.
Quotes and Terms:
“Moreover, the resistivity of the bulk channel increases exponentially with decreasing temperature and does not contribute to the electronic transport below 250K, demonstrating the potential application of BSST-based electronic devices.” (Zhao et al., 2023, p. 2)
“Note that even at 300K, the resistivity from the bulk channel is 5 times greater than from the surface channel, suggesting that BSST is a real room-temperature 3DTI” (Zhao et al., 2023, p. 6)
Hall mobility: A measure of how quickly electrons move in a magnetic field.
