In the present era of modern electronics and fast processing equipment, semiconductor devices are a core technology. Semiconductor materials are characterized by their crystalline structure and the presence of free electrons.1
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Semiconductors are used in diodes, modern electric vehicles, photovoltaic technology, military and defense applications, LED lights, communications systems, medical imaging and diagnostics systems, and many other devices.
Challenges and Innovations in Semiconductor Technology
In 2021, the United States semiconductor industry boasted sales of approximately 258 billion U.S. Dollars.2 However, semiconductor production faces challenges, including the current shortage affecting various industries due to supply chain disruptions. Sustainability is also a growing concern, as semiconductor manufacturing is resource-intensive, prompting a push towards adopting eco-friendly materials and practices.
Despite challenges, the industry is exploring new approaches, materials, and technologies, such as quantum computing, to improve device performance and efficiency.3 Modern semiconductor devices, particularly those based on topological quantum materials and technology, are showcasing much higher efficiency and gaining considerable attention.
Topological Quantum Materials: A Key to Future Innovations
Topological quantum materials (TQMs) are characterized as having symmetrically protected, highly mobile electronic states, which makes them the preferred choice for a variety of unique applications. Topological insulators, a unique class of topological materials, cannot be categorized as pure insulators/semiconductors or metals. These materials feature a band gap separating valence and conduction bands on the sub-atomic scale, while metallic states, known as topological surface states, connect these bands on the material's surface.4
Another subset of TQMs, topological superconductors (TSCs), are capable of hosting Majorana bound states (MBSs), also known as Majorana zero modes (MZMs). These MBSs have potential applications as qubits in topological quantum computation. Majorana fermions, unique in being their own antiparticles, can arise in TSCs but not in conventional metals. In typical metals and insulators, quasiparticles (like electrons or holes) carry an electrical charge, and their antiparticles bear the opposite charge, making the emergence of Majorana fermions improbable in these materials.5
Non-Hermitian Physics and Skin Effects: A GroundBreaking Concept for Modern Quantum Computing
Hermiticity plays a crucial role in conserving energy and influencing the physical reality in various systems. However, in non-conservative systems, interactions with the environment introduce non-Hermitian dynamics.
Over the past decade, there has been a notable increase in research focused on non-Hermitian physics, uncovering unique principles, phenomena, and applications. This exploration extends to open quantum systems, semiconductor electronic systems with interactions, classical systems featuring gain or loss, and various other contexts. 6
Experts have discovered that controlled damping or amplification of electromagnetic (EM) waves can induce non-Hermiticity in photonics applications.7 A notable non-Hermitian phenomenon is the non-Hermitian skin effect (NHSE), which has recently gained significance. The NHSE entails a deviation from conventional bulk-boundary correspondence principles. In a finite lattice with open boundary conditions (OBC), numerous localized "skin modes" can exist, distinct from the extended Bloch modes observed under periodic boundary conditions (PBC).8
In one-dimensional lattices, the NHSE is associated with a non-Hermitian topological band invariant, represented by a nonzero point gap winding in the complex energy spectrum. Despite their non-trivial nature, non-Hermitian systems can exhibit topological characteristics, resulting in robust properties with potential applications in precise sensors, amplifiers, and light funnels.9
A Novel Non-Hermitian Quantum Semiconductor: Revolutionizing Semiconductor-Quantum Intersections
To date, no quantum condensed-matter devices demonstrating non-Hermitian topology have been reported. Experimental observations in this domain have been achieved using ultracold atoms, optical systems, and metamaterials governed by classical physics.10
Physicists from the Würzburg-Dresden Cluster of Excellence—Complexity and Topology in Quantum Matter (CT. QMAT) have published an article in Nature Physics, utilizing the non-reciprocity of quantum Hall edge states, instead of gain and loss, to directly observe non-Hermitian topology in a multi-terminal quantum Hall ring.11
The team designed a multi-terminal quantum Hall device comprising a two-dimensional electron gas ring etched in an AlGaAs/GaAs semiconducting heterostructure. The topological quantum device consisted of arms distributed over the external perimeter, with each arm connected directly to the inner ring via an 'inner' ohmic connection.
The semiconductor design of the quantum Hall ring enables the testing of two different configurations, representing different realizations of the Hatano–Nelson (HN) mode—one of the simplest examples of non-Hermitian topology. The device also allows continuous tuning of the effective HN chain from OBC to PBC.
Similar to the quantized Hall conductance of the quantum Hall effect, the topological, non-Hermitian skin effect serves as a directly observable transport property of the semiconductor device. This property does not require the determination of the G matrix or its numerical diagonalization. The researchers utilized the fact that the skin effect implies the exponential localization of all eigenvectors of the conductance matrix at one boundary of the system.
The robust transport signature of the quantum device is characterized by exponential current and voltage profiles. This signature remains consistent across a broad range of magnetic fields, is independent of the initially chosen currents, and is exclusively present in the OBC configuration. The robustness of this transport signature, originating from the non-Hermitian topology, underscores the device's stability and reliability.
Importance of Topological Quantum Technology for Semiconductors
The topological skin effect ensures that all currents between different contacts on the quantum semiconductor remain unaffected by impurities or external perturbations. This characteristic enhances the appeal of topological devices in the semiconductor industry by eliminating the requirement for extremely high material purity, consequently reducing the costs associated with electronics manufacturing.12
The novel topological quantum device, with a diameter of approximately 0.1 millimeters, demonstrates scalability potential. By strategically arranging materials and contacts on an AlGaAs semiconductor device and subjecting it to ultra-cold conditions and a strong magnetic field, the topological effect is induced. Further exploration of this phenomenon is crucial to harness its potential for future technological innovations, particularly in the development of highly efficient semiconductor devices.
More from AZoQuantum: Emerging Trends in Quantum Semiconductor Devices
References and Further Reading
1. Rahman, M. A. (2014). A review on semiconductors including applications and temperature effects in semiconductors. American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS). Available at: https://core.ac.uk/download/pdf/235049651.pdf
2. H. DeLeon. (2023). What is Semiconductor Technology and Why Is It Important? [Online] USF Corporate Training and Professional Education Blog. Available at: https://corporatetraining.usf.edu/blog/what-is-semiconductor-technology-and-why-is-it-important [Accessed 4 March 2024].
3. C. N. Ferreira Jr. (2023). Semiconductors In The Digital Age: Evolution, Challenges, And Geopolitical Implications. Multidisciplinary Scientific Journal Knowledge Core. doi.org/10.32749/nucleodoconhecimento.com.br/technology-en/semiconductors.
4. Kumar, N., et al. (2020). Topological quantum materials from the viewpoint of chemistry. Chemical Reviews. doi.org/10.1021/acs.chemrev.0c00732.
5. Mandal, M., et al. (2023). Topological superconductors from a materials perspective. Chemistry of Materials. doi.org/10.1021/acs.chemmater.3c00713
6. Zhang, X., et al. (2021). Observation of higher-order non-Hermitian skin effect. Nature communications. doi.org/10.1038/s41467-021-25716-y
7. Feng, L., et al. (2017). Non-Hermitian photonics based on parity–time symmetry. Nature Photonics. doi.org/10.1038/s41566-017-0031-1
8. Wang, Q., et al. (2022). Amplification of quantum signals by the non-Hermitian skin effect. Physical Review B. doi.org/10.1103/PhysRevB.106.024301
9. Bergholtz, EJ., et al. (2021). Exceptional topology of non-Hermitian systems. Reviews of Modern Physics. doi.org/10.1103/RevModPhys.93.015005
10. Wang, H., et al. (2021). Topological physics of non-Hermitian optics and photonics: a review. Journal of Optics. doi.org/10.1088/2040-8986/ac2e15
11. Ochkan, K., et al. (2024). Non-Hermitian topology in a multi-terminal quantum Hall device. Nature Physics. doi.org/10.1038/s41567-023-02337-4
12. TU DRESDEN. (2024). Extremely robust & ultra-sensitive: topological quantum device produced. [Online]. EurekAlert. Available at: https://scitechdaily.com/scientists-create-worlds-first-quantum-semiconductor/. [Accessed 07 March 2024]
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