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1. Quantum transport regimes in quartic dispersion materials with Anderson disorder

Author

Polat, Mustafa, Özkan, Hazan, and Sevinçli, Hâldun

Subjects
Condensed Matter - Disordered Systems and Neural Networks, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

Mexican-hat-shaped quartic dispersion manifests itself in certain families of single-layer twodimensional hexagonal crystals such as compounds of groups III-VI and groups IV-V as well as elemental crystals of group V. Quartic band forms the valence band edge in various of these structures, and some of the experimentally confirmed structures are GaS, GaSe, InSe, SnSb and blue phosphorene. Here, we numerically investigate strictly-one-dimensional (1D) and quasi-one dimensional (Q1D) nanoribbons with quartic dispersion and systematically study the effects of Anderson disorder on their transport properties with the help of a minimal tight-binding model and Landauer formalism. We compare the analytical expression for the scaling function with simulation data to deduce about the domains of diffusion and localization regimes. In 1D, it is shown that conductance drops dramatically at the quartic band edge compared to a quadratic band. As for the Q1D nanoribbons, a set of singularities emerge close to the band edge, which suppress conductance and lead to short mean-free-paths and localization lengths. Interestingly, wider nanoribbons can have shorter mean-free-paths because of denser singularities. However, the localization lengths do not necessarily follow the same trend. The results display the peculiar effects of quartic dispersion on transport in disordered systems.

Published
2023

2. Quantum transport regimes in quartic dispersion materials with Anderson disorder.

Author

Polat, Mustafa, Özkan, Hazan, and Sevinçli, Hâldun

Subjects
*DISPERSION (Chemistry), *NANORIBBONS, *VALENCE bands, *PHOSPHORENE
Abstract

Mexican-hat-shaped quartic dispersion manifests itself in certain families of single-layer two-dimensional hexagonal crystals such as compounds of groups III–VI and groups IV–V as well as elemental crystals of group V. A quartic band forms the valence band edge in various of these structures, and some of the experimentally confirmed structures are GaS, GaSe, InSe, SnSb, and blue phosphorene. Here, we numerically investigate strictly one-dimensional and quasi-one dimensional (Q1D) systems with quartic dispersion and systematically study the effects of Anderson disorder on their transport properties with the help of a minimal tight-binding model and Landauer formalism. We compare the analytical expression for the scaling function with simulation data to distinguish the domains of diffusion and localization regimes. In one dimension, it is shown that conductance drops dramatically at the quartic band edge compared to the quadratic case. As for the Q1D nanoribbons, a set of singularities emerge close to the band edge, suppressing conductance and leading to short mean-free-paths and localization lengths. Interestingly, wider nanoribbons can have shorter mean-free-paths because of denser singularities. However, the localization lengths sometimes follow different trends. Our results display the peculiar effects of quartic dispersion on transport in disordered systems. [ABSTRACT FROM AUTHOR]

Published
2024
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3. Gürültü Etkisinde Uyarımların Taşınımının Kuantum Dinamiği

Author

Özkan, Hazan, Çakır, Özgür, Izmir Institute of Technology. Physics, and Fizik Ana Bilim Dalı

Subjects
Zeno effect, Fizik ve Fizik Mühendisliği, Quantum decoherençe, Anderson localization, Physics and Physics Engineering, Open quantum systems
Abstract

Thesis (Master)--Izmir Institute of Technology, Physics, Izmir, 2018, Includes bibliographical references (leaves: 38-39), Text in English; Abstract: Turkish and English, In this thesis, different types of systems are studied to investigate the effects of the environmental factors on diffusion and transfer time. Each system consists of different energy levels and excitation transfers between them. The mismatch between the energy levels leads to the Anderson localization. Localization has a negative effect on transport. It is shown that Anderson localization is suppressed due to interaction with the environment. To describe the dynamical evolution of the open quantum system Lindblad master equation is used. The transition times of the system from the pure state to the completely mixed state are examined with the help of the density matrix. In consequence of our study, because of the interaction between the system and environment the change in the wavefunction, the loss in the interference terms and an irreversible information flow in the total system are observed. Destructive effects of the environmental noise on localization are observed for different scenarios and diffusion enhanced. However, when the interaction with the environment becomes larger than a critical value, the system exhibits Zeno effect. In the Zeno regime, the time evolution of the quantum state of the system as well as the diffusion is suppressed., Bu tezde, açık kuantum sistemlerinde çevresel etkilerin sistemin difüzyon ve taşınım süreleri üzerindeki etkileri çalışılmıştır. Her bir sistem farklı enerji seviyelerinden oluşur ve egziton bu seviyeler arasında transfer olur. Enerji seviyeleri arasındaki bu fark Anderson lokalizasyonuna neden olur. Lokalizasyonun transfer üzerinde negatif bir etkisi vardır. Çevre ile etkileşimler sayesinde Anderson lokalizasyonun azaldığı gösterilmiştir. Açık kuantum sisteminin zaman içerisindeki değişimini matematiksel olarak ifade edebilmek için Lindblad master denklemi kullanılmıştır. Yoğunluk matrisinin yardımıyla sistemin saf durumdan karmaşık duruma geçiş süreleri incelenmiştir. Çalışmalarımız sonucunda, çevre ve sistem arasındaki etkileşim nedeniyle dalga denklemininde değişim, girişim terimlerinde kayıp ve sistemde tek yönlü bilgi kaybı gözlemlendi. Çevresel gürültünün bazı bölgelerde lokalizasyon üzerindeki yok edici etkisi farklı durumlar için gözlemlendi ve taşınım hızlandı. Ancak çevre ile etkileşim kritik değerden büyük olduğunda, sistem Zeno alanının özelliklerini gösterdi. Zeno alanında sistemin kuantum durumlarının zaman içerisindeki değişimi ve difüzyon baskılandı.

Published
2018

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