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Register a new userTopological Insulating States in Laterally Patterned Ordinary Semiconductors
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We propose that ordinary semiconductors with large spin-orbit coupling (SOC), such as GaAs, can host stable, robust, and {it tunable} topological states in the presence of quantum confinement and superimposed potentials with hexagonal symmetry. We show that the electronic gaps which support chiral spin edge states can be as large as the electronic bandwidth in the heterostructure miniband. The existing lithographic technology can produce a topological insulator (TI) operating at temperature $10- 100K$. Improvement of lithographic techniques will open way to tunable room temperature TI.
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Identifying the two-dimensional (2D) topological insulating (TI) state in new materials and its control are crucial aspects towards the development of voltage-controlled spintronic devices with low power dissipation. Members of the 2D transition metal dichalcogenides (TMDCs) have been recently predicted and experimentally reported as a new class of 2D TI materials, but in most cases edge conduction seems fragile and limited to the monolayer phase fabricated on specified substrates. Here, we realize the controlled patterning of the 1T-phase embedded into the 2H-phase of thin semiconducting molybdenum-disulfide (MoS2) by laser beam irradiation. Integer fractions of the quantum of resistance, the dependence on laser-irradiation conditions, magnetic field, and temperature, as well as the bulk gap observation by scanning tunneling spectroscopy and theoretical calculations indicate the presence of the quantum spin Hall phase in our patterned 1T phases.
We study the possibility of transferring fermions from a trivial system as particle source to an empty system but at topological phase as a mold for casting a stable topological insulator dynamically. We show that this can be realized by a non-Hermitian unidirectional hopping, which connects a central system at topological phase and a trivial flat-band system with a periodic driving chemical potential, which scans over the valence band of the central system. The near exceptional-point dynamics allows a unidirectional dynamical process: the time evolution from an initial state with full-filled source system to a stable topological insulating state approximately. The result is demonstrated numerically by a source-assistant QWZ model and SSH chain in the presence of random perturbation. Our finding reveals a classical analogy of quench dynamics in quantum matter and provides a way for topological quantum state engineering.
The non-Hermitian skin effect (NHSE) in non-Hermitian lattice systems depicts the exponential localization of eigenstates at systems boundaries. It has led to a number of counter-intuitive phenomena and challenged our understanding of bulk-boundary correspondence in topological systems. This work aims to investigate how the NHSE localization and topological localization of in-gap edge states compete with each other, with several representative static and periodically driven 1D models, whose topological properties are protected by different symmetries. The emerging insight is that at critical system parameters, even topologically protected edge states can be perfectly delocalized. In particular, it is discovered that this intriguing delocalization occurs if the real spectrum of the systems edge states falls on the same systems complex spectral loop obtained under the periodic boundary condition. We have also performed sample numerical simulation to show that such delocalized topological edge states can be safely reconstructed from time-evolving states. Possible applications of delocalized topological edge states are also briefly discussed.
We present a detailed investigation of different excitonic states weakly confined in single GaAs/AlGaAs quantum dots obtained by the Al droplet-etching method. For our analysis we make use of temperature-, polarization- and magnetic field-dependent $mu$-photoluminescence measurements, which allow us to identify different excited states of the quantum dot system. Besides that, we present a comprehensive analysis of g-factors and diamagnetic coefficients of charged and neutral excitonic states in Voigt and Faraday configuration. Supported by theoretical calculations by the Configuration interaction method, we show that the widely used single-particle Zeeman Hamiltonian cannot be used to extract reliable values of the g-factors of the constituent particles from excitonic transition measurements.
We demonstrate the manipulation of the Curie temperature of buried layers of the ferromagnetic semiconductor (Ga,Mn)As using nanolithography to enhance the effect of annealing. Patterning the GaAs-capped ferromagnetic layers into nanowires exposes free surfaces at the sidewalls of the patterned (Ga,Mn)As layers and thus allows the removal of Mn interstitials using annealing. This leads to an enhanced Curie temperature and reduced resistivity compared to unpatterned samples. For a fixed annealing time, the enhancement of the Curie temperature is larger for narrower nanowires.
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