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Register a new userAnomalous magneto-transport properties of bilayer phosphorene
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The magneto-transport properties of phosphorene are investigated by employing the generalized tight-binding model to calculate the energy bands. For bilayer phosphorene, a composite magnetic and electric field is shown to induce a feature-rich Landau level (LL) spectrum which includes two subgroups of low-lying LLs. The two subgroups possess distinct features in level spacings, quantum numbers, as well as field dependencies. These together lead to anomalous quantum Hall (QH) conductivities which include a well-shape, staircase and composite quantum structures with steps having varying heights and widths. The Fermi energy-magnetic field-Hall conductivity ($E_{F}-B_{z}-sigma_{xy}$) and Fermi energy-electric field-Hall conductivity ($E_{F}-E_{z}-sigma_{xy}$) phase diagrams clearly exhibit oscillatory behaviors and cross-over from integer to half-integer QH effect. The predicted results should be verifiable by magneto-transport measurements in a dual-gated system.
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The generalized tight-binding model is developed to investigate the magneto-electronic properties in twisted bilayer graphene system. All the interlayer and intralayer atomic interactions are included in the Moire superlattice. The twisted bilayer graphene system is a zero-gap semiconductor with double-degenerate Dirac-cone structures, and saddle-point energy dispersions appearing at low energies for cases of small twisting angles. There exist rich and unique magnetic quantization phenomena, in which many Landau-level subgroups are induced due to specific Moire zone folding through modulating the various stacking angles. The Landau-level spectrum shows hybridized characteristics associated with the those in monolayer, and AA $&$ AB stackings. The complex relations among the different sublattices on the same and different graphene layers are explored in detail.
We numerically study the electrical and thermoelectric transport properties in phosphorene in the presence of both a magnetic field and disorder. The quantized Hall conductivity is similar to that of a conventional two-dimensional electron gas, but the positions of all the Hall plateaus shift to the left due to the spectral asymmetry, in agreement with the experimental observations. The thermoelectric conductivity and Nernst signal exhibit remarkable anisotropy, and the thermopower is nearly isotropic. When a bias voltage is applied between top and bottom layers of phosphorene, both thermopower and Nernst signal are enhanced and their peak values become large.
Moire superlattices of van der Waals heterostructures provide a powerful new way to engineer the electronic structures of two-dimensional (2D) materials. Many novel quantum phenomena have emerged in different moire heterostructures, such as correlated insulators, superconductors, and Chern insulators in graphene systems and moire excitons in transition metal dichalcogenide (TMDC) systems. Twisted phosphorene offers another attractive system to explore moire physics because phosphorene features an anisotropic rectangular lattice, different from the isotropic hexagonal lattice in graphene and TMDC. Here we report emerging anisotropic moire optical transitions in twisted monolayer/bilayer phosphorene. The optical resonances in phosphorene moire superlattice depend sensitively on the twist angle between the monolayer and bilayer. Surprisingly, even for a twist angle as large as 19{deg} the moire heterostructure exhibits optical resonances completely different from those in the constituent monolayer and bilayer phosphorene. The new moire optical resonances exhibit strong linear polarization, with the principal axis lying close to but different from the optical axis of bilayer phosphorene. Our ab initio calculations reveal that the {Gamma}-point direct bandgap and the rectangular lattice of phosphorene, unlike the K-point bandgap of hexagonal lattice in graphene and TMDC, give rise to the remarkably strong moire physics in large-twist-angle phosphorene heterostructures. Our results highlight the exciting opportunities to explore moire physics in phosphorene and other van der Waals heterostructures with different lattice configurations.
The low-frequency magneto-optical absorption spectra of bilayer Bernal graphene are studied within the tight-binding model and gradient approximation. The interlayer interactions strongly affect the electronic properties of the Landau levels (LLs), and thus enrich the optical absorption spectra. According to the characteristics of the wave functions, the low-energy LLs can be divided into two groups. This division results in four kinds of optical absorption peaks with complex optical selection rules. Observing the experimental convergent absorption frequencies close to zero magnetic field might be useful and reliable in determining the values of several hopping integrals. The dependence of the optical absorption spectra on the field strength is investigated in detail, and the results differ considerably from those of monolayer graphene.
The low-frequency magneto-optical properties of bilayer Bernal graphene are studied by the tight-binding model with four most important interlayer interactions taken into account. Since the main features of the wave functions are well depicted, the Landau levels can be divided into two groups based on the characteristics of the wave functions. These Landau levels lead to four categories of absorption peaks in the optical absorption spectra. Such absorption peaks own complex optical selection rules and these rules can be reasonably explained by the characteristics of the wave functions. In addition, twin-peak structures, regular frequency-dependent absorption rates and complex field-dependent frequencies are also obtained in this work. The main features of the absorption peaks are very different from those in monolayer graphene and have their origin in the interlayer interactions.
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