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Herein, we investigate the effect of tilt mismatch on the quantum oscillations of spin transport properties in two-dimensional asymmetrically tilted Dirac cone systems. This study involves the examination of conductance oscillation in two distinct junction types: transverse- and longitudinal-tilted Dirac cones (TTDCs and LTDCs). Our findings reveal an unusual quantum oscillation of spin-polarized conductance within the TTDC system, characterized by two distinct anomaly patterns within a single period, labeled as the linear conductance phase and the oscillatory conductance phase. Interestingly, these phases emerge in association with tilt-induced orbital pseudo-magnetization and exchange interaction. Our study also demonstrates that the structure of the LTDC can modify the frequency of spin conductance oscillation, and the asymmetric effect within this structure results in a quantum beating pattern in oscillatory spin conductance. We note that an enhancement in the asymmetric longitudinal tilt velocity ratio within the structure correspondingly amplifies the beating frequency. Our research potentially contributes valuable insights for detecting the asymmetry of tilted Dirac fermions in type-I Dirac semimetal-based spintronics and quantum devices. [ABSTRACT FROM AUTHOR]

Herein, we investigate the effect of tilt mismatch on the quantum oscillations of spin transport properties in two-dimensional asymmetrically tilted Dirac cone systems. This study involves the examination of conductance oscillation in two distinct junction types: transverse- and longitudinal-tilted Dirac cones (TTDCs and LTDCs). Our findings reveal an unusual quantum oscillation of spin-polarized conductance within the TTDC system, characterized by two distinct anomaly patterns within a single period, labeled as the linear conductance phase and the oscillatory conductance phase. Interestingly, these phases emerge in association with tilt-induced orbital pseudo-magnetization and exchange interaction. Our study also demonstrates that the structure of the LTDC can modify the frequency of spin conductance oscillation, and the asymmetric effect within this structure results in a quantum beating pattern in oscillatory spin conductance. We note that an enhancement in the asymmetric longitudinal tilt velocity ratio within the structure correspondingly amplifies the beating frequency. Our research potentially contributes valuable insights for detecting the asymmetry of tilted Dirac fermions in type-I Dirac semimetal-based spintronics and quantum devices.

Analogous to real spins, valleys as carriers of information can play significant roles in physical properties of two-dimensional Dirac materials. On the other hand, utilizing external periodic potential is an efficient method to manipulate their band structures and transport properties. In this work, we investigate the valley dependent optics-like behaviors based on an 8- Pmmn borophene superlattice with the transfer matrix method and effective band approach. Firstly, it is found that the band structure is renormalized, more tilted Dirac cones are generated, and the group velocities are modified by the periodic potentials. Secondly, due to the exotic tilted Dirac cones in 8- Pmmn borophene, a perfect valley selected angle filter can be realized. The electrons with a specific incident angle can transmit completely in an energy window, which is flexibly tunable by changing the periodic potential. Thirdly, by using the Green’s function to simulate the time evolution of wave packets, electrons can be shown to propagate without any diffraction, valley electron beam supercollimation happens by modulating the potential parameters. Different from the graphene superlattice, the electron supercollimation here is valley dependent and can be used as a valley electron beam collimator. Fourthly, we can tune the polarization and supercollimation angles by changing the superlattice direction. These intriguing results in an 8- Pmmn borophene-based superlattice offer more opportunities in diverse electronic transport phenomena and may facilitate the devices applications in valleytronics and electron-optics.

The dynamical property of electrons with the tilted Dirac cone was examined using the tilted Weyl equation. The polarization function exhibits cusps and nonmonotonic structures by varying both the frequency and the momentum. A pair of tilted Dirac cones exhibits a new plasmon for the intermediate magnitude of momentum owing to the combined effects of two tilted cones. Dirac electrons with the zero-gap state (ZGS) in organic conductor α-(BEDT-TTF)2I3 are examined by calculating the Berry curvature, which displays the peak structure for a pair of Dirac particles between the conduction band and the valence band. The ZGS is theoretically predicted for α-(BEDT-TTF)2NH4Hg(SCN)4 under uniaxial pressure. Examining the band structure of the stripe charge ordered state of α-(BEDT-TTF)2I3 under pressure, we have found a topological transition from a conventional insulator to a new phase of a pair of Dirac electrons with a finite mass. Further, investigating the zero-energy (N = 0) Landau level under a strong magnetic field, we propose ferromagnetism breaking the SU(2) valley-pseudo-spin symmetry, and the phase fluctuations of the order parameters leading to Kosterlitz-Thouless transition at lower temperatures.

When transition-metal dichalcogenide monolayers lack inversion symmetry, their low-energy single particle spectrum near some high-symmetry points can, in some cases, be described by tilted massive Dirac Hamiltonians. The so-called Janus materials fall into that category. Inversion symmetry can also be broken by the application of out-of-plane electric fields, or by the mere presence of a substrate. Here we explore the properties of excitons in TMDC monolayers lacking inversion symmetry. We find that exciton binding energies can be larger than the electronic band gap, making such materials promising candidates to host the elusive exciton insulator phase. We also investigate the excitonic contribution to their optical conductivity and discuss the associated optical selection rules., (Creative Commons Attribution license.)

The dynamical property of electrons with the tilted Dirac cone was examined using the tilted Weyl equation. The polarization function exhibits cusps and nonmonotonic structures by varying both the frequency and the momentum. A pair of tilted Dirac cones exhibits a new plasmon for the intermediate magnitude of momentum owing to the combined effects of two tilted cones. Dirac electrons with the zero-gap state (ZGS) in organic conductor α-(BEDT-TTF)2I3 are examined by calculating the Berry curvature, which displays the peak structure for a pair of Dirac particles between the conduction band and the valence band. The ZGS is theoretically predicted for α-(BEDT-TTF)2NH4Hg(SCN)4 under uniaxial pressure. Examining the band structure of the stripe charge ordered state of α-(BEDT-TTF)2I3 under pressure, we have found a topological transition from a conventional insulator to a new phase of a pair of Dirac electrons with a finite mass. Further, investigating the zero-energy (N = 0) Landau level under a strong magnetic field, we propose ferromagnetism breaking the SU(2) valley-pseudo-spin symmetry, and the phase fluctuations of the order parameters leading to Kosterlitz-Thouless transition at lower temperatures. [ABSTRACT FROM AUTHOR]

We study the effects of the Dirac cones tilts on coupled plasmon modes arising from the Coulomb electron–electron interaction for a system consisting of a two-dimensional (2D) system of Dirac electrons embedded in a three-dimensional (3D) Dirac semimetal. We particularly take into account the long-range Coulomb electron–electron interaction between electrons from two subsystems with the tilted Dirac cone anisotropic energy band dispersions and obtain the resulting coupled optical and acoustic plasmon modes from the dielectric functions of the subsystems for their various separations. The tilts of Dirac cones anisotropically increase the coupled plasmon mode energies and renormalize their spectral weights compared to the results for the untilted energy band dispersions. We demonstrate that the effects of tilts are more pronounced for the larger separations of the subsystems when their Coulomb coupling is weaker. [ABSTRACT FROM AUTHOR]