Articles
4 results
Test Ground-based gamma-ray astronomy: status and futureFelix Aharonian
Test In this video article the author covers the history and current status of ground-based gamma-ray astronomy. The recent results in this field have brought important implications to various aspects in astrophysics, such as cosmic ray science and black holes and dark matters, and thus advanced our understanding of the dynamic non-thermal universe. The author also discusses the future prospects in this field, especially the possible imaging air Cherenkov telescopes in GeV energy range.
Spin Resolved Zero-Line Modes in Minimally Twisted Bilayer Graphene from Exchange Field and Gate Voltage
The reliance on spin-orbit coupling or strong magnetic fields has always posed significant challenges for the mass production and even laboratory realization of most topological materials. Valley-based topological zero-line modes have attracted widespread attention due to their substantial advantage of being initially realizable with just an external electric field. However, the uncontrollable nature of electrode alignment and precise fabrication has greatly hindered the advancement in this field. By utilizing minimally twisted bilayer graphene and introducing exchange fields from magnetic substrates, we successfully realize a spin-resolved, electrode-free topological zero- line mode. Further integration of electrodes that do not require alignment considerations significantly enhances the tunability of the system’s band structure. Our approach offers a promising new support for the dazzling potential of topological zero-line mode in the realm of low-energy-consumption electronics.
Equivalence of semiclassical and response theories for second-order nonlinear ac Hall effects
It has been known that the semiclassical and the response theories can equivalently give the Drude and the intrinsic anomalous Hall conductivities in the linear order of electric field. However, recent theoretical advances implied that the second-order nonlinear conductivities calculated with both approaches are no longer equivalent, which leads to various experimental explanations even in a similar experimental setup conducted in [Science 381, 181 (2023) and Nature (London) 621, 487 (2023), respectively]. Herein, by extending the ac semiclassical theory up to the second order of electric field, we show that the semiclassical theory is still equivalent to the response theory in the second order of electric field when the relaxation is taken into account on the same footing. In particular, we show that the familiar second-order nonlinear current responses, including the nonlinear Drude current and the Berry curvature (quantum metric) dipole driven extrinsic (intrinsic) nonlinear Hall current, can be derived by both approaches. Further, we show that the quantum-corrected intrinsic nonlinear longitudinal current, as recently proposed by the response theory or in a similar manner, can also be reproduced by the semiclassical theory. Beyond those known second-order current responses, with both approaches, we uncover two previously overlooked nonlinear displacement currents unique to the ac electric field. As a consequence of this equivalence, (i) we suggest that the energy of the equilibrium Fermi distribution particularly in the semiclassical theory should be the unperturbed one by assuming that both approaches give the same intrinsic responses; (ii) we unify the intrinsic second-order nonlinear longitudinal current responses calculated with both approaches; and (iii) we argue that the scheme of introducing relaxation in the response theory by modifying the quantum Liouville equation needs to be reconsidered. Our work explicitly shows the equivalence of the ac semiclassical theory and the response theory when calculating the second-order nonlinear conductivities under the electric field and highlights the influence of the ac electric field.
Braiding induced by the finite-size effect in one-dimensional topological superconductors
We investigate the transport properties of Majorana zero modes (MZMs) and Majorana Kramers pairs (MKPs) in one-dimensional topological superconductors, respectively. An effective model is established for the braiding of MZMs and MKPs. We employ dx2 −y2 -wave topological superconductors to embody the effective model for the braiding of MKPs by utilizing the finite-size effect and minimal locally tunable coupling parameters. We show how to construct the state initialization and readout via gate control. We also use this method for the braiding of MZMs in s-wave topological superconductors. Our proposal presents a promising avenue for experimentally verifying the non-Abelian statistical properties of MZMs and MKPs, with implications for topological quantum computing.