Presented By: Department of Physics
CM-AMO Seminar | Double Feature
Heqiu Li (U-M Physics) and Eunice Paik (U-M Physics)
Pfaffian Formalism for Higher-Order Topological Insulators
Higher-order topological insulators (HOTIs) are characterized by gapless modes that occur at lower-dimensional boundaries than the conventional (first-order) topological insulators (TIs). For example, a 3D second-order TI has gapless 1D hinge modes and gapped 2D surface and gapped 3D bulk, whereas a 3D first-order TI has gapless 2D surface modes. In general, n-th order TI in d-dimensional space has gapless modes at (d-n) dimensional boundary.
In this work, we generalize the Pfaffian formalism, which has been playing an important role in the study of time-reversal invariant first-order topological insulators, to 3D chiral higher-order topological insulators protected by the product of four-fold rotational symmetry C_4 and the time-reversal symmetry T. This Pfaffian description reveals a deep and fundamental link between TIs and HOTIs, and allows important conclusions about TIs to be generalized to HOTIs. In particular, we can generalize Fu-Kane's parity criterion for TIs to HOTIs, and also present a general method to efficiently compute the Z_2 index of 3D chiral HOTIs without a global gauge.
Spatially Coherent Lasing in an Atomically-Thin Heterostructure
Atomically thin two-dimensional (2D) semiconductors are a promising gain media for the next generation of semiconductor lasers and nanophotonics. They have advantages over the traditional III-V semiconductors because they exhibit strong light-matter interaction, are flexible and compact, and allow easy integration with various substrates. Utilizing these advantages, we engineer a lasing device with a rotationally aligned WSe2-MoSe2 van der Waals heterostructure integrated with a one-dimensional (1D) silicon nitride (SiN) grating resonator. Angle-resolved micro-photoluminescence and spatial coherence measurements show signatures of lasing, which include bright emission intensity and formation of extended spatial coherence. This work establishes 2D semiconductor heterostructures as a new type of gain medium.
Higher-order topological insulators (HOTIs) are characterized by gapless modes that occur at lower-dimensional boundaries than the conventional (first-order) topological insulators (TIs). For example, a 3D second-order TI has gapless 1D hinge modes and gapped 2D surface and gapped 3D bulk, whereas a 3D first-order TI has gapless 2D surface modes. In general, n-th order TI in d-dimensional space has gapless modes at (d-n) dimensional boundary.
In this work, we generalize the Pfaffian formalism, which has been playing an important role in the study of time-reversal invariant first-order topological insulators, to 3D chiral higher-order topological insulators protected by the product of four-fold rotational symmetry C_4 and the time-reversal symmetry T. This Pfaffian description reveals a deep and fundamental link between TIs and HOTIs, and allows important conclusions about TIs to be generalized to HOTIs. In particular, we can generalize Fu-Kane's parity criterion for TIs to HOTIs, and also present a general method to efficiently compute the Z_2 index of 3D chiral HOTIs without a global gauge.
Spatially Coherent Lasing in an Atomically-Thin Heterostructure
Atomically thin two-dimensional (2D) semiconductors are a promising gain media for the next generation of semiconductor lasers and nanophotonics. They have advantages over the traditional III-V semiconductors because they exhibit strong light-matter interaction, are flexible and compact, and allow easy integration with various substrates. Utilizing these advantages, we engineer a lasing device with a rotationally aligned WSe2-MoSe2 van der Waals heterostructure integrated with a one-dimensional (1D) silicon nitride (SiN) grating resonator. Angle-resolved micro-photoluminescence and spatial coherence measurements show signatures of lasing, which include bright emission intensity and formation of extended spatial coherence. This work establishes 2D semiconductor heterostructures as a new type of gain medium.
Co-Sponsored By
Explore Similar Events
-
Loading Similar Events...
