Majorana Corner Modes and Flat-Band Majorana Edge Modes in Superconductor/Topological-Insulator/Superconductor Junctions

Recently,superconductors with higher-order topology have stimulated extensive attention and research interest.Higher-order topological superconductors exhibit unconventional bulk-boundary correspondence,thus allow exotic lower-dimensional boundary modes,such as Majorana corner and hinge modes.However,higher-order topological superconductivity has yet to be found in naturally occurring materials.We investigate higher-order topology in a two-dimensional Josephson junction comprised of two s-wave superconductors separated by a topological insulator thin film.We find that zero-energy Majorana corner modes,a boundary fingerprint of higherorder topological superconductivity,can be achieved by applying magnetic field.When an in-plane Zeeman field is applied to the system,two corner modes appear in the superconducting junction.Furthermore,we also discover a two-dimensional nodal superconducting phase which supports flat-band Majorana edge modes connecting the bulk nodes.Importantly,we demonstrate that zero-energy Majorana corner modes are stable when increasing the thickness of topological insulator thin film.

Photoinduced Floquet higher-order Weyl semimetal in C_(6) symmetric Dirac semimetals

Topological Dirac semimetals are a parent state from which other exotic topological phases of matter, such as Weyl semimetals and topological insulators, can emerge. In this study, we investigate a Dirac semimetal possessing sixfold rotational symmetry and hosting higher-order topological hinge Fermi arc states, which is irradiated by circularly polarized light. Our findings reveal that circularly polarized light splits each Dirac node into a pair of Weyl nodes due to the breaking of time-reversal symmetry, resulting in the realization of the Weyl semimetal phase. This Weyl semimetal phase exhibits rich boundary states, including two-dimensional surface Fermi arc states and hinge Fermi arc states confined to six hinges.Furthermore, by adjusting the incident direction of the circularly polarized light, we can control the degree of tilt of the resulting Weyl cones, enabling the realization of different types of Weyl semimetals.

Insufficiency of Mrpl40 disrupts testicular structure and semen parameters in a murine model

Approximately 31%of patients with 22q11.2 deletion syndrome(22q11.2DS)have genitourinary system disorders and 6%of them have undescended testes.Haploinsufficiency of genes on chromosome 22q11.2 might contribute to the risk of 22q11.2DS.In this study,we used mice with single-allele deletion in mitochondrial ribosomal protein L4o(Mrpl40-)as models to investigate the function of Mrpl40 in testes and spermatozoa development.The penetrance of cryptorchidism in Mrpl40+-mice was found to be higher than that in wild-type(WT)counterparts.Although the weight of testes was not significantly different between the WT and Mrpl40+-mice,the structure of seminiferous tubules and mitochondrial morphology was altered in the Mrpl40+-mice.Moreover,the concentration and motility of spermatozoa were significantly decreased in the Mrpl4O+-mice.In addition,data-independent acquisition mass spectrometry indicated that the expression of genes associated with male infertility was altered in Mrpl40+-testes.Our study demonstrated the important role of Mrpl40 in testicular structure and spermatozoa motility and count.These findings suggest that Mrpl4o is potentially a novel therapeutic target for cryptorchidism and decreased motility and count of spermatozoa.

Evolution of Berry curvature and reentrant quantum anomalous Hall effect in an intrinsic magnetic topological insulator

Recently, the magnetic topological insulator(TI) MnBi2Te4 emerged as a competitive platform to realize quantum anomalous Hall(QAH) states. We report a Berry curvature splitting mechanism to realize the QAH effect in the disordered magnetic TI multilayers when switching from an antiferromagnetic order to a ferromagnetic order. We reveal that the splitting of spin-resolved Berry curvature, originating from the separation of the critical points during the magnetic switching, can give rise to a QAH insulator. We present a global phase diagram, and also provide a phenomenological picture to elucidate the Berry curvature splitting mechanism by the evolution of topological charges. At last, we predict that the Berry curvature splitting mechanism will lead to a reentrant QAH effect, which can be detected by tuning the gate voltage. Our theory will be instructive for the studies of the QAH effect in MnBi2Te4 in future experiments.

Emergent Z2 topological invariant and robust helical edge states in two-dimensional topological metals

In this work,we study the effects of disorder on topological metals that support a pair of helical edge modes deeply embedded inside the gapless bulk states.Strikingly,we predict that a quantum spin Hall(QSH)phase can be obtained from such topological metals without opening a global band gap.To be specific,disorder can lead to a pair of robust helical edge states which is protected by an emergent Z2 topological invariant,giving rise to a quantized conductance plateau in transport measurements.These results are instructive for solving puzzles in various transport experiments on QSH materials that are intrinsically metallic.This work also will inspire experimental realization of the QSH effect in disordered topological metals.

Quantum to classical crossover under dephasing effects in a two-dimensional percolation model

Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class(i.e., with timereversal symmetry and spin-rotation symmetry). The conductance g behaves as g^exp(-L/l) with system size L and localization length l in the strong disorder limit. However, classical systems can always have metallic states in which Ohm’s law shows a constant g in d=2. We study a two-dimensional quantum percolation model by controlling dephasing effects. The numerical investigation of g aims at simulating a quantum-to-classical percolation evolution. An unexpected metallic phase, where g increases with L, generates immense interest before the system becomes completely classical. Furthermore, the analysis of the scaling plot of g indicates a metal-insulator crossover.