Field canalization using anisotropic 2D plasmonics

Optical devices capable of suppressing diffraction nature of light are of great technological importance to many nanophotonic applications. One important technique to achieve diffractionless optics is to exploit field canalization effect. However, current technological platforms based on metamaterial structures typically suffer from strict loss-confinement trade-off, or lack dynamic reconfigurability over device operations. Here we report an integrated canalization platform that can alleviate this performance trade-off. It is found that by leveraging material absorption of anisotropic 2D materials, the dispersion of this class of materials can flatten without increasing propagation losses and compromising confinement. The realization of such plasmon canalization can be considered using black phosphorus (BP), where topological transition from elliptic to hyperbolic curves can be induced by dynamically leveraging material absorption of BP. At the transition point, BP film can support long range, deeply subwavelength, near-diffractionless field propagation, exhibiting diffraction angle of 5.5°, propagation distance of 10λspp, and λspp < λ0/300.

Tunable and programmable topological valley transport in photonic crystals with liquid crystals

Topological valley transport in photonic crystals (PCs) has attracted great attention owing to its edge modes immune to backscattering. However, flexibly dynamically controlling and reconfiguring the pathway of the topological one-way propagation is still challenging. Here, we propose a tunable and programmable valley PC structure based on nematic liquid crystals (LCs). Inversion symmetry breaking and topological transition are implemented through controlling the relative permittivity of the LC cells. Topological protection of valley edge states and valley-locked beam splitting are demonstrated. Moreover, the LC-based PC can be discretized to a number of supercells, each of which can be coded with “0” or “1”. The wave propagation pathway can be dynamically reconfigured by programming different coding patterns.

Instability of Majorana states in Shiba chains due to leakage into a topological substrate

We revisit the problem of Majorana states in chains of scalar impurities deposited on a superconductor with a mixed s-wave and p-wave pairing. We also study the formation of Majorana states for magnetic impurity chains. We find that the magnetic impurity chains exhibit well-localized Majorana states when the substrate is trivial, but these states hybridize and get dissolved in the bulk when the substrate is topological. Most surprisingly, and contrary to previous predictions, the scalar impurity chain does not support fully localized Majorana states except for very small and finely tuned parameter regimes, mostly for a non-topological substrate close to the topological transition. Our results indicate that a purely p-wave or a dominant p-wave substrate are not good candidates to support either magnetic or scalar impurity topological Shiba chains.

Magnetism-induced topological transition in EuAs3

The nature of the interaction between magnetism and topology in magnetic topological semimetals remains mysterious, but may be expected to lead to a variety of novel physics. We systematically studied the magnetic semimetal EuAs3, demonstrating a magnetism-induced topological transition from a topological nodal-line semimetal in the paramagnetic or the spin-polarized state to a topological massive Dirac metal in the antiferromagnetic ground state at low temperature. The topological nature in the antiferromagnetic state and the spin-polarized state has been verified by electrical transport measurements. An unsaturated and extremely large magnetoresistance of ~2 × 105% at 1.8 K and 28.3 T is observed. In the paramagnetic states, the topological nodal-line structure at the Y point is proven by angle-resolved photoemission spectroscopy. Moreover, a temperature-induced Lifshitz transition accompanied by the emergence of a new band below 3 K is revealed. These results indicate that magnetic EuAs3 provides a rich platform to explore exotic physics arising from the interaction of magnetism with topology.

First principles band structure investigation of cubic spinel CuMn2Te4Compound for thermoelectric applications

Spinel CuMn2Te4 material is investigated for its nonmagnetic and ferromagnetic phases by first principles calculation using the FP-LAPW method. Exchange and correlation are treated with GGA. T otal energy calculations reveal that CuMn2T e4 compound tend to stabilise at ferromagnetic phase. Non vanishing bands at the Fermi Energy level illustrates the metallic nature of CuMn2Te4at both of its nonmagnetic and ferromagnetic phases. Transport properties are studied using the BoltzTraP code at 325K. Thermo power of -26.22μv/k is estimated for nonmagnetic CuMn2Te4. At ferromagnetic phase, these values are predicted as 84.85μv/kand 53.39μv/k respectively for spin-up and spin-down states. Computed power factor values are 2.29 x1014Wm-1s-1K-2for NM phase and 2.33×1017Wm−1s−1K−2/1.001×1010Wm−1s-−1K-−2respectivelyfor FM up-spin/down-spin phases. A total magnetic moment of 7.11003 μB/F.U. is obtained for the energetically favourable ferromagnetic phase of CuMn2Te4 compound. High pressure investigations reveal the possibility of electronic topological transition that may lead to changes in the Fermi Surface topology and hence changes in the physical properties of nonmagnetic CuMn2Te4.

PT -symmetric classical mechanics

This paper reports the results of an ongoing in-depth analysis of the classical trajectories of the class of non-Hermitian PT -symmetric Hamiltonians H = p2 + x2 (ix) ε (ε ⩾ 0). A variety of phenomena, heretofore overlooked, have been discovered such as the existence of infinitely many separatrix trajectories, sequences of critical initial values associated with limiting classical orbits, regions of broken PT -symmetric classical trajectories, and a remarkable topological transition at ε = 2. This investigation is a work in progress and it is not complete; many features of complex trajectories are still under study.