RESUMEN
Strain plays an important role in condensed matter physics and materials science because it can strongly modify the mechanical, electrical, and optical properties of a material and even induce a structural phase transition. Strain effects are especially interesting in atomically thin two-dimensional (2D) materials, where unusually large strain can be achieved without breaking them. Measuring the strain distribution in 2D materials at the nanometer scale is therefore greatly important but is extremely challenging experimentally. Here, we use near-field infrared nanoscopy to demonstrate phonon polariton-assisted mapping and quantitative analysis of strain in atomically thin polar crystals of hexagonal boron nitride (hBN) at the nanoscale. A local strain as low as 0.01% can be detected using this method with â¼20 nm spatial resolution. Such ultrasensitive nanoscale strain imaging and analysis technique opens up opportunities for exploring unique local strain structures and strain-related physics in 2D materials. In addition, experimental evidence for local strain-induced phonon polariton reflection is also provided, which offers a new approach to manipulate light at deep subwavelength scales for nanophotonic devices.
RESUMEN
As a class of remarkable spintronic materials, intrinsic antiferromagnetic (AFM) metals are rare. The exploration and investigation of AFM metals are still in its infancy. Based on first-principles calculations, the interface-induced magnetic phenomena in the (CrO2)m/(TaO2)nsuperlattices are investigated, and a new series of AFM metals is predicted. Under different ratios ofm:nwith varying valence states of Cr, the (CrO2)m/(TaO2)nsuperlattices exhibit three different phases, including the AFM metal, the AFM semiconductor, and the ferromagnetic (FM) metal. In the AFM semiconducting phases, theintra-CrO2-monolayer magnetic exchange interaction is systematically discussed, corresponding tom = 1 orm = 2. Both the localization of the Cr 3 dorbitals and the crystal-field splitting are crucial for magnetic ordering in super-exchange interactions. Based on the analyses of the AFM semiconducting phases withm = 1 andm = 2, the mechanisms of AFM metallic phases with radios ofm:n<1/2and1/2
RESUMEN
Various interfacial emergent phenomena have been discovered in tunable nanoscale materials, especially in artificially designed epitaxial superlattices. In conjunction, the atomically fabricated superlattices have exhibited a plethora of exceptional properties compared to either bulk materials separately. Here, the (CrO2)m/(TaO2)nsuperlattices composed of two lattice-matched metallic metal oxides are constructed. With the help of first-principle density-functional theory calculations, a computational and theoretical study of (CrO2)m/(TaO2)nsuperlattices manifests the interfacial electronic properties in detail. The results suggest that emergent properties result from the charge transfer from the TaO2to CrO2layers. At two special ratios of1:1and1:2betweenmandn, the superlattices undergo metal-to-insulator transition. Additionally, the bands below the Fermi level become narrower with the increasing thickness of the CrO2and TaO2layers. The study reveals that the electronic reconstruction at the interface of two metallic materials can generate interesting physics, which points the direction for the manipulation of functionalities in artificial superlattices or heterostructures within a few atomic layers.
RESUMEN
One Majorana doublet can be realized at each end of the time-reversal-invariant Majorana nanowires. We investigate the Josephson effect in the Majorana-doublet-presented junction modified by different inter-doublet coupling manners. It is found that when the Majorana doublets couple indirectly via a non-magnetic quantum dot, only the normal Josephson effect occurs, and the fermion parity in the system just affects the current direction and amplitude. However, one magnetic field applied on the dot can induce the fractional Josephson effect in the odd-parity case. Next if the direct and indirect couplings between the Majorana doublets coexist, no fractional Josephson effect takes place, regardless of the presence of magnetic field. Instead, there almost appears the π-period-like current in some special cases. All the results are clarified by analyzing the influence of the fermion occupation in the quantum dot on the parity conservation in the whole system. We ascertain that this work will be helpful for describing the dot-assisted Josephson effect between the Majorana doublets.
RESUMEN
We investigate the Josephson effects in the junction formed by the indirect coupling between DIII-class topological and s-wave superconductors via an embedded quantum dot. Due to the presence of two kinds of superconductors, three dot-superconductor coupling manners are considered, respectively. As a result, the Josephson current is found to oscillate in period 2π. More importantly, the presence of Majorana doublet in the DIII-class superconductor renders the current finite at the case of zero phase difference, with its sign determined by the fermion parity of such a junction. In addition, the dot-superconductor coupling plays a nontrivial role in adjusting the Josephson current. When the s-wave superconductor couples to the dot in the weak limit, the current direction will have an opportunity to reverse. It is believed that these results will be helpful for understanding the transport properties of the DIII-class superconductor.