Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new user$h/e$ Oscillations in Interlayer Transport of Delafossites
343
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Transport of electrons in a bulk metal is usually well captured by their particle-like aspects, while their wave-like nature is commonly harder to observe. Microstructures can be are fully designed to reveal the quantum phase, for example mesoscopic metal rings resembling interferometers. Here we report a new type of phase coherent oscillation of the out-of-plane magnetoresistance in the layered delafossites PdCoO$_2$ and PtCoO$_2$. The oscillation period is equivalent to that determined by the magnetic flux quantum, $h/e$, threading an area defined by the atomic interlayer separation and the sample width. The phase of the electron wave function in these crystals appears remarkably robust over macroscopic length scales exceeding 10$mu$m and persisting up to elevated temperatures of $T$>50K. We show that, while the experimental signal cannot be explained in a standard Aharonov-Bohm analysis, it arises due to periodic field-modulation of the out-of-plane hopping. These results demonstrate extraordinary single-particle quantum coherence lengths in the delafossites, and identify a new form of quantum interference in solids.
rate research
Read More
Photoluminescence (PL) from excitons serves as a powerful tool to characterize the optoelectronic property and band structure of semiconductors, especially for atomically thin 2D transition metal chalcogenide (TMD) materials. However, PL quenches quickly when the thickness of TMD material increases from monolayer to few-layers, due to the change from direct to indirect band transition. Here we show that PL can be recovered by engineering multilayer heterostructures, with the band transition reserved to be direct type. We report emission from layer engineered interlayer excitons from these multilayer heterostructures. Moreover, as desired for valleytronic devices, the lifetime, valley polarization, and the valley lifetime of the generated interlayer excitons can all be significantly improved as compared with that in the monolayer-monolayer heterostructure. Our results pave the way for controlling the properties of interlayer excitons by layer engineering.
Diverse interlayer tunability of physical properties of two-dimensional layers mostly lies in the covalent-like quasi-bonding that is significant in electronic structures but rather weak for energetics. Such characteristics result in various stacking orders that are energetically comparable but may significantly differ in terms of electronic structures, e.g. magnetism. Inspired by several recent experiments showing interlayer anti-ferromagnetically coupled CrI3 bilayers, we carried out first-principles calculations for CrI3 bilayers. We found that the anti-ferromagnetic coupling results from a new stacking order with the C2/m space group symmetry, rather than the graphene-like one with R3 as previously believed. Moreover, we demonstrated that the intra- and inter-layer couplings in CrI3 bilayer are governed by two different mechanisms, namely ferromagnetic super-exchange and direct-exchange interactions, which are largely decoupled because of their significant difference in strength at the strong- and weak-interaction limits. This allows the much weaker interlayer magnetic coupling to be more feasibly tuned by stacking orders solely. Given the fact that interlayer magnetic properties can be altered by changing crystal structure with different stacking orders, our work opens a new paradigm for tuning interlayer magnetic properties with the freedom of stacking order in two dimensional layered materials.
The exchange coupling underlies ferroic magnetic coupling and is thus the key element that governs statics and dynamics of magnetic systems. This fundamental interaction comes in two flavors - symmetric and antisymmetric coupling. While symmetric coupling leads to ferro- and antiferromagnetism, antisymmetric coupling has attracted significant interest owing to its major role in promoting topologically non-trivial spin textures that promise high-speed and energy-efficient devices. So far, the antisymmetric exchange coupling rather short-ranged and limited to a single magnetic layer has been demonstrated, while the symmetric coupling also leads to long-range interlayer exchange coupling. Here, we report the missing component of the long-range antisymmetric interlayer exchange coupling in perpendicularly magnetized synthetic antiferromagnets with parallel and antiparallel magnetization alignments. Asymmetric hysteresis loops under an in-plane field unambiguously reveal a unidirectional and chiral nature of this novel interaction, which cannot be accounted for by existing coupling mechanisms, resulting in canted magnetization alignments. This can be explained by spin-orbit coupling combined with reduced symmetry in multilayers. This new class of chiral interaction provides an additional degree of freedom for engineering magnetic structures and promises to enable a new class of three-dimensional topological structures.
We investigate electronic transport property of a graphene monolayer covered by a graphene nanoribbon. We demonstrate that electronic transmission of a monolayer can be reduced when covered by a nanoribbon. The transmission reduction occurs at different energies determined by the width of nanoribbon. We explain the transmission reduction by using interference between wavefunctions in the monolayer and the nanoribbon. Furthermore, we show the transmission reduction of a monolayer is combinable when covered by more than one nanoribbon and propose a concept of combination of control for nano-application design.
The magnetic flux periodicity of superconducting loops as well as flux quantization itself are a manifestation of macroscopic quantum phenomena with far reaching implications. They provide the key to the understanding of many fundamental properties of superconductors and are the basis for most bulk and device applications of these materials. In superconducting rings the electrical current has been known to periodically respond to a magnetic flux with a periodicity of $bm{h/2e}$. Here, the ratio of Plancks constant and the elementary charge defines the magnetic flux quantum $bm{h/e}$. The well-known $bm{h/2e}$ periodicity is viewed to be a hallmark for electronic pairing in superconductors and is considered evidence for the existence of Cooper pairs. Here we show that in contrast to this long-term belief, rings of many superconductor bear an $bm{h/e}$ periodicity. These superconductors include the high-$bm{T_c}$ cuprates, Sr$_2$RuO$_4$, the heavy-fermion superconductors, as well as all other unconventional superconductors with nodes in the energy gap functions, and s-wave superconductors with small gaps or states in the gap. As we show, the 50-year-old Bardeen--Cooper--Schrieffer theory of superconductivity implies that for multiply connected paths of such superconductors the ground-state energies and consequently also the supercurrents are generically $bm{h/e}$ periodic. The origin of this periodicity is a magnetic-field driven reconstruction of the condensate and a concomitant Doppler-shifted energy spectrum. The robust, flux induced reconstruction of the condensate will be an important aspect to understand the magnetic properties of mesoscopic unconventional superconductors.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
