53 research outputs found
Synthesis of a magnetic π-extended carbon nanosolenoid with Riemann surfaces
Riemann surfaces are deformed versions of the complex plane in mathematics. Locally they look like patches of the complex plane, but globally, the topology may deviate from a plane. Nanostructured graphitic carbon materials resembling a Riemann surface with helicoid topology are predicted to have interesting electronic and photonic properties. However, fabrication of such processable and large π-extended nanographene systems has remained a major challenge. Here, we report a bottom-up synthesis of a metal-free carbon nanosolenoid (CNS) material with a low optical bandgap of 1.97 eV. The synthesis procedure is rapid and possible on the gram scale. The helical molecular structure of CNS can be observed by direct low-dose high-resolution imaging, using integrated differential phase contrast scanning transmission electron microscopy. Magnetic susceptibility measurements show paramagnetism with a high spin density for CNS. Such a π-conjugated CNS allows for the detailed study of its physical properties and may form the base of the development of electronic and spintronic devices containing CNS species
Helical Luttinger liquid on the edge of a 2-dimensional topological antiferromagnet
Boundary helical Luttinger liquid (HLL) with broken bulk time-reversal
symmetry belongs to a unique topological class which may occur in
antiferromagnets (AFM). Here, we search for signatures of HLL on the edge of a
recently discovered topological AFM, MnBi2Te4 even-layer. Using scanning
superconducting quantum interference device, we directly image helical edge
current in the AFM ground state appearing at its charge neutral point. Such
helical edge state accompanies an insulating bulk which is topologically
distinct from the ferromagnetic Chern insulator phase as revealed in a magnetic
field driven quantum phase transition. The edge conductance of the AFM order
follows a power-law as a function of temperature and source-drain bias which
serves as strong evidence for HLL. Such HLL scaling is robust at finite fields
below the quantum critical point. The observed HLL in a layered AFM
semiconductor represents a highly tunable topological matter compatible with
future spintronics and quantum computation
Two types of zero Hall phenomena in few-layer MnBiTe
The van der Waals antiferromagnetic topological insulator MnBiTe
represents a promising platform for exploring the layer-dependent magnetism and
topological states of matter. Despite the realization of several quantized
phenomena, such as the quantum anomalous Hall effect and the axion insulator
state, the recently observed discrepancies between magnetic and transport
properties have aroused controversies concerning the topological nature of
MnBiTe in the ground state. Here, we demonstrate the existence of two
distinct types of zero Hall phenomena in few-layer MnBiTe. In addition
to the robust zero Hall plateau associated with the axion insulator state, an
unexpected zero Hall phenomenon also occurs in some odd-number-septuple layer
devices. Importantly, a statistical survey of the optical contrast in more than
200 MnBiTe reveals that such accidental zero Hall phenomenon arises
from the reduction of effective thickness during fabrication process, a factor
that was rarely noticed in previous studies of 2D materials. Our finding not
only resolves the controversies on the relation between magnetism and anomalous
Hall effect in MnBiTe, but also highlights the critical issues
concerning the fabrication and characterization of devices based on 2D
materials.Comment: 21 pages, 4 figure
Structural and functional changes of the cerebellum in temporal lobe epilepsy
AimsThis study aimed to comprehensively explore the cerebellar structural and functional changes in temporal lobe epilepsy (TLE) and its association with clinical information.MethodsThe SUIT toolbox was utilized to perform cerebellar volume and diffusion analysis. In addition, we extracted the average diffusion values of cerebellar peduncle tracts to investigate microstructure alterations. Seed-based whole-brain analysis was used to investigate cerebellar–cerebral functional connectivity (FC). Subgroup analyses were performed to identify the cerebellar participation in TLE with/without hippocampal sclerosis (HS)/focal-to-bilateral tonic–clonic seizure (FBTCS) and TLE with different lateralization.ResultsTLE showed widespread gray matter atrophy in bilateral crusII, VIIb, VIIIb, left crusI, and left VIIIa. Both voxel and tract analysis observed diffusion abnormalities in cerebellar afferent peduncles. Reduced FC between the right crus II and the left parahippocampal cortex was found in TLE. Additionally, TLE showed increased FCs between left lobules VI–VIII and cortical nodes of the dorsal attention and visual networks. Across all patients, decreased FC was associated with poorer cognitive function, while increased FCs appeared to reflect compensatory effects. The cerebellar structural changes were mainly observed in HS and FBTCS subgroups and were regardless of seizure lateralization, while cerebellar–cerebral FC alterations were similar in all subgroups.ConclusionTLE exhibited microstructural changes in the cerebellum, mainly related to HS and FBTCS. In addition, altered cerebellar–cerebral functional connectivity is associated with common cognitive alterations in TLE
- …