Highly tunable optical antennas in teraherz range based on graphene ring structures are proposed, which employ graphene plasmons instead of traditional metallic plasmons. The plasmon resonances of the perfect graphene ring (PGR) can be understood with the edge plasmons in graphene ribbons. While in the nonconcentric graphene ring, the multipolar plasmon modes appear and anti-symmetric mode splits due to symmetry breaking. Furthermore, the symmetric plasmon mode in a graphene ring can concentrate electromagnetic field with an enhancement factor as large as 103 in terahertz waveband, which is almost 20 times larger than a gold ring with the same size.

BackgroundStudies have confirmed that the thalamus and the primary somatosensory cortex (SI) are associated with cognitive function. These two brain regions are closely related in structure and function. The interactions between SI and the thalamus are of crucial significance for the cognitive process. Patients with major depressive disorder (MDD) have significant cognitive impairment. Based on these observations, we used resting-state functional magnetic resonance imaging (rs-fMRI) to investigate whether there is an abnormality in the SI-thalamic functional connection in MDD. Furthermore, we explored the clinical symptoms related to this abnormality.MethodsWe included 31 patients with first-episode major depressive disorder and 28 age-, gender-, and education-matched healthy controls (HC). The SI-thalamic functional connectivity was compared between the MDD and HC groups. The correlation analyses were performed between areas with abnormal connectivity and clinical characteristics.ResultsCompared with healthy subjects, the MDD patients had enhanced functional connectivity between the thalamus and SI (p < 0.05, corrected). Brain areas with significantly different levels of connectivity had a negative correlation with the Assessment of Neuropsychological Status total score (r = − 0.383, p = 0.033), delayed memory score (r = − 0.376, p = 0.037) and two-digit continuous operation test score (r = − 0.369, p = 0.041) in MDD patients.ConclusionsThese results demonstrate that SI-thalamic functional connectivity is abnormal and associated with the core clinical symptoms in MDD. The SI-thalamic functional connectivity functions as a neurobiological feature and potential biomarker for MDD.

Surface plasmon modes at terahertz-infrared waveband in subwavelength graphene wedge and groove waveguides are investigated, which can be categorized into perfect electric conductor and perfect magnetic conductor symmetric modes with different propagation characteristics. The electromagnetic near-fields are localized strongly in different regions for these two kinds of modes. Moreover, these modes can be interpreted by the folded graphene ribbon modes. The brim width of the waveguides and the Fermi energy of the graphene strongly influence the dispersion and propagation distances of the plasmon modes, which can be used for tuning the plasmon modes in graphene wedge and groove waveguides efficiently.

No abstract