40 research outputs found
Electronic response of graphene to linelike charge perturbations
The problem of electrostatic screening of a charged line by undoped or weakly
doped graphene is treated beyond the linear-response theory. The induced
electron density is found to be approximately doping independent, n(x)~(log
x)^2/x^2, at intermediate distances x from the charged line. At larger x, twin
p-n junctions may form if the external perturbation is repulsive for graphene
charge carriers. The effect of such inhomogeneities on conductance and quantum
capacitance of graphene is calculated. The results are relevant for transport
properties of graphene grain boundaries and for local electrostatic control of
graphene with ultrathin gates.Comment: Fixed typos and added reference
Theory of plasmon reflection by a 1D junction
We present a comprehensive study of the reflection of normally incident
plasmon waves from a low-conductivity 1D junction in a 2D conductive sheet.
Rigorous analytical results are derived in the limits of wide and narrow
junctions. Two types of phenomena determine the reflectance, the cavity
resonances within the junction and the capacitive coupling between the leads.
The resonances give rise to alternating strong and weak reflection but are
vulnerable to plasmonic damping. The capacitive coupling, which is immune to
damping, induces a near perfect plasmon reflection in junctions narrower than
of the plasmon wavelength. Our results are important for infrared 2D
plasmonic circuits utilizing slot antennas, split gates or nanowire gates. They
are also relevant for the implementation of nanoscale terahertz detectors,
where optimal light absorption coincides with the maximal junction reflectance
Tunable plasmonic reflection by bound 1D electron states in a 2D Dirac metal
We show that surface plasmons of a two-dimensional Dirac metal such as
graphene can be reflected by line-like perturbations hosting one-dimensional
electron states. The reflection originates from a strong enhancement of the
local optical conductivity caused by optical transitions involving these bound
states. We propose that the bound states can be systematically created,
controlled, and liquidated by an ultranarrow electrostatic gate. Using infrared
nanoimaging, we obtain experimental evidence for the locally enhanced
conductivity of graphene induced by a carbon nanotube gate, which supports this
theoretical concept.Comment: 14 pages, 12 figures, submitted to PR
Nanoplasmonic Phenomena at Electronic Boundaries in Graphene
We review recent discoveries of the intriguing plasmonic phenomena at a variety of electronic boundaries (EBs) in graphene including a line of charges in graphene induced by a carbon nanotube gate, grain boundaries in chemical vapor deposited graphene films, an interface between graphene and moiré patterned graphene, an interface between graphene and bilayer graphene, and others. All these and other EBs cause plasmonic impedance mismatch at the two sides of the boundaries. Manifestations of this effect include plasmonic fringes that stem from plasmon reflections and interference. Quantitative analysis and modeling of these plasmonic fringes uncovered intriguing properties and underlying physics of the EBs. Potential plasmonic applications associated with these EBs are also briefly discussed
Plasmon reflections by topological electronic boundaries in bilayer graphene
Domain walls separating regions of AB and BA interlayer stacking in bilayer
graphene have attracted attention as novel examples of structural solitons,
topological electronic boundaries, and nanoscale plasmonic scatterers. We show
that strong coupling of domain walls to surface plasmons observed in infrared
nanoimaging experiments is due to topological chiral modes confined to the
walls. The optical transitions among these chiral modes and the band continua
enhance the local ac conductivity, which leads to plasmon reflection by the
domain walls. The imaging reveals two kinds of plasmonic standing-wave
interference patterns, which we attribute to shear and tensile domain walls. We
compute the electronic structure of both wall varieties and show that the
tensile wall contain additional confined bands which produce a
structure-specific contrast of the local conductivity. The calculated plasmonic
interference profiles are in quantitative agreement with our experiments.Comment: 14 pages, 5 figure
Phonon Polaritons in Monolayers of Hexagonal Boron Nitride.
Phonon polaritons in van der Waals materials reveal significant confinement accompanied with long propagation length: important virtues for tasks pertaining to the control of light and energy flow at the nanoscale. While previous studies of phonon polaritons have relied on relatively thick samples, here reported is the first observation of surface phonon polaritons in single atomic layers and bilayers of hexagonal boron nitride (hBN). Using antenna-based near-field microscopy, propagating surface phonon polaritons in mono- and bilayer hBN microcrystals are imaged. Phonon polaritons in monolayer hBN are confined in a volume about one million times smaller than the free-space photons. Both the polariton dispersion and their wavelength-thickness scaling law are altered compared to those of hBN bulk counterparts. These changes are attributed to phonon hardening in monolayer-thick crystals. The data reported here have bearing on applications of polaritons in metasurfaces and ultrathin optical elements
Women with endometriosis have higher comorbidities: Analysis of domestic data in Taiwan
AbstractEndometriosis, defined by the presence of viable extrauterine endometrial glands and stroma, can grow or bleed cyclically, and possesses characteristics including a destructive, invasive, and metastatic nature. Since endometriosis may result in pelvic inflammation, adhesion, chronic pain, and infertility, and can progress to biologically malignant tumors, it is a long-term major health issue in women of reproductive age. In this review, we analyze the Taiwan domestic research addressing associations between endometriosis and other diseases. Concerning malignant tumors, we identified four studies on the links between endometriosis and ovarian cancer, one on breast cancer, two on endometrial cancer, one on colorectal cancer, and one on other malignancies, as well as one on associations between endometriosis and irritable bowel syndrome, one on links with migraine headache, three on links with pelvic inflammatory diseases, four on links with infertility, four on links with obesity, four on links with chronic liver disease, four on links with rheumatoid arthritis, four on links with chronic renal disease, five on links with diabetes mellitus, and five on links with cardiovascular diseases (hypertension, hyperlipidemia, etc.). The data available to date support that women with endometriosis might be at risk of some chronic illnesses and certain malignancies, although we consider the evidence for some comorbidities to be of low quality, for example, the association between colon cancer and adenomyosis/endometriosis. We still believe that the risk of comorbidity might be higher in women with endometriosis than that we supposed before. More research is needed to determine whether women with endometriosis are really at risk of these comorbidities