The unique optical properties of metals are at the core of many areas of research and applications, including plasmonics, metamaterials, superlensing and subdiffraction focusing, optical antennas and ...surface enhanced Raman scattering. One important length scale inherent in metamaterials and plasmonics research activities in the microwave, terahertz, infrared, visible and ultraviolet ranges is the skin depth of metal, which remains at the submicrometre level throughout the broad spectral range. One prominent question is whether terahertz electromagnetic waves can be controlled on the nanoscale to achieve new functionalities in the sub-skin-depth regime. Here, we show that a λ/30,000 slit on metal film acts as a nanogap-capacitor charged by light-induced currents, enhancing the electric field by orders of magnitudes.
We fabricated large arrays of suspended, single-layer graphene membrane resonators using chemical vapor deposition (CVD) growth followed by patterning and transfer. We measure the resonators using ...both optical and electrical actuation and detection techniques. We find that the resonators can be modeled as flat membranes under tension, and that clamping the membranes on all sides improves agreement with our model and reduces the variation in frequency between identical resonators. The resonance frequency is tunable with both electrostatic gate voltage and temperature, and quality factors improve dramatically with cooling, reaching values up to 9000 at 10 K. These measurements show that it is possible to produce large arrays of CVD-grown graphene resonators with reproducible properties and the same excellent electrical and mechanical properties previously reported for exfoliated graphene.
With only a few exceptions that are well understood, conventional superconductivity does not coexist with long-range magnetic order (for example, ref. 1). Unconventional superconductivity, on the ...other hand, develops near a phase boundary separating magnetically ordered and magnetically disordered phases. A maximum in the superconducting transition temperature T(c) develops where this boundary extrapolates to zero Kelvin, suggesting that fluctuations associated with this magnetic quantum-critical point are essential for unconventional superconductivity. Invariably, though, unconventional superconductivity masks the magnetic phase boundary when T < T(c), preventing proof of a magnetic quantum-critical point. Here we report specific-heat measurements of the pressure-tuned unconventional superconductor CeRhIn5 in which we find a line of quantum-phase transitions induced inside the superconducting state by an applied magnetic field. This quantum-critical line separates a phase of coexisting antiferromagnetism and superconductivity from a purely unconventional superconducting phase, and terminates at a quantum tetracritical point where the magnetic field completely suppresses superconductivity. The T --> 0 K magnetic field-pressure phase diagram of CeRhIn5 is well described with a theoretical model developed to explain field-induced magnetism in the high-T(c) copper oxides, but in which a clear delineation of quantum-phase boundaries has not been possible. These experiments establish a common relationship among hidden magnetism, quantum criticality and unconventional superconductivity in copper oxides and heavy-electron systems such as CeRhIn5.
Conventional, thermally driven continuous phase transitions are described by universal critical behavior that is independent of the specific microscopic details of a material. However, many current ...studies focus on materials that exhibit quantum-driven continuous phase transitions (quantum critical points, or QCPs) at absolute zero temperature. The classification of such QCPs and the question of whether they show universal behavior remain open issues. Here we report measurements of heat capacity and de Haas-van Alphen (dHvA) oscillations at low temperatures across a field-induced antiferromagnetic QCP (Bc0 ≈ 50 T) in the heavy-fermion metal CeRhIn5. A sharp, magnetic-field-induced change in Fermi surface is detected both in the dHvA effect and Hall resistivity at B0* ≈ 30 T, well inside the antiferromagnetic phase. Comparisons with band-structure calculations and properties of isostructural CeCoIn5 suggest that the Fermi-surface change at B0* is associated with a localized-to-itinerant transition of the Ce-4f electrons in CeRhIn5. Taken in conjunction with pressure experiments, our results demonstrate that at least two distinct classes of QCP are observable in CeRhIn5, a significant step toward the derivation of a universal phase diagram for QCPs.
The behaviour of nanoscale optical devices in a variety of burgeoning research areas, such as photonic crystals, near-field microscopy, surface plasmonics and negative index of refraction materials, ...is governed by strongly localized electromagnetic waves. Although such light waves are analogous to the localized electronic wavefunctions that determine the properties of solid-state quantum devices, unlike matter waves, these optical fields are vectorial in nature, and their orientation and magnitude vary on a subwavelength scale. In order to obtain a complete description of light in nanoscale devices, it is therefore crucial to be able to map the field vectors with subwavelength resolution. Thus far, local field vectors have mostly been studied by theoretical means. Here, we describe and demonstrate the first experimental mapping of vector fields of light on the nanoscale. By directly accessing the local field in its entirety, new capabilities and applications in nanophotonics may emerge.
We report spatial domain measurements of the damping of surface-plasmon excitations in metal films with periodic nanohole arrays. The measurements reveal a short coherent propagation length of a few ...microm inside nanohole arrays, consistent with delays of about 10 fs in ultrafast transmission experiments. This implies that the transmission spectra of the entire plasmonic band-gap structure are homogeneously broadened by radiative damping of surface-plasmon excitations. We show that a Rayleigh-like scattering of surface plasmons by the periodic hole array is the microscopic origin of this damping, allowing the reradiation rate to be controlled.
The Asian ginseng root (Panax ginseng C.A. Meyer) is a very commonly used herbal medicine worldwide. Ginseng fruit, including the berry (or pulp) and seed, is also valuable for several health ...conditions including immunostimulation and cancer chemoprevention. In this study, the anticancer and anti-proliferative effects of the extracts of ginseng berry and seed were evaluated. The ginsenosides in the ginseng berry concentrate (GBC) and ginseng seed extract (GSE) were analyzed. We then evaluated their anti-colorectal cancer potentials, including antiproliferation, cell cycle arrest, and apoptotic induction. Further investigation consisted of the berry's adaptive immune responses, such as the actions on the differentiation of T helper cells Treg, Th1, and Th17. The major constituents in GBC were ginsenosides Re and Rd, which can be compared to those in the root. The GBC significantly inhibited colon cancer cell growth, and its anti-proliferative effect involved mechanisms including G2/M cell cycle arrest via upregulation of cyclin A and induction of apoptosis via regulation of apoptotic related gene expressions. GBC also downregulated the expressions of pro-inflammatory cytokine genes. For the adaptive immune responses, GBC did not influence Th1 and Treg cell differentiation but significantly inhibited Th17 cell differentiation and thus regulated the balance of Th17/Treg for adaptive immunity. Although no ginsenoside was detected in the GSE, interestingly, it obviously enhanced colon cancer cell proliferation with the underlined details to be determined. Our results suggested that GBC is a promising dietary supplement for cancer chemoprevention and immunomodulation.
Spinal arteriovenous shunts below the conus constitute 3 types of lesions, which have previously been mainly described in case reports, given their rarity, and are sometimes misdiagnosed. The purpose ...of this study was to describe the features of each type and compare these types as to epidemiologic features, clinical and radiologic presentations, treatment, and outcomes in a consecutive series of 48 cases.
The prospectively collected data bases of 2 referral centers for spinal vascular lesions were retrospectively reviewed. Spinal arteriovenous shunts below the conus were defined as all dural and intradural shunts below the conus medullaris. Clinical features, radiologic findings, treatment results, and clinical outcomes were assessed.
There were filum terminale arteriovenous fistulas in 11 patients (22.9%), radicular arteriovenous shunts in 7 patients (14.6%), and spinal dural arteriovenous fistulas in 30 patients (62.5%). Radicular arteriovenous shunts presented at a younger age (
= .017) and with a higher incidence of back pain symptoms (
= .037). A tethered spinal cord was found in 54.5% of patients with filum terminale arteriovenous fistulas and 23.3% of patients with spinal dural arteriovenous fistulas. After treatment, the angiographic complete obliteration rate was 89.4% and spinal function was improved significantly (
< .001).
Three groups of spinal arteriovenous shunts below the conus can be differentiated according to clinical and radiologic features. Filum terminale arteriovenous fistulas are frequently associated with dysraphic malformations, which may suggest a particular embryologic origin.
We present 2D measurements of the full THz electric field behind a sample consisting of multiple slits in a metal foil. Our measurements, which have a sub-wavelength spatial, and a sub-period ...temporal resolution, reveal electric field lines, electric field vortices and saddle points. From our measurements we are able to reconstruct the magnetic field and, finally, the position and time-dependent Poynting vector which shows the flow of energy behind the sample. Our results show that it is possible to study the flow of light near sub-wavelength plasmonic structures such as slit-arrays and, by implication, other metamaterial samples.
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