No abstract

High-temperature superconductivity (HTSC) mysteriously emerges upon doping holes 1 or electrons 2 into insulating copper oxides with antiferromagnetic (AFM) order. It has been thought that the large energy scale of magnetic excitations, compared to phonon energies for example, lies at the heart of an electronically-driven superconducting phase with high transition temperatures (T c ) 3-5 . Comparison of high-energy magnetic excitations of hole-and electron-doped superconductors in connection with the respective T c provides an exceptional, yet un-capitalized opportunity to test this hypothesis 6-9 . Here, we use resonant inelastic x-ray scattering (RIXS) at the Cu L 3 -edge 10,11 to reveal high-energy collective excitations in the archetypical electron-doped cuprate Nd 2-x Ce x CuO 4 (NCCO) 2 . Surprisingly, despite the fact that the AFM correlations are short-ranged 12 , magnetic excitations harden significantly across the AFM-HTSC phase boundary, in stark contrast with the hole-doped cuprates 6,7 . Furthermore, we find an unexpected and highly dispersive branch of collective modes in superconducting NCCO that are absent in hole-doped compounds. These modes emanate from zone center and weaken with increasing temperature, which signal a quantum phase distinct from superconductivity. The asymmetry uncovered between electron-and hole-doped cuprates provides new, unexpected dimensions to collective excitations that are generally important to the mechanism of superconductivity in these materials. Hole-doped cuprates display compelling evidence for the surprising persistence of magnetic excitations beyond the AFM phase boundary 6,7 , as well as the existence of symmetrybroken phases, such as charge density waves 13,14,15 and orbital loop currents 16 , distinct from superconductivity. Whether these are universal and exist on the other side of the cuprate phase diagram, i.e. with electron-doping, remains an important open question. To address this issue,

We experimentally demonstrate a visible light communication (VLC) system based on a single commercially available RGB-type LED. High spectrally efficient carrierless amplitude and phase (CAP) modulation and orthogonal frequency-division multiplexing (OFDM) are adopted in the intensity-modulation and direct-detection VLC system of limited bandwidth. In order to achieve higher capacity of the uneven-frequency-response LEDbased VLC system, OFDM signals are combined with the bit-and power-loading techniques, and CAP signals of various modulation are pre-emphasized to modulate one of the RGB chips. To reach the BER of less than 10 À3 , CAP and OFDM signals demonstrate the maximum data rates of 1.32 and 1.08 Gb/s, respectively, employing the blue chip. In addition to spectrally efficient formats, the wavelength-division-multiplexing (WDM) scheme is applied to further increase the capacity. After individually optimizing RGB chips, the maximum aggregate data rates of CAP and OFDM are 3.22 and 2.93 Gb/s, respectively, in our RGB-LED-based WDM VLC system. Hence, compared with OFDM, the CAP scheme shows competitive performance and provides an alternative spectrally efficient modulation for next generation optical wireless networks.

The strong association of both the mild and severe types of allopurinol cADRs with the HLA-B*58:01 allele were observed. The results indicated that the prospective use of a genetic test of HLA-B*58:01 might reduce the prevalence of allopurinol-induced cADRs. Original submitted 7 March 2012; Revision submitted 21 May 2012.