G. T. Liu

Experimental demonstration of illusion optics with “external cloaking” effects

A metamaterial “illusion optics” with “complementary medium” and “restoring medium” is designed by using inductor-capacitor (L-C) network medium. The unprecedented effects of “external cloaking” and “transforming one object to appear as another” are demonstrated experimentally. We also demonstrate that the non-resonant nature of the L-C network decreases the sensitivity of the “external cloaking” effect to the variation of the frequency and results in an acceptable bandwidth of the whole device.

Metamagnetic Transition in Na~0~.~8~5CoO~2 Single Crystals

We report the magnetization, specific heat, and transport measurements of a high quality Na(0.85)CoO2 single crystal in applied magnetic fields up to 14 T. At high temperatures, the system is in a paramagnetic phase. It undergoes a magnetic phase transition below approximately 20 K. For the field H||c, the measurement data of magnetization, specific heat, and magnetoresistance reveal a metamagnetic transition from an antiferromagnetic state to a quasiferromagnetic state at about 8 T at low temperatures. However, no transition is observed in the magnetization measurements up to 14 T for H perpendicular c. The low temperature magnetic phase diagram of Na(0.85)CoO2 is determined.

Anisotropic magnetoresistance in charge-ordered Na-0.34(H3O)(0.15)CoO2: Strong spin-charge coupling and spin ordering

We use near-field scanning optical microscopy (NSOM) operating in collection mode to map the optical field distribution of continuous wave infrared light propagating along an air-bridged W3 silicon photonic crystal (PC) slab multimode waveguide in a subwavelength resolution. The detected near-field optical intensity distribution patterns show very different longitudinal propagation features and transverse field profiles at different wavelength ranges. We have analyzed the dispersion of the guided modes in the PC waveguide and the corresponding eigenfield profile for each guided mode by means of the three-dimensional plane-wave expansion simulations. It is found that the experimentally observed complex while interesting near-field pattern features can be well explained by the field profiles of the multiple waveguide modes and their superposition at different excitation wavelengths. The detection and analysis of this multimode PC slab waveguide via NSOM could help us to understand complex wave propagation behavior and to further design novel PC devices.

Thermal hysteresis and anisotropy in the magnetoresistance of antiferromagnetic Nd2-xCexCuO4

The out-of-plane resistivity (rho(c)) and magnetoresistivity (MR) are studied in antiferromangetic (AF) Nd2-xCexCuO4 single crystals, which have three types of noncollinear antiferromangetic spin structures. The apparent signatures are observed in rho(c)(T) measured at the zero-field and 14 T at the spin structure transitions, giving a definite evidence for the itinerant electrons directly coupled to the localized spins. One of the striking features is an anisotropy of the MR with a fourfold symmetry upon rotating the external field (B) within ab plane in the different phases, while twofold symmetry at spin reorientation transition temperatures. The intriguing thermal hysteresis in rho(c)(T,B) and magnetic hysteresis in MR are observed at spin reorientation transition temperatures.

Doping effects on the two-dimensional spin dimer compound SrCu2(BO3)(2)

A series of compounds M0.1Sr0.9Cu2(BO3)(2) with Sr substituted by M=Al, La, Na, and Y and YxSr1-xCu2(BO3)(2) with x=0.06, 0.08, 0.10, 0.20, and 0.30 were prepared by solid state reaction. X-ray diffraction analysis showed that these doping compounds are isostructural to SrCu2(BO3)(2). The resistivity at room temperature, the magnetic susceptibility from 1.9 to 300 K in an applied magnetic field of 1.0 T and the specific heat from 1.9 to 25 K in applied fields up to 14 T were measured, respectively. The spin gap is deduced from the low temperature susceptibility as well as the specific heat. It is found that the spin gap is strongly suppressed by magnetic fields and the doping content. No superconductivity is observed in all doping samples.

Experimental verification of field rotating with invisibility by full tensor transmission-line metamaterials

We demonstrate the experimental realization of a field rotator based on transmission line (TL) networks. The anisotropic and non-diagonal medium parameters of the field rotator are controlled by the coupling between the different branches of tensor TL metamaterials. Taking advantages of full parameters realization, the effect of field rotating companied with invisibility is verified. The non-resonant property of the TL structure also leads to a relatively broad bandwidth of the field rotation function, which is quantitatively evaluated based on our experimental results.

Optical properties ofMgCNi3in the normal state

We present the optical reflectance and conductivity spectra for non-oxide antiperovskite superconductor

Electromagnetic complementary media with arbitrary geometries and non-conformal boundaries

MgCNi_{3}

Angular-dependent magnetoresistance oscillations in Na0.48CoO2 single crystals

at different temperatures. The reflectance drops gradually over a large energy scale up to 33,000 cm

Evidence of s-wave pairing symmetry in the layered superconductor Li0.68NbO2 from specific heat measurements

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