Quasiparticle dispersion in Bi2Sr2CaCu2O8 is investigated with improved angular resolution as a function of temperature and doping. Unlike the linear dispersion predicted by the band calculation, the data show a sharp break in dispersion at 50+/-15 meV binding energy where the velocity changes by a factor of 2 or more. This change provides an energy scale in the quasiparticle self-energy. This break in dispersion is evident at and away from the d-wave node line, but the magnitude of the dispersion change decreases with temperature and with increasing doping.

Tensile deformation behavior of silicon ͑Si͒ wires with nanometer widths, synthesized by nanometer-tip contact and successive retraction, was studied by atomistic combined microscopy of high-resolution transmission electron microscopy/scanning probe microscopy. The elastic limit, Young's modulus, and strength of individual Si nanowires were investigated based on the mechanics of materials at an atomic scale. It was found that both Young's modulus and strength increased to 18± 2 and 5.0± 0.3 GPa, respectively. The elastic limit was 0.10± 0.02 and fracture strain was estimated to be 0.30± 0.01. Experimental results show that mechanical properties of Si wires transform due to size reduction from micrometer to nanometer scale.

No abstract

No abstract

Strong, monochromatic, coherent and continuous terahertz (THz) radiation was generated from the intrinsic Josephson junctions in a cylindrical stand-alone mesa sandwich structure fabricated from a single crystal of the high-temperature superconductor Bi2Sr2CaCu2O8+δ. By varying the base temperature and the dc bias current-voltage characteristic (IVC) points, the emission frequency is tunable from 0.5 to a record high 2.4 THz observed on two inner IVC branch points. Strong emission power peaks were observed at 1.0 THz and 1.6 THz. This device is hence an excellent candidate to fill the “THz gap” between ∼1.4 and 2.0 THz.

Shubnikov de Haas(SdH) oscillations have been measured for the semiconducting single domain SrTiO3 with Carrier concentration of 3.4×1018 cm-3 and 5.9×1018 cm-3. From the temperature dependence of the SdH amplitude, the cyclotron mass values are determined for the [001] and [110] magnetic field directions. We have found, from the angular dependence of the SdH oscillation, that there exist several branches of the frequencies among which the highest and lowest branches originate from the Fermi spheres at the Brillouin zone center, and the other ones from the extremal area which is interconnected through the magnetic breakdown tunneling paths. Energy band parameters based on the k p perturbation method are determined.

To obtain higher power P and frequency f emissions from the intrinsic Josephson junctions in a high-Tc superconducting Bi2Sr2CaCu2O8+δ single crystal, we embedded a rectangular stand-alone mesa of that material in a sandwich structure to allow for efficient heat exhaust. By varying the current-voltage (I-V) bias conditions and the bath temperature Tb, f is tunable from 0.3 to 1.6 THz. The maximum P of a few tens of μW, an order of magnitude greater than from previous devices, was found at Tb∼55 K on an inner I-V branch at the TM(1,0) cavity resonance mode frequency. The highest f of 1.6 THz was found at Tb=10 K on an inner I–V branch, but away from cavity resonance frequencies. A possible explanation is presented.

We report angle-resolved photoemission spectra both above and below T c in the single-plane cuprate superconductor Bi 2 Sr 22x La x CuO 61d . The superconducting state measurements show a highly anisotropic excitation gap with a maximum magnitude smaller than that of the bilayer compound Bi 2 Sr 2 CaCu 2 O 8 by a factor of 3. For a range of doping, the gap persists well above T c , behavior previously associated with underdoped bilayer cuprates. The anisotropy and magnitude of the normalstate gap are very similar to the superconducting state gap, indicating that the two gaps may have a common origin in a pairing interaction.[S0031-9007(97) A central issue in the physics of high-T c superconductivity is the role of coupling between the two-dimensional copper-oxygen planes in producing superconductivity. The T c of these materials tends to increase with the number of layers per unit cell. It is currently an open question whether the superconducting state order parameter symmetry will be the same in one-layer and the more strongly coupled two-layer compounds. Angle-resolved photoemission spectroscopy (ARPES) has the potential to resolve this issue since it is able to measure directly the anisotropy of the superconducting state gap (the magnitude of the order parameter). In the two-plane material Bi 2 Sr 2 -CaCu 2 O 81d (Bi2212), the gap was found by ARPES to be highly anisotropic and consistent with a d x 2 2y 2 order parameter [1,2]. We report measurements of the one-plane material Bi2201 that show a similarly large anisotropy with a smaller overall gap magnitude.In underdoped Bi2212, ARPES measurements have shown that the anisotropic gap persists well above T c [3,4], consistent with many other experiments that have shown a pseudogap or spin gap in the normal state of cuprate superconductors [5]. Current evidence for the normalstate gap in one-plane materials is much weaker than in two-plane materials, and its existence is controversial [6]. Our results show a clear normal-state gap up to high temperatures in optimally doped and underdoped Bi2201, but not in overdoped Bi2201.Single crystal samples of Bi 21x Sr 22͑x1y͒ La y CuO 61d were grown using a floating zone method, and for comparison by a self-flux method. X-ray scattering confirms that the crystals are single-phase Bi2201, and electron-probe microanalysis was used to measure the atomic ratios of the cations. Substitution of trivalent La or Bi for divalent Sr reduces the hole concentration in the CuO 2 planes. The effect of La doping goes beyond changing the carrier density [7], however, and raises the maximum T c from 10 to 30 K.A roughly parabolic dependence of T c on ͑x 1 y͒ has been observed [8]. Our optimally doped crystals (T c 29 K) come from substituting La 0.35 for Sr. With no La substitution, Bi͞Sr ratios of 2.3͞1.7 and 2.1͞1.9 give the underdoped samples with T c , 4 K and the overdoped samples with T c 8 K, respectively. The transition temperatures were taken as the zero resistance values and confirmed by SQUID magnetization measurements. The tr...