Superconducting properties of V/Fe superlattices

We report measurements on the superconducting properties of V/Fe superlattices with various layer thicknesses. These samples were prepared with a novel UHV evaporator which can produce up to twenty different samples in the same run. The Fe layer, a strong pair breaker, suppresses the superconducting transition temperature in a systematic way. When the V layer thickness is on the order of the BCS coherence length and the Fe layer is only a few atomic planes thick, a 2D–3D crossover has been observed in the temperature dependence of the parallel upper critical field H_C2∥. This implies the coexistence of superconductivity and ferromagnetismm. We observe three dimensional behavior for thinner Fe layers (～1 atomic plane) and two dimensional behavior for thicker Fe layers (greater than 10 atomic planes).     

Structural and thermoelectric properties in (Sb<Subscript>1-x</Subscript>Bi<Subscript>x</Subscript>)<Subscript>2</Subscript>Te<Subscript>3</Subscript> thin films

We have investigated the structural and thermoelectric properties of (Sb_1-xBi_x)₂Te₃ thin films on CdTe(111)B. Analysis of X-ray diffraction patterns (–2 scans and rocking curves) of the films shows that they are of high quality and that they are well aligned with their (00.1) axis normal to the substrates. Measurements of the temperature-dependent thermoelectric power, resistivity, and Hall coefficient of the films were performed with respect to the binary composition, x. For the samples in the range 0.2<x<0.3, the room-temperature thermopower values were in the range 159–184 V/K, the room-temperature carrier concentrations were 3.93–5.13×10¹⁹ cm^-3, and the room-temperature mobilities were 24.6–64.0 cm²V^-1s^-1. PACS 72.20.Pa; 72.80.Jc; 73.6l.Le     

Polarity inversion in polar-nonpolar-polar heterostructures

We have observed an epilayer-thickness-dependent polarity inversion for the growth of CdTe on Sb(Bi)/CdTe(111)B. For films with Sb(Bi) thicknesses of less than 40 A (15 A), the CdTe layer shows a B (Te-terminated) face, but it switches to an A (Cd-terminated) face for thicker layers. On the other hand, a CdTe layer grown on Bi(Sb)/CdTe(111)A always shows the A face regardless of Sb or Bi layer thicknesses. In order to address the observations we have performed ab initio calculations, which suggest that the polarity of a polar material on a nonpolar one results from the binding energy difference between the two possible surface configurations.     

Band structure observed in the current-voltage characteristics of SINININIS-type junctions

Band structure in the conductivity of 4-barrier Nb/Al-AlO_x-Al-AlO_x-Al-AlO_x-Al-AlO_x-Nb (SINININIS) tunnel junctions is observed at low temperatures. This structure is explained in terms of the interference of quasiparticle waves in a periodic barrier.     

Long-range surface plasmon polaritons propagating on a dielectric waveguide support

In the traditional long-range surface plasmon geometry, an ultrathin metal film is sandwiched between two layers having identical dielectric constants. Here we demonstrate the long-range surface plasmon polariton (LRSPP) properties for a new structure where a thin layer with a dielectric constant exceeding that of the surroundings is inserted within the sandwich, provided the layer thickness d satisfies the condition k(⊥)d=mπ where k(⊥) is the component of the guide wavevector perpendicular to the layer and m is an integer. The resulting plasmon modes have smaller losses and nearly the same phase velocity as the original LRSPP. This provides a strategy to support silver films having thicknesses of 10's of nanometers to create plasmonic devices for sensor applications.     

X-ray reflectivity study on gold films during sputter deposition

We performed in-situ X-ray reflectivity measurements of gold films during sputter deposition on polished silicon substrates. The measurements were performed at several substrate temperatures and under two argon pressures. The gold surfaces were also examined by scanning tunneling microscopy after deposition to obtain their real-space topographic images. These images were used to complement the X-ray reflectivity measurements in determining the effect of argon pressure on the gold surface and its height-height difference functions. An approximation for height-height difference functions was employed to analyze the X-ray reflectivity data. The measured interface width during growth followed a simple power law, consistent with recent theoretical results of dynamic scaling behavior. The scaling exponents, however, do not agree well with predictions based on some models in 2 + 1 dimensions.     

Experimental magnetic form factor of platinum metal

The induced magnetic form factor of paramagnetic platinum was measured in an external field of 73 kOe at a temperature of 78 K. The data obtained for the six innermost Bragg reflections show that the spherically average magnetization density is in excellent agreement with that calculated by Watson-Yang. Freeman and Koelling. The result confirms the reliability of the present day band calculations, as well as assuring that the nontrivial orbital contribution to the form factor (g = 2.61) has been handled properly. The asphericity of the magnetization was more poorly determined, yielding at t_2g population of 70 ± 17%, to be compared with a calculated value of 93%. An attempt at a more direct determination of the role of the orbital contribution is described.     

Nonresonant two-photon generation of excitonic matter in a CuCl pellet

A pressed CuCl pellet is optically excited at 2 K using an excitation energy in the range from 1892 to 2843 meV, which is far below the bandgap. The steady-state population dynamics unambiguously indicates an unusual two-photon generation of ground-state excitons. At high-excitation levels, the observed spectra exhibit rich spectral features arising from electron-hole plasma and electron-hole droplets formation. This nonresonant two-photon excitation is presumably assisted by impurity bands due to grain boundaries and surfaces in this random semiconductor.