Todd Holden

CONTACTLESS ELECTROREFLECTANCE STUDY OF A VERTICALLY COUPLED QUANTUM DOT-BASED INAS/GAAS LASER STRUCTURE

Contactless electroreflectance, at both 300 and 20 K, has been used to investigate a vertically coupled quantum dot (QD)-based InAs/GaAs laser structure. Signals have been observed from all the relevant portions of the sample including the QDs and wetting layer. The energies of the QD transitions provide evidence for both lateral as well as vertical coupling.

Moss–Burstein and plasma reflection characteristics of heavily doped n-type InxGa1−xAs and InPyAs1−y

Degenerately doped (>1019 cm−3) n-type InxGa1−xAs (x∼0.67) and InPyAs1−y (y∼0.65) possess a number of intriguing electrical and optical properties relevant to electro-optic devices and thermophotovoltaic devices in particular. Due to the low electron effective mass of these materials (m*<0.2) and the demonstrated ability to incorporate n-type dopants into the high 1019 cm−3 range, both the Moss–Burstein band gap shift and plasma reflection characteristics are particularly dramatic. For InGaAs films with a nominal undoped band gap of 0.6 eV and N=5×1019 cm−3, the fundamental absorption edge increased to 1.27 eV. InPAs films exhibit a shorter plasma wavelength (λp∼5 μm) in comparison to InGaAs films (λp∼6 μm) with similar doping concentrations. The behavior of the plasma wavelength and the fundamental absorption edge are investigated in terms of conduction band nonparabolicity and Γ-L valley separation using detailed band structure measurements and calculations.

Muon spin relaxation study of the magnetic penetration depth in MgB2

The magnetic vortex lattice (VL) of polycrystalline MgB 2 has been investigated by transverse-field muon spin relaxation (TF-μSR). The evolution of the TF-μSR depolarization rate σ, which is proportional to the second moment of the field distribution of the VL, has been studied as a function of temperature and applied magnetic field. The low-temperature value σ exhibits a pronounced peak near H e x t = 75 mT. This behavior is characteristic of strong-pinning-induced distortions of the VL which put into question the interpretation of the low-field TF-μSR data in terms of the magnetic penetration depth λ(T). An approximately constant value of σ, such as expected for an ideal VL in the London limit, is observed at higher fields of H e x t >0.4 T. The TF-μSR data at H e x t = 0.6 T are analyzed in terms of a two-gap model. We obtain values for the gap size of Δ 1 = 6.0(3) meV[2Δ 1 /k B T c = 3.6(2)], Δ 2 = 2.6(2) meV [2Δ 2 /k B T c = 1.6(1)], a comparable spectral weight of the two bands, and a zero-temperature value for the magnetic penetration depth of λ a b 100 nm. In addition, we performed μSR measurements in zero external field. We obtain evidence that the muon site (at low temperature) is located on a ring surrounding the center of the boron hexagon. Muon diffusion sets in already at rather low temperature of T>10 K. The nuclear magnetic moments can account for the observed relaxation rate and no evidence for electronic magnetic moments has been obtained.

In-plane polarized collective modes in detwinned YBa2Cu3O6.95 observed by spectral ellipsometry

Abstract The in-plane dielectric response of detwinned YBa 2 Cu 3 O 6.95 has been studied by far-infared ellipsometry. A surprisingly large number of in-plane polarized modes are observed. Some of them correspond to pure phonon modes. Others possess a large electronic contribution which strongly increases in the superconducting state. The free carrier response and the collective modes exhibit a pronounced a – b anisotropy. We discuss our results in terms of a charge density wave state in the 1-D CuO chains and induced charge density fluctuations within the 2-D CuO 2 planes.

c-axis lattice dynamics in Bi-based cuprate superconductors

We present the results of a systematic study of the c-axis lattice dynamics in single-layer

Josephson plasma resonance and phonon anomalies in trilayer Bi2Sr2Ca2Cu3O10.

{\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CuO}}_{6}

Reflection anisotropy spectroscopy study of the near surface electric field in low-temperature grown GaAs (001)

(Bi2201), bilayer

Correlation between the Josephson coupling energy and the condensation energy in bilayer cuprate superconductors

{\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}

Exploratory bioinformatics study of lncRNAs in Alzheimer's disease mRNA sequences with application to drug development.

(Bi2212), and trilayer

Far-infrared c -axis conductivity of flux-grown Y 1 − x Pr x Ba 2 Cu 3 O 7 single crystals studied by spectral ellipsometry

{\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{10}