We investigate the upper critical field in a dirty two-band superconductor within quasiclassical Usadel equations. The regime of very high anisotropy in the quasi-2D band, relevant for MgB2, is considered. We show that strong disparities in pairing interactions and diffusion constant anisotropies for two bands influence the in-plane Hc2 in a different way at high and low temperatures. This caus...

Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series o...

Desorption and subsequent rehydrogenation of Mg(BH4)2 with and without 5 mol % TiF3 and ScCl3 have been investigated. Temperature programmed desorption (TPD) experiments revealed a significant increase in the rate of desorption as well as the weight percentage of hydrogen released with additives upon heating to 300 °C. Stable Mg(BxHy)n intermediates were formed at 300 °C, whereas MgB2 was the m...

We have studied temperature evolution of the local as well as the average crystal structure of MgB2 using real-space atomic pair distribution function (PDF) measured by high resolution neutron powder diffraction in a wide temperature range of T = 10–600 K. We find small positive correlation factors for the B–B and B–Mg pairs, determined by mean-square displacements (MSD) and the mean-square rel...

The transformation of zero-field-cooled (ZFC) magnetization curves of PLD MgB2 films annealed in situ for different dwell times and at different temperatures is studied within the context of structural analysis. The PLD films were deposited using an off-axis geometry followed by two series of annealing conditions: the dwell time series and the annealing temperature series. ZFC magnetization cur...

We report a large normal-state magnetoresistance with temperature-dependent anisotropy in very clean epitaxial MgB2 thin films (residual resistivity much smaller than 1 microOmega cm) grown by hybrid physical-chemical vapor deposition. The magnetoresistance shows a complex dependence on the orientation of the applied magnetic field, with a large magnetoresistance (Delta(rho)/(rho)0=136%) observ...

In this paper we compare the performance of MgB2 Hot-Electron Bolometer Mixers operating at Local Oscillator frequencies of 0.6 THz and 1.63 THz. The minimum noise temperatures that were obtained are 700 K and 1150 K for 0.6 THz and 1.63THz respectively. The receiver noise bandwidth is of the order of 2.2-3GHz for 10nm thick HEB devices with a Tc of 8.5K. Sub-micrometer size HEBs were also fabr...

MgB2 superconducting bulk materials have excellent potential for various applications. In this review, the characteristics and challenges of as a material, recent research trends, such synthesis dense bulks using high pressure process, atmospheric process liquid gas diffusion, are introduced.

The temperature dependence of the real part of the microwave complex conductivity at 17.9 GHz obtained from surface impedance measurements of two c-axis oriented MgB2 thin films reveals a pronounced maximum at a temperature around 0.6 times the critical temperature. Calculations in the frame of a two-band model based on Bardeen-Cooper-Schrieffer (BCS) theory suggest that this maximum correspond...

Superconducting transition temperatures (Tc’s) of MgB2, Mg1−xCaxB2, Mg1−xNaxB2, and Mg1−xAlxB2 are studied within the McMillan approximation using electronic and structural information obtained from density functional theory within the generalized gradient approximation. The density of states and Tc of MgB2 are both shown to be extremely sensitive to volume; in fact the density of states around...