Chenggang Zhuang

Ultrahigh current-carrying capability in clean MgB2 films

We have studied the current-carrying capability of high quality epitaxial MgB2 films synthesized using the hybrid physical-chemical vapor deposition technique by both transport measurement in nanobridge constrictions and magnetization measurement. An extremely high self-field critical current density Jc(0)>108A∕cm2, approaching the theoretical depairing current of MgB2, was observed on a 150nm bridge, indicating an excellent current-carrying capability in these films. The magnetization measurement also showed very high Jc.

Fully Band-Resolved Scattering Rate in MgB2 Revealed by the Nonlinear Hall Effect and Magnetoresistance Measurements

We have measured the normal state temperature dependence of the Hall effect and magnetoresistance in epitaxial MgB2 thin films with variable disorders characterized by the residual resistance ratio RRR ranging from 4.0 to 33.3. A strong nonlinearity of the Hall effect and magnetoresistance have been found in clean samples, and they decrease gradually with the increase of disorders or temperature. By fitting the data to the theoretical model based on the Boltzmann equation and ab initio calculations for a four-band system, for the first time, we derived the scattering rates of these four bands at different temperatures and magnitude of disorders. Our method provides a unique way to derive these important parameters in multiband systems.

Penetration depth of MgB2 measured using Josephson junctions and SQUIDs

The penetration depth of MgB2 was measured using two methods of different mechanisms. The first method used MgB2 Josephson junctions and the magnetic field dependence of the junction critical current. The second method deduced the penetration depth from the inductance of a MgB2 microstrip used to modulate the voltage of a MgB2 DC SQUID. The two methods showed a consistent value of the low-temperature penetration depth for MgB2 to be about 40 nm. Both the small penetration depth value and its temperature dependence are in agreement with a microscopic theory for MgB2 in the clean limit.

Surface morphology and thickness dependence of the properties of MgB2 thin films by hybrid physical–chemical vapor deposition

The influence of growth parameters in hybrid physical?chemical vapor deposition (HPCVD) on surface morphologies of MgB2 thin films, and the dependence of their properties on film thickness are systematically studied. As the HPCVD MgB2 films grow in the Volmer?Weber mode, where islands coalesce into continuous films, the grain size has an important influence on the film morphology. We found that films deposited with higher growth rates have larger grains, and a larger grain size appears to correspond to a larger film roughness. Under optimized deposition conditions, the surface root mean square (RMS) roughness is 1.2?nm over a 1??m ? 1??m area for a 100?nm thick film. The surface morphology does not directly affect the structural and superconducting properties of the MgB2 films. The results of ultrathin MgB2 films, as thin as 10?nm, with excellent superconducting properties are also presented in this paper.

A comparative study of the dendritic avalanche in MgB2 thin films synthesized by pulsed laser deposition and hybrid physical chemical vapor deposition methods

It is known that MgB2 thin films synthesized by using hybrid physical chemical vapor deposition (HPCVD) do not show dendritic avalanche, which is in contrast to those prepared by using pulsed laser deposition (PLD). To find the cause that makes the difference between the two cases, we studied the microscopic film structure by the scanning electron microscopy and the magnetic hysteresis by using the superconducting quantum interference device magnetometry. The critical current density (Jc), estimated from the magnetic hysteresis based on the Bean’s critical-state model, shows a much higher Jc in the PLD film than in a HPCVD film. This indicates higher vortex pinning in the PLD film. We surmise that high local joule heating beyond the high Jc in the PLD film, as a vortex penetrates into the superconducting thin film, gives a path for the next vortex and induces a positive feedback effect that is absent in the HPCVD film.

Influence of intrinsic electronic properties on light transmission through subwavelength holes on gold and MgB2 thin films

We show how intrinsic material properties modify light transmission through subwavelength hole arrays on thin metallic films in the THz regime. We compare the temperature-dependent transmittance of Au films and MgB

Upper critical field and Raman spectra of MgB2 thin films irradiated with low energy oxygen ion

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MgB2 thin films by hybrid physical–chemical vapor deposition

films. The experimental data are consistent with analytical calculations and are attributed to the temperature change of the conductivity of both films. The transmission versus conductivity is interpreted within the open resonator model when taking the skin depth into consideration. We also show that the efficiency of this temperature control depends on the ratio of the transmission peak frequency to the superconducting energy gap in MgB

Clean MgB2 thin films on different types of single-crystal substrate fabricated by hybrid physical–chemical vapor deposition

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Fully Band Resolved Scattering Rate in MgB2 Revealed by Nonlinear Hall Effect and Magnetoresistance

films.