Vortex Glass Transition in a MgB₂ Film at High Magnetic Fields

Vortex Glass Transition in a MgB₂ Film at High Magnetic Fields
MgB₂膜の高磁場中におけるボルテックスグラス転移

The vortex glass transitions in a c-axis oriented MgB₂ film with H_c2^//c(0) exceeding 20 T, prepared by rf-sputtering methods, have been investigated using the transport measurements. The scaling analyses of I-V characteristics based on the vortex glass theory reveal that the observed vortex glass transitions have a universal nature in the wide range of mixed state down to 2 K and up to 17.5 T, with critical exponents, n and z, independent of magnetic field. It is also found that the glass transition line T_g(H) shows a tendency to approach H_c2^//c(0) with decreasing temperature, indicating the quantum vortex liquid phase does not exit, or is in practically narrow region around T = 0.

Center for Low Temp. Sci., Tohoku University: T. Nojima, H. Nagano
IMR, Tohoku University: T. Nishizaki, N. Kobayashi

Reference: T. Nojima, H. Nagano, S. Takeuchi, H. Aoki, T. Nishizaki, N. Kobayashi,
“Vortex glass transition in a MgB₂ film under high magnetic fields”, to be published.

H_c2^//c(0)が20 Tを越えるMgB₂のスパッタc軸配向膜におけるVortex glass（VG）転移を輸送特性により測定した．2Kまでの低温，17.5Tまでの強磁場といったほとんどすべての混合状態において，一定の静的・動的臨界指数nとzを持つI-V特性のVGスケーリング則が観測され，この系においてのVG転移は混合状態の全領域でユニバーサルな性質をもつことがわかった．またT→0の極限でグラス転移線は上部臨界磁場と一致する傾向にあり，磁束系の量子液体相はほとんど存在しないこともわかった．

東北大学極低温科学センター：野島　勉，永野広志
東北大学金属材料研究所：西嵜照和，小林典男