Vortex Glass Transition in a MgB2 Film at High Magnetic Fields

The vortex glass transitions in a c-axis oriented MgB2 film with Hc2//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 Tg(H) shows a tendency to approach Hc2//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.

Hc2//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nz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