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Magnetic Susceptibility in 2D Superconductor NaxHfNCl System
Authors:Shin-Ichi Shamoto  Keigo Iizawa  Yusuke Asano  Kenji Ohoyama  Tsuyoshi Kajitani
Institution:1. Department of Applied Physics, Faculty of Engineering , Tohoku University , Sendai , 980-8579 , JAPAN;2. Institute for Materials Research, Tohoku University , Sendai , 980-8577 , JAPAN
Abstract:Abstract

Superconducting critical temperature, Tc and the shielding volume fraction, SVF, of layered nitride superconductor NaxHfNCl have been studied as a function of x, i.e. Na concentration. Although Tc decreases gradually with increasing x from 20.0 K at x=0.11 to 16.5 K at x=0.85, SVF has a sharp peak around x=1/6, where strong coupling between local ordering of Na atoms and Fermi surface instability can be expected. Structural disorder in the samples above x=0.5, observed by powder neutron diffraction, does not affect the superconductivity appreciably. Electronic specific heat coefficient, γ, is estimated to be about 7.7 mJ/mol/K2 by its difference of magnetic susceptibility between HfNCl and Na0.5HfNCl. The γ value is relatively small compared with the high Tc value, revealing double honeycomb lattice system as new potential higher Tc superconductor series by intercalation.
Keywords:2D superconductor  NaxHfNCl  magnetic susceptibility  volume fraction  neutron diffraction  Fermi surface nesting
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