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Pressure dependence of upper critical fields in FeSe single crystals
Kang, Ji-Hoon,Jung, Soon-Gil,Lee, Sangyun,Park, Eunsung,Lin, Jiunn-Yuan,Chareev, Dmitriy A,Vasiliev, Alexander N,Park, Tuson IOP 2016 Superconductor science & technology Vol.29 No.3
<P>We investigate the pressure dependence of the upper critical fields (<I>μ</I> <SUB>0</SUB> <I>H</I> <SUB>c2</SUB>) for FeSe single crystals with pressure up to 2.57 GPa. The superconducting (SC) properties show a disparate behavior across a critical pressure where the pressure-induced antiferromagnetic phase coexists with superconductivity. The magnetoresistance for <I>H</I>//<I>ab</I> and <I>H</I>//<I>c</I> is very different: for <I>H</I>//<I>c</I>, magnetic field induces and enhances a hump in the resistivity close to the <I>T</I> <SUB>c</SUB> for pressures higher than 1.2 GPa, while it is absent for <I>H</I>//<I>ab</I>. Since the measured <I>μ</I> <SUB>0</SUB> <I>H</I> <SUB>c2</SUB> for FeSe samples is smaller than the orbital limited upper critical field <img ALIGN='MIDDLE' ALT='$({{{H}}^{{\rm{orb}}}}_{{\rm{c}}2})$' SRC='http://ej.iop.org/images/0953-2048/29/3/035007/sustaa1185ieqn1.gif'/> estimated by the Werthamer, Helfand and Hohenberg model, the Maki parameter (<I>α</I>) related to Pauli spin-paramagnetic effects is additionally considered to describe the temperature dependence of <I>μ</I> <SUB>0</SUB> <I>H</I> <SUB>c2</SUB>(<I>T</I>). Interestingly, the <I>α</I> value is hardly affected by pressure for <I>H</I>//<I>ab</I>, while it strongly increases with pressure for <I>H</I>//<I>c</I>. The pressure evolution of the <I>μ</I> <SUB>0</SUB> <I>H</I> <SUB>c2</SUB>(0) for the FeSe single crystals is found to be almost similar to that of <I>T</I> <SUB>c</SUB>(<I>P</I>), suggesting that the pressure-induced magnetic order adversely affects the upper critical fields as well as the SC transition temperature.</P>