We investigated the thermodynamic property of the heavy fermion superconductor UTe$_2$ in pulsed high magnetic fields. The superconducting transition in zero field was observed at $T_{\rm c}$=1.65 K as a sharp heat capacity jump. Magnetocaloric effect measurements in pulsed-magnetic fields obviously detected a thermodynamic anomaly accompanied by a first-order metamagnetic transition at $μ$$_{0}$$H_{\rm m}$=36.0 T when the fields are applied nearly along the hard-magnetization $b$-axis. From the results of heat capacity measurements in magnetic fields, we found a drastic diverging electronic heat capacity coefficient of the normal state $γ$$_{\rm N}$ with approaching $H_{\rm m}$. Comparing with the previous works via the magnetic Clausius-Clapeyron relation, we unveil the thermodynamic details of the metamagnetic transition. The enhancement of the effective mass observed as the development of $γ_{\rm N}$ indicates that quantum fluctuation strongly evolves around $H_{\rm m}$; it assists the superconductivity emerging even in extremely high fields.
Metamagnetism in UTe2: the roles of itinerancy and localization
Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室）；Department of Physics, University of Wisconsin-Madison（威斯康星大学麦迪逊分校物理系）；National High Magnetic Field Laboratory（国家高磁场实验室）；Department of Physics, Washington University in St. Louis（圣路易斯华盛顿大学物理系）；School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院）；Department of Physics, Clarendon Laboratory, University of Oxford（牛津大学克拉伦登实验室物理系）；Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所凝聚态物理国家实验室）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Hochfeld-Magnetlabor Dresden (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf（德累斯顿强磁实验室（HLD-EMFL），德累斯顿-罗斯多夫亥姆霍兹中心）；Charles University, Faculty of Mathematics and Physics（查理大学数学与物理学院）
Different metamagnetism between paramagnetic Ce and Yb isomorphs
为了解决重费米子系统中的变磁现象之谜，我们比较了顺磁同质结构Ce和Yb系统，CeNi $_2$ Ge $_2$和YbNi $_2$ Ge $_2$，它们都位于磁不稳定性附近。最有趣的结果是在脉冲磁场中的磁化测量发现了两个系统中的变磁性转变。这是Ce和Yb类质同象顺磁系统的变磁性的首次观测。类似于其他的变磁体，两种化合物的变磁性转变场都很好地由温度$T_χ^{\rm max}$来缩放，在该温度下磁化率显示出最大值。此外，CeNi $_2$ Ge $_2$的非线性磁化率$χ_3$的峰值出现在$T_χ^{\rm max}/2$附近，与其它重费米子超磁体一样。相反，YbNi $_2$ Ge $_2$在$T_χ^{\rm max}$处仅显示$χ_3$的符号变化，如在位于铁磁临界点附近的巡游变磁体中所观察到的。CeNi $_2$ Ge $_2$的变磁性对应于典型的近藤晶格系统，而YbNi $_2$ Ge $_2$的变磁性类似于近铁磁巡游系统。本文还讨论了YbNi $_2$ Ge $_2$变磁行为的其它可能性。
Metamagnetic ripples in the UTe2 high magnetic field phase diagram
Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室）；Wuhan National High Magnetic Field Center（武汉国家强磁场中心）；University of Wisconsin-Madison（威斯康星大学麦迪逊分校）；National High Magnetic Field Laboratory（国家高磁场实验室）；Washington University in St. Louis（圣路易斯华盛顿大学）；Charles University（查理大学）
High-field metamagnetism in the antiferromagnet CeRh$_2$Si$_2$
本文研究了反铁磁体CeRh $_2$ Si $_2$在高达50特斯拉的脉冲磁场中的转矩、磁致伸缩和输运以及在高达13特斯拉的静磁场中的热膨胀。从这些测量中推导出CeRh $_2$ Si $_2$的磁场-温度相图，其中磁场沿易磁化轴$\mathbf{c}$施加。二级相变温度$T_{N}$和一级相变温度$T_{1,2}$（零场时分别为~36 K和26 K）随电场的增加而降低。场致反铁磁-顺磁边界线$H_c$在1.5 K时为26 T，从低温时的一阶变为高温时的二阶。磁场-温度相图被发现是由（至少）三个不同的反铁磁相。它们被一阶谱线$H_{1,2}$和$H_{2,3}$分开，前者对应于H=0时的$T_{1,2}$，后者在1.5 K时等于25.5 T。的最大值的$T^2$ -系数$A$的电阻率观察在发病的高场极化制度，这被解释为一个增强的有效质量的签名在场诱导的量子不稳定性。将CeRh $_2$ Si $_2$中$A$系数的磁场依赖性与其压力依赖性进行了比较，并与原型重费米子系统CeRu $_2$ Si $_2$中$A$的场依赖性进行了比较。
Strange metallicity encompasses high magnetic field-induced superconductivity in UTe2
Charles University, Faculty of Mathematics and Physics（查理大学数学物理学院）；Hochfeld-Magnetlabor Dresden (HLD-EMFL), Helmholtz-Zentrum Dresden-Rossendorf（德累斯顿强磁场实验室（HLD-EMFL），德累斯顿罗森多夫亥姆霍兹中心）；Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室）
