具有极小超流密度的凝聚体的通用热力学——应用于UTe$_2$与隐藏的第二相变
Generic thermodynamics of condensates with extremely small superfluid density ---Application to UTe$_2$ and hidden second phase transition---
- Department of Physics, Ritsumeikan University（立命馆大学）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
针对UTe$_2$实验发现，本文通过热力学分析识别隐藏超导相$A_2$，揭示其在不同磁场方向的重现及水平相变线，并基于非幺正自旋三重态配对对称性统一描述$H$-$T$-$P$相图。
AI中文摘要：
受近期UTe$_2$核磁共振和比热实验发现的启发，我们在理论上探索了具有小超流密度的凝聚体的热力学特征，并表征了其物理性质。我们识别出在UTe$_2$常压下较低温度（$T$）和磁场（$H$）区域由自旋向上库珀对组成的隐藏超导相$A_2$，并表明$A_2$在三个主磁场方向（$a$、$b$和$c$轴）的较高$H$下重新出现。在$H$-$T$平面上，从具有自旋向下对的$A_1$相到$A_2$相的相变线均呈水平走向，这暗示了一个普遍的物理起源，即随着磁场增加，自旋向上配对态获得磁能增益。该多相图被推广到压力（$P$）条件下，基于非幺正自旋三重态配对对称性$^3B_{3u}$得到了一个简明的图像，使我们能够一致地捕捉整个$H$-$T$-$P$相空间中超导相的演化。
英文摘要：
Motivated by recent experimental findings on UTe$_2$ via NMR and specific heat experiments, we theoretically explore the thermodynamic signatures of condensates with small superfluid density and characterize their physical properties. We identify the hidden superconducting phase $A_2$ composed of spin-up Cooper pairs at lower temperature ($T$) and field ($H$) under ambient pressure of UTe$_2$ and show that $A_2$ reappears at higher $H$ for all three principal field directions, $a$, $b$, and $c$-axis. The phase transition lines from the $A_1$ phase with spin down pairs to the $A_2$ phase in the $H$-$T$ plane are all horizontal in common, implying a universal physical origin due to the originating from the magnetic-energy gain of the spin-up pairing state with increasing magnetic field. This multiple-phase diagram is extended to these under pressure ($P$), resulting in a simple picture based on non-unitary spin-triplet pairing symmetry $^3B_{3u}$, which enables us to consistently capture the evolution of the superconducting phases throughout the entire $H$-$T$-$P$ phase space.
