Various single-crystal growth techniques have been presented for the unconventional superconductor UTe₂. The molten salt flux liquid transport (MSFLT) method is employed to grow high-quality and large single crystals, exhibiting a high residual resistivity ratio (RRR ∼ 200–800). However, the Te self-flux and chemical vapor transport (CVT) methods produce samples of lower quality. The MSFLT method is a hybrid approach combining the molten salt flux (MSF) and CVT methods. One significant advantage is that the materials gradually crystallize at a relatively low temperature, which is maintained throughout the main process. This may be crucial for preventing U deficiency and obtaining high-quality large single crystals of UTe₂. Many different single crystals obtained using different techniques have been characterized by resistivity and specific heat measurements. The superconducting transition temperature T_c decreases with residual resistivity ρ₀, followed by the Abrikosov–Gor’kov pair-breaking theory, and reaches 2.1 K for ρ₀ → 0. The residual γ-value of the specific heat for the highest quality sample was only 3% of the normal-state γ-value. The specific heat jump, ΔC_e/(γT_c) reached approximately 2.7 for high-quality samples, indicating a strong-coupling superconductor. Furthermore, the magnetic susceptibility for H || a-axis in a high-quality single crystal does not show an up-turn behavior on cooling, which is consistent with the results of NMR Knight shift and μSR experiments.

中文翻译：

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超净单晶UTe2的熔盐助熔剂液体传输方法

_{已经针对非常规超导体UTe 2}提出了各种单晶生长技术。采用熔盐熔剂液体传输（MSFLT）方法生长高质量和大的单晶，表现出高残余电阻率比（RRR∼200-800）。然而，Te 自通量和化学气相传输 (CVT) 方法产生的样品质量较低。MSFLT 方法是熔盐通量 (MSF) 和 CVT 方法相结合的混合方法。一个显着的优点是材料在整个主要过程中保持相对较低的温度下逐渐结晶。_{这对于防止U缺乏和获得高质量的大UTe 2}单晶可能至关重要。使用不同技术获得的许多不同的单晶已通过电阻率和比热测量进行了表征。超导转变温度T _c随着残余电阻率ρ ₀降低，遵循 Abrikosov-Gor'kov 断对理论，当ρ ₀ → 0 时，超导转变温度 T c 达到 2.1 K。最高质量样品的比热的残余γ值仅为正常状态γ值的3%。对于高质量样品，比热跃变ΔC e _/ ( γT _c )达到约2.7，表明强耦合超导体。此外， H ||的磁化率 高质量单晶中的a轴在冷却时没有表现出上转行为，这与 NMR Knight 位移和μ SR 实验的结果一致。