物理学报2025，Vol.74Issue(8)：194-206,13.DOI:10.7498/aps.74.20241778
新型非常规超导体UTe2的单晶生长方法研究进展
Advances in single crystal growth methods for novel unconventional superconductor UTe2
摘要
Abstract
Heavy fermion compound UTe2,as a recently discovered unconventional superconductor,has received significant attention due to its potential spin-triplet superconducting pairing,high-field re-entrant superconducting phases,and unique quantum critical characteristics.However,experimental results of this system show significant changes and discrepancies,primarily due to difference in sample quality.The key unresolved issues include whether the system exhibits multi-component superconducting order parameters,whether time-reversal symmetry is spontaneously broken,and whether multiple field-induced superconducting phases share a common origin.These unsolved issues hinder an in-depth understanding of the intrinsic superconducting pairing mechanism in the UTe2 system. This paper reviews recent advances in single-crystal growth methods for UTe2,including chemical vapor transport(CVT),Te-flux,molten salt flux(MSF),and molten salt flux liquid transport(MSFLT).We systematically analyze how growth conditions influence superconductivity and crystal quality.Although the CVT method was initially employed in UTe2 studies,the samples grown by this method exhibit poor quality and significant compositional inhomogeneity,even in individual samples.Consequently,the CVT method has been progressively supplanted by the recently developed MSF method.In contrast,the MSF method and MSFLT method yield high-quality UTe2 single crystals with Tc achieving a value as high as 2.1 K and residual resistivity ratio(RRR)reaching up to 1000;however,the sample sizes are smaller than those grown by the CVT and Te-flux methods.Notably,MSF-grown samples occasionally contain magnetic impurities such as U7Te12,so careful screening is required in the sample collection process.The MSFLT combines the advantages of CVT and MSF methods to grow high-quality UTe2 single crystals while producing larger sample sizes than MSF.Our research findings highlight the importance of optimizing growth parameters such as Te/U ratio,temperature gradient,and cooling rate.For instance,lower growth temperature and precise control of the Te/U ratio can significantly enhance Tc and sample quality.Several controversies have been identified regarding high-quality MSF and MSFLT samples,including clarifying the single-component nature of the superconducting order parameter and confirming the absence of time-reversal symmetry breaking in optimized samples. This review underscores the pivotal role of advanced single-crystal growth techniques in advancing the study of UTe2.Future research should focus on utilizing these high-quality UTe2 samples grown by MSF and MSFLT methods to accurately determine superconducting order parameters,elucidate mechanisms behind high-field re-entrant superconducting phases,and explore topological properties,such as potential Majorana fermions.These efforts will deepen our understanding of unconventional superconductivity,spin fluctuations,and quantum critical phenomena in the UTe2 system.关键词
二碲化铀/非常规超导电性/化学气相输运法/熔盐助熔剂法Key words
UTe2/unconventional superconductivity/chemical vapor transport method/molten salt flux method引用本文复制引用
薛子威,袁登鹏,谭世勇..新型非常规超导体UTe2的单晶生长方法研究进展[J].物理学报,2025,74(8):194-206,13.基金项目
国家自然科学基金联合基金(批准号:U23A20580)和四川省自然科学基金杰出青年科学基金(批准号:2025NSFJQ0040)资助的课题. Project supported by the Joint Funds of the National Natural Science Foundation of China(Grant No.U23A20580)and the Sichuan Provincial Natural Science Foundation for Distinguished Young Scholars,China(Grant No.2025NSFJQ0040). （批准号:U23A20580）
