Search for the thermodynamic anomaly at extremely low temperatures in the carrier-doped organic superconductors using a microchip calorimeter

在本项目中，我们的目标是设计用于测量有机超导体小单晶热容的量热计。在研究的前半部分，我们搭建了在15T以下磁场下可用的量热计，然后测量了给体和阴离子比例为非化学计量比的有机盐样品。首先，我们研究了(MDT-TSF)(AuI_2)_&lt；0.436&GT；(T_c=4.3K)，在3.8K左右观察到一个广泛的极大值。虽然峰本身展宽，但观察到高达6T的磁场依赖关系，这与磁行为和输运行为是一致的。由于施主层和阴离子层之间的非公度关系，施主层中的电子感觉到一种无规电势，在这种盐中似乎发生了本征的峰展宽效应。还研究了κ-(BEDT-TTf)_4Hg_&lt；2.89&GT；Br8的热容。除了作为超导转变峰展宽的非公度效应外，我们还观察到电子热容系数提高到50Mjk^&lt；-2；mol^&lt；-1。还观察到了超导转变温度附近热容异常随冷却速度的急剧变化。通过该项目开发的技术也适用于其他通常以小晶体形式产生的分子材料。

In this project, we aim at designing calorimeter for measuring heat capacities of small single crystals of organic superconductors. In the former half of the research period, we constructed calorimeter available under magnetic fields up to 15T, and then we measured the samples of organic salts of which donor and anion ratio is non-stoichiometric.At first, we studied (MDT-TSF)(AuI_2)_<0.436> (T_c=4.3K) and observed a broad maximum at about 3.8K. Although the peak itself is broadened, the magnetic field dependence was observed up to 6T which is consistent with the magnetic and transport behaviors. Since the incommensurate relation between donor layers and anion layers, the electrons in the donor layers feels a kind of random potential and intrinsic peak-broadening effect seems to be occurring in this salt. The heat capacity of κ-(BEDT-TTF)_4Hg_<2.89>Br_8 is also studied. In addition to the incommensurate effect appears as a peak-broadening of the superconductive transitions, we have observed that the electronic heat capacity coefficient is enhanced up to the 50 mJK^<-2>mol^<-1>. The drastic cooling rate dependence of heat capacity anomalies around the superconductive transition temperature is also observed.The technique developed through this project is available to the other molecular materials which usually yielded as a small pieces of crystals.