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

本项目旨在设计一种用于测量有机超导体小单晶热容的量热计。在前半部分的研究中，我们制作了磁场强度可达15 T的量热计，并对非化学计量比的有机盐样品进行了测量，首先研究了（MDT-TSF）（AuI_2）_<0.436>（T_c=4.3K），在3.8K附近观察到一个宽的极大值。虽然峰本身被加宽，但观察到高达6 T的磁场依赖性，这与磁性和输运行为一致。由于施主层和阴离子层之间的不相称关系，施主层中的电子感受到一种随机势，在这种盐中似乎发生了本征峰展宽效应。本文还研究了κ-（BEDT-TTF）_4Hg_Br_8的热容<2.89>。除了无公度效应表现为峰加宽的电子跃迁外，我们还观察到电子热容系数提高到50 mJ·K·<-2>mol·L-1<-1>。通过该项目开发的技术也适用于其他通常以小块晶体形式产出的分子材料。

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.