Thermal Study of phase transition for π-d organic conductor under pressure

Many materials in organic conductor undergo low dimensional characteristic phase transitions，for example， CDW， SDW, spin-Peierls, some magnetic ordering，superconductivity and so on with strong electron-electron interaction.我们有开发specificheat measurement system in the wide temperature range between 5k and 300k for the sample with theweight of 0.3mg with relative accuracy of 0.1% to quantitatively discuss the above phasetransitions.我们succeeded in the measurements of 1st order phase transition in the cooling andheating processes by a method based on DTA (Differential Thermal Analysis). We summarized followingresults.1. (DMe-DCNQI)_2Cu system Deuterium degrees of freedom in methyl basis：Specific heat measurements are system performed for the systems having various methyl basesof ch_3, ch_2d, chd2_and cd_3 . In these systems，我们发现了anomalous specific heat due to deuterium degrees of freedom.我们系统clarified the specific heat of selectiv…More ely deuterated methyl bases in the (DMe-DCNQI)_2Cu system. Under equilibrium condition，这些系统不显示sharp peak induced by the phase transitionbut exhibit the Schottky type specific heat in the systems having ch_2d and chd_2 bases. Theirenergy schemes are determined only by the deuterium atom in the methyl bases.2. Anew type phase transition for the system of et_2 me_2 Sb[Pd(dmit)_2]_2：In this transition，Pd(dmit)^2. having localized magnetic moments s=1/2 change into neutral Pd(dmit)_2^0. and divalentPd(dmit)_2 -spin-less states. We have studied the thermal properties of this system and observed abroad hump above critical temperature as well as the sharp peak with small hysteresis in the典型的phase transition. Resulting total entropy absorbed around the transition Resultingreaches to 13j /molK，这是最重要的价值，在组织系统exhibiting charge ordering transitions. We found thatspin freedom and lattice modulation cooperatively drive这些新类型的phase transition.3Mysterious metal-insulator transition induced by a charge ordering for θ-(BEDT-TTF)_2RbZn(SCN)_4：这些anomalies at the phase transition have large temperature hysteresis and show different shapesof the peak，huge和sharp peak in heating process and broad hump in cooling process.我们观察anomalousspecific heat caused by this phase transition and discussed quantitatively degrees of freedomthis transition. Less

Many materials in organic conductor undergo low dimensional characteristic phase transitions, for example, CDW, SDW, spin-Peierls, some magnetic ordering, superconductivity and so on with strong electron-electron interaction. We have developed specific heat measurement system in the wide temperature range between 5K and 300K for the sample with the weight of 0.3mg with relative accuracy of 0.1% to quantitatively discuss the above phase transitions. We succeeded in the measurements of 1st order phase transition in the cooling and heating processes by a method based on DTA (Differential Thermal Analysis). We summarized following results.1. (DMe-DCNQI)_2Cu system・Deuterium degrees of freedom in methyl basis: Specific heat measurements are systematically performed for the systems having various methyl bases of CH_3, CH_2D, CHD2_and CD_3. In these systems, we discovered the anomalous specific heat due to deuterium degrees of freedom. We systematically clarified the specific heat of selectiv … More ely deuterated methyl bases in the (DMe-DCNQI)_2Cu system. Under equilibrium condition, these systems do not show the sharp peak induced by the phase transition, but exhibit the Schottky type specific heat in the systems having CH_2D and CHD_2 bases. Their energy schemes are determined only by the position of the deuterium atom in the methyl bases.2. A new type phase transition for the system of Et_2Me_2Sb[Pd(dmit)_2]_2: In this transition, Pd(dmit)^2. having localized magnetic moments s=1/2 change into neutral Pd(dmit)_2^0. and divalent Pd(dmit)_2^2-spin-less states. We have studied the thermal properties of this system and observed a broad hump above critical temperature as well as the sharp peak with small hysteresis in the vicinity of the phase transition. Resulting total entropy absorbed around the transition region reaches to 13J/molK, which is largest value in the organic systems exhibiting charge ordering transitions. We found that spin freedom and lattice modulation cooperatively drive these new type phase transition.3. Mysterious metal-insulator transition induced by a charge ordering for θ-(BEDT-TTF)_2RbZn(SCN)_4: These anomalies at the phase transition have large temperature hysteresis and show different shapes of the peak, huge and sharp peak in heating process and broad hump in cooling process. We observed anomalous specific heat caused by this phase transition and discussed quantitatively degrees of freedom of this transition. Less