Thermodynamic Properties of a nano-gram NbN crystal by 3ω Method

Niobium nitride is a well-known superconductor, which has several structure phases, including cubic, hexagonal, and tetragonal. Among them, the cubic phase has been extensively studied, and shows a superconductivity transition temperature (T_C) in a wide range of T_C =9 ~ 17 K. In order to study the superconductivity of a single crystalline NbN, a NbN crystal with um size was selected from a commercial powder. The phase of selected crystals were confirmed by powder x-ray diffraction and electron backscatter diffraction (EBSD) analysis. In this work, crystals placed on a nanowire-device (ND) for studying its thermodynamic properties by 3ω method. The fabricated ND (30 μm × 600 nm × 100 nm) was carried out by means of thermal and sputtering deposition, and optical and e-beam lithography on a Si₃N₄/Si wafer. The chemical etching techniques followed up to realize the sagging of the ND from the membrane for thermal isolation. By 3w technique, the temperature dependent specific heat and thermal conductivity of a NbN crystal at low temperatures were investigated. The details will be discussed in the presentation.