Here we report a novel nitridation technique for transforming niobium into hexagonal Nb 2 N which appears to be superconducting below 1K. The nitridation is achieved by high temperature annealing of Nb films grown on Si 3 N 4 /Si (100) substrate under high vacuum. The structural characterization directs the formation of a majority Nb 2 N phase while the morphology shows granular nature of the films. The temperature dependent resistance measurements reveal a wide metal-to-superconductor transition featuring two distinct transition regions. The region close to the normal state varies strongly with the film thickness, whereas, the second region in the vicinity of the superconducting state remains almost unaltered but exhibiting resistive tailing. The current-voltage characteristics also display wide transition embedded with intermediate resistive states originated by phase slip lines. The transition width in current and the number of resistive steps depend on film thickness and they both increase with decrease in thickness. The broadening in transition width is explained by progressive establishment of superconductivity through proximity coupled superconducting nano-grains while finite size effects and quantum fluctuation may lead to the resistive tailing. Finally, by comparing with Nb control samples, we emphasize that Nb 2 N offers unconventional superconductivity with promises in the field of phase slip based device applications.

The elemental Nb is mainly investigated for its eminent superconducting properties. In contrary, we report of a relatively unexplored property, namely, its superior optoelectronic property in reduced dimension. We demonstrate here that nanostructured Nb thin films (NNFs), under optical illumination, behave as room temperature photo-switches and exhibit bolometric features below its superconducting critical temperature. Both photo-switch and superconducting bolometric behavior are monitored by its resistance change with light in visible and near infrared (NIR) wavelength range. Unlike the conventional photodetectors, the NNF devices switch to higher resistive states with light and the corresponding resistivity change is studied with thickness and grain size variations. At low temperature in its superconducting state, the light exposure shifts the superconducting transition towards lower temperature. The room temperature photon sensing nature of the NNF is explained by the photon assisted electron-phonon scattering mechanism while the low temperature light response is mainly related to the heat generation which essentially changes the effective temperature for the device and the device is capable of sensing a temperature difference of few tens of milli-kelvins. The observed photo-response on the transport properties of NNFs can be very important for future superconducting photon detectors, bolometers and phase slip based device applications.The refractory metal Nb is famous for its superconducting properties and it is known to provide the highest critical temperature (T c ) (bulk T c = 9.2 K) for any elemental superconductor. Being one of the most used primary superconductors, Nb is well explored material in the field of superconducting photon detectors 1, 2 and bolometric applications 3 . Besides, it exhibits various physical properties like high melting point, high thermal conductivity, high critical current density etc 4 . Since decades, dimensional effects of niobium on its physical properties like critical temperature, superconducting energy gap, critical field, coherence length, penetration depth etc. have been explored. These properties vary with the dimension of niobium particles/grains and/or films 5 . It is well known that nanomaterials can exist as various nanostructures such as quantum dots, nanowires, nanoparticles, etc. which play key role in upgrading their optoelectronic properties, mainly controlled by the quantum effect, as compared to their bulk counterpart 6,7 . For example, granular Nb thin films have been shown to act like Josephson junctions 5,8 . During 1970's the effects of light on conventional superconductors have been explored intensely 9 . The effect of light and transient photo-response on oxide based high-T c superconductors have also garnered a reasonable attention in the field of superconductivity based optoelectronic applications 10 . Here, we explore optoelectronic properties of NNFs at room temperature (RT) and at low temperature (LT), above and below the T c . To the best of ou...

We report transport studies through Nb-based superconducting meander wires fabricated by focused ion beam milling technique. The effect of meandering on quantum transport has been probed experimentally by a direct comparison with the pristine thin-film device before meandering. The normal metal (NM) to superconductor (SC) phase transition becomes a wide and multi-step transition by meandering. Below the transition temperature (T c), the resistance-versus-temperature measurements reveal resistive tailing which is explained by the thermally activated phase slip (TAPS) mechanism. The TAPS fit indicates a selective region of the meander to be responsible for the resistive tailing. Besides, the phase slip (PS) mechanism in the meander is evident in its current–voltage characteristics that feature the stair-case type intermediate resistive steps (IRSs) during the SC–NM transition. The modulation of the IRSs is investigated with respect to temperature and external magnetic field. It is observed that the PS events are facilitated by magnetic fields up to about 250 mT. Further, the critical current varies strongly on the temperature and magnetic field for T < 0.5 T c and H ⩽ 100 mT where it fluctuates in an oscillatory manner. Finally, Nb based meander structures can be promising candidates for future PS based studies and applications.

Being one of the strongest materials, ternary TiSiN exhibits a very interesting family of binary transition metal nitride and silicide systems. A novel technique to fabricate morphologically fascinating nano and micro structures of TiSiN is reported here. The referred TiSiN films, majorly constituted with cubic TiN phase, are enriched with crystalline nanoparticles, microflowers and faceted micro-crystals which possess attractive functionalities towards plasmon mediated optoelectronic applications. Reactivity of titanium to silicon nitride based dielectric topping on the substrate at high temperature plays the key role in nitride formation for the demonstrated protocol. The optoelectronic response for these morphologically enriched composite films indicates an influential role of photo-induced surface plasmon polaritons (SPPs) on their dc transport properties. A plasmonically tuned resistive switching, controlled by the surface morphology in association with the film thickness, is observed under light illumination. Using Drude's modified frequency dependent bulk electron scattering rates and surface mediated SPPs-electron scattering rates, a generic model is proposed for addressing unambiguously the increased device resistance in response to light. The featured synthesis process opens a new direction towards the growth of transition metal nitrides while the proposed model serves as a basic platform to understand photo-induced electron scattering mechanisms in metal. annealing of Si/Ti/Si based thin film tri-layers on Si 3 N 4 /Si (100) substrate, one can successfully fabricate crystalline nanoparticles, faceted micro-crystals, and crystalline microflowers on Ti-Si-N based nanostructured composite film (NCF) which are predominantly occupied with cubic fcc-phased nano and micro structures of TiN, [1] Coupling with optical excitation in the visible and NIR wavelength range, the Ti-Si-N based NCFs having devices on top exhibit surface morphology dependent anomalous photo-response which shows switching to a highly resistive state.Recently, there are many reports of negative photoconductivity (NPC) observed in materials like semiconducting nanostructures, [25][26][27] topological insulators, [28] graphene based composite systems, [29][30][31] metallic nanostructures [32][33][34][35] etc. Trapping of photo-excited electrons by localized trapped states, [36] band gap opening, [28] e-SPPs scattering mechanisms [32] are commonly used to address the origin of the NPC. However, if a generic model were available to understand the origin of NPC particularly for metallic systems, the performance could be tuned in a preferable way by controlling the morphology. Considering the possible scattering mechanisms for the conduction electrons, we introduce a simple but competent model primarily constituted with frequency dependent bulk electron scattering rate and surface mediated scattering of electrons with photo-induced SPPs [32] . The observed NPC, controlled by the morphology induced SPPs and the film thickness, can be justified a...