Ballistic effects in a proximity induced superconducting diffusive metal

Using a Scanning Tunneling Microscope (STM), we investigate the Local Density of States (LDOS) of artificially fabricated normal metal nano-structures in contact with a superconductor. Very low temperature local spectroscopic measurements (100 mK) reveal the presence of well defined subgap peaks at energy |E|<Delta in the LDOS at various positions of the STM tip. Although no clear correlations between the LDOS and the shape of the samples have emerged, some of the peak features suggest they originate from quasi-particle bound states within the normal metal structures (De Gennes St James states). Refocusing of electronic trajectories induced by the granular srtucture of the samples can explain the observation of spatially uncorrelated interference effects in a non-ballistic medium.Comment: 4 pages, 4 figure

Superconducting properties of very high quality NbN thin films grown by high temperature chemical vapor deposition

Niobium nitride (NbN) is widely used in high-frequency superconducting electronics circuits because it has one of the highest superconducting transition temperatures ($T_c$ $\sim$ 16.5 K) and largest gap among conventional superconductors. In its thin-film form, the $T_c$ of NbN is very sensitive to growth conditions and it still remains a challenge to grow NbN thin film (below 50 nm) with high $T_c$. Here, we report on the superconducting properties of NbN thin films grown by high-temperature chemical vapor deposition (HTCVD). Transport measurements reveal significantly lower disorder than previously reported, characterized by a Ioffe-Regel ($k_F$$\ell$) parameter of $\sim$ 14. Accordingly we observe $T_c$ $\sim$ 17.06 K (point of 50% of normal state resistance), the highest value reported so far for films of thickness below 50 nm, indicating that HTCVD could be particularly useful for growing high quality NbN thin films

Low-temperature transport in highly boron-doped nanocrystalline diamond

International audienceWe studied the transport properties of highly boron-doped nanocrystalline diamond thin films at temperatures down to 50 mK. The system undergoes a doping-induced metal-insulator transition with an interplay between intergranular conductance g and intragranular conductance g0, as expected for a granular system. The conduction mechanism in the case of the low-conductivity films close to the metal-insulator transition has a temperature dependence similar to Efros-Shklovskii type of hopping. On the metallic side of the transition, in the normal state, a logarithmic temperature dependence of the conductivity is observed, as expected for a metallic granular system. Metallic samples far away from the transition show similarities to heavily borondoped single-crystal diamond. Close to the transition, the behavior is richer. Global phase coherence leads in both cases to superconductivity also checked by ac susceptibility , but a peak in the low-temperature magnetoresistance measurements occurs for samples close to the transition. Corrections to the conductance according to superconducting fluctuations account for this negative magnetoresistance

Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition

Scanning tunneling spectroscopy at very low temperature on homogeneously disordered superconducting Titanium Nitride thin films reveals strong spatial inhomogeneities of the superconducting gap $\Delta$ in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature $T_c$ towards zero, enhancement of spatial fluctuations in $\Delta$, and growth of the $\Delta/T_c$ ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition.Comment: 4 pages, 3 figures. Minor changes. Accepted for publication in Phys. Rev. Let

Chest Wall Resection for Adult Soft Tissue Sarcomas and Chondrosarcomas: Analysis of Prognostic Factors

Background: Wide resection with tumor-free margins is necessary in soft-tissue sarcomas to minimize local recurrence and to contribute to long-term survival. Information about treatment outcome and prognostic factors of adult sarcoma requiring chest wall resection (CWR) is limited. Methods: Sixty consecutive patients were retrospectively studied for overall survival (OS), local recurrence-free survival (LRFS), and disease-free survival (DFS). Twenty-one prognostic factors regarding survival were analyzed by univariate analysis using the Kaplan-Meier method and the log-rank test. Results: With a median survival of 2.5 years, the OS was 46% (33%) at 5 (10) years. The LRFS was 64% at 5 and 10 years, and the DFS was 30% and 25% at 5 and 10 years. At the end of the study period, 26 patients (43%) were alive, of which 20 patients (33%) had no evidence of disease and 40 patients (67%) had no chest wall recurrence. In the group of 9 patients with a radiation-induced soft-tissue sarcoma, the median survival was 8 months. Favorable outcome in univariate analysis in OS and LRFS applied for the low-grade sarcoma, bone invasion, and sternal resection. For OS only, age below 60 years and no radiotherapy were significant factors contributing to an improved survival. CWR was considered radical (R0) at the pathological examination in 43 patients. There were 52 patients with an uneventful recovery. There was one postoperative death. Conclusions: CWR for soft-tissue sarcoma is a safe surgical procedure with low morbidity and a mortality rate of less than 1%. With proper patient selection acceptable survival can be reached in a large group of patients. Care must be given to patients with radiation-induced soft-tissue sarcoma who have a significantly worse prognosis