Investigating Quantum Griffiths Singularity in 3D MoTiN Films

Quantum Griffiths singularity (QGS) has been observed in many two-dimensional (2D) superconducting systems and has gained significant interest in recent years. This phenomenon occurs when certain properties of a system behave unusually close to a critical point. In 2D superconductors, researchers noticed that the resistance of the material did not behave in a straightforward manner, crossing at various points instead of just one, which indicated QGS. While QGS has been identified in 3D magnetic materials, evidence of QGS in 3D superconductors is still lacking. This study aims to investigate whether QGS exists in 3D superconductors using MoTiN films.

#Background

MoTiN films are of particular interest because they have a specific structure that could exhibit QGS. Previous predictions suggested that these films might have a high superconducting transition temperature, but these temperatures have not been reached, possibly due to structural issues. Adding titanium to the molybdenum nitride helps stabilize the material. The goal here is to analyze a series of MoTiN films of varying compositions to probe their low-temperature electrical properties and check for the presence of QGS.

#Experimental Setup

The MoTiN films were created using a method called reactive magnetron sputtering on magnesium oxide (MgO) substrates. The films had a thickness of 80 nanometers and were made in an environment with specific gas ratios to control the nitrogen content. Several techniques were used to gather data on the films, including X-ray diffraction to check the structure, X-ray photoelectron spectroscopy to analyze composition, and various electrical measurements to explore their Resistivity and other properties under different Magnetic Fields.

#Film Structure and Composition

Data from the X-ray diffraction showed distinct patterns that indicated a successful formation of the MoTiN structure. The peaks represented the specific crystalline structure of the film, confirming it was indeed a face-centered cubic layout. The analysis of the film's atomic composition revealed a consistent ratio of molybdenum, titanium, and nitrogen across the different samples. Changes in the nitrogen content significantly affected the physical properties of the films, which is crucial for understanding how they behave in different conditions.

#Electrical Properties

The main focus of the study was the resistivity of the MoTiN films at low temperatures. As the temperature decreased, the resistivity of the films typically decreased until reaching the superconducting state. However, this drop varied based on the nitrogen content, with some films exhibiting Superconductivity more readily than others. This behavior was crucial for determining the films’ potential to show QGS.

#Quantum Phase Transition

A significant aspect of the research involved examining how applying a magnetic field influenced the superconductivity of the films. When a field was applied, the films transitioned from the superconducting state to a weakly disordered metallic state. This transition demonstrated the complex interplay between superconductivity and magnetic fields.

In some cases, the films displayed properties consistent with QGS, as the resistance behavior was not straightforward. Instead of crossing at a single critical point, the films’ resistance varied across a broader range of magnetic fields, suggesting the presence of QGS.

#Analysis of Quantum Griffiths Singularity

To further investigate the possibility of QGS, the low-temperature magnetoresistance characteristics of the films were closely analyzed. Results indicated that, when an appropriate magnetic field was applied, the resistance did not converge into a single point but spanned across multiple temperatures and fields. This behavior strongly suggested the occurrence of QGS in these films.

#Comparison with Theoretical Models

The theoretical models for understanding QGS in 2D systems helped frame the analysis of the 3D MoTiN films. The research found similarities between the observed behaviors and predictions from these models, which indicated that rare regions within the material contributed to the unusual electrical characteristics. The rare regions, thought to be caused by structural imperfections in the films, created a disordered superconducting state leading to QGS.

#Conclusion

The research provided compelling evidence supporting the existence of QGS in 3D MoTiN superconducting films. The electrical properties showed significant deviations from expected behavior as the films approached critical points under magnetic influence. The findings suggest that the presence of structural defects and variations in composition play crucial roles in the emergence of QGS. Overall, the results deepen the understanding of superconductivity in three-dimensional systems and present exciting possibilities for future research in condensed matter physics.

#Future Directions

Moving forward, further examinations into the properties of MoTiN films and similar materials could reveal more about superconductivity and phase transitions at the quantum level. Researchers may explore additional compositions and structures to see if different combinations yield stronger indications of QGS or other unique behaviors. The implications of these findings may extend beyond academic interest, potentially influencing the development of novel superconducting materials for practical applications.

#Summary

In summary, this investigation demonstrated that 3D MoTiN superconducting films exhibit behaviors consistent with quantum Griffiths singularity, providing a new perspective on superconductivity in three-dimensional materials. As research in this area progresses, the potential for discovering new phenomena and applications in superconducting technologies remains promising.