Scientists discover zero-magnetic-field pair density wave in iron-based superconductor

Superconductivity, a phenomenon where electrons can flow through a material with zero resistance, holds great potential if a superconductor that operates at everyday temperatures and pressures can be discovered. However, current high-temperature superconductors still require extremely low temperatures to function effectively, limiting their practical applications.

Scientists face challenges in understanding superconductors due to their complex nature, with intertwined magnetic and electronic states. One such state is a pair density wave (PDW), an alternate form of superconductivity characterized by moving pairs of electrons. Until recently, PDWs were thought to only exist in the presence of a large magnetic field.

In a breakthrough study, researchers from Brookhaven National Laboratory, Columbia University, and Japan’s National Institute of Advanced Industrial Science and Technology observed a PDW in an iron-based superconductor without the need for a magnetic field. The findings, published in Nature, provide clear evidence of a zero-magnetic-field PDW and open new possibilities for superconductivity research.

The material under investigation, EuRbFe4As4 (Eu-1144), possesses both superconductivity and ferromagnetism, making it intriguing for the researchers. The study aimed to explore the connection between these two phenomena and determine if their coexistence was coincidental or related.

Using an advanced spectroscopic-imaging scanning tunneling microscope (SI-STM) at Brookhaven’s ultra-low vibration laboratory, the team investigated Eu-1144. The SI-STM measured electron tunneling between the sample’s surface and the microscope’s tip, creating a map of the crystal lattice and the number of electrons at different energies.

By increasing the temperature and passing through the critical points of magnetism and superconductivity, the researchers detected spatially modulated superconductivity associated with the appearance of magnetism. Below the critical superconducting temperature, the measurements revealed a gap in the electron energy spectrum, representing the energy required to break the electron pairs responsible for superconductivity. Modulations in the gap indicated oscillations in the electrons’ binding energies, providing direct evidence of a PDW.

The discovery opens up new research avenues, such as attempting to reproduce this phenomenon in other materials. Scientists can also explore indirect detection methods to observe the movement of electron pairs through signatures present in other material properties.

The team’s findings have garnered significant interest from collaborators, who plan to conduct further experiments using techniques like X-rays and muons to delve deeper into this material.

Overall, the study’s groundbreaking results offer promising prospects for understanding and harnessing the potential of PDWs and advancing the field of superconductivity.

Source: Brookhaven National Laboratory

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