Tag: superconductors

Cu2Ge: A New 2D Topological Semimetal

Cu2Ge: A New 2D Topological Semimetal

Members of the “Spectroscopy of Novel Quantum States” team from the Paris Institute of Nanosciences, Sorbonne University, came to the URANOS beamline (synchrotron Solaris) to study the electronic properties of a recently synthetized material: Cu2Ge which is a so-called “nodal line” topological semi-metal. More generally, their scientific objectives are focused on understanding the electronic and magnetic properties of low-dimensional systems such as superconductors, topological and magnetic materials, or Mott insulators.

Among various metal/semiconductor systems, copper/germanium alloys have been studied since the 1990s to understand the formation mechanisms of Schottky barriers, fundamental to diodes of the same name. This Cu2Ge system has attracted renewed interest due to recent predictions of density functional theory (DFT) calculations. Indeed, these calculations predict that the 2D alloy Cu2Ge has a band structure with a 1D intersection of valence and conduction bands, characteristic of a topological semimetal with a Dirac nodal line. In this work, we have experimentally demonstrated for the first time that it is possible to synthesize Cu2Ge on a surface of a copper crystal and that its electronic structure exhibits the expected characteristics of the purely 2D case. Its properties make this alloy a promising candidate for high-frequency electronic applications and an ideal system for studying exotic properties that can emerge in nodal line materials.
Two-dimensional materials are widely studied for their exceptional properties, which allow for potential applications in various fields such as photovoltaics, catalysis, microelectronics, and biomedicine. Additionally, some of these 2D systems exhibit topological properties, further increasing the possibility of discovering new electronic behaviors without a bulk equivalent. Such is the case for Cu2Ge, an alloy consisting of an atomic plane of copper and germanium. Although Cu/Ge alloys were studied several decades ago for Schottky barrier formation, more recent DFT calculations shed new light on these systems. They reveal that, in the case of a 2D Cu2Ge layer, the band structure should exhibit cones intersecting along two closed loops. These “loops” are known as Dirac lines. When these lines are close to the Fermi level, the material noteworthy properties: the potential for higher carrier densities than graphene while maintaining very high carrier velocity.

Read more on SOLARIS website

Unveiling finer details in the physics of materials

Unveiling finer details in the physics of materials

Scientists at the European XFEL’s SCS instrument routinely use a technique called transient X-ray absorption spectroscopy (XAS) to investigate materials that have applications in data storage and processing, catalysis, or in the search for room temperature superconductors. Investigating very small changes in the motion of electrons within a material’s structure on ultrashort timescales provides scientists with fingerprints of the complex processes at play within them. This helps them characterise samples that are important for energy and materials research.

Using the European XFEL’s brilliant pulses, researchers can overcome some of the issues of conventional transient XAS—such as long measurement times—but the varying intensity of European XFEL’s pulses provides its own challenges. Now, scientists at SCS have implemented a new sampling scheme for improving the efficiency of such measurements.

Read more on the European XFEL website

Image: The X-ray beam is split into three copies. Two of these copies are passed through identical samples of the material under investigation, with one of these samples also being illuminated by a laser (‘optical laser’ in the figure). This transforms it into a new state, interesting to researchers. From this, scientists are able to ‘subtract’ detrimental noise, revealing the finest details of the sample under investigation.