A small crystal of the niobium and germanium superconductor is mounted on a device to examine the behavior of the new electron-phonon liquid. The inset shows the atomic arrangement of the material. Image: Fazel Tafti, Boston College.A team of researchers from Boston College has created a new metallic superconducting specimen where the motion of electrons flows in the same way as water flows in a pipe, switching from particle-like to fluid-like dynamics. The team reports it findings in a paper in Nature Communications.
Led by Fazel Tafti, assistant professor of physics at Boston College, the team found that a strong interaction between electrons and phonons in a novel superconductor made from niobium and germanium (NbGe2) alters the transport of electrons from a diffusive, or particle-like, regime to a hydrodynamic, or fluid-like, regime. These findings mark the first discovery of an electron-phonon liquid inside NbGe2.
“We wanted to test a recent prediction of the ‘electron-phonon fluid’,” said Tafti, noting that phonons are vibrations of a crystal structure. “Typically, electrons are scattered by phonons, which leads to the usual diffusive motion of electrons in metals. A new theory shows that when electrons strongly interact with phonons, they will form a united electron-phonon liquid. This novel liquid will flow inside the metal exactly in the same way as water flows in a pipe.”
By confirming the predictions of theoreticians, the experimental physicist Tafti – working with Kenneth Burch, professor of physics at Boston College, Luis Balicas of Florida State University and Julia Chan of the University of Texas at Dallas – says the discovery will spur further exploration of this superconductor and its potential applications.
Our daily lives depend on the flow of both water in pipes and electrons in wires. As similar as they may sound, the two phenomena are fundamentally different. Water molecules flow as a fluid continuum, not as individual molecules, obeying the laws of hydrodynamics. In contrast, electrons flow as individual particles and diffuse inside metals as they get scattered by lattice vibrations.
The team’s investigation –with significant contributions from graduate student researcher Hung-Yu Yang, who earned his doctorate from Boston College in 2021 – focused on the conduction of electricity in NbGe2. The researchers combined three experimental methods: electrical resistivity measurements showed a higher-than-expected mass for electrons; Raman scattering showed a change of behavior in the vibration of the NbGe2 crystal due to the special flow of electrons; and X-ray diffraction revealed the crystal structure of the material.
By using a specific technique known as the 'quantum oscillations' to evaluate the mass of electrons in the material, the researchers found that their mass in all trajectories was three times larger than the expected value.
“This was truly surprising because we did not expect such ‘heavy electrons’ in a seemingly simple metal,” Tafti said. “Eventually, we understood that the strong electron-phonon interaction was responsible for the heavy electron behavior. Because electrons interact with lattice vibrations, or phonons, strongly, they are ‘dragged’ by the lattice, and it appears as if they have gained mass and become heavy.”
According to Tafti, the next step is to find other materials in this hydrodynamic regime by leveraging the electron-phonon interactions. His team will also focus on controlling the hydrodynamic fluid of electrons in such materials and engineering new electronic devices.
This story is adapted from material from Boston College, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.