Topological Semimetal KAlGe with Novel Electronic Instability

TL;DR

This paper reports the synthesis and characterization of KAlGe, a new topological semimetal with a structural phase transition and high mobility, revealing complex electronic interactions and potential for novel physical phenomena.

Contribution

The study introduces KAlGe as a new compound with unique electronic and structural properties, expanding the understanding of topological semimetals with phase transitions.

Findings

KAlGe undergoes a metal-to-metal transition at 89 K

KAlGe exhibits high mobility and low carrier density at low temperatures

Structural change breaks fourfold symmetry during phase transition

Abstract

Compounds with the anti-PbFCl structure exhibit a variety of electronic instabilities and intriguing physical properties. NaAlSi and NaAlGe are similar topological nodal-line semimetals, but they have distinct properties. NaAlSi is a superconductor at 6.8 K, whereas NaAlGe is an insulator with a pseudogap of approximately 100 K. Using the potassium-indium flux method, we succeeded in synthesizing a single crystal of KAlGe, a new anti-PbFCl compound. First principles electronic structure calculations reveal that KAlGe is isoelectronic with NaAlSi and NaAlGe. KAlGe undergoes a metal-to-metal transition at 89 K and exhibits no superconductivity above 1.8 K. The low temperature phase has significantly lower carrier density and extremely high mobility, similar to Dirac electron systems. Furthermore, X-ray diffraction experiments show a structural change that breaks the fourfold symmetry during the phase transition. Electron-phonon interactions may be responsible for superconductivity in NaAlSi, whereas excitonic electron-hole interactions are thought to play an important role in KAlGe and possibly NaAlGe. Our findings demonstrate that fascinating physics lies within the compound family.