The non-symmorphic rutile space group enforces the existence of a network of Dirac nodal lines in the Brillouin zones of transition metal rutiles like RuO₂ and IrO₂ A recent report published in Nature Communications demonstrates that oxygen vacancies in IrO₂ and RuO₂ nanowires drive a fragile many-body state known as the orbital Kondo effect.

Interestingly, the symmetries that enforce the existence of DNLs also promote the formation of nonmagnetic Kondo correlations. The demonstration that the non-symmorphic rutile space group supports oxygen-driven orbital Kondo effects in transition metal rutiles holds promise for the realization of novel states of matter and may have ramifications in other materials featuring oxygen vacancies. 

Angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) have become indispensable tools in the study of correlated quantum materials. A new review article, published in the Colloquiua section of Reviews of Modern Physics, explicates the potential of these techniques in the context of heavy-electron quantum criticality.

In “Colloquium: Heavy-electron quantum criticality and single-particle spectroscopy“, the authors survey recent progress and possible challenges in the experimental investigations. The STM and ARPES spectra for several quantum-critical heavy-electron compounds are compared, and the prospects for further advances are outlined.