Unconventional Superconductivity in electron-doped layered metal nitride halides $M$N$X$ ($M$ = Ti, Zr, Hf; $X$ = Cl, Br, I)

Abstract

In this review, we present a comprehensive overview of superconductivity in electron-doped metal nitride halides $M$N$X$ ($M$ = Ti, Zr, Hf; $X$ = Cl, Br, I) with layered crystal structure and two-dimensional electronic states. The parent compounds are band insulators with no discernible long-range ordered state. Upon doping tiny amount of electrons, superconductivity emerges with several anomalous features beyond the conventional electron-phonon mechanism, which stimulate theoretical investigations. We will discuss experimental and theoretical results reported thus far and compare the electron-doped layered nitride superconductors with other superconductors.

14 pages, 18 figures, accepted for publication in Physica C Special Issue on Superconducting Materials

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• Spin-triplet superconductivity from interband effect in doped insulators
• The Rise of Refractory Transition-Metal Nitride Films for Advanced Electronics and Plasmonics
• Quantum geometry encoded to pair potentials
• Vortex dynamics in the two-dimensional BCS-BEC crossover
• High-$T_c$ superconductivity in weakly electron-doped HfNCl
• Computational design of a new layered superconductor LaOTlF2