On the superconductivity of TiNCl and ZrNCl: A local bonding perspective

TL;DR

This paper examines the local bonding and structural features of TiNCl and ZrNCl superconductors, revealing similarities in bonding and structural changes upon doping that may influence their superconducting properties.

Contribution

It provides a local bonding perspective on TiNCl and ZrNCl, highlighting structural similarities and the role of metal-metal interactions in their superconductivity.

Findings

Both compounds have layered metal-N networks with similar local bonding.

Doping induces structural changes leading to short metal-metal distances.

Superconductivity may be linked to bonding interactions near a charge density wave instability.

Abstract

We analyze the superconductors TiNCl and ZrNCl from a local bonding perspective. Although TiNCl crystallizes in an orthorhombic structure and ZrNCl crystallizes in a hexagonal structure, both compounds show significant structural similarities, for example that both consist of layered metal-Nitrogen networks. The local bonding in those two structures is very similar, giving rise to a dispersive conduction band mostly consisting of metal-d -states. Upon doping both compounds show structural changes, which lead to short metal-metal distances, indicating a bonding interaction that might be important for the appearance of superconductivity in these systems. We furthermore draw analogies to other superconductors that are close to a charge density wave instability around a d 1 -configuration and offer a different perspective on this class of superconductors, which show non-BCS-like superconductivity.