Bulk 1T-NbSe2 Superconductor Stabilized by the Doped Ti-3d0 Electronic Configuration

Abstract

Metastable 1T-phase transition-metal dichalcogenides host rich strongly correlated electronic phenomena, yet the synthesis of bulk 1T-NbSe2 remains a challenge. This difficulty stems from the energetic penalty associated with the octahedral coordination of Nb4+, whose 4d1 electronic configuration drives the 1T phase to relax into the thermodynamically stable 2H phase. Herein, we successfully synthesized 1T-Nb0.92Ti0.08Se2 crystals through a chemical vapor transport method. The intralayer Ti atoms induce the Nb4+ d-electron configuration to favor octahedral coordination, while a minority of intercalated Ti covalently pins the 1T layers. Angle-resolved photoemission spectroscopy reveals an intact metallic Fermi surface and a narrow band near the Fermi level, indicating the suppression of charge-density-wave reconstruction and an enhanced density of electronic states. In contrast to the Mott-insulating monolayer 1T NbSe2, bulk 1T-Nb0.92Ti0.08Se2 exhibits robust type-II superconductivity with a transition temperature of 7.2 K and an in-plane upper critical field of 13.46 T, exceeding the Pauli paramagnetic limit. Furthermore, angle-dependent magnetotransport shows an anomalous 4-fold in-plane superconducting anisotropy that is unexpected for a trigonal lattice. This work establishes heteroatom doping as a powerful strategy for unlocking metastable 1T polymorphs, providing a highly versatile platform for exploring quantum physics.