Gap collapse and flat band induced by uniaxial strain in 1T-TaS2

Abstract

Interlayer coupling is strongly implicated in the complex electronic properties of 1T-TaS2. Uniaxial strain engineering offers a route to modify this coupling in order to elucidate its interplay with the electronic structure and electronic correlations. Here, we employ angle-resolved photoemission spectroscopy (ARPES) to reveal the effect of uniaxial strain on the electronic structure in 1T-TaS2. The gap of the normally insulating ground state is significantly reduced, with a correlated flat band appearing close to the Fermi level. Temperature-dependent ARPES measurements reveal that the flat band only develops below the commensurate charge density wave (CCDW) transition, where interlayer dimerization produces a band insulator in unstrained samples. Electronic structure calculations suggest that the correlated flat band is stabilized by a modified interlayer coupling of the Ta dz2 electrons. Further hints of a strain-induced structural modification of the interlayer order are obtained from x-ray diffraction. Our combined approach provides critical input for understanding the complex phase diagram of this platform material for correlated physics.