Abstract
The vicinity of a Mott insulating phase has constantly been a fertile ground for finding exotic quantum states, most notably the high Tc cuprates and colossal magnetoresistance manganites. The layered transition metal dichalcogenide 1T-TaS2 represents another intriguing example, in which the Mott insulator phase is intimately entangled with a series of complex charge-density-wave (CDW) orders. More interestingly, it has been recently found that 1T-TaS2 undergoes a Mott-insulator-to-superconductor transition induced by high pressure, charge doping, or isovalent substitution. The nature of the Mott insulator phase and transition mechanism to the conducting state is still under heated debate. Here, by combining scanning tunneling microscopy (STM) measurements and first-principles calculations, we investigate the atomic scale electronic structure of 1T-TaS2 Mott insulator and its evolution to the metallic state upon isovalent substitution of S with Se. We identify two distinct types of orbital textures - one localized and the other extended - and demonstrates that the interplay between them is the key factor that determines the electronic structure. Especially, we show that the continuous evolution of the charge gap visualized by STM is due to the immersion of the localized-orbital-induced Hubbard bands into the extended-orbital-spanned Fermi sea, featuring a unique evolution from a Mott gap to a charge-transfer gap. This new mechanism of orbital-driven Mottness collapse revealed here suggests an interesting route for creating novel electronic state and designing future electronic devices.
Highlights
The vicinity of a Mott insulating phase has constantly been a fertile ground for finding exotic quantum states, most notably the high Tc cuprates and colossal magnetoresistance manganites
Relax the atomic coordination self-consistently until the forces are less than 0.p00ffiffi2ffiffiffi eVp=Åffiffiffi.ffiffi To simulate the commensurate CDW (CCDW) order, we employ a 13 × 13 supercell consisting of 13 Ta atoms forming a Star of David (SD) structure
According to the transport data, this domained phase in the x 1⁄4 1 sample should adiabatically extend to the high-T nearly commensurate CDW (NCCDW) regime, in which the domains might shrink in size and the sharp domain boundaries melt into finite-width interdomain channels free of CCDW order [16]
Summary
The vicinity of a Mott insulating phase has constantly been a fertile ground for finding exotic quantum states, most notably the high Tc cuprates and colossal magnetoresistance manganites. Recent STM experiments on the pristine 1T-TaS2 [24] and its pulses-induced states [26,27] have revealed interesting spectral features due to the interplay of CDW and electron correlation Both the CDW and Mott gap can be clearly resolved. Compared with the empirical model calculation, such as tight binding or the one-band Hubbard model solved using the dynamic mean-field approximation, the advantage of DFT þ U is that the interorbital hybridization and spillover associated with the CDW order are selfconsistently captured without tunable parameters This property is considered to be important in our Se-substitution experiment. By combining STM measurements and ab initio Wannier function analysis, we single out two distinct types of orbital textures and formulate a multiorbital effective Hamiltonian based on these two orbital textures This construction reveals a new origin of the Mott-insulatorto-superconductivity transition in 1T-TaS2.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
