Understanding the Mott insulating state in 1T-TaS2 and 1T-TaSe2

Abstract

In this article, we review the recent progress of the scanning tunneling microscopy studies of 1T-TaS2 and 1T-TaSe2 for bulk single crystals and molecular beam epitaxy monolayer films. We focus on how to understand the Mott insulating state in the whole set of materials, even when the stacking order takes effect. Based on this understanding, we discuss tuning the Mott insulator to a metallic state with different techniques, with Mott physics information revealed from the tuning process. The Kondo physics and quantum spin liquid state of 1T-TaS2 and 1T-TaSe2 are further discussed. This good platform of strong correlation must bring more intriguing phenomenon and physics in the future.

Effect of Charge Density Wave on the Electronic Transport in Graphene

“…Especially in the CCDW phase, the SOD clusters form a regular lattice structure. ,− The electron in the SOD central atom is localized, leading to an insulating Mott state. ,,,, Upon cooling from a high-temperature ICCDW phase to the NCCDW and CCDW phases, a series of transitions occur exhibiting hysteretic transport behavior due to its first-order transition nature. Diverse experimental efforts have been made to understand the nature of these rich CDW phases of 1T-TaS 2 including the effect of doping, pressure, or substrate, and scanning tunneling microscope (STM) and scanning tunneling spectroscopy (STS) experiments. ,,− The low-temperature CCDW phase disappears and new hidden states appear upon perturbations such as electrical currents and pulse or laser pulse irradiation. ,− The applications within memory devices and sensors for light or heat have been explored by employing the hysteresis property and collective excitation. − …”

Spin–orbit and exchange proximity couplings in graphene/1T-TaS2 heterostructure triggered by a charge density wave

“…Structural CDW distortions have the form of David stars [32]-clusters of 13 transition metal atoms in which an excess electron is effectively trapped at the star center [33][34][35][36][37][38]. What is particularly interesting, the commensurate √ 13 × √ 13 CDW phase of TaS 2 forming the superlattice of David stars [39] possesses below 180 K [40] enough electronic correlations [41] to develop the Mott phase [42][43][44][45][46] and even superconductivity under pressure [32,47]. Formation of CDW in 1T-TaS 2 results from the subtle interplay of lattice, orbital and spin degrees of freedom [48], along with the electron-phonon coupling [49,50] which results in strongly localized electronic states near the Fermi level [51].…”

Layer Sliding And Twisting Induced Electronic Transitions In Correlated Magnetic 1t‐Nbse2 Bilayers

“…1T‐NbSe 2 is a CT insulator, in which the VB, comprised of the Se p z states, appreciably interferes with the LHB, [ 7 ] different from the Mott insulating states in 1T‐Ta‐dichalcogenides. [ 22,23 ] These Se states are directly interlayer overlapped, rather than those$${\mathrm{\ d}}_{{{\mathrm{z}}}^2}\ $$states from the embedded and ≈6 Å apart metal (Ta) atoms. [ 27,28,30 ] However, the 1T‐NbSe 2 mono‐ and few‐layers are, so far, experimentally accessible using molecular beam epitaxy solely.…”

“…1H-phase layers of group-5 dichalcogenides, for example, 1H-TaS 2 [14,15] and 1H-NbSe 2 , [16][17][18] show abundant quantum phenoma like charge density wave (CDW) [14][15][16] and superconductivity. [15,17,18] Their 1T-phase counterparts exhibit even diverse electron-correlated properties, including CDW, [5,8,[19][20][21] quantum spin liquid, [5,22] Mott [23,24] or CT [7] insulating states at low temperatures.…”

“…1T-NbSe 2 is a CT insulator, in which the VB, comprised of the Se p z states, appreciably interferes with the LHB, [7] different from the Mott insulating states in 1T-Ta-dichalcogenides. [22,23] These Se states are directly interlayer overlapped, rather than those d z 2 states from the embedded and ≈6 Å apart metal (Ta) atoms. [27,28,30] However, the 1T-NbSe 2 mono-and few-layers are, [3] Reg-L (red) and Reg-D (blue) marked in (d) represent the localized and delocalized regions, respectively.…”