Spectroscopic Signatures of a Bandwidth-Controlled Mott Transition at the Surface of1T−TaSe2

Abstract

High-resolution angle-resolved photoemission (ARPES) data show that a metal-insulator Mott transition occurs at the surface of the quasi-two dimensional compound 1T -TaSe2. The transition is driven by the narrowing of the Ta 5d band induced by a temperature-dependent modulation of the atomic positions. A dynamical mean-field theory calculation of the spectral function of the halffilled Hubbard model captures the main qualitative feature of the data, namely the rapid transfer of spectral weight from the observed quasiparticle peak at the Fermi surface to the Hubbard bands, as the correlation gap opens up.PACS numbers: 71.30.+h,79.60.Bm,71.45.Lr,71.10.Fd Electronic correlations can modify the electronic structure of solids not only quantitatively, but also qualitatively, inducing new broken-symmetry phases which exhibit charge, spin or orbital-order, and more exotic states in low dimensions. One of the most notable consequences of electronic correlations is the much studied metal-insulator (M-I) Mott transition [1,2]. Recently, new theoretical approaches have considerably extended our understanding of this fundamental problem [2,3].Many physical properties indirectly reflect the dramatic rearrangement of the electronic structure at the transition. Photoelectron spectroscopy, which probes the single-particle spectral function, can provide a direct view of such changes [4,5,6]. However, comparing samples with different compositions faces materials problems like stoichiometry, defects, and disorder. A quantitative analysis is further complicated by the known surface sensitivity of the technique [7][8]. An ideal experiment would record the energy and momentum-dependent spectrum, while tuning the crucial (W/U ) parameter (U is the onsite Coulomb correlation energy; W is the bandwidth) in the same single crystal sample. Remarkably, it is possible to approach this ideal situation exploiting the occurrence of modulated structures (charge-density-waves; CDWs) in appropriate low-dimensional systems. There, the lattice distortion modulates the transfer integrals and therefore modifies the bandwidth. In materials that are close enough to a Mott transition, the reduced bandwidth may lead to an instability. There are strong indications for this scenario in the layered chalcogenide 1T -TaS 2 , which presents a sharp order-of-magnitude increase of the resistivity at T=180 K [9, 10], with a strong rearrangement of the electronic states [11,12,13,14,15]. However, the complex phase diagram of the CDW in 1T -TaS 2 affects the electronic transition, which cannot be considered as a typical Mott transition.Isostructural and isoelectronic 1T -TaSe 2 exhibits a similar CDW, but only one phase below T C =475 K. Its electrical resistivity remains metallic -albeit rather large -to very low temperatures [9], suggesting that the Se compound lies further from the instability than the S analog. Nevertheless, a transition could still occur at the crystal surface, where the U/W ratio is expected to be larger as a result of smaller screening and...

Fermi-surface-induced lattice distortion inNbTe2

“…This opens up the possibility of increased correlation effects. Mott scenarios have been suggested for 1T -TaS 2 [48] and 1T -TaSe 2 [23]. However, instead of trying to explain the discrepancy between experiment and theory with the insufficient treatment of correlation effects within LDA or GGA, we wish to point out that the disagreement between theory and experiment may be caused by the theoretical treatment of the distorted structure within DFT or more generally within the Bloch theory of periodic crystals.…”

“…Our low energy electron diffraction (LEED) measurements will allow an alternative parametrization of the structure proposed by X-ray diffraction measurements, which is more appropriate in the discussion of electron dynamics. Numerous studies of the electronic properties have been carried out for disulfides [13,14,15,16,17,18,19,20,21] and diselenides [16,18,22,23,24]. Direct measurements of the Fermi surface topology of NbTe 2 and TaTe 2 have never been reported.…”

Direct observation of an optically induced charge density wave transition in1T−TaSe2

“…In this paper, we will report on a study of the CDW phase transition in 1T-TaSe 2 between a commensurate phase (C-phase, q C = 0.225a* + 0.07b*) and an incommensurate phase (IC-phase, q IC = 0.278b*) induced by the fs-laser excitation. Theoretical analysis of the topology of the Fermi surface suggests that CDW in the IC-phase can be connected by the modulation wave vector as predicted by Peierls model [13][14], however, the nature of the C-phase and CDW transitions, is still under debate [15][16][17][18].…”

Strain tuning of the charge density wave in monolayer and bilayer 1T-TaS2

“…Layered transition metal dichalcogenides, such as 1T-TaS 2 , 2H-TaSe 2 , and 1T-TiSe 2 , have received renewed interest in recent years due to a wealth of physics, [1][2][3][4][5] ranging from charge density waves (CDWs) 6,7 to metal-insulator transitions 8 and superconductivity. 3 Particularly, 1T-TaS 2 has been extensively investigated because of its rich phase behavior as a function of the temperature.…”

“…3 Particularly, 1T-TaS 2 has been extensively investigated because of its rich phase behavior as a function of the temperature. 1,3,4,[9][10][11][12] At 540 K an incommensurate CDW develops from the undistorted metallic structure, at 350 K an almost commensurate CDW is adopted, and further cooling to 180 K leads to a commensurate CDW, which exhibits a "Star-of-David" structure with an inplane √13 × √13 periodic lattice distortion. The origin of the CDW, the pseudo-gapped Fermi surface, and the rich phase diagram are some of the topics that have motivated experimental and theoretical studies.…”