Temperature-dependent Fermi surface of 2H-TaSe2 driven by competing density wave order fluctuations (original) (raw)
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Fermi surface nesting in several transition metal dichalcogenides
New Journal of Physics, 2008
By means of high-resolution angle resolved photoelectron spectroscopy (ARPES) we have studied the fermiology of 2H transition metal dichalcogenide polytypes TaSe 2 , NbSe 2 , and Cu 0.2 NbS 2 . The tightbinding model of the electronic structure, extracted from ARPES spectra for all three compounds, was used to calculate the Lindhard function (bare spin susceptibility), which reflects the propensity to charge density wave (CDW) instabilities observed in TaSe 2 and NbSe 2 . We show that though the Fermi surfaces of all three compounds possess an incommensurate nesting vector in the close vicinity of the CDW wave vector, the nesting and ordering wave vectors do not exactly coincide, and there is no direct relationship between the magnitude of the susceptibility at the nesting vector and the CDW transition temperature. The nesting vector persists across the incommensurate CDW transition in TaSe 2 as a function of temperature despite the observable variations of the Fermi surface geometry in this temperature range. In Cu 0.2 NbS 2 the nesting vector is present despite different doping level, which lets us expect a possible enhancement of the CDW instability with Cu-intercalation in the Cu x NbS 2 family of materials. PACS numbers: 71.45.Lr 79.60.-i 71.18.+y 74.25.Jb
Temperature-dependent pseudogap and electron localization in 1T-TaS2
Physical Review B, 1992
Photoelectron spectroscopy reveals a striking correspondence between charge-density-wave-related phase transitions and modifications of the electronic structure in 1T-TaS2. High-energy-resolution spectra indicate that the collapse of the Fermi surface is abrupt at the quasicommensurate-commensurate transition (~185 K) and that, below this critical temperature, the Fermi level lies in a deep, temperature-dependent pseudogap. These results strongly suggest successive localizations due to electron
Journal of the Physical Society of Japan, 2004
We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation on layered transition-metal dichalcogenide 1T-VSe 2 to study the mechanism of the three-dimensional charge-density-wave (CDW) transition. We found that the Fermi surface around the M(L) and K(H) points shows considerable wiggling along the wave vector normal to the layer (k z) despite the apparently two-dimensional crystal structure. ARPES spectra below the CDW transition temperature show a signature of pseudogap opening at a specific k z-region on the Fermi surface, demonstrating that the CDW transition of 1T-VSe 2 is driven by three-dimensional Fermi-surface nesting.
Physical Review B
We report an in-depth Angle Resolved Photoemission Spectroscopy (ARPES) study on 2H-TaS2 , a canonical incommensurate Charge Density Wave (CDW) system. This study demonstrates that just as in related incommensurate CDW systems, 2H-TaSe2 and 2H-NbSe2 , the energy gap (∆ cdw) of 2H-TaS2 is localized along the K-centered Fermi surface barrels and is particle-hole asymmetric. The persistence of ∆ cdw even at temperatures higher than the CDW transition temperature T cdw in 2H-TaS2 , reflects the similar pseudogap (PG) behavior observed previously in 2H-TaSe2 and 2H-NbSe2. However, in sharp contrast to 2H-NbSe2 , where ∆ cdw is non-zero only in the vicinity of a few "hot spots" on the inner K-centered Fermi surface barrels, ∆ cdw in 2H-TaS2 is non-zero along the entirety of both K-centered Fermi surface barrels. Based on a tight-binding model, we attribute this dichotomy in the momentum dependence and the Fermi surface specificity of ∆ cdw between otherwise similar CDW compounds to the different orbital orientations of their electronic states that participate in the CDW pairing. Our results suggest that the orbital selectivity plays a critical role in the description of incommensurate CDW materials.
Spectroscopic Signatures of a Bandwidth-Controlled Mott Transition at the Surface of 1T-TaSe_{2}
Physical Review Letters, 2003
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.
Lattice-distortion-enhanced electron-phonon coupling and Fermi surface nesting in 1T-TaS_ {2}
2006
The temperature dependence of the electronic structure of the quasi-two-dimensional material 1T-TaS 2 is revisited by considering angle-resolved photoemission spectroscopy ͑ARPES͒ and density functional theory to calculate the imaginary part of the static electronic susceptibility characterizing the nesting strength. While nesting appears to play a role in the high temperature phase, the ARPES line shapes reveal peculiar spectral properties which are not consistent with the standard two-dimensional Peierls scenario for the formation of a charge density wave. The temperature dependence of these anomalous spectral features suggests a latticedistortion enhanced electron-phonon interaction.
Persistent Charge-Density-Wave Order in Single-Layer TaSe2
Nano letters, 2018
We present the electronic characterization of single-layer 1H-TaSe2 grown by molecular beam epitaxy using a combined angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and density functional theory calculations. We demonstrate that 3 × 3 charge-density-wave (CDW) order persists despite distinct changes in the low energy electronic structure highlighted by the reduction in the number of bands crossing the Fermi energy and the corresponding modification of Fermi surface topology. Enhanced spin-orbit coupling and lattice distortion in the single-layer play a crucial role in the formation of CDW order. Our findings provide a deeper understanding of the nature of CDW order in the two-dimensional limit.
Physical Review Letters, 2006
An unexpected feature common to 2H transition metal dichalcogenides (2H TMDs) is revealed with a first-principles Wannier function analysis of the electronic structure of the prototype 2H TaSe 2 : The lowenergy Ta ''5d z 2 '' bands governing the physics of a charge-density wave (CDW) is dominated by hopping between next-nearest neighbors. With this motivation we develop a minimal effective model for the CDW formation, in which the unusual form of the hopping leads to an approximate decoupling of the three sublattices. In the CDW phase one sublattice remains undistorted, leaving the bands associated with it ungapped everywhere in the Fermi surface, resolving the long-standing puzzle of the coexistence of gapless excitations and commensurate CDW in the 2H TMDs.
Fermi surface of layered compounds and bulk charge density wave systems
Journal of Physics: Condensed Matter, 2007
A review is given of recent angle-resolved photoemission (ARPES) experiments and analyses on a series of layered charge density wave materials. Important aspects of ARPES are recalled in view of its capability for bulk band, Fermi surface and spectral function mapping despite its surface sensitivity. Discussed are TaS 2 , TaSe 2 , NbTe 2 , TiSe 2 and TiTe 2 with structures related to the so-called 1T polytype. Many of them undergo charge density wave transitions or exist with a distorted lattice structure. Attempts to explain the mechanism behind the structural reconstruction are given. Depending on the filling of the lowest occupied band a drastically different behaviour is observed. Whereas density functional calculations of the electronic energy and momentum distribution reproduce well the experimental spectral weight distribution at the Fermi energy, the ARPES energy distribution curves reveal that for some of the compounds the Fermi surface is pseudo-gapped. Two different explanations are given, the first based on density functional calculations accounting for the charge-density-wave-induced lattice distortion and the second relying on many-body physics and polaron formation. Qualitatively, both describe the observations well. However, in the future, in order to be selective, quantitative modelling will be necessary, including the photoemission matrix elements.