Electronic Structure of Solids with Competing Periodic Potentials

Voit, Johannes; Perfetti, L.; Zwick, F.; Berger, H.; Margaritondo, G.; Grüner, G.; Höchst, H.; Grioni, M.

doi:10.1126/science.290.5491.501

Cited by 185 publications

(169 citation statements)

References 15 publications

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“…Such atomic displacements, in terms of a band Jahn-Teller effect, were suggested as a driving force for the transition. However, the key point is that, although the lattice distortion may shift the conduction band, the very small atomic displacements (≈ 0.02Å [3]) in 1T -TiSe 2 are expected to lead to a negligable spectral weight in the backfolded bands [20]. As an example, 1T -TaS 2 , another CDW compound known for very large atomic displacements [22] (of order > 0.1Å) introduces hardly detectable backfolding of spectral weight in ARPES.…”

Section: Pacs Numbersmentioning

confidence: 99%

“…Such a large transfer of spectral weight into the backfolded bands is a very uncommon and striking feature. Indeed, in most compounds with competing potentials (CDW systems, vicinal surfaces,...), the backfolded bands carry an extremely small spectral weight [18,19,20]. In these systems the backfolding results mainly from the influence of the modified lattice on the electron gas, and the weight transfer is related to the strength of the new crystal potential component.…”

Section: Pacs Numbersmentioning

confidence: 99%

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Evidence for an Excitonic Insulator Phase in1T−TiSe2

et al. 2007

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We present a new high-resolution angle-resolved photoemission study of 1T -TiSe2 in both, its room-temperature, normal phase and its low-temperature, charge-density wave phase. At low temperature the photoemission spectra are strongly modified, with large band renormalisations at highsymmetry points of the Brillouin zone and a very large transfer of spectral weight to backfolded bands. A theoretical calculation of the spectral function for an excitonic insulator phase reproduces the experimental features with very good agreement. This gives strong evidence in favour of the excitonic insulator scenario as a driving force for the charge-density wave transition in 1T -TiSe2. PACS numbers:Transition-metal dichalcogenides (TMDC's) are layered compounds exhibiting a variety of interesting physical properties, mainly due to their reduced dimensionality [1]. One of the most frequent characteristics is a ground state exhibiting a charge-density wave (CDW), with its origin arising from a particular topology of the Fermi surface and/or a strong electron-phonon coupling [2]. Among the TMDC's 1T -TiSe 2 shows a commensurate 2×2×2 structural distortion below 202 K, accompanied by the softening of a zone boundary phonon and with changes in the transport properties [3,4]. In spite of many experimental and theoretical studies, the driving force for the transition remains controversial. Several angle-resolved photoelectron spectroscopy (ARPES) studies suggested either the onset of an excitonic insulator phase [5,6] or a band Jahn-Teller effect [7]. Furthermore, TiSe 2 has recently attracted strong interest due to the observation of superconductivity when intercalated with Cu [8]. In systems showing exotic properties, such as Kondo systems for example [9], the calculation of the spectral function has often been a necessary and decisive step for the interpretation of the ARPES data and the determination of the ground state of the systems. In the case of 1T -TiSe 2 , such a calculation for an excitonic insulator phase lacked so far.In this letter we present a high-resolution ARPES study of 1T -TiSe 2 , together with theoretical calculations of the excitonic insulator phase spectral function for this compound. We find that the experimental ARPES spectra show strong band renormalisations with a very large transfer of spectral weight into backfolded bands in the low-temperature phase. The spectral function calculated for the excitonic insulator phase is in strikingly good * Electronic address: herve.cercellier@unine.ch agreement with the experiments, giving strong evidence for the excitonic origin of the transition.The excitonic insulator model was first introduced in the sixties, for a semi-conductor or a semi-metal with a very small indirect gap E G [10,11,12,13]. Thermal excitations lead to the formation of holes in the valence band and electrons in the conduction band. For low free carrier densities, the weak screening of the electronhole Coulomb interaction leads to the formation of stable electron-hole bound states, called excito...

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Section: Pacs Numbersmentioning

confidence: 99%

Section: Pacs Numbersmentioning

confidence: 99%

Evidence for an Excitonic Insulator Phase in1T−TiSe2

et al. 2007

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“…-10 momentum distribution of the spectral function in a standard band-folding or nesting scenario 26,27 . However, as it is presently unknown whether the HO state corresponds to a conventional density wave, and how the coherence factors should be calculated, a quantitative explanation of the observed distribution of spectral weight at E F lies beyond the scope of this work.…”

Section: Articlementioning

confidence: 99%

Momentum-resolved hidden-order gap reveals symmetry breaking and origin of entropy loss in URu2Si2

et al. 2014

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Spontaneous symmetry breaking in physical systems leads to salient phenomena at all scales, from the Higgs mechanism and the emergence of the mass of the elementary particles, to superconductivity and magnetism in solids. The hidden-order state arising below 17.5 K in URu 2 Si 2 is a puzzling example of one of such phase transitions: its associated broken symmetry and gap structure have remained longstanding riddles. Here we directly image how, across the hidden-order transition, the electronic structure of URu 2 Si 2 abruptly reconstructs. We observe an energy gap of 7 meV opening over 70% of a large diamond-like heavy-fermion Fermi surface, resulting in the formation of four small Fermi petals, and a change in the electronic periodicity from body-centred tetragonal to simple tetragonal. Our results explain the large entropy loss in the hidden-order phase, and the similarity between this phase and the high-pressure antiferromagnetic phase found in quantum-oscillation experiments.

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“…2 In these systems, such as charge-and spindensity waves (CDW and SDW), 3 Wigner cristals, superconductors in magnetic fields, 4 structurally incommensurate crystal phases, 5 the superstructure periodicities could be varied by external fields or temperature changes. The resulting metastable configurations can be reflected back onto the elastic properties and size of the underlying lattice, [3][4][5] though this question is still poorly understood.…”

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Coupling of the Lattice and Superlattice Deformations and Hysteresis in Thermal Expansion for the Quasi-One-Dimensional ConductorTaS3

2002

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An original interferometer-based setup for measurements of length of needle-like samples is developed, and thermal expansion of o-TaS3 crystals is studied. Below the Peierls transition the temperature hysteresis of length L is observed, the width of the hysteresis loop δL/L being up to 5 · 10 −5 . The behavior of the loop is anomalous: the length changes so that it is in front of its equilibrium value. The hysteresis loop couples with that of conductivity. The sign and the value of the length hysteresis are consistent with the strain dependence of the charge-density waves (CDW) wave vector. With lowering temperature down to 100 K the CDW elastic modulus grows achieving a value comparable with the lattice Young modulus. Our results could be helpful in consideration of different systems with intrinsic superstructures.PACS Numbers: 71.45.Lr, 65.40.De Internal degrees of freedom is a feature of a random system; in principle, they can give rise to metastable size states resulting, say, to hysteresis in thermal expansion. 1 A special class form the compounds with intrinsic superstructures.Comprising two periodicities, generally incommensurate, the compounds occupy intermediate place between genuine aperiodic and truly periodic systems. 2 In these systems, such as charge-and spindensity waves (CDW and SDW), 3 Wigner cristals, superconductors in magnetic fields, 4 structurally incommensurate crystal phases, 5 the superstructure periodicities could be varied by external fields or temperature changes. The resulting metastable configurations can be reflected back onto the elastic properties and size of the underlying lattice, 3-5 though this question is still poorly understood.Quasi 1-dimensional conductors with CDW belong to a widely studied class of materials, in which intrinsic superstructure develops through the Peierls transition 6 . When electrons condense into CDW they form a deformable medium, -an electronic crystal. Deformation of the CDW affects their main static and dynamic properties and gives rise to metastability and hysteresis.The straightforward treatment of the CDW as a spring, whose strain is just applied to the crystal at the ends or via the impurities is not valid. Moreover, in the simple one-dimensional model the strains of the CDW and the crystal do not couple at all: if initially the CDW are relaxed, any change of the crystal length would not draw the CDW away from the equilibrium, i.e. give rise to a CDW deformation, 7 as it was noticed in Refs. 8-11. Similarly, once the CDW is deformed, any change of the lattice constant, c, would neither decrease nor increase the deviation of the CDW wavelength λ from the equilibrium value, λ eq . So, within this model a CDW deformation would not give rise to a length change.At the same time, the interaction of the CDW and the lattice is clearly seen from the elastic anomalies, including a drop of the Young modulus of the lattice, 8-11 Y l , up to 4%, 10 when the CDW become depinned.Mozurkewich 8 has concluded that the lattice deformation does give rise to a de...

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Electronic Structure of Solids with Competing Periodic Potentials

Cited by 185 publications

References 15 publications

Evidence for an Excitonic Insulator Phase in1T−TiSe2

Evidence for an Excitonic Insulator Phase in1T−TiSe2

Momentum-resolved hidden-order gap reveals symmetry breaking and origin of entropy loss in URu2Si2

Coupling of the Lattice and Superlattice Deformations and Hysteresis in Thermal Expansion for the Quasi-One-Dimensional ConductorTaS3

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