Electron-hole fluctuation phase in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>1</mml:mn><mml:mi>T</mml:mi></mml:mrow></mml:math>-TiSe<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mn>2</mml:mn></mml:msub></mml:math>

Monney, Claude; Monney, Gaël; Aebi, Philipp; Beck, H. P.

doi:10.1103/physrevb.85.235150

Cited by 47 publications

(93 citation statements)

References 35 publications

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“…3c, is significantly smaller at only ∼ 1.5 %. This observation agrees with the suggestion that the overall temperature dependence of ρ(T ) is determined primarily by the evolution of the carrier density [29], while the variations in anisotropy are determined by the temperature dependence The principal components of resistivity as a function of temperature. Notice that the scales for the two curves differ by a factor of ∼ 575. b) The derivatives of both curves, displaying sharp minima at T CDW , the initial onset temperature of (non-chiral) charge order.…”

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confidence: 81%

“…The temperature profiles of ρ ab and ρ c are also almost identical, although their absolute values differ by an anisotropy factor of ∼ 575. Each resistivity component exhibits a maximum close to 168 K, which has previously been suggested to arise from an initial decrease in the density of available carriers, caused by the opening of a gap in the charge ordered phase, which is overtaken at lower temperatures by both the decrease of scattering channels due to the developing order, and an increase in density of states due to the downward shift of the conduction band minimum below T CDW [29]. The position of the maximum thus does not coincide with any charge ordering transition.…”

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confidence: 99%

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Chiral Phase Transition in Charge Ordered1T−TiSe2

et al. 2013

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It was recently discovered that the low temperature, charge ordered phase of 1T-TiSe 2 has a chiral character. This unexpected chirality in a system described by a scalar order parameter could be explained in a model where the emergence of relative phase shifts between three charge density wave components breaks the inversion symmetry of the lattice. Here, we present experimental evidence for the sequence of phase transitions predicted by that theory, going from disorder to non-chiral and finally to chiral charge order. Employing X-ray diffraction, specific heat, and electrical transport measurements, we find that a novel phase transition occurs ∼ 7 K below the main charge ordering transition in TiSe 2 , in agreement with the predicted hierarchy of charge ordered phases. Introduction.-The modulation of electronic density which emerges in charge ordered materials reduces the translational symmetry of the underlying lattice. Additional symmetries may be broken through the coupling to atomic displacements, and these are often key in understanding the material properties of charge ordered systems. The broken rotational symmetry in 2H-TaSe 2 , for example, yields a reentrant phase transition under pressure [1], while the broken inversion symmetry in rare-earth nickelates RNiO 3 , renders them multiferroic [2].Recently, it was discovered that the breakdown of inversion symmetry in the charge ordered phase of 1T-TiSe 2 leads to the presence of a chiral structure at low temperatures [3][4][5][6][7][8][9]. In this phase, a helical charge density distribution arises from a rotation of the dominant charge density wave component as one progresses through consecutive atomic layers. While helical phases are common among spin-density waves, with vectorial order parameters, 1T-TiSe 2 is one of only very few materials so far in which a chiral charge ordered phase, with a scalar order parameter, has been suggested to exist [10,11]. A mechanism for the formation of this scalar chirality in TiSe 2 was recently proposed, in which the chiral phase is interpreted to be simultaneously charge and orbital ordered [5].The scanning tunneling microscopy experiments in which the chirality of TiSe 2 was initially revealed, were performed well below the onset temperature of charge order in this material [3]. There is currently no experimental information on the nature of the transition between the chiral and the normal state. Here, we present experimental evidence for a sequence of two transitions, the well-known onset of charge order at ∼ 190 K and a novel transition at ∼ 183 K. The temperature dependence of X-ray superlattice reflections unnoticed in previous studies, combined with an analysis of their structure factors, and the temperature dependences of the specific heat and resistance anisotropy, strongly suggests a scenario in which the transition at ∼ 183 K indicates the emergence of chiral charge order out of the non-chiral charge density wave state. The existence of this hierarchy of transitions, as well as the observed experimental s...

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confidence: 81%

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confidence: 99%

Chiral Phase Transition in Charge Ordered1T−TiSe2

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“…In these systems, the valence and conduction bands are formed by orbitals located on different atoms. For example, in 1T -TiSe 2 , the 4p orbitals of Se ions account for the valence bands and the 3d orbitals of Ti ions account for the conduction bands [7][8][9][10][11][12][13][14] , and in Ta 2 NiSe 5 , the 3d orbitals of Ni ions form the valence bands and the 5d orbitals of Ta ions form the conduction bands [21][22][23][24] . Hund's rule coupling, acting between electrons on different orbitals of a single ion and favoring the spin-triplet excitons, is therefore negligible.…”

Section: Discussionmentioning

confidence: 99%

“…Including thereby the Hund's rule coupling is known to stabilize the spin-triplet excitonic phase in the otherwise degenerate spin-singlet and spintriplet excitonic phases [18][19][20]28,42,43 . On the other hand, we have shown in our previous work 43 that taking into account electronic interactions only, a spin-singlet excitonic phase cannot be stabilized, which may however be realized in 1T -TiSe 2 and Ta 2 NiSe 5 , where the importance of electron-phonon coupling was recently pointed out [10][11][12][13][14]23 . Although the spin-singlet excitonic state has been investigated in the spinless multiband model with electron-phonon coupling 12,44,45 , not much is known about the role of the electron-phonon coupling played in the excitonic density wave states in the spinful multiband Hubbard model.…”

Section: Introductionmentioning

confidence: 99%

“…In this regard, Tm(Se,Te) was argued to exhibit a pressureinduced excitonic instability, related to an anomalous increase in the electrical resistivity and thermal diffusivity 5,6 . The charge-density-wave (CDW) state observed in 1T -TiSe 2 was claimed to be of excitonic origin [7][8][9][10][11][12][13][14] . In Ca 1−x La x B 6 , the weak ferromagnetism was interpreted in terms of doped spin-triplet excitons [15][16][17] .…”

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confidence: 99%

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Competition between excitonic charge and spin density waves: Influence of electron-phonon and Hund's rule couplings

et al. 2015

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We analyze the stability of excitonic ground states in the two-band Hubbard model with additional electron-phonon and Hund's rule couplings using a combination of mean-field and variational cluster approaches. We show that both the interband Coulomb interaction and the electron-phonon interaction will cooperatively stabilize a charge density wave (CDW) state which typifies an "excitonic" CDW if predominantly triggered by the effective interorbital electron-hole attraction or a "phononic" CDW if mostly caused by the coupling to the lattice degrees of freedom. By contrast, the Hund's rule coupling promotes an excitonic spin density wave. We determine the transition between excitonic charge and spin density waves and comment on a fixation of the phase of the excitonic order parameter that would prevent the formation of a superfluid condensate of excitons. The implications for exciton condensation in several material classes with strongly correlated electrons are discussed.

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Data on Specific Polymers

Wypych¹

2013

Handbook of Material Weathering

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Electron-hole fluctuation phase in1T-TiSe2

Cited by 47 publications

References 35 publications

Chiral Phase Transition in Charge Ordered1T−TiSe2

Chiral Phase Transition in Charge Ordered1T−TiSe2

Competition between excitonic charge and spin density waves: Influence of electron-phonon and Hund's rule couplings

Data on Specific Polymers

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