Chiral symmetry breaking and charge order

Wezel, Jasper van; Littlewood, P. B.

doi:10.1103/physics.3.87

Cited by 29 publications

(35 citation statements)

References 36 publications

(33 reference statements)

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“…2(c)). The chiral structure realized in β-Po was once proposed in Te [22], which was recently explained in terms of the orbital-ordered chiral charge-density wave (CDW) [23,24]. This orbital-ordered CDW would be suppressed, if the SOC were larger, as will be discussed in [25].…”

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confidence: 96%

Phonon softening and superconductivity triggered by spin-orbit coupling in simple-cubicα-polonium crystals

2012

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We have investigated the mechanism of stabilizing the simple-cubic (sc) structure in polonium (α-Po), based on the phonon dispersion calculations using the first-principles all-electron band method. We have demonstrated that the stable sc structure results from the suppression of the Peierls instability due to the strong spin-orbit coupling (SOC) in α-Po. We have also discussed the structural chirality realized in β-Po, as a consequence of the phonon instability. Further, we have explored the possible superconductivity in α-Po, and predicted that it becomes a superconductor with Tc ∼ 4 K. The transverse soft phonon mode at q ≈ 2 3 R, which is greatly influenced by the SOC, plays an important role both in the structural stability and the superconductivity in α-Po.

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confidence: 96%

Phonon softening and superconductivity triggered by spin-orbit coupling in simple-cubicα-polonium crystals

2012

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“…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.…”

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“…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.…”

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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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“…Only recently, it was discovered that it is possible for the atomic displacements accompanying charge order to break the inversion symmetry of the atomic lattice in a chiral way [5,6]. How such a helical configuration of charge density can be formed is not a priori obvious, because CDW materials, unlike spin density waves, have a scalar order parameter which cannot straightforwardly be made chiral.…”

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Polar charge and orbital order in2H-TaS2

Wezel

2012

Phys. Rev. B

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It was recently discovered that in spite of the scalar nature of its order parameter, the charge order in 1T-TiSe2 can be chiral. This is made possible by the emergence of orbital order in conjunction with the charge density modulations. Here we show that a closely related charge and orbital ordered state arises in 2H-TaS2. In both materials, the microscopic mechanism driving the transition is based on the interaction between three differently polarized displacement waves. The relative phase shifts between these waves lead both to the formation of orbital order and to the breakdown of inversion symmetry. In contrast to 1T-TiSe2 however, the presence of a mirror plane in the lattice of 2H-TaS2 prevents the distorted structure in this material from being chiral, and a polar charge and orbital ordered state arises instead. It is stressed that bulk experiments are indispensable in differentiating between the chiral and polar phases.

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Chiral symmetry breaking and charge order

Cited by 29 publications

References 36 publications

Phonon softening and superconductivity triggered by spin-orbit coupling in simple-cubicα-polonium crystals

Phonon softening and superconductivity triggered by spin-orbit coupling in simple-cubicα-polonium crystals

Chiral Phase Transition in Charge Ordered1T−TiSe2

Polar charge and orbital order in2H-TaS2

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