Ferroelectric quantum criticality

Rowley, S. E.; Spalek, Leszek J.; Smith, Robert P.; Dean, M. P. M.; Itoh, Makoto; Scott, J. F.; Lonzarich, G. G.; Saxena, S. S.

doi:10.1038/nphys2924

Cited by 288 publications

(331 citation statements)

References 60 publications

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“…So, according to the experimental data [6,8], the paraelectric ground state can be stable at P > 1.5 GPa for Sn 2 P 2 S 6 , and at y > 0.7 and normal pressure for (Pb y Sn 1−y ) 2 P 2 S 6 mixed crystals. At 0 K, the quantum critical point (QCP) can be reached by variation of pressure or composition [9]. Early the QCP have been obviously found in the quantum paraelectric SrTiO 3 at increase of 18 O isotope concentration only [10].…”

Section: Introductionmentioning

confidence: 99%

Valence fluctuations in Sn(Pb)2P2S6 ferroelectrics

Yevych

Haborets

Medulych

et al. 2016

Low Temperature Physics

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The valence fluctuations which are related to the charge disproportionation of phosphorous ions P 4+ + P 4+ → P 3+ + P 5+ are the origin of ferroelectric and quantum paraelectric states in Sn(Pb)2P2S6 semiconductors. They involve recharging of SnPS3 or PbPS3 structural groups which could be represented as half-filled sites in the crystal lattice. Temperature-pressure phase diagram for Sn2P2S6 compound and temperature-composition phase diagram for (PbySn1−y)2P2S6 mixed crystals, which include tricritical points and where a temperature of phase transitions decrease to 0 K, together with the data about some softening of low energy optic phonons and rise of dielectric susceptibility at cooling in quantum paraelectric state of Pb2P2S6 are analyzed by GGA electron and phonon calculations and compared with electronic correlations models. The anharmonic quantum oscillators model is developed for description of phase diagrams and temperature dependence of dielectric susceptibility.

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Section: Introductionmentioning

confidence: 99%

Valence fluctuations in Sn(Pb)2P2S6 ferroelectrics

Yevych

Haborets

Medulych

et al. 2016

Low Temperature Physics

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“…This provides a new input for the ongoing debate on the microscopic origin of superconductivity 4,[8][9][10] . Calcium substitution leads to a higher dielectric constant at low temperature (Fig.…”

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confidence: 99%

“…It turns into a ferroelectric upon substitution of a tiny fraction of strontium atoms with calcium 3 . The two orders may be accidental neighbours or intimately connected, as in the picture of quantum critical ferroelectricity 4 . Here, we show that in Sr 1−x Ca x TiO 3−δ (0.002 < x < 0.009, δ < 0.001) the ferroelectric order coexists with dilute metallicity and its superconducting instability in a finite window of doping.…”

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confidence: 99%

“…In many unconventional superconductors, another electronic order competes with superconductivity. Here, the ferroelectric order is an obvious candidate 4,9 . It emerges in SrTiO 3 by isotopic substitution of 16 O oxygen atoms with 18 O (ref.…”

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confidence: 99%

“…They predicted that such a substitution would enhance the highest critical temperature and shift it to lower doping. This is a quantum critical ferroelectric 4 scenario, in which the maximum T c is pinned to the destruction of the ferroelectric order. Our observation is in qualitative agreement with this scenario.…”

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A ferroelectric quantum phase transition inside the superconducting dome of Sr1−xCaxTiO3−δ

Rischau¹,

Lin²,

Grams³

et al. 2017

Nature Phys

218

230

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SrTiO 3 , a quantum paraelectric 1 , becomes a metal with a superconducting instability after removal of an extremely small number of oxygen atoms 2 . It turns into a ferroelectric upon substitution of a tiny fraction of strontium atoms with calcium 3 . The two orders may be accidental neighbours or intimately connected, as in the picture of quantum critical ferroelectricity 4 . Here, we show that in Sr 1−x Ca x TiO 3−δ (0.002 < x < 0.009, δ < 0.001) the ferroelectric order coexists with dilute metallicity and its superconducting instability in a finite window of doping. At a critical carrier density, which scales with the Ca content, a quantum phase transition destroys the ferroelectric order. We detect an upturn in the normal-state scattering and a significant modification of the superconducting dome in the vicinity of this quantum phase transition. The enhancement of the superconducting transition temperature with calcium substitution documents the role played by ferroelectric vicinity in the precocious emergence of superconductivity in this system, restricting possible theoretical scenarios for pairing.A perovskite of the ABO 3 family, SrTiO 3 is a quantum paraelectric whose dielectric constant rises to ∼20,000 at low temperature 1 , but avoids long-range ferroelectric order. It becomes a metal by substituting Sr with La, Ti with Nb, or by removing O. It has been known for half a century that this metal is a superconductor at low temperatures 2 . More recently, a sharp Fermi surface and a superconducting ground state have been found to persist down to a carrier concentration of 10 17 cm −3 in SrTiO 3−δ (refs 5,6 However, mobile electrons screen polarization and therefore only insulating solids are expected to host a ferroelectric order. Hitherto, as a paradigm, ferroelectric quantum criticality, in contrast to its magnetic counterpart, was deprived of an experimental phase diagram in which a superconducting phase and a ferroelectric order share a common boundary.Here, we produce such a phase diagram in the case of Sr 1−x Ca x TiO 3−δ . The main new observations are the following: metallic Sr 1−x Ca x TiO 3−δ hosts a phase transition structurally indistinguishable from the ferroelectric phase transition in insulating Sr 1−x Ca x TiO 3 ; the coexistence between this ferroelectric-like order and superconductivity ends beyond a threshold carrier concentration; and, in the vicinity of this quantum phase transition, calcium substitution enhances the superconducting critical temperature and induces an upturn in the normal-state resistivity.Figure 1 summarizes what we know about the emergence of ferroelectricity, metallicity and superconductivity in this system. When a small fraction of Sr atoms (x > 0.002) is replaced with isovalent Ca, Sr 1−x Ca x TiO 3 becomes ferroelectric 3 , with a Curie temperature steadily increasing with Ca content in the dilute limit 0.002 < x < 0.02 (refs 3,13,14). Macroscopic polarization below the Curie temperature has been observed in dielectric and linear birefringence measurements, a...

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Structures and Properties of Dielectrics and Ferroelectrics

Itoh

2017

Handbook of Solid State Chemistry

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From the chemical viewpoint, it is usually unapproachable to the basic concept of physics, especially in the field of dielectric, ferroelectric, and piezoelectric materials due to the reason that these fields are closely related to the phase transition mechanism, which is mainly described by the phenomenology based on Landau theory. For chemists who are required to design new materials in ferroelectric and piezoelectric materials, comprehension of the physical background including phenomenology, phase transition mechanism, phonon physics, and tensor is indispensable. In this chapter, first, it is explained that insulating materials are generally classified into paraelectric, piezoelectric, pyroelectric, and ferroelectric ones. Second, the importance of the relationship between crystal symmetry and dielectric property is figured out. In the next sections, second‐ and first‐order phase transitions in ferroelectric are roughly explained based on the Landau theory. This explanation is finally conducted to a formula for real ferroelectric. Explanation for antiferroelectric and ferrielectric are also included in the last part. In the succeeding sections, important ferroelectric materials including Rochelle salts (order–disorder type), KDP (hydrogen bonded system), and perovskites are explained. Finally, recent topics on quantum paraelectricity, relaxor ferroelectric, piezoelectric PZT, and organic ferroelectric are introduced.

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Ferroelectric quantum criticality

Cited by 288 publications

References 60 publications

Valence fluctuations in Sn(Pb)2P2S6 ferroelectrics

Valence fluctuations in Sn(Pb)2P2S6 ferroelectrics

A ferroelectric quantum phase transition inside the superconducting dome of Sr1−xCaxTiO3−δ

Structures and Properties of Dielectrics and Ferroelectrics

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