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Quantum ferroelectricity in charge-transfer complex crystals.

Horiuchi S, Kobayashi K, Kumai R, Minami N, Kagawa F, Tokura Y - Nat Commun (2015)

Bottom Line: Here we have developed chemically pure tetrahalo-p-benzoquinones of n iodine and 4-n bromine substituents (QBr4-nIn, n=0-4) to search for ferroelectric charge-transfer complexes with tetrathiafulvalene (TTF).Quantum critical behaviour is accompanied by a much larger permittivity than those of other neutral-ionic transition compounds, such as well-known ferroelectric complex of TTF-QCl4 and quantum antiferroelectric of dimethyl-TTF-QBr4.By contrast, TTF-QBr3I complex, another member of this compound family, shows complete suppression of the ferroelectric spin-Peierls-type phase transition.

View Article: PubMed Central - PubMed

Affiliation: 1] National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8562, Japan [2] CREST, Japan Science and Technology Agency (JST), Tokyo 102-0076, Japan.

ABSTRACT
Quantum phase transition achieved by fine tuning the continuous phase transition down to zero kelvin is a challenge for solid state science. Critical phenomena distinct from the effects of thermal fluctuations can materialize when the electronic, structural or magnetic long-range order is perturbed by quantum fluctuations between degenerate ground states. Here we have developed chemically pure tetrahalo-p-benzoquinones of n iodine and 4-n bromine substituents (QBr4-nIn, n=0-4) to search for ferroelectric charge-transfer complexes with tetrathiafulvalene (TTF). Among them, TTF-QBr2I2 exhibits a ferroelectric neutral-ionic phase transition, which is continuously controlled over a wide temperature range from near-zero kelvin to room temperature under hydrostatic pressure. Quantum critical behaviour is accompanied by a much larger permittivity than those of other neutral-ionic transition compounds, such as well-known ferroelectric complex of TTF-QCl4 and quantum antiferroelectric of dimethyl-TTF-QBr4. By contrast, TTF-QBr3I complex, another member of this compound family, shows complete suppression of the ferroelectric spin-Peierls-type phase transition.

No MeSH data available.


Related in: MedlinePlus

Temperature- and pressure-dependent properties of TTF–QBr2I2 crystal.(a) Temperature dependence of the relative permittivity under various hydrostatic pressures. The applied pressure value, corrected considering its thermal change in the medium for each measurement, is represented by the value at the transition point or lowest temperature when the phase transition is absent. The inset depicts the data in the low-pressure range. (b) Temperature–pressure phase diagram; linear extrapolation of the phase boundary at high-temperature region points to 1.64 GPa at room temperature. The inset represents the quantum critical behaviour of ferroelectrics obeying the relation Tc∝(p–pc)1/2 in the low-critical temperature region. The open square represents the pressure at which the room temperature conductivity exhibited a sharp peak caused by the pressure-induced NIT. (c) Inverse relative permittivity as the function of the square of the temperature. The solid line represents the quantum critical behaviour ɛr–1∝T2.
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f3: Temperature- and pressure-dependent properties of TTF–QBr2I2 crystal.(a) Temperature dependence of the relative permittivity under various hydrostatic pressures. The applied pressure value, corrected considering its thermal change in the medium for each measurement, is represented by the value at the transition point or lowest temperature when the phase transition is absent. The inset depicts the data in the low-pressure range. (b) Temperature–pressure phase diagram; linear extrapolation of the phase boundary at high-temperature region points to 1.64 GPa at room temperature. The inset represents the quantum critical behaviour of ferroelectrics obeying the relation Tc∝(p–pc)1/2 in the low-critical temperature region. The open square represents the pressure at which the room temperature conductivity exhibited a sharp peak caused by the pressure-induced NIT. (c) Inverse relative permittivity as the function of the square of the temperature. The solid line represents the quantum critical behaviour ɛr–1∝T2.

Mentions: At ambient and low pressures, the relative permittivity around the lowest temperature (4 K) exhibits saturation behaviour and increases from 200 to 700 with pressure (Fig. 3a). According to the fit with the Barrett formula, T0 increases to +18.2(6) K at 0.23 GPa with T1=68.7(7) K and C=1.22(2) × 105 K. Although the phase transition is expected near this positive T0 in the classical picture, it is suppressed by the quantum fluctuations. Beyond the critical pressure of pc=0.25 GPa, a sharp peak indicative of the phase transition appears and shifts towards a higher temperature with further increasing pressure. The phase transition is accompanied by a small peak anomaly in the temperature dependence of dielectric loss (that is, imaginary part of dielectric constant).


Quantum ferroelectricity in charge-transfer complex crystals.

Horiuchi S, Kobayashi K, Kumai R, Minami N, Kagawa F, Tokura Y - Nat Commun (2015)

Temperature- and pressure-dependent properties of TTF–QBr2I2 crystal.(a) Temperature dependence of the relative permittivity under various hydrostatic pressures. The applied pressure value, corrected considering its thermal change in the medium for each measurement, is represented by the value at the transition point or lowest temperature when the phase transition is absent. The inset depicts the data in the low-pressure range. (b) Temperature–pressure phase diagram; linear extrapolation of the phase boundary at high-temperature region points to 1.64 GPa at room temperature. The inset represents the quantum critical behaviour of ferroelectrics obeying the relation Tc∝(p–pc)1/2 in the low-critical temperature region. The open square represents the pressure at which the room temperature conductivity exhibited a sharp peak caused by the pressure-induced NIT. (c) Inverse relative permittivity as the function of the square of the temperature. The solid line represents the quantum critical behaviour ɛr–1∝T2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4490386&req=5

f3: Temperature- and pressure-dependent properties of TTF–QBr2I2 crystal.(a) Temperature dependence of the relative permittivity under various hydrostatic pressures. The applied pressure value, corrected considering its thermal change in the medium for each measurement, is represented by the value at the transition point or lowest temperature when the phase transition is absent. The inset depicts the data in the low-pressure range. (b) Temperature–pressure phase diagram; linear extrapolation of the phase boundary at high-temperature region points to 1.64 GPa at room temperature. The inset represents the quantum critical behaviour of ferroelectrics obeying the relation Tc∝(p–pc)1/2 in the low-critical temperature region. The open square represents the pressure at which the room temperature conductivity exhibited a sharp peak caused by the pressure-induced NIT. (c) Inverse relative permittivity as the function of the square of the temperature. The solid line represents the quantum critical behaviour ɛr–1∝T2.
Mentions: At ambient and low pressures, the relative permittivity around the lowest temperature (4 K) exhibits saturation behaviour and increases from 200 to 700 with pressure (Fig. 3a). According to the fit with the Barrett formula, T0 increases to +18.2(6) K at 0.23 GPa with T1=68.7(7) K and C=1.22(2) × 105 K. Although the phase transition is expected near this positive T0 in the classical picture, it is suppressed by the quantum fluctuations. Beyond the critical pressure of pc=0.25 GPa, a sharp peak indicative of the phase transition appears and shifts towards a higher temperature with further increasing pressure. The phase transition is accompanied by a small peak anomaly in the temperature dependence of dielectric loss (that is, imaginary part of dielectric constant).

Bottom Line: Here we have developed chemically pure tetrahalo-p-benzoquinones of n iodine and 4-n bromine substituents (QBr4-nIn, n=0-4) to search for ferroelectric charge-transfer complexes with tetrathiafulvalene (TTF).Quantum critical behaviour is accompanied by a much larger permittivity than those of other neutral-ionic transition compounds, such as well-known ferroelectric complex of TTF-QCl4 and quantum antiferroelectric of dimethyl-TTF-QBr4.By contrast, TTF-QBr3I complex, another member of this compound family, shows complete suppression of the ferroelectric spin-Peierls-type phase transition.

View Article: PubMed Central - PubMed

Affiliation: 1] National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8562, Japan [2] CREST, Japan Science and Technology Agency (JST), Tokyo 102-0076, Japan.

ABSTRACT
Quantum phase transition achieved by fine tuning the continuous phase transition down to zero kelvin is a challenge for solid state science. Critical phenomena distinct from the effects of thermal fluctuations can materialize when the electronic, structural or magnetic long-range order is perturbed by quantum fluctuations between degenerate ground states. Here we have developed chemically pure tetrahalo-p-benzoquinones of n iodine and 4-n bromine substituents (QBr4-nIn, n=0-4) to search for ferroelectric charge-transfer complexes with tetrathiafulvalene (TTF). Among them, TTF-QBr2I2 exhibits a ferroelectric neutral-ionic phase transition, which is continuously controlled over a wide temperature range from near-zero kelvin to room temperature under hydrostatic pressure. Quantum critical behaviour is accompanied by a much larger permittivity than those of other neutral-ionic transition compounds, such as well-known ferroelectric complex of TTF-QCl4 and quantum antiferroelectric of dimethyl-TTF-QBr4. By contrast, TTF-QBr3I complex, another member of this compound family, shows complete suppression of the ferroelectric spin-Peierls-type phase transition.

No MeSH data available.


Related in: MedlinePlus