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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 dependence of dielectric and magnetic properties of 1:1 TTF–QBr4–nIn complexes.(a) The spin susceptibility χs for ionic TTF–QBr4 and TTF–QBr3I crystals. The inset shows the corresponding χsT–T plot. (b) The relative permittivity measured with an a.c. electric field applied along the crystallographic b axis parallel to the DA stack of ionic TTF–QBr4 and TTF–QBr3I crystals. (c) The relative permittivity measured with an a.c. electric field applied along the DA stack (parallel to the crystallographic b axis) for neutral 1:1 TTF–QBr2I2, TTF–QBrI3 and TTF–QI4 crystals at ambient pressure.
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f2: Temperature dependence of dielectric and magnetic properties of 1:1 TTF–QBr4–nIn complexes.(a) The spin susceptibility χs for ionic TTF–QBr4 and TTF–QBr3I crystals. The inset shows the corresponding χsT–T plot. (b) The relative permittivity measured with an a.c. electric field applied along the crystallographic b axis parallel to the DA stack of ionic TTF–QBr4 and TTF–QBr3I crystals. (c) The relative permittivity measured with an a.c. electric field applied along the DA stack (parallel to the crystallographic b axis) for neutral 1:1 TTF–QBr2I2, TTF–QBrI3 and TTF–QI4 crystals at ambient pressure.

Mentions: The 1:1 complex of 2-iodo-3,5,6-tribromo-p-benzoquinone (QBr3I) crystallizes as an isomorphous form of the fully ionic TTF–QBr4 (ref. 15), the SP-type ferroelectric. Crystal structural analysis determined an analogous triclinic lattice with a space group of P-1 and two formula units (Z=2; Fig. 1c). The D and A molecules, occupying their respective inversion centres, are alternately stacked with a regular separation. The lattice constants of the a and b axes, which are both parallel to the DA stack, are elongated by 1.2% and 1.1%, respectively, compared with those of the TTF–QBr4 crystal. Figure 2a,b depicts the temperature-dependent magnetic susceptibility and dielectric constant of these two isomorphous compounds. The magnetic susceptibility in the high-temperature region indicates the analogous paramagnetism arising from the spin-1/2 residing on each D+ and A− radical, but its monotonous increase on cooling in the case of TTF–QBr3I represents the absence of the SP transition. In accord with this, the dielectric permittivity has no peak anomaly characteristic of the ferroelectric transition down to the lowest temperature. Nevertheless, the gradual increase in the permittivity with decreasing temperature may reflect the quantum fluctuations of the polar dimerization.


Quantum ferroelectricity in charge-transfer complex crystals.

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

Temperature dependence of dielectric and magnetic properties of 1:1 TTF–QBr4–nIn complexes.(a) The spin susceptibility χs for ionic TTF–QBr4 and TTF–QBr3I crystals. The inset shows the corresponding χsT–T plot. (b) The relative permittivity measured with an a.c. electric field applied along the crystallographic b axis parallel to the DA stack of ionic TTF–QBr4 and TTF–QBr3I crystals. (c) The relative permittivity measured with an a.c. electric field applied along the DA stack (parallel to the crystallographic b axis) for neutral 1:1 TTF–QBr2I2, TTF–QBrI3 and TTF–QI4 crystals at ambient pressure.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Temperature dependence of dielectric and magnetic properties of 1:1 TTF–QBr4–nIn complexes.(a) The spin susceptibility χs for ionic TTF–QBr4 and TTF–QBr3I crystals. The inset shows the corresponding χsT–T plot. (b) The relative permittivity measured with an a.c. electric field applied along the crystallographic b axis parallel to the DA stack of ionic TTF–QBr4 and TTF–QBr3I crystals. (c) The relative permittivity measured with an a.c. electric field applied along the DA stack (parallel to the crystallographic b axis) for neutral 1:1 TTF–QBr2I2, TTF–QBrI3 and TTF–QI4 crystals at ambient pressure.
Mentions: The 1:1 complex of 2-iodo-3,5,6-tribromo-p-benzoquinone (QBr3I) crystallizes as an isomorphous form of the fully ionic TTF–QBr4 (ref. 15), the SP-type ferroelectric. Crystal structural analysis determined an analogous triclinic lattice with a space group of P-1 and two formula units (Z=2; Fig. 1c). The D and A molecules, occupying their respective inversion centres, are alternately stacked with a regular separation. The lattice constants of the a and b axes, which are both parallel to the DA stack, are elongated by 1.2% and 1.1%, respectively, compared with those of the TTF–QBr4 crystal. Figure 2a,b depicts the temperature-dependent magnetic susceptibility and dielectric constant of these two isomorphous compounds. The magnetic susceptibility in the high-temperature region indicates the analogous paramagnetism arising from the spin-1/2 residing on each D+ and A− radical, but its monotonous increase on cooling in the case of TTF–QBr3I represents the absence of the SP transition. In accord with this, the dielectric permittivity has no peak anomaly characteristic of the ferroelectric transition down to the lowest temperature. Nevertheless, the gradual increase in the permittivity with decreasing temperature may reflect the quantum fluctuations of the polar dimerization.

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