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Gapless spin liquid of an organic triangular compound evidenced by thermodynamic measurements.

Yamashita S, Yamamoto T, Nakazawa Y, Tamura M, Kato R - Nat Commun (2011)

Bottom Line: In frustrated magnetic systems, long-range ordering is forbidden and degeneracy of energy states persists, even at extremely low temperatures.This compound is an organic dimer-based Mott insulator with a two-dimensional triangular lattice structure.We also report anomalous enhancement of γ, produced by a kind of criticality inherent to the Pd(dmit)(2) phase diagram.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043, Japan.

ABSTRACT
In frustrated magnetic systems, long-range ordering is forbidden and degeneracy of energy states persists, even at extremely low temperatures. Under certain conditions, these systems form an exotic quantum spin-liquid ground state, in which strongly correlated spins fluctuate in the spin lattices. Here we investigate the thermodynamic properties of an anion radical spin liquid of EtMe(3)Sb[Pd(dmit)(2)](2), where dmit represents 1,3-dithiole-2-thione-4,5-dithiolate. This compound is an organic dimer-based Mott insulator with a two-dimensional triangular lattice structure. We present distinct evidence for the formation of a gapless spin liquid by examining the T-linear heat capacity coefficient, γ , in the low-temperature heat capacity. Using comparative analyses with κ-(BEDT-TTF)(2)Cu(2)(CN)(3), a generalized picture of the new spin liquid in dimer-based organic systems is discussed. We also report anomalous enhancement of γ, produced by a kind of criticality inherent to the Pd(dmit)(2) phase diagram.

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Comparison of electronic heat capacity coefficient γ between EtMe3Sb[Pd(dmit)2]2 and d9-EtMe3Sb[Pd(dmit)2]2.(a) Low-temperature heat capacities of h9-EtMe3Sb[Pd(dmit)2]2 (h9-EtMe3Sb; 0 T red squares, 2 T blue diamonds) and d9-EtMe3Sb[Pd(dmit)2]2 (d9-EtMe3Sb; 0 T purple pluses, 2 T ocher filled circles) below 3.1 K. Upward deviation of heat capacities of d9-EtMe3Sb[Pd(dmit)2]2 is observed below 2 K. The enhancement of the electronic heat capacity of d9-EtMe3Sb[Pd(dmit)2]2 is realized in this temperature region. (b) Low-temperature heat capacities of d9-EtMe3Sb[Pd(dmit)2]2 0 T (purple crosses), 2 T (ocher filled circles), 5 T (aqua blue squares) and 9 T (orange triangles) below 0.65 K plotted in CpT−1 versus T2. The enhanced T-linear contribution in heat capacity does not have drastic magnetic field dependence.
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f3: Comparison of electronic heat capacity coefficient γ between EtMe3Sb[Pd(dmit)2]2 and d9-EtMe3Sb[Pd(dmit)2]2.(a) Low-temperature heat capacities of h9-EtMe3Sb[Pd(dmit)2]2 (h9-EtMe3Sb; 0 T red squares, 2 T blue diamonds) and d9-EtMe3Sb[Pd(dmit)2]2 (d9-EtMe3Sb; 0 T purple pluses, 2 T ocher filled circles) below 3.1 K. Upward deviation of heat capacities of d9-EtMe3Sb[Pd(dmit)2]2 is observed below 2 K. The enhancement of the electronic heat capacity of d9-EtMe3Sb[Pd(dmit)2]2 is realized in this temperature region. (b) Low-temperature heat capacities of d9-EtMe3Sb[Pd(dmit)2]2 0 T (purple crosses), 2 T (ocher filled circles), 5 T (aqua blue squares) and 9 T (orange triangles) below 0.65 K plotted in CpT−1 versus T2. The enhanced T-linear contribution in heat capacity does not have drastic magnetic field dependence.

Mentions: In order to confirm that the upturn is originated from the rotational tunnelling, we also measured the heat capacity of a d9-EtMe3Sb[Pd(dmit)2]2 compound in which three Me groups in the cation had been deuterated during synthesis. As is shown in Figure 2b, the upturn was reduced down to a few percent due to the increased mass of Me groups. The residual upturn is inferred to be a trace of non-deuterated Me groups and Et groups remaining in the cations. The magnetic field dependence of the residual upturn of the deuterated compound shown in Figure 2b is the same as that of the pristine compound, which also ensures that this term is arisen by rotational tunnelling. Interestingly, we found that the deuterated compound in Figure 2b has a larger CpT−1 in the higher-temperature region up to about 2 K, which should be considered separately from the contribution of Me groups. Comparison of heat capacity data of the deuterated compound and pristine compound is shown in a wider temperature scale in Figure 3a. The temperature dependence of CpT−1 of the deuterated compound coincides well with that of the pristine compound above 2 K; however, below this temperature, it deviates upward with decreasing temperature. This deviation is gradual and insensitive to the external magnetic field of 2 T, but extrapolation down to T=0 gives a γ of about 40 mJ K−2 mol−1, which is nearly twice as large as that of the pristine compound. Figure 3b shows the data in the lower-temperature region under magnetic fields. The enhancement of the γ is retained and is observed under magnetic fields up to 9 T.


Gapless spin liquid of an organic triangular compound evidenced by thermodynamic measurements.

Yamashita S, Yamamoto T, Nakazawa Y, Tamura M, Kato R - Nat Commun (2011)

Comparison of electronic heat capacity coefficient γ between EtMe3Sb[Pd(dmit)2]2 and d9-EtMe3Sb[Pd(dmit)2]2.(a) Low-temperature heat capacities of h9-EtMe3Sb[Pd(dmit)2]2 (h9-EtMe3Sb; 0 T red squares, 2 T blue diamonds) and d9-EtMe3Sb[Pd(dmit)2]2 (d9-EtMe3Sb; 0 T purple pluses, 2 T ocher filled circles) below 3.1 K. Upward deviation of heat capacities of d9-EtMe3Sb[Pd(dmit)2]2 is observed below 2 K. The enhancement of the electronic heat capacity of d9-EtMe3Sb[Pd(dmit)2]2 is realized in this temperature region. (b) Low-temperature heat capacities of d9-EtMe3Sb[Pd(dmit)2]2 0 T (purple crosses), 2 T (ocher filled circles), 5 T (aqua blue squares) and 9 T (orange triangles) below 0.65 K plotted in CpT−1 versus T2. The enhanced T-linear contribution in heat capacity does not have drastic magnetic field dependence.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3104558&req=5

f3: Comparison of electronic heat capacity coefficient γ between EtMe3Sb[Pd(dmit)2]2 and d9-EtMe3Sb[Pd(dmit)2]2.(a) Low-temperature heat capacities of h9-EtMe3Sb[Pd(dmit)2]2 (h9-EtMe3Sb; 0 T red squares, 2 T blue diamonds) and d9-EtMe3Sb[Pd(dmit)2]2 (d9-EtMe3Sb; 0 T purple pluses, 2 T ocher filled circles) below 3.1 K. Upward deviation of heat capacities of d9-EtMe3Sb[Pd(dmit)2]2 is observed below 2 K. The enhancement of the electronic heat capacity of d9-EtMe3Sb[Pd(dmit)2]2 is realized in this temperature region. (b) Low-temperature heat capacities of d9-EtMe3Sb[Pd(dmit)2]2 0 T (purple crosses), 2 T (ocher filled circles), 5 T (aqua blue squares) and 9 T (orange triangles) below 0.65 K plotted in CpT−1 versus T2. The enhanced T-linear contribution in heat capacity does not have drastic magnetic field dependence.
Mentions: In order to confirm that the upturn is originated from the rotational tunnelling, we also measured the heat capacity of a d9-EtMe3Sb[Pd(dmit)2]2 compound in which three Me groups in the cation had been deuterated during synthesis. As is shown in Figure 2b, the upturn was reduced down to a few percent due to the increased mass of Me groups. The residual upturn is inferred to be a trace of non-deuterated Me groups and Et groups remaining in the cations. The magnetic field dependence of the residual upturn of the deuterated compound shown in Figure 2b is the same as that of the pristine compound, which also ensures that this term is arisen by rotational tunnelling. Interestingly, we found that the deuterated compound in Figure 2b has a larger CpT−1 in the higher-temperature region up to about 2 K, which should be considered separately from the contribution of Me groups. Comparison of heat capacity data of the deuterated compound and pristine compound is shown in a wider temperature scale in Figure 3a. The temperature dependence of CpT−1 of the deuterated compound coincides well with that of the pristine compound above 2 K; however, below this temperature, it deviates upward with decreasing temperature. This deviation is gradual and insensitive to the external magnetic field of 2 T, but extrapolation down to T=0 gives a γ of about 40 mJ K−2 mol−1, which is nearly twice as large as that of the pristine compound. Figure 3b shows the data in the lower-temperature region under magnetic fields. The enhancement of the γ is retained and is observed under magnetic fields up to 9 T.

Bottom Line: In frustrated magnetic systems, long-range ordering is forbidden and degeneracy of energy states persists, even at extremely low temperatures.This compound is an organic dimer-based Mott insulator with a two-dimensional triangular lattice structure.We also report anomalous enhancement of γ, produced by a kind of criticality inherent to the Pd(dmit)(2) phase diagram.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Graduate School of Science, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043, Japan.

ABSTRACT
In frustrated magnetic systems, long-range ordering is forbidden and degeneracy of energy states persists, even at extremely low temperatures. Under certain conditions, these systems form an exotic quantum spin-liquid ground state, in which strongly correlated spins fluctuate in the spin lattices. Here we investigate the thermodynamic properties of an anion radical spin liquid of EtMe(3)Sb[Pd(dmit)(2)](2), where dmit represents 1,3-dithiole-2-thione-4,5-dithiolate. This compound is an organic dimer-based Mott insulator with a two-dimensional triangular lattice structure. We present distinct evidence for the formation of a gapless spin liquid by examining the T-linear heat capacity coefficient, γ , in the low-temperature heat capacity. Using comparative analyses with κ-(BEDT-TTF)(2)Cu(2)(CN)(3), a generalized picture of the new spin liquid in dimer-based organic systems is discussed. We also report anomalous enhancement of γ, produced by a kind of criticality inherent to the Pd(dmit)(2) phase diagram.

Show MeSH
Related in: MedlinePlus