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.

Thermodynamic properties of the proton-mediated single component dimer-Mott insulator of $\kappa \text{−}{\mathrm{H}}_3{\left(\mathrm{Cat}\text{−}\mathrm{EDT}\text{−}\mathrm{TTF}\right)}_2$, which has a two-dimensional triangle lattice structure of $S=1/2$ spins, are reported. The extraordinary large electronic heat capacity coefficient $\gamma =58.8\mathrm{mJ}{\mathrm{K}}^{-2}\mathrm{mo}{\mathrm{l}}^{-1}$ observed by the low-temperature heat capacity measurements up to 6 T suggests the formation of the gapless spin liquid ground state. Although the magnetic interaction $J/k_{\mathrm{B}}$ is quite different from those of other dimer-Mott spin liquids, the thermodynamic feature scales well with the Wilson ratio of 1.4–1.6. The heat capacity measurements also detected that the deuteration of the proton-linkage changes the ground state to the nonmagnetic one with almost vanishing γ. Using the data of the deuterated compound, the accurate temperature dependence of the magnetic heat capacity reflecting on the low-energy excitations from the gapless spin liquids ground state is discussed.

Peculiar low-temperature electronic properties induced by the filling change from a half-filled band realized in $\kappa \text{−}{\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_4{\mathrm{Hg}}_{2.89}{\mathrm{Br}}_8$ and $\kappa \text{−}{\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_4{\mathrm{Hg}}_{2.78}{\mathrm{Cl}}_8$, which belong to the well-known $\kappa$-type family of organic conductors, were studied by thermodynamic measurements. We observed unusual behaviors both in the lattice and the electronic heat capacities. The former is associated with the dimensional crossover in the acoustic phonons, which is attributable to the peculiarity of mercury chains in the anion layers. The electronic heat capacity represented by the $\gamma$ term at low temperatures is enhanced up to $52–55\mathrm{mJ}{\mathrm{K}}^{-2}{\mathrm{mol}}^{-1}$ [for the formula ${\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_2{\mathrm{Hg}}_{1.5-1∕2\delta }{X}_4$] due to anomalous growth of the antiferromagnetic spin fluctuations in these salts.

Heat capacity measurements of κ-(BEDT-TTF)₂X (BEDT-TTF: Bis(ethylendithio) tetrathiafulvalene, X: counteranions) which are classified as two-dimensional (2D) dimer-Mott system are reported. At first, we explain structural and electronic features originated from rigid dimerization in donor arrangement in 2D layers. The antiferromagnetic Mott insulating phase located at low-pressure region in the phase diagram shows vanishing γ electronic heat capacity coefficient in the heat capacity, which claims opening of a charge-gap in this insulating state. Then, a systematic change of the γ around the Mott boundary region is reported in relation to the glass freezing of ethylene dynamics. The thermodynamic parameters determined by ∆C_p/γT_c of 10 K class superconductors, κ-(BEDT-TTF)₂Cu(NCS)₂ and κ-(BEDT-TTF)₂Cu[N(CN)₂]Br demonstrate that a rather large gap with a strong coupling character appears around the Fermi-surface. On the other hand, the low temperature heat capacity clearly shows a picture of nodal-gap structure due to an anisotropic pairing. The comparison with lower T_c compounds in the κ-type structure is also performed so as to discuss overall features of the κ-type superconductors. The heat capacity measurements of hole-doped systems containing mercury in the counteranions show an anomalous enhancement of γ, which is consistent with the T₁⁻¹ of NMR experiments etc. The results of heat capacity measurements under high pressures are also reported.

We employ Green’s function method for describing multiband models with magnetic impurities and apply the formalism to the problem of chromium impurities adsorbed onto a carbon nanotube. Density functional theory is used to determine the bandstructure, which is then fit to a tight-binding model to allow for the subsequent Green’s function description. Electron–electron interactions, electron–phonon coupling, and disorder scattering are all taken into account (perturbatively) with a theory that involves a cluster extension of the coherent potential approximation. We show how increasing the cluster size produces more accurate results and how the final calculations converge as a function of the cluster size. We examine the spin-polarized electrical current on the nanotube generated by the magnetic impurities adsorbed onto the nanotube surface. The spin polarization increases with both increasing concentration of chromium impurities and with increasing magnetic field. Its origin arises from the strong electron correlations generated by the Cr impurities.