Electronic Heat Capacity Coefficient Research Articles

Low- and high-temperature heat capacity of metallic technetium

The heat capacity of technetium metal has been measured from 2.1 K to 293 K using relaxation calorimetry and the enthalpy increment up to 1700 K using drop calorimetry. The low-temperature calorimetry measurements revealed a superconducting transition temperature of TC = (7.76 ± 0.08) K. The zero-degree Debye temperature(θE) and the electronic heat capacity coefficient (γe) of the normal state were derived as (307 ± 5) K and (4.22 ± 0.20) mJ·K−2·mol−1, respectively. The standard entropy of the superconducting standard state was derived as Sm° (298.15) = (36.8 ± 1.3) J·K−1·mol−1. The fitting of enthalpy-increment data together with high-temperature heat capacity data reported in literature yielded a heat capacity equation up to 1700 K.

A Third Generation Calphad Description of Fe: Revisions of Fcc, Hcp and Liquid

The thermodynamic description of pure Fe was re-assessed using updated third generation Calphad models and taking into account the most recent theoretical data. In the present re-assessment, a critical evaluation was performed for the magnetic properties of the fcc and hcp phases yielding different descriptions from those accepted in the SGTE database. The selected magnetic properties enable us to model the thermodynamic properties of fcc satisfactorily without using the magnetic two-state model. A new method was applied to extrapolate the thermodynamic data for the solid phases, i.e. a single Gibbs energy expression is used for the entire temperature range for the bcc, fcc and hcp phases. The description of the liquid phase was re-evaluated following a recent suggestion on estimating the electronic heat capacity coefficient for the liquid phase. Overall, the present Calphad description can reproduce the selected experimental and theoretical data well.

Comparison of the electronic transport of ThN against ThC

We compared the electronic heat capacity coefficient, thermal conductivity and resistivity of ThN and ThC. We found that the electronic heat capacity coefficient of both compounds was very low as evaluated using Quantum Espresso and GGA of the Perdew, Burke, and Ernzerhof (PBE) functional. The calculated electronic heat coefficient was further reduced (∼three times for ThN and four times for ThC) when the non-local hybrid functional (B3LYP) was used. QE combined with EPW code were used to calculate integrated electron-phonon coupling strength, the Eliashberg transport coupling function and electron-phonon scattering rates. The electronic resistivity was calculated using Ziman's formula for metals as implemented in EPW code and compared to the values derived from experimental data correlations. Furthermore, the effective number (neff) of electronic carriers was calculated. The electronic thermal conductivity was evaluated from the calculated electronic resistivity via Wiedemann-Franz law using the derived number of mobility electrons: nav (averaged over the temperature range 300 K–1000 K). We found that the only way to reproduce exactly the experimental electrical resistivity and electronic thermal conductivity in both ThN and ThC was to incorporate the number of electrons contributing to thermal mobility (neff), which increase with temperature. We estimated that in ThN the number of electronic carriers is two times larger and electron-phonon coupling strength lower by a factor ∼ two, which led to about five times higher electronic thermal conductivity than calculated for ThC.

The boson-based quantized dynamics of solids

Available experimental data of the Debye temperature (ΘD) and of the coefficient of the low-temperature electronic heat capacity (γ) of the condensed elements are analyzed in a rather heuristic way. Since the two associated heat capacities exhibit the same universal temperature dependence in all solids (∼T3 and ∼T, respectively), they have to be identified as the heat capacities of boson fields. In the elastic case the bosons are the well-known sound waves. Neither the dispersion relation nor the sources of the bosons of the metallic continuum are known. The bosons interact surprisingly strong with the corresponding atomistic degrees of freedom, i.e. phonons and electron-band states, and modify their dispersion relations strongly. The actual values of ΘD and γ therefore depend considerably on the interaction strength to these atomistic excitations. The experimental indications will be discussed that this interaction is according to discrete modes and appears to be quantized.

Heat capacity, entropy, formation energy and spin-fluctuation behavior of U3Si5 from 2.4 to 397.4 K

• Heat capacity data of U3Si5 were obtained using a Quantum Design Physical Properties Measurement System (PPMS) from 2.4 to 397.4 K. • An upturn characteristic of spin-fluctuations in Cp/T (T) was observed below 10 K. • The Gibbs free energy of formation of U3Si5 from the elements was determined to be –45.2 ± 9.0 kJ•mol−1•atom−1. U-Si intermetallic compounds are of considerable interest for their applications as accident-tolerant nuclear fuels. Here we present low-temperature heat capacity (LTHC) measurements of one of the U-Si phases, U 3 Si 5 , using a Quantum Design Physical Properties Measurement System (PPMS) from 2.4 to 397.4 K. We observed an upturn in C p /T (T) below 10 K and have attributed this behavior to potential spin-fluctuations (SF) with an SF temperature (T sf ) of 27 K. An enhancement of LTHC was also observed, as manifested by a large electronic heat capacity coefficient (γ el ) of 342.9 mJ/mol•K 2 . From the heat capacity data, the following thermodynamic parameters were determined: the characteristic Debye temperature ( θ D ) over the temperature range 30 – 397 K is 177 ± 2 K, and the standard entropy ( Δ 0 298 . 15 S ∘ ) is 283.3 ± 5.7 J•mol −1 •K −1 (equivalent to 35.4 ± 0.7 J•mol −1 •atom −1 •K −1 ). Combined with our previously measured formation enthalpy ( Δ f H e l ∘ ) of U 3 Si 5 , the Gibbs free energy of formation of U 3 Si 5 from the elements ( Δ f G e l ∘ ) was determined to be –45.2 ± 9.0 kJ•mol −1 •atom −1 .

Suppression of antiferromagnetic order and strong ferromagnetic spin fluctuations in Ca(Co1−xNix)2−yAs2 single crystals

${\mathrm{CaCo}}_{2\ensuremath{-}y}{\mathrm{As}}_{2}$ is a unique itinerant system having strong magnetic frustration. Here, we report the effect of electron doping on the physical properties resulting from Ni substitutions for Co. The single crystals of $\mathrm{Ca}{({\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x})}_{2\ensuremath{-}y}{\mathrm{As}}_{2}$ were characterized by single-crystal x-ray diffraction, energy-dispersive x-ray spectroscopy, magnetization $M$ versus temperature $T$, magnetic field $H$, time $t$, and heat capacity ${C}_{\mathrm{p}}(H,T)$ measurements. The A-type antiferromagnetic (AFM) transition temperature ${T}_{\mathrm{N}}=52$ K for $x=0$ decreases to 22 K with only 3% Ni substitution and is completely suppressed for $x>0.16$. For $0.11\ensuremath{\le}x\ensuremath{\le}0.52$ strong ferromagnetic (FM) fluctuations develop as revealed by magnetic susceptibility $\ensuremath{\chi}(T)=M(T)/H$ measurements. For $x=0.11$ and 0.16 competing AFM and FM interactions result in a reentrant spin-glass behavior below ${T}_{\mathrm{N}}$, as evidenced by the observations of thermomagnetic hysteresis and magnetic relaxation. Enhanced FM fluctuations are also found for the $x=0.21$ and 0.31 crystals, where ${\ensuremath{\chi}}_{c}$ increases significantly at low $T$. A large $\ensuremath{\chi}$ anisotropy in these compositions where ${\ensuremath{\chi}}_{c}$ is up to a factor of two larger than ${\ensuremath{\chi}}_{ab}$ suggests that the FM spin fluctuations are quasi-1D in nature. Weak ferromagnetic contributions to the magnetization are found at $T=2$ K for $x=0.11$--0.31. Heat-capacity ${C}_{\mathrm{p}}(T)$ measurements reveal the presence of FM quantum spin fluctuations for $0.11\ensuremath{\le}x\ensuremath{\le}0.52$, where a logarithmic $T$ dependence of ${C}_{\mathrm{p}}(T)/T$ is observed at low $T$. The suppression of AFM order by the development of strong FM fluctuations in $\mathrm{Ca}{({\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x})}_{2\ensuremath{-}y}{\mathrm{As}}_{2}$ crystals suggests the presence of a FM quantum-critical point at $x\ensuremath{\approx}0.20$. Our density-functional theory (DFT) calculations confirm that FM fluctuations are enhanced by Ni substitutions for Co in ${\mathrm{CaCo}}_{2\ensuremath{-}y}{\mathrm{As}}_{2}$. The Sommerfeld electronic heat-capacity coefficient is enhanced for $x=0$, 0.21, and 0.42 by about a factor of two compared to DFT calculations of the density of states (DOS) at the Fermi energy, suggesting an enhancement of the DOS from electron-phonon and/or electron-electron interactions. The crystals with $x>0.52$ do not exhibit FM spin fluctuations or magnetic order at $T\ensuremath{\ge}1.8$ K, which was found from the DFT calculations to arise from a Stoner transition. Superconductivity is not observed above 1.8 K for any of the compositions. Neutron-diffraction studies of crystals with $x=0.11$ and 0.16 in the crossover regime $(0.1\ensuremath{\lesssim}x\ensuremath{\lesssim}0.2)$ show no evidence of A-type ordering as observed in the parent compound with $x=0$. Furthermore, no other common magnetic structures, such as ferromagnetic (FM), helical stacking of in-plane FM layers, or in-plane AFM structure, are found with an ordered moment greater than the uncertainty of $0.05\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ per transition-metal atom.

ВЛИЯНИЕ ДОБАВОК ГАЛЛИЯ НА ТЕПЛОЕМКОСТЬ И ТЕРМОДИНАМИЧЕСКИЕ ФУНКЦИИ АЛЮМИНИЕВОГО СПЛАВА АЖ5К10

Heat capacity is the most important characteristic of substances, and from its change with temperature one can determine the type of phase transformation, Debye temperature, energy of vacancy formation, coefficient of electronic heat capacity and other properties. In this work, the heat capacity of the АЖ5К10 aluminum alloy was determined in the "cooling" mode, according to the known heat capacity of a reference sample made of M00 copper. To do that, the equations describing their cooling rates were obtained by processing the cooling curves of the samples from the alloys of the АЖ5К10-Ga system and the standard. Further, according to the experimentally found values of the cooling rates of the samples from the alloys and the standard, knowing their masses, the polynomials of the temperature dependence of the heat capacity of the alloys were established, which are described by a four-term equation. Using integrals of specific heat capacity, the temperature dependence of changes in enthalpy, entropy and Gibbs energy was calculated. The obtained dependences show that with an increase in temperature, the heat capacity, heat transfer coefficient, enthalpy and entropy of alloys increase, while the values of the Gibbs energy decrease. In that case, the addition of gallium reduces the heat capacity, enthalpy, and entropy of the АЖ5К10 alloy, while the value of the Gibbs energy increases

Effect of alkaline earth metals on the heat capacity and change of thermodynamic function of AK1M2 alloy on the basis of specific aluminum

It is known that high purity aluminum with a minimum content of impurities is widely used in electronic technology for the manufacture of conductive paths in integrated circuits. Hence the development of new compositions of alloys based on such a metal is a very urgent task. One of the promising alloys based on such a metal is alloy AK1M2 (Al + 1 % Si + 2 % Cu). This alloy was accepted by us as a model alloy and subjected to modification by alkaline earth metals.Heat capacity is the most important characteristic of substances and by its variation with temperature one can determine the type of phase transformation, the Debye temperature, the energy of formation of vacancies, the coefficient of electronic heat capacity, and other properties. In the present work, the heat capacity of the AK1M2 alloy with alkaline earth metals was determined in the “cooling” mode from the known heat capacity of a reference sample from copper. For which, by processing the curves of the cooling rate of samples from the alloy AK1M2 with alkaline earth metals and the standard, polynomials were obtained which describe their cooling rates. Further, by experimentally found values of the cooling rates of the standard and samples from alloys, knowing their masses, the polynomials of the temperature dependence of the heat capacity of the alloys and the standard were established, which are described by a four-term equation. Using the integrals of the specific heat, the models of temperature dependence of the change in enthalpy, entropy and Gibbs energy were established.The dependences obtained show that with an increase in temperature, the heat capacity, enthalpy, and entropy of alloys increase, and the values of Gibbs energy decrease. At the same time, additives of alkaline earth metals do not significantly reduce the heat capacity, enthalpy and entropy of the original alloy AK1M2 and increase the value of Gibbs energy. During the transition from alloys with calcium with barium, the heat capacity of the alloys decreases, which correlates with the heat capacity of pure alkaline earth metals within the subgroup.

Ferromagnetic cluster-glass phase in Ca(Co1−xIrx)2−yAs2 crystals

Single crystals of Ca[Co_(2-x)Ir_(x)]_(2-y)As2 with 0 <= x <= 0.35 and 0.10 <= y <= 0.14 have been grown using the self-flux technique and characterized by single-crystal x-ray diffraction (XRD), energy-dispersive x-ray spectroscopy, magnetization M and magnetic susceptibility chi measurements versus temperature T, magnetic field H, and time t, and heat capacity Cp(H,T) measurements. The XRD refinements reveal that all the Ir-substituted crystals crystallize in a collapsed-tetragonal structure as does the parent CaCo_(2-y)As2 compound. A small 3.3% Ir substitution for Co in CaCo_(1.86)As2 drastically lowers the A-type antiferromagnetic (AFM) transition temperature TN from 52 to 23 K with a significant enhancement of the Sommerfeld electronic heat-capacity coefficient. The positive Weiss temperatures obtained from Curie-Weiss fits to the chi(T>TN) data indicate that the dominant magnetic interactions are ferromagnetic (FM) for all x. A magnetic phase boundary is inferred to be present between x = 0.14 and x = 0.17 from a discontinuity in the x dependences of the effective moment and Weiss temperature in the Curie-Weiss fits. FM fluctuations that strongly increase with increasing x are also revealed from the chi(T) data. The magnetic ground state for x >= 0.17 is a spin glass as indicated by hysteresis in chi(T) between field-cooling and zero-field-cooling measurements and from the relaxation of M in a small field that exhibits a stretched-exponential time dependence. The spin glass has a small FM component to the ordering and is hence inferred to be comprised of small FM clusters. A logarithmic T dependence of Cp at low T for x = 0.14 is consistent with the presence of significant FM quantum fluctuations. This composition is near the T = 0 boundary at x = 0.16 between the A-type AFM phase containing ferromagnetically-aligned layers of spins and the FM cluster-glass phase.

Analysis of Electronic Properties from Magnetotransport Measurements on Ba(Fe1xNix)2As2 Thin Films.

We performed a detailed structural, magnetotransport, and superconducting analysis of thin epitaxial Ba(Fe1−xNix)2As2 films with Ni doping of x = 0.05 and 0.08, as prepared by pulsed laser deposition. X-ray diffraction studies demonstrate the high crystalline perfection of the films, which have a similar quality to single crystals. Furthermore, magnetotransport measurements of the films were performed in magnetic fields up to 9 T. The results we used to estimate the density of electronic states at the Fermi level, the coefficient of electronic heat capacity, and other electronic parameters for this compound, in their dependence on the dopant concentration within the framework of the Ginzburg–Landau–Abrikosov–Gorkov theory. The comparison of the determined parameters with measurement data on comparable Ba(Fe1−xNix)2As2 single crystals shows good agreement, which confirms the high quality of the obtained films.

Pressure effects on the electronic structure and superconductivity of (TaNb)0.67(HfZrTi)0.33 high entropy alloy

Effects of pressure on the electronic structure, electron-phonon interaction, and superconductivity of the high entropy alloy (TaNb)$_{0.67}$(HfZrTi)$_{0.33}$ are studied in the pressure range 0 - 100 GPa. The electronic structure is calculated using the Korringa-Kohn-Rostoker method with the coherent potential approximation. Effects of pressure on the lattice dynamics are simulated using the Debye-Gr\"{u}neisen model and the Gr\"{u}neisen parameter at ambient conditions. In addition, the Debye temperature and Sommerfeld electronic heat capacity coefficient were experimentally determined. The electron-phonon coupling parameter $\lambda$ is calculated using the McMillan-Hopfield parameters and computed within the rigid muffin tin approximation. We find, that the system undergoes the Lifshitz transition, as one of the bands crosses the Fermi level at elevated pressures. The electron-phonon coupling parameter $\lambda$ decreases above 10 GPa. The calculated superconducting $T_c$ increases up to 40 - 50 GPa and, later, is stabilized at the larger value than for the ambient conditions, in agreement with the experimental findings. Our results show that the experimentally observed evolution of $T_c$ with pressure in (TaNb)$_{0.67}$(HfZrTi)$_{0.33}$ can be well explained by the classical electron-phonon mechanism.

Thermodynamic Investigation of Metamagnetism in Pulsed High Magnetic Fields on Heavy Fermion Superconductor UTe2

We investigated the thermodynamic property of the heavy fermion superconductor UTe$_2$ in pulsed high magnetic fields. The superconducting transition in zero field was observed at $T_{\rm c}$=1.65 K as a sharp heat capacity jump. Magnetocaloric effect measurements in pulsed-magnetic fields obviously detected a thermodynamic anomaly accompanied by a first-order metamagnetic transition at $\mu$$_{0}$$H_{\rm m}$=36.0 T when the fields are applied nearly along the hard-magnetization $b$-axis. From the results of heat capacity measurements in magnetic fields, we found a drastic diverging electronic heat capacity coefficient of the normal state $\gamma$$_{\rm N}$ with approaching $H_{\rm m}$. Comparing with the previous works via the magnetic Clausius-Clapeyron relation, we unveil the thermodynamic details of the metamagnetic transition. The enhancement of the effective mass observed as the development of $\gamma_{\rm N}$ indicates that quantum fluctuation strongly evolves around $H_{\rm m}$; it assists the superconductivity emerging even in extremely high fields.

Thermodynamic Picture of Dimer-Mott Organic Superconductors Revealed by Heat Capacity Measurements with External and Chemical Pressure Control

This article reviews and discusses the thermodynamic properties of dimer-Mott-type molecular superconductive compounds with (BEDT-TTF)2X composition, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X denotes counter-anions, respectively. We focus mainly on the features occurring in the κ-type structure in which the d-wave superconductive phase appears depending on the Coulomb repulsion U and the bandwidth W, which is tunable by external and chemical pressures. First, we report the high-pressure ac (alternating current) calorimetry technique and experimental system constructed to measure single-crystal samples of molecule-based compounds to derive low-temperature thermodynamic parameters. Using extremely small resistance chips as a heater and a thermometer allows four-terminal detection of an accurate temperature and its oscillation in the sample part with sufficient sensitivity. From the analyses of the temperature dependence of the ac heat capacity of κ-(BEDT-TTF)2Cu(NCS)2 under external pressures, we discuss the changes in the peak shape of the thermal anomaly at the superconductive transition temperature Tc at various external pressures p. The rather sharp peak in CpT−1 at Tc = 9.1 K with a strong coupling character at ambient pressure is gradually reduced to weaker coupling as the pressure increases to 0.45 GPa concomitant with suppression of the transition temperature. This feature is compared with the systematic argument of the chemical–pressure effect on the basis of thermal anomalies around the superconductive transition of κ-(BEDT-TTF)2X compounds and other previously studied typical dimer-Mott 2:1 compounds. Finally, the discussion is extended to the chemical pressure effect on the normal state electronic heat capacity coefficient γ obtained by applying magnetic fields higher than Hc2 and the residual γ*, which remains in the superconductive state due to the induced electron density of states around the node structure. From the overall arguments with respect to both chemical and external pressures, we suggest that a crossover of the electronic state inside the superconductive phase occurs and the coupling strength of electron pairs varies from the electron correlation region near the metal-insulator boundary to the band picture region.

Molar Heat Capacity of Potassium Alum KAl(SO4)2 ·12H2O at Low Temperatures: Revisited with Determination of the Debye Temperature

Two earlier published experimental data [C. H. Shomate, J. Am. Chem. Soc. 67, 765 (1945); D. G. Kapadnis and R. Hartmans, Physica 22, 173 (1956)] of the molar heat capacity C p of potassium alum, KAl(SO4)2·12H2O, are revisited. From analysis of the temperature dependence of C p [D. G. Kapadnis and R. Hartmans, Physica 22, 173 (1956)] below 20 K by using the experimental values of C p represented as a plot of C p /T = γ+AT2, the Sommerfeld parameter γ (electronic heat capacity coefficient) and the slope A (lattice heat capacity coefficient) are estimated as γ = 0 JK −2mol −1 and A = 3.35×10 −3 JK −4mol −1, respectively. This indicates that only acoustic phonons contribute to the heat capacity below 4 K. The Debye T3-law is found to hold good to 4 K, i.e., to T < θ D /20, where θ D is the calorimetric Debye temperature calculated as θ D = 83.4 K, indicative of the strength of the chemical bonding in the system.

First-principles calculations of lattice dynamics and thermodynamic properties for Yb14MnSb11

Systematic first-principles calculations were performed to study the lattice dynamics of Yb14MnSb11 and hence to obtain a wide range of its thermodynamic properties at high temperatures. The calculated results were analyzed in terms of the lattice contribution and the electronic contribution, together with a comparison with a collection of experimental thermochemical data. At 0 K, the electronic density of states showed the typical feature of a p-type semiconductor—a small amount of unoccupied electronic states exclusively made of the major spin by a range of ∼0.6 eV above the Fermi energy. It showed that the Mn atom had a ferromagnetic spin moment of ∼4 μB. As a semiconductor, it was found that the electronic contribution to the heat capacity was substantial, with an electronic heat capacity coefficient of ∼0.0006 J/mole-atom/K2.

Dielectric functions of Pd and Zr transition metals: an application of Drude-Lorentz models with simulated annealing optimization.

An accepted-probability-controlled simulated annealing (APCSA) method has shown to be a valuable tool to describe, in parametric form, by means of an extended Drude-Lorentz model, the dielectric function of several metals through infrared, visible, and ultraviolet photon energies [Appl. Opt.37, 5271 (1998)APOPAI0003-693510.1364/AO.37.005271]. In this work, an improved APCSA approach is used to estimate the parameters involved in an extended Drude-Lorentz type model which incorporates the dielectric constant due to a background electronic polarization in the Drude term and the normalization of the individual oscillation strengths involved in the Lorentz contributions to the dielectric function. This last approach allows us to introduce a new parameter z to be optimized: the number density ratio, i.e., the ratio between number density of conduction electrons and number density of metal ions. From the optimization of the z value within this novel approach, we evaluate other parameters: electrical resistivity, electron mean free path, effective mass of conduction electrons and relaxation time, Fermi energy, electronic density of states at the Fermi level, and electronic heat capacity coefficient. Application of the model is carried out to describe the dielectric functions of two transition metals, Pd and Zr, through ultraviolet, visible, and infrared photon energies.

T/Bscaling without quasiparticle mass divergence:YbCo2Ge4

YbCo$_2$Ge$_4$ is a clean paramagnetic Kondo lattice which displays non-Fermi liquid behavior. We report a detailed investigation of the specific heat, magnetic Gr\"uneisen parameter ($\Gamma_{\rm mag}$) and temperature derivative of the magnetization ($M$) on a high-quality single crystal at temperatures down to $0.1$~K and magnetic fields up to 7~T. $\Gamma_{\rm mag}$ and $dM/dT$ display a divergence upon cooling and obey $T/B$ scaling. Similar behavior has previously been found in several other Yb-based Kondo lattices and related to a zero-field quantum critical point without fine tuning of pressure or composition. However, in the approach of $B\rightarrow 0$ the electronic heat capacity coefficient of YbCo$_2$Ge$_4$ saturates at low $T$, excluding ferromagnetic quantum criticality. This indicates that $T/B$ scaling is insufficient to prove a zero-field quantum critical point.

Thermal properties and electronic structure of superconducting germanide skutterudites and : a multi-band perspective

We present the temperature (T) and magnetic field (H) dependence of heat capacity (C) of the superconducting skutterudite compounds and along with their electronic band structure. We show that the zero-field C(T) in the superconducting state of both the samples cannot be explained using an isotropic single gap or an anisotropic single gap perspective. We find that it can only be explained in terms of two superconducting gaps. The Sommerfeld coefficient of electronic heat capacity in the mixed superconducting state of these compounds obtained from the C(T) closely follows the measured C(H) at 2 K. Observation of two distinct linear regions in with a change of slope in between for both the samples supports the fact that the two gap superconductivity is intrinsic to this family of skutterudites. A large observed in the limit of zero magnetic field for both the samples indicates the possibility of anisotropy in the superconducting gaps of these compounds. Apart from supporting the evidence for the above experimental observations, the band structure calculations also show that the anisotropy of the gaps in is different from that of .

Rotational tunneling of methyl groups and the electronic heat capacity of EtMe3Sb[Pd(dmit)2]2 under magnetic fields

In order to discuss the stability of the gapless features in the spin liquid state against magnetic fields, we report results and analyses of low-temperature heat capacity measurements of EtMe3Sb[Pd(dmit)2]2 under magnetic fields. The large upturn of [Formula: see text] at 0 T observed previously in EtMe3Sb[Pd(dmit)2]2 can be attributed to the rotational tunneling of the methyl groups in the counter cations and this upturn is suppressed by applying magnetic fields. The phenomenological resemblance of the feature under magnetic field was confirmed by comparative discussion of heat capacity measurement of metal complex of [Cu(acac)(OCH[Formula: see text]]2 having similar methyl groups. The gapless character evidenced by the finite electronic heat capacity coefficient, [Formula: see text] was found to be retained upon applying 17 T in EtMe3Sb[Pd(dmit)2]2, which means that spin liquid ground state is stable against high magnetic fields. The finite [Formula: see text] in the spin liquid compounds is considered to be related to a kind of density of states in spin excitations rather than those determined by disorders such as spin glasses.

Thermodynamic Evidence of d-Wave Superconductivity of the Organic Superconductor λ-(BETS)2GaCl4

Low-temperature heat capacity of the organic superconductor λ-(BETS)2GaCl4 in a temperature range between 0.6 and 10 K was measured for a single crystal sample by relaxation calorimetry technique. The contribution of electronic heat capacity in the superconducting state shows T2 dependence at lower temperature that indicates the existence of quasi-particle excitations from the line-nodal gap structure of d-wave pairing. The recovery of the electronic heat capacity coefficient, γ by magnetic field shows H1/2 dependence that is consistent with the picture of line-nodal superconductor. In spite of the different packing from typical organic superconductors κ-(BEDT-TTF)2X, the λ-type BETS salt also shows a feature of d-wave symmetry pairing.