Behavior Of Specific Heat Research Articles

Muon spin relaxation study of spin dynamics on a Kitaev honeycomb material H3LiIr2O6

The vacancy effect in quantum spin liquid (QSL) has been extensively studied. A finite density of random vacancies in the Kitaev model can lead to a pileup of low-energy density of states (DOS), which is generally experimentally determined by a scaling behavior of thermodynamic or magnetization quantities. Here, we report detailed muon spin relaxation (μSR) results of H3LiIr2O6, a Kitaev QSL candidate with vacancies. The absence of magnetic order is confirmed down to 80 mK, and the spin fluctuations are found to be persistent at low temperatures. Intriguingly, the time-field scaling law of longitudinal-field (LF)-μSR polarization is observed down to 0.1 K. This indicates a dynamical scaling, whose critical exponent of 0.46 is excellently consistent with the scaling behavior of specific heat and magnetization data. All the observations point to the finite DOS with the form N(E)∼E−ν\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$N(E)\\sim {E}^{-\ u }$$\\end{document}, which is expected for the Kitaev QSL in the presence of vacancies. Our μSR study provides a dynamical fingerprint of the power-law low-energy DOS and introduces a crucial new insight into the vacancy effect in QSL.

Even–Odd Layer Oscillatory Behavior of Electronic and Phononic Specific Heat in an Ultra-Thin Metal Film

Both electronic and phononic statistical and thermal properties, modulated by the quantum size effect, are suggested in a thin metal film. In order to show the quantum size effect of specific heat, the densities of the electron and phonon states of an ultra-thin film are treated within the framework of quantum statistics. It was found that strong and weak “even–odd layer oscillatory behavior” was exhibited by the ultra-thin metal film in electronic and lattice specific heat, respectively. Such a behavior, which depends on film thickness, results from the quantum confinement of electrons and phonons in the vertical (thickness) direction of the film, where both electrons and phonons form their respective quantum well standing wave modes. If, for example, the thickness of the ultra-thin metal film is exactly an integer multiple of a half wavelength of the standing wave of electrons in the thickness direction, the corresponding density of states would become maximized, and the electronic specific heat would take its maximum. In the literature, less attention has been paid to the size-dependent electron Fermi wavelength for quantum size effects, i.e., the Fermi wavelength in ultra-thin metal films has always been identified as a constant. We shall show how the Fermi wavelength varies with the size of a nanofilm, including an explicit analytic formulation for the thickness dependence of the electron Fermi wavelength. Size-dependent resonantly oscillatory behavior, depending on the ultra-thin or nanoscale film thickness, would have possible significance for researching some fundamental physical characteristics (e.g., low-dimensional quantum statistics) and may find potential applications in new thermodynamic device design.

Blume-Capel model analysis with a microcanonical population annealing method.

We present a modification of the Rose-Machta algorithm [N. Rose and J. Machta, Phys. Rev. E 100, 063304 (2019)2470-004510.1103/PhysRevE.100.063304] and estimate the density of states for a two-dimensional Blume-Capel model, simulating 10^{5} replicas in parallel for each set of parameters. We perform a finite-size analysis of the specific heat and Binder cumulant, determine the critical temperature along the critical line, and evaluate the critical exponents. The obtained results are in good agreement with those previously obtained using various methods-Markov chain Monte Carlo simulation, Wang-Landau simulation, transfer matrix, and series expansion. The simulation results clearly illustrate the typical behavior of specific heat along the critical lines and through the tricritical point.

Performance enhancement of quantum Brayton engine via Bose-Einstein condensation.

Bose-Einstein condensation is a quintessential characteristic of Bose systems. We investigate the finite-time performance of an endoreversible quantum Brayton heat engine operating with an ideal Bose gas with a finite number of particles confined in a d-dimensional harmonic trap. The working medium of these engines may work in the condensation, noncondensation, and near-critical point regimes, respectively. We demonstrate that the existence of the phase transition during the cycle leads to enhanced engine performance by increasing power output and efficiencies corresponding to maximum power and maximum efficient power. We also show that the quantum engine working across the Bose-Einstein condensation in N-particle Bose gas outperforms an ensemble of independent single-particle heat engines. The difference in the machine performance can be explained in terms of the behavior of specific heat at constant pressure near the critical point regime.

Electronic, optical, and thermodynamic properties of a quantum spin liquid candidate NaRuO2: Ab-initio investigation

Quantum spin liquids (QSLs), known for their competing interactions that prevent conventional ordering, exhibit emergent phenomena and exotic properties resulting from quantum correlations. Despite these recent advancements of QSLs, a significant portion of the optical and thermodynamic properties in the Kagome lattice remains unknown. In addition, the thermodynamic phenomenology of NaRuO2 bears resemblance that of highly frustrated magnets. Here, we employed ab-initio calculations to explore the electronic, optical and thermodynamic properties of NaRuO2, a new QSL candidate. NaRuO2 was identified as a semiconductor with a small bandgap energy of 0.69 eV. Our results reveal a huge anisotropic optical properties, in which distinct refractive index within the ab-plane indicating an impressive birefringent character of the NaRuO2 system, and a significant enhancement of the optical absorption coefficient and optical conductivity in the in-plane with respect the c-axis. The investigation also examines the electronic anisotropy of the gap energy, by applying strain the gap energy displays significant variations in the ab-plane compared to the out-of-plane direction. Conversely, calculations of the thermodynamic properties reveal a low thermal conductivity (2.5–0.5 W m−1. K−1) and specific heat, which suggests the existence of strong interactions among the NaRuO2 quantum spins. The calculated linear specific heat behavior in NaRuO2 suggests the fractionalization of electrons and the presence of a spinons Fermi surface. These findings hold promising potential for future quantum applications.

Prediction of nonlinear specific heat during single crystal HMX phase transition

We develop a thermodynamically consistent chemo-thermo-mechanical model for the β→δ phase transition of energetic HMX crystals. In contrast to previous models, which either considered specific heat to be a constant or utilized a calibrated function, this model provides novel expressions for the specific heats at constant volume and constant elastic strains derived directly from continuum mechanics. In addition, the model provides a novel prediction for the critical temperature at which the chemical heating rate achieves its extremum for Arrhenius kinetics. The numerical solution predicts highly nonlinear specific heat behavior including order of magnitude changes.

Weyl–Kondo semimetal behavior in the chiral structure phase of Ce3Rh4Sn13

The spin dynamics, crystalline-electric-field (CEF) level scheme, specific heat, and x-ray photoemission spectra (XPS) of ${\mathrm{Ce}}_{3}{\mathrm{Rh}}_{4}{\mathrm{Sn}}_{13}$ were investigated, which exhibits anomalous semimetal transport in the chiral crystallographic phase. CEF excitations observed at approximately 7 and 39 meV are consistent with the two inequivalent Ce-ion cites in the chiral structure. Because of broader CEF excitations and a strong $4{f}^{1}$ peak at the Fermi level in the Ce $4f$ on-resonance spectrum, the hybridized Ce $4f$ electrons contribute to the semimetal carriers. In addition, the spin fluctuation associated with the Kramers doublet ground state is characterized by the peak located at 0.15 meV. The electronic state involving the spin fluctuation causes the ${T}^{3}$ behavior of specific heat below 0.6 K, which is attributed to linear dispersion relations of electrons of the Weyl--Kondo semimetal in the chiral-lattice symmetry.

Crystalline-liquid duality of specific heat in halide perovskite semiconductor

Crystalline-liquid duality in specific heat is observed in lead-free bismuth halide perovskite A3Bi2×9 [A= FA, MA, Cs, and X = I, Br, Cl] semiconductor. All crystals exhibit unusual liquid-like behavior and show substantial deviation from the classical Dulong-Petit law at room temperature. This unusual liquid-like behavior of specific heat is attributed to the dynamic disorder and strong anharmonicity in the soft crystal lattice. The low-temperature specific heat was modeled using the combined Debye-Einstein model and obtained Einstein modes demonstrate strong anharmonic coupling of the low-energy optical modes with acoustic modes resulting in ultrasoft frequency dampening of acoustic phonons. The combination of strong acoustic−optical phonon coupling, soft elastic layered structure, and abundance of low-energy optical phonons results in anomalous thermodynamic specific heat duality in these bismuth-based phonon glass electron crystals. Our study is of fundamental interest in thermodynamics and will help to design novel thermoelectric materials.

First-Principle Study of the Thermodynamic Properties of VSb<sub>2</sub> Compound as a Function of Pressure and Temperature

In our paper, we interested in the study of the thermodynamic properties of the compound VSb2. For this, we used the full potential linearized augmented plane wave (FP-LAPW) method implemented in the Wien2k code. The latter is based on the density functional theory (DFT). We also used the Quasi-Harmonic Debye model implemented in the Gibbs2 code. The exchange-correlation energy of electrons was treated using the generalized gradient approximation (GGA) parameterized by Perdew-Burke and Ernzerhof. The calculation of the pressure and the temperature dependence of the thermodynamic properties of VSb2 material is obtained from that of the electronic structure, within the framework of the Quasi-Harmonic Approximation (QHA). We selected a volumes grid enclosing the equilibrium geometry. At these fixed volumes, the rest of the structural parameters are relaxed and we obtain the energy curve as a function of the volume E(V). The thermodynamic properties such as the primitive cell volume V(Bohr3), the bulk modulus B (GPa), the heat capacities CV(J.mol-1.K-1) and CP(J.mol-1.K-1), the thermal expansion coefficient α (K-1), the Grüneisen parameter γ, and the Debye temperature θD(K) have been studied depending on the temperature (T) in the range [0 ; 500 K], and the pressure (P) in the interval [0 ; 15 GPa]. The increase of the bulk modulus is in agreement with the decrease of the volume, also the volume of the primitive cell and bulk modulus are more sensitive to pressure than to temperature. The thermal expansion is more sensitive at low temperatures than at high temperatures. A specific heat behavior of was found, with a Dulong-Petit limit value of 48.16 J.mol-1.K-1. The effect of the pressure on the Grüneisen parameter is opposite to Debye temperature.

Comparative study on the specific heat of ferroelectrics with a structural quantum critical point

The low-temperature behavior of the lattice specific heat near structural quantum critical points (sQCPs) is compared between Sr1–x Ca x TiO3 and Ba1–x Sr x Al2O4 with optical and acoustic soft modes, respectively. We will show that the low–temperature lattice specific heat of Sr1–x Ca x TiO3 is almost independent of the Ca concentration, although a small dip appears in the Debye temperature (ΘD) at x = 0.001 near the sQCP composition. This behavior is in sharp contrast to that of Ba1–x Sr x Al2O4 that exhibits a large decrease in ΘD toward the sQCP. These results indicate that the character of the soft mode significantly affects the thermal nature at the sQCP.

Thermodynamic signature of SU(4) spin-orbital liquid and symmetry fractionalization from Lieb-Schultz-Mattis theorem

The state-of-the-art numerical simulation of the SU(4) Heisenberg model on a honeycomb lattice reveals a characteristic peak-and-shoulder specific heat behavior. The low-temperature peak is associated with a color gap, which suggests the existence of a gapped symmetric ground state in this model.

Structural, magnetic and dielectric properties of Ni doped LiInCr4O8 breathing pyrochlore

Herein, polycrystalline compounds of breathing pyrochlore LiInCr4-xNixO8 (x = 0, 0.1, 0.2, 0.4) were synthesized by the solid state method. Structure, magnetism, and dielectric properties have been investigated with x-ray diffraction, Raman spectroscopy, magnetic susceptibility, isothermal magnetization, AC impedance, and heat capacity measurements. The mean particle size of the Ni substituted samples decreased from 1.95 μm to 1.22 μm, which is larger than the size determined by the Scherrer formula and the Williamson-Hall method. Raman scattering revealed slightly red-shifted modes Eg, F2g(2), F2g(3), and A1g, which were caused by higher effective atomic mass and increased bond strength. At low temperatures, field cooled and zero field cooled susceptibility measurements, as well as frequency dependent χac data, show a spin-glass type freezing. The resulting Mydosh parameter p of x = 0.4 is 0.01, suggesting the spin glass state. Magnetic measurements exhibit a large negative CW temperature (|θCW| > 290 K), initially decreasing and then increasing at high Ni concentration, in support of the relationship between magnetic interactions and the structural parameters of Cr–Cr spins. Despite the large negative θCW in substituted samples, long-range magnetic order was suppressed at high Ni contents. With increasing nickel concentration, the spin gap gradually vanished, indicating a significant reduction in breathing distortion. The isothermal magnetization at 2 K confirms antiferromagnetic characteristics and weak ferromagnetic components in the substituted samples. When the frequency is increased at room temperature, the dielectric data shows a drop in dielectric constant as well as lower dielectric loss. At low frequencies, interfacial polarization mechanisms play a crucial role. In contrast, at high frequencies, the dielectric constant becomes frequency independent up to ∼ 105 Hz, due to reverse electron motion. The low temperature specific heat behavior implies the good insulator characteristic of LiInCr3.6Ni0.4O8 and a residual entropy feature related to spin-glass type freezing.

Resolving the information loss paradox from the five-dimensional minimal supergravity black hole

In this paper, we study the Hawking tunneling radiation of the charged rotating black hole in five-dimensional minimal supergravity theory by using the semiclassical Hamilton-Jacobi equation. By using two separated ways we obtain the corrected entropy of the black hole. Equality of results gives us a special condition that may solve the information loss paradox. Then, we focus on the phase transitions, and the results show that if the effects of thermal fluctuations are incorporated in the entropy, the black hole is unstable, while there are phase transitions according to the sign-changing behavior of the black hole specific heat. We find that, in presence of thermal fluctuations, the black holes of five-dimensional minimal supergravity behave like the black holes in Horava-Lifshitz gravity hence the second-order phase transition is possible.

On the Possible Nature of Armchair-Zigzag Structure Formation and Heat Capacity Decrease in MWCNTs.

Structural disorder and temperature behavior of specific heat in multi walled carbon nanotubes (MWCNTs) have been investigated. The results of X-ray diffractometry, Raman spectroscopy, and transmission electron microscopy (TEM) images are analyzed. The thermodynamic theory of the zigzag-armchair domain structure formation during nanotube synthesis is developed. The influence of structural disorder on the temperature behavior of specific heat is investigated. The size of domains was estimated at ~40 nm. A decrease in heat capacity is due to this size effect. The revealed dependence of the heat capacity of MWCNTs on the structural disorder allows control over thermal properties of nanotubes and can be useful for the development of thermoelectric, thermal interface materials and nanofluids based on them.

The effect of phase transition of crednerite/delafossite CuMn1−xCrxO2 on optical, thermal, and power factor properties

AbstractThis study aims to investigate the effect of the phase transition of CuMn1−xCrxO2 compound on the Jahn–Teller effect which in turn affects the optical, thermal, and thermoelectric power factor properties. The CuMn1−xCrxO2 samples were synthesized by a solid‐state reaction method. The ab initio computation was applied to evaluate the electronic and optical properties in order to confirm the experiment data. The appearance of the phase transition from crednerite CuMnO2 to delafossite CuCrO2 was confirmed by X‐ray diffraction (XRD) and the ab initio computation through displaying the mixed crednerite/delafossite phase; and, the existence of the Jahn–Teller effect was confirmed by the X‐ray photoelectron spectroscopy (XPS) technique exhibiting the occurrence of mixed‐state Mn3+/Mn4+ ions. The results obtained from XRD, XPS, and the ab initio computation implied the decrease of the Jahn–Teller behavior with increased x content under the influence of the phase transition from the crednerite phase to the delafossite phase of CuMn1−xCrxO2. Surprisingly, the Jahn–Teller distortion reduction caused an increase in the energy gap of the optical property, electrical resistivity, and activation energy in thermally activated band conduction. The effect suffered the specific heat behavior by being separated into two groups of crednerite and delafossite, and enhanced the small polaron behavior by increasing the activation energy of thermally activated band conduction. The phase transition reduced the results of thermal conductivity, thermopower, and thermoelectric power factor properties. In other words, the effect of the phase transition from the crednerite CuMnO2 phase to the delafossite CuCrO2 phase on CuMn1−xCrxO2 compound reduced the Jahn–Teller effect with increased Cr content which in turn caused changes in the optical, thermal, and thermoelectric power factor properties. The effect of the phase transition is advantageous for the improvement of material properties.

Electric field- and strain-induced quantum phase transitions in a spin chain

The effect of the external electric field and/or the external strain on the low-temperature behavior of the quantum spin chain model is studied. The external electric field or the strain can cause the quantum magnetic structural phase transition between two magnetically ordered phases with different order parameters. Such a quantum critical point can be observed in the special behavior of the low-temperature specific heat: At the critical value the low-temperature specific heat manifests linear in temperature behavior instead of the exponentially small one for other values of the field. The magnetic susceptibility also manifests the special behavior, in which quantum phase transitions are revealed.

Magnetocaloric effect, magnetic susceptibility and specific heat of tuned quantum dot/ring systems

In this paper, we have considered a GaAs quantum dot/quantum ring with a parabolic-inverse square confinement potential in addition to modified Gaussian potential in the presence of a perpendicular magnetic field. The energy levels were first determined and then the behavior of specific heat, magnetic susceptibility and magnetic entropy change of the system were investigated. We have presented the effect of magnetic field and the system parameters on temperature dependence of specific heat and magnetic susceptibility over wide temperature ranges. It is found that the magnetic susceptibility shows both positive and negative values with using different parameters. Also, the temperature dependence of the magnetic entropy change ( Δ S ) (magnetocaloric effect) shows a pronounced minimum at low temperatures. • A GaAs quantum dot/quantum ring with a parabolic-inverse square confinement potential in the presence of a magnetic field. • Investigating the behavior of specific heat, magnetic susceptibility and magnetic entropy change. • The magnetic susceptibility shows both positive and negative values with using different parameters.

Microscale Thermal Modelling of Multifunctional Composite Materials Made from Polymer Electrolyte Coated Carbon Fibres Including Homogenization and Model Reduction Strategies

Polymer electrolyte coated carbon fibres embedded in polymeric matrix materials represent a multifunctional material with several application scenarios. Structural batteries, thermal management materials as well as stiffness adaptive composites, made from this material, are exposed to significant joule heat, when electrical energy is transferred via the carbon fibres. This leads to a temperature increase of up to 100 K. The thermal behaviour of this composite material is characterized in this numerical study based on a RVE representation for the first time. Compared to classical fibre reinforced plastics, this material comprises a third material phase, the polymer electrolyte coating, covering each individual fibre. This material has not been evaluated for effective thermal conductivity, specific heat and thermal behaviour on the microscale before. Therefore, boundary conditions, motivated from applications, are applied and joule heating by the carbon fibres is included as heat source by an electro-thermal coupling. The resulting temperature field is discussed towards its effect on the mechanical behaviour of the material. Especially the temperature gradient is pronounced in thickness direction, leading to a temperature drop of 1 °Cmm, which needs to be included in thermal stress analysis in future thermo-mechanically coupled models. Another important emphasis is the identification of suitable homogenization and model reduction strategies in order to reduce the numerical effort spent on the thermal problem. Therefore, traditional analytical homogenization methods as well as a newly proposed “Two-Level Lewis-Nielsen” approach are discussed in comparison to virtually measured effective quantities. This extensive comparison of analytical and numerical methods is original compared to earlier works dealing with PeCCF composites. In addition, the accuracy of the new Two-Level Lewis-Nielsen method is found to fit best compared to classical methods. Finally, a first efficient and accurate 2D representation of the thermal behaviour of the PeCCF composite is shown, which reduces computational cost by up to 97%. This benefit comes with a different Temperature drop prediction in thickness direction of 1.5 °Cmm. In the context of future modelling of multifunctional PeCCF composite materials with multiphysical couplings, this deviation is acceptable with respect to the huge benefit for computational cost.

Effects of diffused hydrogen atoms on thermomechanical properties and contact behavior of a diamond-like carbon film

Hydrogen atoms are doped to diamond-like carbon (DLC) to improve its thermomechanical properties and tribological performance as a surface protective coating. In this study, molecular dynamics (MD) simulations are performed to investigate the impacts of diffused H atoms on the mechanical stiffness, surface energy, specific heat, and thermomechanical contact behavior of DLC. The hydrogenated DLC (a-C:H) is prepared by adding H atoms to a fixed amount of C atoms (method 1) and by replacing C atoms in DLC with H atoms (method 2). The atomic percentage of hydrogen (at. % H) in DLC is varied from 0 to 8.6%. From the systematic MD simulation results, it is observed that the DLC's mechanical stiffness increases with at. % H due to the increasing density with a higher sp3%, but it shows a decreasing trend for method 2 due to the decreasing density. During the sliding contact with a hemispherical diamond tip, the a-C:H samples show a lower coefficient of friction (COF) than the hydrogen-free DLC (ta-C) sample for method 1 but a higher COF for method 2, which can be attributed to the changes in density and surface energy with respect to hydrogen contents in DLC.

Statistical Mechanics of an Integrable System

We provide here an explicit example of Khinchin's idea that the validity of equilibrium statistical mechanics in high dimensional systems does not depend on the details of the dynamics. This point of view is supported by extensive numerical simulation of the one-dimensional Toda chain, an integrable non-linear Hamiltonian system where all Lyapunov exponents are zero by definition. We study the relaxation to equilibrium starting from very atypical initial conditions and focusing on energy equipartion among Fourier modes, as done in the original Fermi-Pasta-Ulam-Tsingou numerical experiment. We find evidence that in the general case, i.e., not in the perturbative regime where Toda and Fourier modes are close to each other, there is a fast reaching of thermal equilibrium in terms of a single temperature. We also find that equilibrium fluctuations, in particular the behaviour of specific heat as function of temperature, are in agreement with analytic predictions drawn from the ordinary Gibbs ensemble, still having no conflict with the established validity of the Generalized Gibbs Ensemble for the Toda model. Our results suggest thus that even an integrable Hamiltonian system reaches thermalization on the constant energy hypersurface, provided that the considered observables do not strongly depend on one or few of the conserved quantities. This suggests that dynamical chaos is irrelevant for thermalization in the large-$N$ limit, where any macroscopic observable reads of as a collective variable with respect to the coordinate which diagonalize the Hamiltonian. The possibility for our results to be relevant for the problem of thermalization in generic quantum systems, i.e., non-integrable ones, is commented at the end.