Metallic Temperature Dependence Research Articles

First-order transition under a magnetic ordered state in SmPtSi2

We have synthesized polycrystalline and single-crystalline samples of SmPtSi2, and measured their resistivity, specific heat, magnetization, and Seebeck coefficient. The existence of two magnetic phase transitions has been confirmed, one at T H = 8.6 K and the other T L = 5.6 K. A hump-type anomaly in resistivity, a lambda-type anomaly in specific heat, a downward bend in magnetization, and a semiconductor-like increase in the Seebeck coefficient were observed at T H, indicating an antiferromagnetic transition accompanied by a gap opening on the Fermi surface. In contrast, a sharp drop in resistivity, a sharp spike in specific heat, and a drop in magnetization were observed at T L. The Seebeck coefficient showed metallic temperature dependence below T L. With increasing pressure, T H and T L shifted to higher temperatures. The transition at T L was no longer observed at pressures above 1.5 GPa. These findings suggest that the transition at T L is a transition from an antiferromagnetic ordered state with the gap on the Fermi surface to a different antiferromagnetic state.

Structural Phase Transition and Possible Valence Instability of Ce-4f Electron Induced by Pressure in CeCoSi

X-ray powder diffraction and electrical resistivity measurements were performed on the tetragonal compound CeCoSi under pressure to elucidate the phase boundary of the pressure-induced structural transition and the change in the 4$f$ electronic state. The temperature-pressure phase diagram has been determined from the shift of the Bragg peaks and from the anomaly in the resistivity. The critical pressure, $P_{\rm s}$ $\sim$ 4.9 GPa at 300 K, decreases to $P_{\rm s}$ $\sim$ 3.6 GPa at 10 K. The decrease of $P_{\rm s}$ is due not only to the decrease in volume of the unit cell but also to an anisotropic shrinkage by cooling. When crossing the boundary to the high-pressure phase, the resistivity shows a significant drop to exhibit a metallic temperature dependence. The results of this study strongly suggest that the structural phase transition can be ascribed to valence instability of Ce-$4f$ electron.

Anisotropy and size effects in Bi1-xSbx semiconductor wires in a magnetic field

The electron transport and longitudinal and transverse magnetoresistance (MR) of glass-insulated Bi0.92Sb0.08 single-crystal wires with diameters of 180 nm to 2.2 μm and the (1011) orientation along the wire axis have been studied. The wires have been prepared by liquid-phase casting. It has been first found that the energy gap ΔE increases by a factor of 4 with a decrease in wire diameter d due to the manifestation of the quantum size effect, which can occur under conditions of a linear energy–momentum dispersion law characteristic of both the gapless state and the surface states in topological insulators (TIs). It has been revealed that, in strong magnetic fields at low temperatures, a semiconductor–semimetal transition occurs, which is evident as an anomalous decrease in the transverse MR anisotropy and the appearance of a metallic temperature dependence of resistance at T < 100 K. It has been found that the effect of negative MR, the appearance of an anomalous maximum in the longitudinal MR, and the dependence of Hmax ~ d-1 at 4.2 K is a manifestation of the classical MacDonald–Chambers size effect. The calculated value of the component of the Fermi momentum perpendicular to the magnetic induction vector H is 2 times higher than the value for pure bismuth wires. The features of the manifestation of the quantum size effect in Bi0.92Sb0.08 wires, semiconductor–semimetal electronic transitions induced by a magnetic field, and a decrease in the transverse MR anisotropy indicate the occurrence of new effects in low-dimensional structures based on semiconductor wire TIs, which require new scientific approaches and applications.

Synthesis and Electrical Properties of a New Compound (BiSe)0.97(Bi2Se3)1.26(BiSe)0.97(MoSe2) Containing Metallic 1T-MoSe2

The synthesis and electrical properties of a new misfit compound containing BiSe, Bi2Se3, and MoSe2 constituent layers are reported. The reaction pathway involves competition between the formation of (BiSe)1+x(Bi2Se3)1+y(BiSe)1+x(MoSe2) and [(Bi2Se3)1+y]2(MoSe2). Excess Bi and Se are required in the precursor to synthesize (BiSe)1+x(Bi2Se3)1+y(BiSe)1+x(MoSe2). High-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) confirm the stacking sequence of the heterostructure. Small grains of both 2H- and 1T-MoSe2 are observed in the MoSe2 layers. X-ray photoelectron spectroscopy (XPS) indicates that there is a significantly higher percentage of 1T-MoSe2 in (BiSe)1+x(Bi2Se3)1+y(BiSe)1+x(MoSe2) than in (BiSe)0.97(MoSe2), suggesting that more charge transfer to MoSe2 occurs due to the additional BiSe layer. The additional charge transfer results in (BiSe)1+x(Bi2Se3)1+y(BiSe)1+x(MoSe2) having a low resistivity (14–19 μΩ m) with metallic temperature dependence. The heterogeneous mix of MoSe2 polytypes observed in the XPS complicates the interpretation of the Hall data as two bands contribute to the electrical continuity.

Crystal structure and physical properties of Ba2Nb3S8I: A new misfit-layered transition-metal dichalcogenide superconductor

Single crystals of Ba2Nb3S8I have been grown using iodine-vapor transport in fused-quartz tubes. The crystals form as flakes with typical areas of 5–10 mm2 and thicknesses of 5–11 μm. The crystal structure was determined using single-crystal x-ray diffraction with the aid of an APEX II CCD diffractometer. The structure shows trigonal symmetry with space group P31c and lattice parameters a = b = 10.0156(5) Å and c = 25.1414(15) Å. Compositional analysis via x-ray spectroscopy confirms the presence of iodine. Superlattice reflections are evident in x-ray precession images. Measurements of the electrical resistivity reveal a metallic temperature dependence and superconductivity near 1 K. Polycrystalline samples of Ba2Nb3S8I were made in order to have samples large enough for other bulk physical properties measurements. Magnetic susceptibility reveals antiferromagnetism below 275 K. The coexistence of antiferromagnetism and superconductivity is surprising. Specific heat measurements reveal the electronic coefficient γ = 3.95(66) mJ/mol K2. The jump in the specific heat at the superconducting transition temperature Tc (ΔC/γTc = 1.4(2)) and the energy gap associated with the superconducting state (Eg = 0.405(17) meV) agree well with BCS theory.

Thermoelectric transport properties of the van der Waals-type layered rhombohedral SnAs-based compound, EuSn2As2

The thermoelectric transport properties of the van der Waals-type layered rhombohedral SnAs-based compound, EuSn2As2, have been investigated. A densified polycrystalline sample of EuSn2As2 with porosity (ϕ) of 2.4(9) vol.% exhibited a weak orientation to the c-axis for hexagonal coordination system; the weak orientation is parallel (P ∥) to the pressing direction of hot pressing. Measurements of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) were conducted perpendicular (P ⊥) to the pressing direction. The experimental values of ρ and S exhibit metallic temperature dependence and p-type carrier polarity. The power factor (P) was 0.51(8) mW m−1 K−2 at 673(4) K. Using the Wiedemann–Franz–Lorenz law, the phonon thermal conductivity (κ ph) was estimated to be 0.4(6) W m−1 K−1 at 673(6) K. The dimensionless figure of merit, ZT, was 0.092(17) at 673(3) K.

Structures and Conducting Properties of Molecular Conductors Based on Dimethyl-Substituted DTDA-TTP and DTDH-TTP

Abstract Dimethyl substituted donors, 2-(4,5-dimethyl-1,3-dithiol-2-ylidene)-5-(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (DMDT-DA-TTP) and 2-(4,5-dimethyl-1,3-dithiol-2-ylidene)-5-(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (DMDT-DH-TTP), were successfully synthesized, and (DMDT-DA-TTP)2X (X− = PF6−, AsF6−, and SbF6−) and (DMDT-DH-TTP)2X (X− = PF6− and AsF6−) were prepared. All the DMDT-DA-TTP and DMDT-DH-TTP salts adopt β-type molecular packing with a head-to-tail molecular stacking. Although the overlap modes of donor molecules in the DMDT-DA-TTP and DMDT-DH-TTP salts are similar, the degree of dimerization of donor molecules is quite different. That is, electronically strong dimerization of the DMDT-DA-TTP molecules was assessed in the salts, while the DMDT-DH-TTP molecules have electronically almost uniform stacking in the salts. A tight-binding band calculation suggested that all the DMDT-DA-TTP salts have effectively half-filled energy bands with narrow bandwidths of 0.39–0.40 eV, while the bandwidths of DMDT-DH-TTP salts (0.96 eV) are relatively wide due to the lack of an energy gap. The calculated Fermi surfaces of all the salts are quasi-one-dimensional. In correspondence with the different band structures, all the DMDT-DA-TTP salts exhibited semiconducting behavior derived from the Mott-insulating nature. In contrast, both the DMDT-DH-TTP salts showed metallic temperature dependence down to 5–7 K.

Peierls-type metal-insulator transition in carbon nanostructures

We report the observation of Peierls-type metal-insulator transition in carbon nanostructures formed by chemical vapor deposition inside the pore network of the ZSM-5 zeolite. The Raman spectrum of this nanocarbon@ZSM-5 indicates a clear signature of the radial breathing mode (RBM) for (3,0) carbon nanotubes that can constitute the carbon network segments. Electrical transport measurements on multiple few-micron-sized nanocarbon@ZSM-5 crystals showed metallic temperature dependence of resistance down to 30 K, at which point the resistance exhibited a sharp upturn that is accompanied by the opening of a quasigap at the Fermi level as indicated by the differential resistance measurements. Further Hall measurements have yielded both the sign of the charge carrier and its density. The latter demonstrated excellent consistency with the quasigap data. We employed first-principles calculations to verify that there can indeed be softening of the phonon modes in the (3,0) carbon nanotubes.

Inhomogeneous interface dipole effect at the Schottky junctions of PdCrO2 on β-Ga2O3 (2¯01) substrates

We report the lateral and vertical electrical conduction properties of PdCrO2 thin films grown on insulating Al2O3 (001) and conducting β-Ga2O3(2¯01) substrates. The c-axis oriented PdCrO2 films on the both substrates showed metallic temperature dependence of in-plane resistivity down to 2 K. In PdCrO2/β-Ga2O3 vertical devices, rectifying current density–voltage (J–V) characteristics revealed the formation of a Schottky barrier at the PdCrO2/β-Ga2O3 interface. The Schottky barrier height (SBH) of 1.2–1.8 eV, evaluated by J–V characteristics, is significantly larger than 0.8 eV expected from the usual Mott–Schottky relation based on the electron affinity of β-Ga2O3 (4.0 eV) and the work function of PdCrO2 (4.8 eV) determined by ultraviolet photoelectron spectroscopy. The enhanced SBH at the PdCrO2/β-Ga2O3 interface indicates the existence of interface dipoles, as in the case of PdCoO2/β-Ga2O3. Besides, we observed a large difference of the SBH between the J–V measurements (1.2–1.8 eV) and capacitance measurements (2.0–2.1 eV). While the SBH is definitely enhanced by the interface dipole effect, the level of enhancement at the PdCrO2/β-Ga2O3 interface is rather inhomogeneous, different from that at the PdCoO2/β-Ga2O3. In fact, two typical types of interfaces were found by a high-angle annular dark-field scanning transmission electron microscope, which would be the origin of the inhomogeneous SBH. Further understanding of the interface formation between delafossite oxides and β-Ga2O3(2¯01) will improve the performance of Ga2O3 Schottky junctions as a power diode available at high temperatures.

A single-phase ScTiZrHf high-entropy alloy with thermally stable hexagonal close-packed structure

High-entropy alloys forming non-cubic crystal structures are intriguing systems for both scientific and functional viewpoints. Hexagonal-structured HEAs are among them. In this work, we have fabricated a single-phase hexagonal close-packed phase in ScTiZrHf system. To verify its structural stability, we anneal the alloy samples at 973 K for a long time from 15 up to 140 h. Structural analysis reveals that the HEA retains its single-phase structure after the thermal treatment. To characterize the material, we examine its electron-transport and magnetic properties over a wide temperature range. The alloy electrical resistivity has purely metallic temperature dependence, while its absolute values are rather high. The thermal conductivity in this material is very low. The analysis of the transport properties reveals a noticeable lattice contribution (≈ 50% ) in total thermal conductivity probably caused by a strongly defected crystal structure. The alloy magnetization demonstrates complicated temperature dependence, which is well described by a superposition of Curie–Weiss and valence-electron contributions. Based on this suggestion, we fit experimental magnetization data and extract the electron density of states (DOS) at the Fermi level as ≈1eV−1. To address the properties of interatomic interaction in the system, we perform ab-initio molecular dynamics simulations of the liquid phase. The data obtained indicate unambiguously the absence of strong chemical interaction between alloy components as well as the nearly additive character of the liquid mixture that supports the results obtained experimentally.

Metallic state in a strongly interacting spinless two-valley electron system in two dimensions

We have studied the strongly interacting, two-valley two-dimensional (2D) electron system in ultrahigh mobility SiGe/Si/SiGe quantum wells in parallel magnetic fields strong enough to completely polarize the electron spins thus making the electron system "spinless". It occurs that the metallic temperature dependence of the resistivity, although weaker than that in the absence of magnetic field, still remains strong even when the spin degree of freedom is removed. Several independent methods have been used to establish the existence of the genuine MIT in the spinless two-valley 2D system. This is in contrast to the previous results obtained on more disordered silicon samples, where the polarizing magnetic field causes a complete quench of the metallic temperature behavior.

Isostructural Mott transition in 2D honeycomb antiferromagnet V0.9PS3

The MPX3 family of magnetic van-der-Waals materials (M denotes a first row transition metal and X either S or Se) are currently the subject of broad and intense attention for low-dimensional magnetism and transport and also for novel device and technological applications, but the vanadium compounds have until this point not been studied beyond their basic properties. We present the observation of an isostructural Mott insulator–metal transition in van-der-Waals honeycomb antiferromagnet V0.9PS3 through high-pressure x-ray diffraction and transport measurements. We observe insulating variable-range-hopping type resistivity in V0.9PS3, with a gradual increase in effective dimensionality with increasing pressure, followed by a transition to a metallic resistivity temperature dependence between 112 and 124 kbar. The metallic state additionally shows a low-temperature upturn we tentatively attribute to the Kondo effect. A gradual structural distortion is seen between 26 and 80 kbar, but no structural change at higher pressures corresponding to the insulator–metal transition. We conclude that the insulator–metal transition occurs in the absence of any distortions to the lattice—an isostructural Mott transition in a new class of two-dimensional material, and in strong contrast to the behavior of the other MPX3 compounds.

Measurement and Analysis of Normal-State Transport Properties of FeSe Superconductor

Transport properties such as thermal conductivity (κ), Seebeck coefficient (S) and electrical resistivity (ρ) of the FeSe superconductor were measured and analyzed theoretically. The samples were synthesized through a solid-state reaction route via vacuum encapsulation and characterized by X-ray diffraction and Rietveld refinement analysis. It is found that the Seebeck coefficient, S(T), exhibits an anomalous temperature dependence and shows a crossover of sign at around 190 K, which is an artifact of coexistence of electron and hole bands, wherein carrier diffusive Seebeck coefficient Sdiff(T) and phonon drag contribution Sdrag(T) can successfully explain the experimental results. The measured thermal conductivity κ(T) develops a phonon peak at around 80 K, presumably due to various phonon scattering mechanisms. Our thermal conductivity analysis indicates not only phonon thermal conductivity (κph), but also the carrier contribution to thermal conductivity (κc) is also important, particularly, around room temperatures. Electrical resistivity of FeSe shows superconducting transition (TC) around 10 K and shows a metallic temperature dependence above TC which is explained using the Bloch–Gruneisen function of the temperature-dependent resistivity.

Quantum phase transition in ultrahigh mobility SiGe/Si/SiGe two-dimensional electron system

The metal-insulator transition (MIT) is an exceptional test bed for studying strong electron correlations in two dimensions in the presence of disorder. In the present study, it is found that in contrast to previous experiments on lower-mobility samples, in ultra-high mobility SiGe/Si/SiGe quantum wells the critical electron density, $n_{\text{c}}$, of the MIT becomes smaller than the density, $n_{\text{m}}$, where the effective mass at the Fermi level tends to diverge. Near the topological phase transition expected at $n_{\text{m}}$, the metallic temperature dependence of the resistance should be strengthened, which is consistent with the experimental observation of more than an order of magnitude resistance drop with decreasing temperature below $\sim1$ K.

Fabrication of high quality and large area graphite thin films by pyrolysis and graphitization of polyimides

We have developed large-area, high-quality graphite thin films that are 0.5–3 μm thick. To prepare the graphite films, we used pyrolysis and graphitization of polyimide up to temperatures in the range 2900 °C-3300 °C, which is applicable to industrial-production processing. Given that the graphite layers of the films are highly oriented in the surface plane, they have good physical properties. The resulting electrical conductivity of graphite film of thickness 1.4 μm and area 10 × 10 cm2 that was treated at 3200 °C is 24,800 S/cm, and the electrical conductivity showed metallic temperature dependence. The carrier mobility of the film is 11,700 V/cm2, and the carrier concentrations of electrons (Ne) and holes (Nh) are 6.98 × 1018 cm−3 and 5.90 × 1018 cm−3, respectively. We consider the high electrical conductivity and mobility to have been derived from the homogeneous, highly oriented graphite layers. We found that graphitization of films less than 3 μm thick progresses uniformly throughout the film, and the resulting graphite films have structures with uniform, highly oriented layers. The produced graphite thin films have excellent physical properties and can be easily handled, so we believe that many industrial applications are possible.

Structure, magnetism, and transport of single-crystalline RNiSi3(R = Y, Gd-Tm, Lu)

We report on the physical properties of the intermetallic series $R{\mathrm{NiSi}}_{3}\phantom{\rule{4pt}{0ex}}(R=\text{Y}$, Gd-Tm, Lu). High quality single crystals with platelike morphology were grown using the Sn flux method. X-ray powder diffraction data show that this series crystallizes in the orthorhombic space group Cmmm, and Laue patterns indicate that the b axis remains perpendicular to the plane of the plates. Magnetization measurements show anisotropic antiferromagnetic ground states for $R$ = Gd-Tm with N\'eel temperatures ranging from ${T}_{N}=2.6$ K $({\mathrm{TmNiSi}}_{3})$ up to 32.2 K $({\mathrm{TbNiSi}}_{3})$, as well as metamagnetic transitions that in some cases appear together with hysteresis $({\mathrm{TbNiSi}}_{3},{\mathrm{DyNiSi}}_{3}$, and ${\mathrm{HoNiSi}}_{3})$. The easy axis changes from a axis to b axis on going from $R$ = Gd-Ho to $R$ = Er-Tm. All transitions from antiferromagnetic to paramagnetic states are clearly marked by sharp peaks in specific heat as well as in the derivative of resistivity measurements, which show metallic temperature dependence for all compounds and residual values in the range of $1\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$. ${\mathrm{DyNiSi}}_{3}$ has two close phase transitions, while ${\mathrm{HoNiSi}}_{3}$ presents distinct critical temperatures for applied fields in the $a$ or $c$ directions (10.4 and 6.3 K, respectively), pointing to possible component-specific ordering of the local magnetic moments.

Enhancing Thermoelectric Figure-of-Merit of Polycrystalline Na y CoO2 by a Combination of Non-stoichiometry and Co-substitution

Co-oxides with a layered structure are of interest for high-temperature thermoelectric applications as they can be tuned to enhance their electrical conductivity while retaining their low thermal conductivity. The figure-of-merit of Na y CoO2 has been enhanced using the combined effects of Na-non-stoichiometry and non-isoelectronic Co-substitution. A series of compounds Na0.7Co1−xNi x O2 with x ≤ 0.1 have been synthesized using conventional techniques. Structural analysis using x-ray diffraction and Rietveld refinement shows the formation of a γ-NaCoO2-type phase in all the compounds. The presence of a small amount of NiO for x > 0.05 indicates that the solubility limit of Ni in Na0.7CoO2 is 5 at.%. All the compounds have been found to be p-type with the thermopower reaching a maximum of 220 μV K−1 at 1023 K for x = 0.1. The thermopower has been found to vary linearly with temperature for all the compounds; a degenerate metallic behavior. The electrical resistivity varies between 3 and 10 mΩ cm at all temperatures and has a metallic temperature dependence in agreement with the thermopower results. The power factor for the x = 0.1 compound reaches a maximum value of 0.55 mW m−1 K−2 at ∼ 900 K compared to 0.45 mW m−1 K−2 for the compound with no substitution. The thermal conductivity at 1023 K decreases from 1.2 to 0.9 W m−1 K−1 for x = 0.1. These factors lead to an increase of the figure-of-merit, zT, to 0.58 at 1023 K for x = 0.1, an increase of 57% compared to the unsubstituted compound. The magnetic studies show that Na0.7CoO2 is paramagnetic with an antiferromagnetic transition at ∼ 36 K. Substitution of Ni2+ for Co3+ has been found to induce a ferromagnetic-like transition at ∼ 240 K which is suppressed at high fields.

Magnetostructural properties and electric transport in Mn48+xCr3-xNi38Sn11 (x = 0, 1) ribbons: Mn/Ni ratio versus Cr doping

We report the structural, electrical and magnetic properties of Cr substituted Mn48+xCr3-xNi38Sn11 (x = 0 and 1) Heusler ribbons synthesised by melt spinning of the arc-melted bulk alloy. Composition analysis employing EDAX reveals same Ni and Sn concentrations with difference in the Mn/Cr ratio in both the ribbons. Mn48Cr3Ni38Sn11 ribbons have pure cubic-austenite phase whereas Mn49Cr2Ni38Sn11 show a mixture of the dominant cubic-austenite with traces of the orthorhombic-martensitic phase as confirmed by X-ray analysis. Ribbons having higher Cr content show (i) pure cubic austenite structure (L21 type) at room temperature (ii) canonical paramagnetic-ferromagnetic transition in the austenite phase and (iii) metallic temperature dependence of resistivity. Small decrease in the Cr content produces dramatic changes in the structure-property profile. Hence ribbons having lower Cr content show (i) a mixture of cubic and orthorhombic phases, (ii) paramagnetic-ferromagnetic transition in the austenite phase above the room temperature which is followed by strongly hysteretic martensitic transition and (iii) metal-like temperature dependence of resistivity followed by typical martensitic resistivity and re-entrant metallic behaviour in the lowest temperature region. AC susceptibility measurements show absence of a spin glass like behaviour in Mn48Cr3Ni38Sn11 while the lower Cr variant demonstrates nearly ideal spin glass like characteristics. The high sensitivity of structure-property correlation towards small compositional variations is attributed to the twin effect of Cr substitution at Mn sites and the Mn/Ni ratio.

Single crystal growth and physical properties of the new ternary compound Eu2Mg4Si3

We have studied the magnetic and electrical properties of new ternary europium magnesium silicide Eu2Mg4Si3. The single crystalline Eu2Mg4Si3 has been prepared by the Mg self-flux method. The compound crystalizes in the hexagonal Hf2Co4P3-type structure with space group P6¯2m with unit cell parameters a=14.78(3)Å and c=4.434(6)Å. Magnetic, electrical, and thermal properties indicate that the system undergoes two successive phase transitions, occurring at TN1=9.6K and TN2=8.4K. The estimated effective magnetic moment is close to the moment of free Eu2+ ion. The electrical resistivity data ρ(T) for Eu2Mg4Si3 show a metallic-like behavior from room temperature down to about 100K. However, the ρ(T) data exhibit a notable upturn below 80K and a maximum around TN1 and then suddenly decrease with decreasing temperature. These features are strongly suppressed by applying magnetic fields and a metallic temperature dependence eventually exhibits over the whole temperature range in a magnetic field of 30kOe. Such behavior is observed in some magnetoresistive compounds.

Role of electron-phonon coupling in finite-temperature dielectric functions of Au, Ag, and Cu

Realistic representation of finite temperature dielectric functions of noble metals is crucial in describing the optical properties of advancing applications in plasmonics and optical metamaterials. However, the atomistic origins of the temperature dependence of noble metals' dielectric functions still lack full explanation. In this paper, we implement electronic structure calculations as well as ellipsometry experiments to study the finite temperature dielectric functions of noble metals Au, Ag, and Cu. Theoretically, the intraband dielectric function is described by the Drude model, of which the important quantity electron lifetime is obtained by considering the electron-phonon, electron-electron, and electron-surface scattering mechanism. The electron-phonon coupling is key to determining the temperature dependence of electron lifetime and intraband dielectric function. For the interband dielectric function, it arises from the electronic interband transition. Due to the limitation of incorporating electron-phonon coupling into the interband transition scheme, the temperature dependence of the interband dielectric function is mainly determined by the thermal expansion effect. Experimentally, variable angle spectroscopic ellipsometry measures the dielectric functions of Au and Ag over the temperature range of 300--700 K and spectral range of 2--20 \textmu{}m. Those experimental measurements are consistent with theoretical results and thus verify the theoretical models for the finite temperature dielectric function.