Logarithmic Temperature Dependence Research Articles

Features of the Scaling of the Anomalous Hall Effect in (CoFeB)x(LiNbO3)100 − x Nanocomposite Films Below the Percolation Threshold: Manifestation of the Cotunneling Hall Conductance?

A scaling behavior of the anomalous Hall effect resistivity ρAHEversus the longitudinal resistivity ρ in (CoFeB)x(LiNbO3)100 −xnanocomposites with a low content of dispersed Co and Fe atoms (Nd~ 4 × 1020cm−3) in an amorphous LiNbO3matrix is studied in the rangex≈ 40–48 at % below the percolation thresholdxp≈ 49 at %. A logarithmic temperature dependence of the conductivity σ ~ lnT has been observed in the rangex≈ 44–48 at %, which is transformed in the rangex≈ 40–42 at % to a square root law lnσ ∝ ‒(T0/T)1/2, which is characteristic of cotunneling transport processes in nanocomposites. It has been found that the exponentn≈ 0.24 in the scaling law ρAHE/x∝ [ρ(x)]ncoincides within an accuracy of 5% with the exponentnin a similar dependence for nanocomposites based on the (CoFeB)x(Al2O3)100 −xmatrix with a high contentNd~1021–1022cm–3and with the exponentnin a parametric dependence ρAHE∝ [ρ(T)]nfor the samples with the minimum contentx≈ 40 at %. The found features are attributed to the correlated change in the probability of cotunneling transitions in a set of more than three centers under the effect of spin–orbit coupling. The manifestation of the barrier tunneling anomalous Hall effect at granule interfaces is also p-ossible.

Kondo scattering in underdoped Nd1-xSrxNiO2 infinite-layer superconducting thin films.

The recent discovery of superconductivity in infinite-layer nickelates generates tremendous research endeavors, but the ground state of their parent compounds is still under debate. Here, we report experimental evidence for the dominant role of Kondo scattering in the underdoped Nd1-xSrxNiO2 thin films. A resistivity minimum associated with logarithmic temperature dependence in both longitudinal and Hall resistivities are observed in the underdoped Nd1-xSrxNiO2 samples before the superconducting transition. At lower temperatures down to 0.04K, the resistivities become saturated, following the prediction of the Kondo model. A linear scaling behavior [Formula: see text] between anomalous Hall conductivity [Formula: see text] and conductivity [Formula: see text]is revealed, verifying the dominant Kondo scattering at low temperature. The effect of weak (anti-)localization is found to be secondary. Our experiments can help in clarifying the basic physics in the underdoped Nd1-xSrxNiO2 infinite-layer thin films.

Electrical properties of highly nitrogen-doped 6H-SiC single crystals: Microwave cavity perturbation study

The silicon carbide (SiC) single crystals of 6H polytype with nitrogen donor concentration ND – NA) ≈ 1∙1017 ...4∙1019 cm –3 grown using the modified Lely method were studied applying the cavity perturbation method. From the temperature dependence of the resonant frequency shift and microwave loss of the cavity loaded with samples under study, the temperature dependence of the conductivity was estimated. From the temperature dependence of the natural logarithm of conductivity versus 1000/T, the activation energies for processes corresponding to electron transitions from impurity levels to the conduction band (ε1) and electron hopping over nitrogen donors in the D0 bands (ε3) were determined. It was found that in 6H-SiC ε1 = 50 meV for (ND – NA) ≈ 1∙10 17 cm –3 , ε1 = 32 meV and ε3 = 6 meV for (ND – NA) ≈ 1∙1019cm–3 , ε1 = 13.5 meV and ε3 = 3.5 meV for ((ND – NA) ≈ 4∙1019 cm–3.

In situ electrical and thermal transport properties of FeySe1−xTex films with ionic liquid gating

We combine in-situ electrical transport and Seebeck coefficient measurements with the ionic liquid gating technique to investigate superconductivity and the normal state of FeySe1-xTex (FST) films. We find that the pristine FST films feature a non-Fermi liquid temperature dependence of the Seebeck coefficient, i.e., S/T ~ AS lnT, and AS is strongly correlated with the superconducting transition temperature (Tc). Ionic liquid gating significantly raises Tc of FST films, for which the Seebeck coefficient displays a novel scaling behavior and retains the logarithmic temperature dependence. Moreover, a quantitative relationship between the slope of T-linear resistivity (A\r{ho}) and Tc for gated films is observed, i.e., (A\r{ho})1/2 ~ Tc, consistent with previous reports on cuprates and FeSe. The scaling behaviors of AS and A\r{ho} point to a spin-fluctuation-associated transport mechanism in gated FeySe1-xTex superconductors.

Thermodynamics of trimethyltetradecylammonium bromide – Sodium deoxycholate binary mixed micelle formation in aqueous solution: Regular solution theory with mutual compensation of excess configurational and excess conformational entropy

A binary mixture of trimethyl(tetradecyl)ammonium bromide = TB-SD = sodium deoxycholate surfactants forms non-ideal binary mixed micelles that have molar excess Gibbs free energy described with the Margules function of the first order. Strong synergistic interactions exist between TB and SD particles (interaction coefficient with a magnitude of 10). Based on the temperature dependence of interaction coefficient and temperature dependence of TB and SD micellar molar fractions product logarithm, it follows that the molar excess entropy is zero. Therefore, although the surfactants TB and SD are structurally very different, their binary mixed micelles can still be described with regular solution theory (random mixing of TB and SD). However, the 2D ROESY spectrum indicates that the binary micellar pseudophase is not random in terms of the spatial distribution of TB and SD particles. Namely, intermolecular interactions between deoxycholic acid anions are missing in the binary mixed micelle. This results in the appearance of excess configuration entropy. However, a zero value of the total molar excess entropy and the existence of the first order Margules function for the molar excess Gibbs free energy means that the molar excess configurational entropy is compensated with the molar excess conformational entropy and that there are correlation effects between the excess configurational enthalpy and entropy as well as between the excess conformational enthalpy and entropy.

Evidence of decoupling of surface and bulk states in Dirac semimetal Cd3As2

Dirac semimetals have attracted a great deal of current interests due to their potential applications in topological quantum computing, low-energy electronic devices, and single photon detection in the microwave frequency range. Herein are results from analyzing the low magnetic (B) field weak-antilocalization behaviors in a Dirac semimetal Cd3As2 thin flake device. At high temperatures, the phase coherence length l ϕ first increases with decreasing temperature (T) and follows a power law dependence of l ϕ ∝ T −0.4. Below ∼3 K, l ϕ tends to saturate to a value of ∼180 nm. Another fitting parameter α, which is associated with independent transport channels, displays a logarithmic temperature dependence for T > 3 K, but also tends to saturate below ∼3 K. The saturation value, ∼1.45, is very close to 1.5, indicating three independent electron transport channels, which we interpret as due to decoupling of both the top and bottom surfaces as well as the bulk. This result, to our knowledge, provides first evidence that the surfaces and bulk states can become decoupled in electronic transport in Dirac semimetal Cd3As2.

Self-Doping and the Mott-Kondo Scenario for Infinite-Layer Nickelate Superconductors

We give a brief review of the Mott-Kondo scenario and its consequence in the recently-discovered infinite-layer nickelate superconductors. We argue that the parent state is a self-doped Mott insulator and propose an effective t- J-K model to account for its low-energy properties. At small doping, the model describes a low carrier density Kondo system with incoherent Kondo scattering at finite temperatures, in good agreement with experimental observation of the logarithmic temperature dependence of electric resistivity. Upon increasing Sr doping, the model predicts a breakdown of the Kondo effect, which provides a potential explanation of the non-Fermi liquid behavior of the electric resistivity with a power law scaling over a wide range of the temperature. Unconventional superconductivity is shown to undergo a transition from nodeless (d+is)-wave to nodal d-wave near the critical doping due to competition of the Kondo and Heisenberg superexchange interactions. The presence of different pairing symmetry may be supported by recent tunneling measurements.

Anomalous electron-electron interactions in epitaxial graphene on SiC

Electron-electron interactions (EEI) play a pivotal role in the transport behavior of carriers confined in a two-dimensional system. The strength of the interaction can be tuned by changing carrier concentration in a conventional two-dimensional system, while it expectedly cannot be controlled in monolayer graphene with a linear dispersion relation since the interaction parameter is not related to carrier concentration. Here, an anomalous carrier-concentration dependence of the EEI is observed in epitaxial graphene on SiC. From quantum transport measurement, a logarithmic temperature dependence of the Hall coefficient is obtained, which is a manifestation of the EEI. From the logarithmic temperature dependence, the EEI-related factor Kee is extracted. Unexpectedly, the extracted Kee shows an increase on increasing carrier concentration, which is further confirmed by analyzing logarithmic correction to the Drude conductivity. This can be attributed to the carrier-concentration dependence of Fermi-liquid constant F0σ due to gas absorption, which offers a route to control the EEI in graphene.

An ultra-low power high-precision logarithmic-curvature compensated all-CMOS voltage reference in 65 nm CMOS

In this paper, a low-complexity resistorless high-precision sub-1 V MOSFET-only voltage reference is presented. To obtain an accurate output, a curvature-compensation technique is used, canceling its logarithmic temperature dependence regardless of the value of the mobility temperature exponent $$(\gamma )$$ . The circuit is realized in 65 nm CMOS technology and yields an output voltage of 574 mV, a temperature coefficient of 3.5 $$\frac{{{\text{ppm}}}}{{^\circ {\text{C}}}}$$ in the range of − 50 to 150 °C, a power supply rejection ratio (PSRR) of − 103 dB at 100 Hz, a line sensitivity of $$6\,\frac{{\upmu {\text{V}}}}{{\text{V}}}$$ in the supply voltage range of 1.3–3 V, a power dissipation of 650nW at 1.3 V supply, and an output noise of 1.7 $${\mu V}/\sqrt {{\text{Hz}}}$$ at 100 Hz. The total active area of the design is 0.03 mm2. This voltage reference is suitable for low-power low-voltage applications which also require high precision.

Magnetotransport in hybrid InSe/monolayer graphene on SiC

The magnetotransport properties of a hybrid InSe/monolayer graphene in a SiC system are systematically studied. Compared to those of its bare graphene counterpart, in InSe/graphene, we can effectively modify the carrier density, mobility, effective mass, and electron–electron (e–e) interactions enhanced by weak disorder. We show that in bare graphene and hybrid InSe/graphene systems, the logarithmic temperature (lnT) dependence of the Hall slope R H = δR xy /δB = δρ xy /δB can be used to probe e–e interaction effects at various temperatures even when the measured resistivity does not show a lnT dependence due to strong electron–phonon scattering. Nevertheless, one needs to be certain that the change of R H is not caused by an increase of the carrier density by checking the magnetic field position of the longitudinal resistivity minimum at different temperatures. Given the current challenges in gating graphene on SiC with a suitable dielectric layer, our results suggest that capping a van der Waals material on graphene is an effective way to modify the electronic properties of monolayer graphene on SiC.

A 10 mK hermetic cell for eliminating parasitic heating in cryogen-free dilution refrigerators

AbstractCryogen-free dilution refrigerators generally simplify low temperature research but some types of samples, including superconducting qubits and other nanoelectronic devices, are affected by environmental heat sources such as stray photons or residual helium. We present the design and performance of a hermetic cell installed on the mixing chamber plate of a cryogen-free dilution refrigerator. The performance was quantified by measuring the dependence of the resonance frequency of a mechanical oscillator installed inside the cell on the mixing chamber temperature down to 10 mK. We found the expected logarithmic temperature dependence of the resonance frequency down to the lowest temperatures, demonstrating that the efficiency of the hermetic shield is significantly better than that of a simpler shield with no visible gaps.

Transport Properties of Magnetic Nanogranular Composites with Dispersed Ions in an Insulating Matrix

This review is devoted to an analysis of the electrical resistance, the magnetoresistance, and the anomalous Hall effect in magnetic “ferromagnetic metal–insulator” nanocomposites at a metal content near the percolation threshold and the memristive properties of the capacitor structures based on these nanocomposites. A high content (up to 1022 cm–3) of dispersed atoms in intergranular gaps leads to a logarithmic temperature dependence of the electrical resistance, a positive contribution to the magnetoresistance, the appearance of tunneling anomalous Hall effect, and a multifilament mechanism of resistive switching (which causes an adaptive character of memristor nanocomposites with dispersed atoms).

Metal-to-metal transition and heavy-electron state in Nd4Ni3O10−δ

The trilayer nickelate ${\mathrm{Nd}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10\ensuremath{-}\ensuremath{\delta}}$ was investigated by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility, and heat capacity. The crystal structure data suggest a higher Ni valence in the inner perovskitelike layer. At ambient pressure the resistivity shows a jump at 162 K, indicating a metal-to-metal transition (MMT). The MMT is also characterized by a magnetic susceptibility drop, a sharp specific-heat peak, and an isotropic lattice contraction. Below $\ensuremath{\sim}50\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, a resistivity upturn with $logT$ dependence shows up, accompanied with negative thermal expansion. External hydrostatic pressure suppresses the resistivity jump progressively, coincident with the weakening of the $logT$ behavior. The low-temperature electronic specific-heat coefficient is extracted to be $\ensuremath{\sim}150\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\mathrm{mol}\text{\ensuremath{-}}{\mathrm{f}.\mathrm{u}.}^{\ensuremath{-}1}$, equivalent to $\ensuremath{\sim}50\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\mathrm{mol}\text{\ensuremath{-}}{\mathrm{Ni}}^{\ensuremath{-}1}$, indicating an unusual heavy-electron correlated state. The novel heavy-electron state as well as the logarithmic temperature dependence of resistivity is explained in terms of the ${\mathrm{Ni}}^{3+}$-centered Kondo effect in the inner layer of the ${({\mathrm{NdNiO}}_{3})}_{3}$ trilayers.

Antiferromagnetic Kondo lattice compound Ce2O2Bi with anti-ThCr2Si2-type structure

Abstract The transport, magnetic and thermodynamic properties of the cerium oxide bismuth compound Ce2O2Bi are systematically investigated in a wide temperature regime. The compound crystallizes in the anti-ThCr2Si2-type structure consisting of a separated Bi2− square net layer between the CeO layers. In the high temperature regime 200–300 K, the compound shows the conventional metallic behavior and localized 4 f electrons of Ce3+ ions. In the low temperature regime 15–30 K, the resistivity increases with a logarithmic temperature dependence, accompanied with the negative magnetoresistance and a low carrier density. Further decreasing temperature, the resistivity drops rapidly below 6.2 K, signaling an antiferromagnetic ordering transition within the Kondo phase. Both susceptibility and specific heat display a similar transition around the same temperature, accompanied with a reduced magnetic entropy. A large Sommerfeld coefficient ∼ 336 mJ/mol K2 is obtained by fitting the specific heat data and no superconductivity is observed down to 0.3 K. All these observations suggest that Ce2O2Bi is a rare low carrier density Kondo lattice compound whose interlayer hybridization between 4 f electrons of Ce3+ ions and conduction 6 p electrons of Bi2− ions plays a crucial role.

Iron-based binary ferromagnets for transverse thermoelectric conversion.

Thermoelectric generation using the anomalous Nernst effect (ANE) has great potential for application in energy harvesting technology because the transverse geometry of the Nernst effect should enable efficient, large-area and flexible coverage of a heat source. For such applications to be viable, substantial improvements will be necessary not only for their performance but also for the associated material costs, safety and stability. In terms of the electronic structure, the anomalous Nernst effect (ANE) originates from the Berry curvature of the conduction electrons near the Fermi energy1,2. To design a large Berry curvature, several approaches have been considered using nodal points and lines in momentum space3-10. Here we perform a high-throughput computational search and find that 25 percent doping of aluminium and gallium in alpha iron, a naturally abundant and low-cost element, dramatically enhances the ANE by a factor of more than ten, reaching about 4 and 6 microvolts per kelvin at room temperature, respectively, close to the highest value reported so far. The comparison between experiment and theory indicates that the Fermi energy tuning to the nodal web-a flat band structure made of interconnected nodal lines-is the key for the strong enhancement in the transverse thermoelectric coefficient, reaching a value of about 5 amperes per kelvin per metre with a logarithmic temperature dependence. We have also succeeded in fabricating thin films that exhibit a large ANE at zero field, which could be suitable for designing low-cost, flexible microelectronic thermoelectric generators11-13.

Self-doped Mott insulator for parent compounds of nickelate superconductors

We propose the parent compound of the newly discovered superconducting nickelate Nd$_{1-x}$Sr$_{x}$NiO$_{2}$ as a self-doped Mott insulator, in which the low-density Nd-$5d$ conduction electrons couple to localized Ni-3$% d_{x^{2}-y^{2}}$ electrons to form Kondo spin singlets at low temperatures. This proposal is motivated with our analyses of the reported resistivity and Hall coefficient data in the normal state, showing logarithmic temperature dependence at low temperatures. In the strong Kondo coupling limit, we derive a generalized $t$-$J$ model with both Kondo singlets and nickel holons moving through the lattice of otherwise nickel spin-1/2 background. The antiferromagnetic long-range order is therefore suppressed as observed in experiments. With Sr-doping, the number of holons on the nickel sites increases, giving rise to the superconductivity and a strange metal phase analogous to those in superconducting copper oxides.

Au - Ge Alloys for Wide-Range Low-Temperature On-Chip Thermometry

We present results of a Au-Ge alloy that is useful as a resistance-based thermometer from room temperature down to at least \SI{0.2}{\kelvin}. Over a wide range, the electrical resistivity of the alloy shows a logarithmic temperature dependence, which simultaneously retains the sensitivity required for practical thermometry while also maintaining a relatively modest and easily-measurable value of resistivity. We characterize the sensitivity of the alloy as a possible thermometer and show that it compares favorably to commercially-available temperature sensors. We experimentally identify that the characteristic logarithmic temperature dependence of the alloy stems from Kondo-like behavior induced by the specific heat treatment it undergoes.

Evidence for the Single-Site Quadrupolar Kondo Effect in the Dilute Non-Kramers System Y_{1-x}Pr_{x}Ir_{2}Zn_{20}.

Acoustic signatures of the single-site quadrupolar Kondo effect in Y_{0.966}Pr_{0.034}Ir_{2}Zn_{20} are presented. The elastic constant (C_{11}-C_{12})/2, corresponding to the Γ_{3}(E)-symmetry electric-quadrupolar response, reveals a logarithmic temperature dependence of the quadrupolar susceptibility in the low-magnetic-field region below ∼0.3 K. Furthermore, the Curie-type divergence of the elastic constant down to ∼1 K indicates that the Pr ions in this diluted system have a non-Kramers ground-state doublet. These observations evidence the single-site quadrupolar Kondo effect, as previously suggested based on specific-heat and electrical-resistivity data.

A graphene resonator as an ultrasound detector for generalized Love waves in a polymer film with two level states

We have investigated surface shear waves at 22 MHz in a 0.5 micron thick polymer film on a SiO2/Si substrate at low temperatures using suspended and non-suspended graphene as detectors. By tracking ultrasound modes detected by oscillations of a trilayer graphene membrane both in vacuum and in helium superfluid, we assign the resonances to surface shear modes, generalized Love waves, in the resist/silicon-substrate system loaded with gold. The propagation velocity of these shear modes displays a logarithmic temperature dependence below 1 K, which is characteristic for modification of the elastic properties of a disordered solid owing to a large density of two level state systems. For the dissipation of the shear mode, we find a striking logarithmic temperature dependence, which indicates a basic relation between the speed of the surface wave propagation and the mode dissipation.

Diffuson contribution to anomalous Hall effect in disordered Co2FeSi thin films

A wide variation in the disorder strength, as inferred from an order of magnitude variation in the longitudinal resistivity of Co2FeSi (CFS) Huesler alloy thin films of fixed (50 nm) thickness, has been achieved by growing these films on Si(111) substrates at substrate temperatures ranging from room temperature (RT) to 600 C. An in-depth study of the influence of disorder on anomalous Hall resistivity,longitudinal resistivity(LR) and magnetoresistance, enabled by this approach, reveals the following. The side-jump mechanism gives a dominant contribution to anomalous Hall resistivity (AHR) in the CFS thin films, regardless of the degree of disorder present. A new and novel contribution to both LR and AHR characterized by the logarithmic temperature dependence at temperatures below the minimum, exclusive to the amorphous CFS films, originates from the scattering of conduction electrons from the diffusive hydrodynamic modes associated with the longitudinal component of magnetization, called diffusons. In these amorphous CFS films, the electron-diffuson, e d, scattering and weak localization (WL) mechanisms compete with that arising from the inelastic electron magnon, e m, scattering to produce the minimum in longitudinal resistivity, whereas the minimum in AHR is caused by the competing contributions from the e d and e m scattering, as WL does not make any contribution to AHR. In sharp contrast, in crystalline films, enhanced electron electron Coulomb interaction (EEI), which is basically responsible for the resistivity minimum, makes no contribution to AHR with the result that AHR does not exhibit a minimum.