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The recent claimed room-temperature superconductivity in Cu-doped lead apatite at ambient pressure is under debate. To identify its physical origin, we conducted a detailed analysis of the crystal structure, band structure, lattice dynamics and magnetic properties of the parent Pb${}_{10}$(PO₄)₆O compound and the two different phases of Pb₉Cu(PO₄)₆O (LK-99) compound. Our results show that the parent Pb${}_{10}$(PO₄)₆O compound is an indirect band gap semiconductor, where Cu doping at the 4f site of Pb leads to a semiconducting to half-metallic transition. Two half-filled flat bands spanning the Fermi energy levels are present in the 4f phase of LK-99, which are mainly formed by hybridization of the d orbitals of Cu with the 2p orbitals of O. In addition, 6h phase of LK-99 always has spin polarization at the bottom of the conduction band and at the top of the valence band, making the material a magnetic semiconductor. Our theoretical research reveals recent experimental reports on the different transport properties of LK-99.

Lattice vibrations or phonons play an important role in determining material properties, including thermal conductivity. To model the phenomenon accurately and efficiently, the most important factors governing phonon physics need to be identified, for example, polarization branches. Research continues into many aspects of the fundamental physical processes involved in phonons and into possible applications of these processes in modern physics. One of the most interesting controversies in the thermal properties of graphene involves the importance of out-of-plane acoustic phonons. The need for clarity in understanding this importance dictates that the thermal conductivity of graphene should be evaluated in various circumstances. The nanoscale heat conduction properties of graphene are studied by iteratively solving the Boltzmann transport equation and rigorously treating the normal and Umklapp collisions in the frame of three-phonon interactions. This captures the mechanistic aspects of thermal conductivity by revealing what phonon branches are present. The thermal conductivity is evaluated in different crystallite sizes and at different frequencies and temperatures. The results indicated that out-of-plane acoustic phonons become increasingly important in the frame of three-phonon interactions. The out-of-plane acoustic branch dominates thermal transport whereas the other acoustic branches make small contributions. The importance of this branch is generally attributed to the high density of states and restrictions governing anharmonic effects. The three-phonon normal and Umklapp processes must be clearly accounted for and the contribution from optical branches is not negligible at higher temperatures. The results have implications in the quest for predictive and quantitative calculations of thermal conductivity.

We investigate transport properties of percolating clusters generated by irreversible cooperative sequential adsorption (CSA) on square lattices with Arrhenius rates given by k_i ≡ q^n_i, where n_i is the number of occupied neighbors of the site i, and q a controlling parameter. Our results show a dependence of the prefactors non q and a strong finite size effect for small values of this parameter, both impacting the size of the backbone and the global conductance of the system. These results might be pertinent to practical applications in processes involving adsorption of particles.

In this work, we have extracted the initial temperature from the transverse momentum spectra of charged particles in Au + Au collisions using STAR data at RHIC energies from $\sqrt{s_{NN}}$ = 7.7–200 GeV. The initial energy density $(𝜀)$, shear viscosity to entropy density ratio $(\eta /s)$, trace anomaly $(\mathrm{\Delta })$, the squared speed of sound $(C_s^2)$, entropy density, and bulk viscosity to entropy density ratio $(\zeta /s)$ are obtained and compared with the lattice QCD calculations for (2 + 1) flavor. The initial temperatures obtained are compared with various hadronization and chemical freeze-out temperatures. The analysis of the data shows that the deconfinement-to-confinement transition possibly takes place between $\sqrt{s_{NN}}$ = 11.5 and 19.6 GeV.

Using the AdS/CFT correspondence, we study the anisotropic charge transport properties of both supersymmetric and nonsupersymmetric matter fields on (2+1)-dimensional defects coupled to a (3+1)-dimensional "heat bath." We focus on the cases of a finite external background magnetic field, finite net charge density and finite mass and their combinations. In this context, we also discuss the limitations due to operator mixing that appears in a few situations and that we ignore in our analysis. At high frequencies, we discover a spectrum of quasiparticle resonances due to the magnetic field and finite density and at small frequencies, we perform a Drude-like expansion around the DC limit. Both of these regimes display many generic features and some features that we attribute to strong coupling, such as a minimum DC conductivity and an unusual behavior of the "cyclotron" and plasmon frequencies, which become related to the resonances found in the conformal case in an earlier paper. We further study the hydrodynamic regime and the relaxation properties, from which the system displays a set of different possible transitions to the collisionless regime. The mass dependence can be cast in two regimes: a generic relativistic behavior dominated by the UV and a nonlinear hydrodynamic behavior dominated by the IR. In the massless case, we furthermore extend earlier results from the literature to find an interesting selfduality under a transformation of the conductivity and the exchange of density and magnetic field.

We study the Renormalization Group (RG) flow of AC conductivity in soft wall model of holographic QCD. We consider the charged black hole metric and the explicit form of AC conductivity is obtained at the cutoff surface. We plot the numerical solution of conductivity flow as a function of radial coordinate. The equation of gauge field is also considered and the numerical solution is obtained for AC conductivity as a function of frequency. The results for AC conductivity are also obtained for different values of chemical potential and Gauss–Bonnet couplings.

Magneto-transport and magnetic data on MgB₂ polycrystalline samples are reported for applied magnetic fields up to 9 T. In the normal state we find that MgB₂ compound has a temperature and field-dependent resistivity behavior like a simple metal. The critical magnetic field H_c2(T) and the irreversibility field H_irr(T) curves were determined. The Hall coefficient R_H is slightly temperature dependent. Using the extracted data, we calculated the electronic mean free path, coherency length ξ₀ and London penetration depth λ_L.

The in-plane resistance of single crystal non-magnetic Lu_xY_1-xNi₂B₂C and magnetic Lu_xGd_1-xNi₂B₂C samples as a function of the magnitude and direction of the magnetic field and temperature have been measured. The superconducting upper critical field H_c2(T) is anisotropic for both. A positive curvature in H_c2(T) near T_c(x) is clearly observed only for the non-magnetic impurity. At low temperature H_c2(T) for the sample with magnetic impurities is strongly reduced. Thermopower, thermal conductivity and resistivity as a function of temperature are also reported for Lu_xGd_1-xNi₂B₂C.

Structural and dynamical properties of Pd, Ag pure liquid metals and especially Pd_xAg_1-x alloys are studied by the molecular dynamics simulation. The effects of temperature and concentration on the liquid properties of Pd_xAg_1-x are analyzed. Sutton–Chen (SC) and Quantum Sutton–Chen (Q–SC) many-body potentials are used as interatomic interactions. The calculated diffusion constants and viscosities are in good agreement with the available experimental data and theoretical calculations. The coefficients of Arrhenius equation are also presented to calculate the self-diffusion coefficient and shear viscosity of Pd–Ag alloys at the desired temperature and concentration. We have shown that Q–SC potential parameters are more reliable in determining physical properties of metals and their alloys studied in this work.

Single crystals of Na_0.495CoO₂ were obtained through a flux method followed by de-intercalation of sodium. The resistivity (ρ) and thermal stability were studied for the de-intercalated samples exposed to humid air. It was found that the de-intercalated Na_0.495CoO₂ crystal is vulnerable to water in the air, and a hydration process in which H₂O molecules fill oxygen vacancies in CoO₂ layers instead of being intercalated between CoO₂ layers is suggested to be responsible for the remarkable change in resistivity induced by water absorption. The Na_0.495CoO₂ sample shows a weak localization of carriers just below 200 K and Co³⁺–Co⁴⁺ charge ordering at about 40 K, lower than the corresponding charge ordering transition temperature reported in Na_0.5CoO₂. The lower charge ordering transition temperature might be caused by the slight deviation of Na content (x) from 0.5.

The donor/acceptor heterojunction devices having configuration n-PANI/p-PSi were fabricated by in-situ chemical oxidative polymerization method of aniline on p-type porous silicon. The structure of n-PANI/p-PSi junctions was examined by scanning electron microscopy and X-ray diffraction spectroscopy. The dark current-voltage measurements were performed in the temperature range of 303–393 K to determine the electrical transport mechanisms of these devices. Rectifying properties were obtained and capacitance–voltage at 1 MHz behavior indicates an abrupt interface. At low forward bias, the current was found to be limited by thermionic emission of holes from p-PSi over the PANI/PSi barrier in the PANI thin film. For relatively higher voltage, the conduction was dominated by a space charge limited current mechanism, with an exponential distribution of traps. Also, various electrical parameters were determined from the I-V and C-V analysis.

Glasses of the system x (NiO) (50 – x) PbO: 50V₂O₅ were prepared by melt quenching in the range x = 0 mol% to 15 mol%. Measurements are reported for dc electrical conductivity for the above compositions in the temperature range 300 K–500 K. The experimental results are analyzed with reference to various theoretical models proposed for dc electrical conduction in amorphous semiconductors. The analysis shows that at high temperatures the temperature dependence of dc conductivity is consistent with Mott's model of phonon-assisted hopping conduction, variable range hopping mechanism and Schnakenberg's model mechanism. The hopping in this system is adiabatic in nature.

Ag-doped La_0.7Ca_0.3MnO₃ (LCMO) films were prepared on silicon substrate by RF magnetron sputtering. The dependences of transport properties on annealing temperature were explored. It is shown that the resistivity of the samples decreases and the metal–insulator transition temperature shifts to higher temperature with the increase in annealing temperature. Two metal–insulator transition temperatures are presented in the R – T plots of Ag-doped LCMO films, which can be explained by the Ag¹⁺ substitution of La³⁺ to form La_1-xAg_xMnO₃ compound. Compared with LCMO thin films, Ag-doping can observably improve the T_M-I and decrease the resistivity of the samples.

We investigate, using the exact Langevin equation, the properties of the heat conduction of an individual 1D harmonic chain with harmonic on-site potential. Each particle interacts with its own independent thermal reservoir. The results indicate that there is no rectification effect in this model even with mass gradient in the case of weak interparticle interaction. It may suggest that a system with harmonic on-site potential and asymmetric structure does not guarantee an asymmetric heat transport.

All-manganites Pr_0.7Sr_0.3MnO₃/La_0.5Ca_0.5MnO₃/Pr_0.7Sr_0.3MnO₃ (PSMO/LCMO/PSMO) trilayers were deposited on (001)-oriented single crystal MgO by pulsed laser deposition. The thickness of both PSMO layers was 36 nm while the thickness of LCMO layer varied from 6 to 36 nm. High resolution X-ray diffraction patterns indicated that trilayers were well (001)-oriented grown with high crystalline quality, and that PSMO layers were fully-strain-relaxed while LCMO spacer was partially strained. Studies on transport and magnetic properties of trilayers indicated that metal-insulator transition temperature T_MI increased from 200 K to 260 K and the saturation magnetization was suppressed with decreasing thickness of LCMO spacer from 36 to 6 nm. Transport properties of trilayers are associated with enhancement of volume fraction of ferromagnetic clusters in charge ordered and magnetic phase separated LCMO spacer. Interestingly, exchange bias (EB) was not observed in PSMO/LCMO/PSMO trilayers. It was believed that preferential distribution of metallic ferromagnetic clusters in LCMO layer may result in disappearance of EB.

A series of La_2-x1Sr_x1CuO_4+δ/ La_2-x2Sr_x2CuO_4+δ multilayers were epitaxially grown on (001) LaSrAlO₄ and (001) SrTiO₃ substrates by laser ablation, where x1 = 0.0, 0.08 (underdoped) and x2 = 0.24, 0.32, 0.45 (over-doped). Before the depositions of each multilayer, all of the single layers were deposited and characterized, and then the multilayers were deposited by using the same deposition condition except shifting targets for laser ablation. These multilayers are highly c-axis oriented. Several modulation wavelengths of the sublayers were selected for preparing the multilayers. The resistance measurements of these single layered films of La_2-x1Sr_x1CuO_4+δ, La_2-x2 Sr_x2CuO_4+δ, and multilayers of La_2-x1Sr_x1CuO_4+δ/La_2-x2 Sr_x2CuO_4+δ were performed and compared. The transport measurements suggest that the charge redistribution may be a dominant factor for the superconducting transition temperature in low temperatures.

In this work, the transport properties of carbon atom chains sandwiched between Au (100) nanoelectrodes with different anchored structures have been studied using a combination of first principles and nonequilibrium Green’s function. The results show that the transport properties of the carbon chain are not only related to the chain length and the number of C atoms (odd/even), but also related to the anchoring structure of nanoelectrodes. For the same chain length and bias voltage, the current of the H–H model is about three times that of the T–T model due to more charge transfer. Meanwhile, it was also found that the C atom in contact with the electrode has a large amount of charge transfer, which provides an effective way for the electronic doping of semiconductor devices. These findings can provide theoretical support for the design of molecular devices based on the C-chain.

Structure complexity, adequate electronic character and congenital lower thermal conductivity of zintl phases result in designing thermoelectrics of tremendous efficiency. Such qualities of zintl phases embolden us to present a detailed study of SmMg₂X₂ (X = P, As, Sb, Bi) zintl compounds by first principles. The structural characteristics fit well with the existing data. Electronic properties of titled compounds are scrutinized by adopting PBE-GGA, TB-mBJ and hybrid (YS-PBE0) potentials. The band structure calculations through TB-mBJ and hybrid (YS-PBE0) proclaim the semiconducting behavior of compounds and there is a shrinkage of band gap by changing X anion from P to Bi. The density of states (DOS) calculation reveals that there is a major contribution of Sm-f states and Mg atom in valence band while in conduction band, the prominent role is offered by Sm-d states and p states of X anion. Similarly, the temperature-dependent thermoelectric properties are scrutinized by using BoltzTraP2 code embedded within WIEN2k software for with and without spin–orbit coupling (SOC) and also through hybrid (YS-PBE0) functional. SOC, but even more hybrid functional, has been shown to have a significant effect on the transport behavior. Optimized values of carriers’ concentration are achieved which subsidize thermoelectric parameters like power factor (PF), Seebeck coefficient ($S$) and thermoelectric figure of merit (ZT) at elevated temperature. The compounds show excellent thermoelectric performance in the studied temperature range.

The transport properties across contacts between quantum tubes and metals are studied. The curvature effects on the transmission are also considered. We find that the transmission probability of an electron transporting from the tube into the metal through the contact can be close to 100%. The curvature has a larger effect on the transmission for smaller radii and the effects decrease as the radii increase.

Single-phase metastable α″-niobium nitride thin films have been synthesized on glass substrates by controlled reactive electron beam evaporation technique and are characterized by X-ray diffraction technique. The transport properties down to low temperatures have also been measured. The temperature dependence of resistivity has a minimum at 132 K and shows a remarkable change in the behavior below 25 K. These have been analyzed in the framework of weak localization effects. The analysis shows that the resistance minimum arises on account of three-dimensional weak localization and there is a cross-over to the two-dimensional weak localization regime at lower temperatures.