Three decades after the prediction of charge-vortex duality in the critical vicinity of the two-dimensional superconductor-insulator transition (SIT), one of the fundamental implications of this duality—the charge Berezinskii-Kosterlitz-Thouless (BKT) transition that should occur on the insulating side of the SIT—has remained unobserved. The dual picture of the process points to the existence of a superinsulating state endowed with zero conductance at finite temperature. Here, we report the observation of the charge BKT transition on the insulating side of the SIT in 10 nm thick NbTiN films, identified by the BKT critical behavior of the temperature and magnetic field dependent resistance, and map out the magnetic-field dependence of the critical temperature of the charge BKT transition. Finally, we ascertain the effects of the finite electrostatic screening length and its divergence at the magnetic field-tuned approach to the superconductor-insulator transition.

Charge Berezinskii-Kosterlitz-Thouless transition in superconducting NbTiN films.

A reentrant temperature dependence of the normal state resistance often referred to as the N-shaped temperature dependence, is omnipresent in disordered superconductors – ranging from high-temperature cuprates to ultrathin superconducting films – that experience superconductor-to-insulator transition. Yet, despite the ubiquity of this phenomenon its origin still remains a subject of debate. Here we investigate strongly disordered superconducting TiN films and demonstrate universality of the reentrant behavior. We offer a quantitative description of the N-shaped resistance curve. We show that upon cooling down the resistance first decreases linearly with temperature and then passes through the minimum that marks the 3D–2D crossover in the system. In the 2D temperature range the resistance first grows with decreasing temperature due to quantum contributions and eventually drops to zero as the system falls into a superconducting state. Our findings demonstrate the prime importance of disorder in dimensional crossover effects.

/pdf/reentrant-resistive-behavior-and-dimensional-crossover-in-1n9u17nco8.pdf

Reentrant Resistive Behavior and Dimensional Crossover in Disordered Superconducting TiN Films

The temperature dependence of thermal conductivity and specific heat for detonated nanodiamond ceramics is investigated on specially designed experimental setups, implementing the uniaxial stationary heat flow method and the thermal relaxation method, respectively. Additionally, complementary studies with a commercial setup (Physical Property Measurement System from Quantum Design operating either in Thermal Transport or Heat Capacity Option) were performed. Two types of samples are under consideration. Both ceramics were sintered at high pressures (6–7 GPa) for 11–25 s but at different sintering temperatures, namely 1000 °C and 1600 °C. The effect of changing the sintering conditions on thermal transport is examined. In thermal conductivity κ(T), it provides an improvement up to a factor of 3 of heat flow at room temperature. The temperature dependence of κ(T) exhibits a typical polycrystalline character due to hindered thermal transport stemming from the microstructure of ceramic material but with values around 1–2 W/mK. At the lowest temperatures, the thermal conductivity is very low and increases only slightly faster than linear with temperature, proving the significant contribution of the scattering due to multiple grain boundaries. The specific heat data did not show a substantial difference between detonated nanodiamond ceramics obtained at different temperatures unlike for κ(T) results. For both samples, an unexpected upturn at the lowest temperatures is observed—most likely reminiscent of a low-T Schottky anomaly. A linear contribution to the specific heat is also present, with a value one order of magnitude higher than in canonical glasses. The determined Debye temperature is 482 (±6) K. The results are supported by phonon mean free path calculations.

/pdf/low-temperature-thermal-properties-of-nanodiamond-ceramics-1pgn4544.pdf

Low Temperature Thermal Properties of Nanodiamond Ceramics

The melting-point of nano-diamond was reported in this paper.The Debye characteristic temperature of nano-diamond was calculated based on X-ray diffraction intensities by the methods introduced by LU Xue-Shan and LIANG Jing-Kui.Its Debye characteristic temperature is 411.7 K,which is about one-fifth of the Debye characteristic temperature of bulk diamond single crystal synthesized under high temperature and high-pressure condition.The melting point of nano-diamond is 2070 K calculated with Lindemann's formula.The atom vibration amplitude,which deflected balance position, increases two times or more.This leads to the increasing of activity of nano-diamond.

The Determination of Melting-Point and Debye Characteristic Temperature of Nano-Diamond from X-Ray Diffraction Intensities

M-type barium hexaferrites thin films with molecular formula Ba1-xLaxFe12O19 were prepared using the liquid phase epitaxial (LPE) method, in which Ba2+ was substituted by La3+. The influence of La3+ substitution on the structure and magnetic properties of Ba1-xLaxFe12O19 has been investigated by XRD, VSM, XPS, Ramam, and the Mössbauer spectrum. X-ray diffraction shows all the samples are single-crystal M-type hexaferrites, and with the increase of La3+ substitution amount x, the lattice constant c decreases gradually. It has been found that substitution of La3+ may significantly increase saturation magnetization 4πMs. With the increase of La3+ substitution amount, 4πMs shows a trend of increasing first and then decreasing and reaching a maximum value of 4425 Gs at x=0.20. The coercivity Hc decreases compared to when x=0. The shift of the Raman spectrum confirmed that the substitution of La3+ caused the appearance of some vacancies. Mössbauer spectroscopy of 57Fe and XPS spectra have shown that there is no Fe2+ present in the material, so the substitution of Ba2+ by La3+ does not cause a valence change of Fe3+ to Fe2+. The chemical valence equilibrium of the entire system is achieved through Fe3+ or O2- vacancies. 

Effect of La Substitution on the Structural and Magnetic Properties of Barium Hexaferrite Ba1-Xlaxfe12o19 Single Crystal Films

The Debye characteristic temperature is a useful parameter of nanodiamond thin films. In this paper, the Debye
characteristic temperature of diamond thin films is studied through X-ray diffraction intensity at a fixed temperature.
From x-ray diffraction, we can get the average crystallite size of diamond thin film. By the method of Xueshan Lu and
Jingkui Liang, the Debye-Waller factor and Debye temperature are calculated, they are B=0.010937 nm2 and
ΘD=527.95K, the Debye temperature is about one-fourth of the Debye characteristic temperature of the bulk diamond
single crystal (about 2200K). The relationship between crystal size and Debye characteristic temperature is also
discussed. The Debye characteristic temperature depends on particle size. When the diamond changes from bulk
diamond to diamond films, the crystal size of diamond becomes smaller, so the Debye characteristic temperature
becomes lower. This means that the atom binding force becomes weak, and it can increase the activity of nanodiamond
thin films.

The Debye characteristic temperature of nanodiamond thin films

Effect of annealing temperature on the properties of BaFe12O19 thin films deposited on GGG (1 1 1) substrates by pulsed laser deposition

Ultra-thin rare earth iron garnet (RIG) films with a narrow ferromagnetic resonance (FMR) line width and a low damping factor have attracted a great deal of attention for microwave and spintronic applications. In this work, 200 nm Y3(GaAlFe)5O12 garnet (GaAl-YIG) films were prepared on gadolinium gallium garnet (GGG) substrates by liquid-phase epitaxy (LPE) with low saturation magnetization. The microstructural properties, chemical composition, and magnetostatic and dynamic magnetization characteristics of the films are discussed in detail. According to the structural analysis, these films exhibit a low surface roughness of less than 0.5 nm. The GaAl-YIG films show an obvious temperature dependence of lattice parameter and strain state, and the film's parameter is perfectly matched with that of the GGG substrate at 810°C. There is a clear variation in the Pb level, which brings about a gradual enhancement of the coercivity and a diminution of the squareness ratio of magnetic hysteresis loops as the growth temperature is reduced. Slight changes in surface roughness, strain condition and content of Pb induce the FMR line width and damping factor to vary on a small scale. The line width is less than 10.17 Oe at 12 GHz and the damping factor is of the order of 10-4. All these properties demonstrate that these ultra-thin GaAl-YIG films are of benefit for the development of devices operated at lower frequencies and in lower fields.

Structural and magnetic properties of Y3(GaAlFe)5O12 liquid-phase epitaxy films with low ferromagnetic resonance losses.

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Papers

The Debye characteristic temperature of nanodiamond thin films

Effect of annealing temperature on the properties of BaFe12O19 thin films deposited on GGG (1 1 1) substrates by pulsed laser deposition

Structural and magnetic properties of Y3(GaAlFe)5O12 liquid-phase epitaxy films with low ferromagnetic resonance losses.