Search results for "conductivity"

Thin film preparation of the low charge carrier density Kondo system CeSb

1999

Abstract We report the thin film preparation of CeSb by means of molecular beam epitaxy (MBE) onto sapphire (1 1 −2 0) substrates. Above a substrate temperature of about 300°C CeSb crystallizes in (0 0 1) orientation. The growth mode of the films changes from a fiber textured to an epitaxial mode for deposition temperatures above 900°C. Although the specific resistivity is enhanced the characteristic energy scales, like the Kondo temperature TK and the magnetic ordering temperature TN, are not changed significantly.

Magnetization relaxation in the flux-creep annealing regime across the second magnetization peak of disordered YBa2Cu3O7− crystals

2001

Abstract The relaxation of the irreversible magnetization of disordered YBa 2 Cu 3 O 7− x crystals measured in the “flux-creep annealing” regime reveals that across the second magnetization peak (SMP) the barriers against flux motion remain finite at low current densities, which supports the existence of a crossover to a dissipation process involving the plastic deformation of the vortex system. In our experiments, the vortex creep process appears to be exclusively controlled by collective pinning barriers (diverging at low current densities) only below the onset of the SMP, where the vortex system is stable against dislocation formation. The (elastic) collective pinning barriers observed f…

Transient photoconductivity in a discotic liquid crystal

1993

Using a time-of-flight technique, different transport mechanisms, deep trapping, multiple shallow trapping, and ideal itrinsic transport, can be observed in the different temperature and phase regions of the liquid-crystalline photoconductor hexapentyloxytriphenylene. The temperature and field dependences of carrier mobilities up to 1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{cm}}^{2}$/V s have been determined; this value exceeds considerably the mobilities of the most commonly used organic photoconductors. The experiments reflect a variety of transport phenomena which are novel in the field of liquid-crystalline systems.

Assessment on the use of the amorphous semiconductor theory for the analysis of oxide films

2015

Abstract Although the theory of Schottky barrier in amorphous semiconductors is generally accepted, the limits of validity of such theory have not yet been explored. The classic semi-analytical solution is obtained under the constraint of constant electronic density of states (DOS) distribution in the mobility gap. In order to take into account the presence of a DOS variable in energy, a semi-empirical corrective power law was introduced in this paper. It is shown that the equations derived for thick films maintain their validity also in the case of thin films, provided that the space charge region width remains lower than 70% of the whole film thickness. A new expression based on the use o…

2021

Controlling thermal transport at the nanoscale is vital for many applications. Previously, it has been shown that this control can be achieved with periodically nanostructured two-dimensional phononic crystals for the case of suspended devices. Here, we show that thermal conductance can also be controlled with three-dimensional phononic crystals, allowing the engineering of the thermal contact of more varied devices without the need for suspension in the future. We show the experimental results obtained at sub-Kelvin temperatures for two different period three-dimensional crystals and for a bulk control structure. The results show that the conductance can be enhanced with the phononic cryst…

Electronic properties of *-oriented thin films

2007

Abstract To perform high precision measurements of the transport anisotropy, epitaxial, a *-oriented thin films of UPd 2 Al 3 have been prepared on LaAlO 3 (1 1 0) substrates. The critical temperature T c ≈ 1.75 K and the upper critical field B c 2 ≈ 3 T are comparable to typical bulk values. In contrast to UNi 2 Al 3 , we observed only a weak anisotropy in directional resistivity measurements, especially no dependence of the superconducting transition temperature on the direction of the applied current. Hall effect measurements show two characteristic minima at T = 16 K ≈ T N and T ≈ 6 K , which corresponds to features seen in earlier measurements on c *-oriented films.

Disorder-induced vibrational anomalies from crystalline to amorphous solids

2021

The origin of boson peak -- an excess of density of states over Debye's model in glassy solids -- is still under intense debate, among which some theories and experiments suggest that boson peak is related to van-Hove singularity. Here we show that boson peak and van-Hove singularity are well separated identities, by measuring the vibrational density of states of a two-dimensional granular system, where packings are tuned gradually from a crystalline, to polycrystals, and to an amorphous material. We observe a coexistence of well separated boson peak and van-Hove singularities in polycrystals, in which the van-Hove singularities gradually shift to higher frequency values while broadening th…

Temperature Dependence of Electronic and Magnetic Properties of (DOEO)<sub>4</sub>[HgBr<sub>4</sub>]·TCE Single Crystals

2015

The temperature dependence of electronic and magnetic properties of the organic charge-transfer salt (DOEO)4[HgBr4]·TCE was investigated using magnetometry. The magnetic susceptibility shows a maximum at 40 K followed by an onset of a pronounced increase at 70 K and a constant behavior above 120 K. Implications on the charge carrier density are discussed. Combining the magnetometry with resistivity and ESR measurements we propose a sequence of insulating, metallic and semiconducting behavior with increasing temperature. Our results indicate that (DOEO)4[HgBr4]·TCE is close to the boundary between an insulating and conducting ground state.

Analysis of magnetization relaxation in MgB2 bulk samples obtained by electric-field assisted sintering

2008

Abstract The relaxation of the irreversible magnetization of MgB2 bulk samples obtained by electric-field assisted sintering was investigated using the SQUID magnetometry for a magnetic field H up to 50 kOe applied in zero-field-cooling conditions. We observed a crossover plastic creep at high temperatures T-elastic creep at low T, described by H ∝ T−2 in the low T range, which appears to be caused by the macroscopic currents induced in the sample during magnetization measurements. By decreasing T below this line the determined creep exponent rapidly overcomes the widely accepted theoretical values for elastic (collective) pinning. This behaviour can easily be explained through the occurren…

Large Tunneling Anisotropic Magneto-Seebeck Effect in a CoPt|MgO|Pt Tunnel Junction

2014

We theoretically investigate the Tunneling Anisotropic Magneto-Seebeck effect in a realistically-modeled CoPt|MgO|Pt tunnel junction using coherent transport calculations. For comparison we study the tunneling magneto-Seebeck effect in CoPt|MgO|CoPt as well. We find that the magneto-Seebeck ratio of CoPt|MgO|Pt exceeds that of CoPt|MgO|CoPt for small barrier thicknesses, reaching 175% at room temperature. This result provides a sharp contrast to the magnetoresistance, which behaves oppositely for all barrier thicknesses and differs by one order of magnitude between devices. Here the magnetoresistance results from differences in transmission brought upon by changing the tunnel junction's mag…