Electrical Resistivity Of Single Crystals Research Articles

Thermodynamic and electrical transport properties of UTe2 under uniaxial stress

Despite intense experimental efforts, the nature of the unconventional superconducting order parameter of UTe$_2$ remains elusive. This puzzle stems from different reported numbers of superconducting transitions at ambient pressure, as well as a complex pressure-temperature phase diagram. To bring new insights into the superconducting properties of UTe$_2$, we measured the heat capacity and electrical resistivity of single crystals under compressive uniaxial stress $\sigma$ applied along different crystallographic directions. We find that the critical temperature $T_{\rm c}$ of the single observed bulk superconducting transition decreases with $\sigma$ along $[100]$ and $[110]$ but increases with $\sigma$ along $[001]$. Aside from its effect on $T_{\rm c}$, we notice that $c$-axis stress leads to a significant piezoresistivity, which we associate with the shift of the zero-pressure resistivity peak at $T^\star \approx 15\, \rm K$ to lower temperatures under stress. Finally, we show that an in-plane shear stress $\sigma_{xy}$ does not induce any observable splitting of the superconducting transition over a stress range of $\sigma_{xy}\approx 0.17 \, \rm GPa$. This result suggests that the superconducting order parameter of UTe$_2$ may be single-component at ambient pressure.

Electrical resistivity of single crystals of LaFeAsO under applied pressure

Measurements of electrical resistivity under applied pressure were performed on single-crystalline samples of LaFeAsO grown in a molten NaAs flux. We observe a smooth suppression of spin-density wave order under nearly hydrostatic applied pressures up to 2.6 GPa and in quasihydrostatic pressures up to 14.7 GPa. Similar to some of the other reports on single and polycrystalline samples of LaFeAsO, these crystals exhibit a resistivity that increases as temperature is lowered. By fitting an Arrhenius law to the the semiconducting-like temperature dependence of the electrical resistivity, we extract an energy gap that is suppressed with pressure and vanishes near 10 GPa. This is accompanied by the emergence of a metallic temperature dependence of the electrical resistivity. A similar behavior is also observed in diamond anvil cell experiments carried out to $\ensuremath{\sim}37\phantom{\rule{4pt}{0ex}}\mathrm{GPa}$. Complete transitions to a bulk superconducting phase are not observed in any of the experiments.

A new (TTF)11I8organic molecular conductor: from single crystals to flexible all-organic piezoresistive films

This paper reports selective synthesis of two iodine-containing TTF (tetrathiafulvalene) salts: one, (TTF)11I8, is a new molecular conductor while another is the known non-conducting (TTF)I3 compound. Single crystals of both salts were prepared using different amounts of iodine in the redox process between TTF and I2. X-ray data showed that the resulting conducting (TTF)11I8 salt might be considered as a new modulated phase of the non-stoichiometric (TTF)I0.7+δ salts. The electrical resistance of single crystals of (TTF)11I8 reveals a semiconducting-like behaviour. The paper presents also a study of electromechanical properties of organic conductive bi-layer (BL) films prepared by covering different organic polymeric films with a thin network of oriented submicrocrystals of (TTF)I0.7+δ phases. These BL films exhibit a combination of flexibility, lightweight, and high piezo-resistivity properties showing therefore a potential interest for electronic sensing applications where lightweight, large area coverage and flexibility are required.

Pressure-induced metal-insulator transition of the mott insulator Ba2IrO4

The electrical resistivity of single crystals of the spin-orbit Mott insulator Ba2IrO4 has been measured at pressures up to 30 GPa and at temperatures from 100 mK to 300 K. Ba2IrO4 shows a metal-insulator transition at around Pc = 24 GPa, though it does not show superconductivity down to 100 mK. The low-temperature resistivity in the metallic state does not obey a conventional Fermi-liquid description. This suggests that carriers are incoherently scattered by antiferromagnetic quantum spin fluctuations. The critical exponent δ for the metal-insulator transition is about 1.6, indicating that Ba2IrO4 is located near the boundary between a Mott and an Anderson insulator. This means that even in a single crystal, the effect of crystallographic disorder should not be ignored.

Elastic, thermodynamic, and electronic properties of MnSi, FeSi, and CoSi

Measurements of the sound velocities, heat capacities, magnetic susceptibilities, and electrical resistivities of single crystals of MnSi, FeSi, and CoSi were performed in the temperature range 2.5--300 K and the elastic constants were calculated. The temperature dependence of the mentioned quantities reveals nontrivial features, reflecting specifics of magnetic and electron subsystems in these materials.

Magnetic order and heavy fermion behavior in CePd 1+xAl 6−x: Synthesis, structure, and physical properties

The physical properties including magnetic susceptibility, specific heat, and electrical resistivity of single crystals are reported for the compound CePd 1+ x Al 6− x ( x=0.5) which crystallizes in the tetragonal SrAu 2Ga 5-type structure (space group P4/ mmm). The compound was grown from an excess of molten Al flux from the respective elements and the crystal structure was established from single-crystal X-ray diffraction. Anomalies in the low temperature specific heat C p ( T) and electrical resistivity ρ( T) show that the compound undergoes ferromagnetic order at T C =2.8 K. In the ordered state, CePd 1.5Al 5.5 displays heavy fermion behavior with a Sommerfeld coefficient of ca. 500 mJ/mol-K 2.

Nearly isotropic superconductivity in (Ba,K)Fe2As2

Superconductivity was recently observed in iron-arsenic-based compounds with a superconducting transition temperature (T(c)) as high as 56 K, naturally raising comparisons with the high-T(c) copper oxides. The copper oxides have layered crystal structures with quasi-two-dimensional electronic properties, which led to speculation that reduced dimensionality (that is, extreme anisotropy) is a necessary prerequisite for superconductivity at temperatures above 40 K (refs 8, 9). Early work on the iron-arsenic compounds seemed to support this view. Here we report measurements of the electrical resistivity in single crystals of (Ba,K)Fe(2)As(2) in a magnetic field up to 60 T. We find that the superconducting properties are in fact quite isotropic, being rather independent of the direction of the applied magnetic fields at low temperature. Such behaviour is strikingly different from all previously known layered superconductors, and indicates that reduced dimensionality in these compounds is not a prerequisite for 'high-temperature' superconductivity. We suggest that this situation arises because of the underlying electronic structure of the iron-arsenic compounds, which appears to be much more three dimensional than that of the copper oxides. Extrapolations of low-field single-crystal data incorrectly suggest a high anisotropy and a greatly exaggerated zero-temperature upper critical field.

Recent high-magnetic-field studies of unusual groundstates in quasi-two-dimensional crystalline organic metals and superconductors

After a brief introduction to crystalline organic superconductors and metals, we shall describe two recently-observed exotic phases that occur only in high magnetic fields. The first involves measurements of the non-linear electrical resistance of single crystals of the charge-density-wave (CDW) system (Per)$_2$Au(mnt)$_2$ in static magnetic fields of up to 45 T and temperatures as low as 25 mK. The presence of a fully gapped CDW state with typical CDW electrodynamics at fields higher that the Pauli paramagnetic limit of 34 T suggests the existence of a modulated CDW phase analogous to the Fulde-Ferrell-Larkin-Ovchinnikov state. Secondly, measurements of the Hall potential of single crystals of $\alpha$-(BEDT-TTF)$_2$KHg(SCN)$_4$, made using a variant of the Corbino geometry in quasistatic magnetic fields, show persistent current effects that are similar to those observed in conventional superconductors. The longevity of the currents, large Hall angle, flux quantization and confinement of the reactive component of the Hall potential to the edge of the sample are all consistent with the realization of a new state of matter in CDW systems with significant orbital quantization effects in strong magnetic fields.

Behaviour of electrical resistivity in single crystals of Cu-Zn-Al and Cu-Al-Be under stress

Electrical resistivity measurement (ER) has been one of the main experimental techniques used in researches that involve alloys with martensitic transformation, due to its susceptibly to detect crystalline structure modifications. In alloys that present shape memory effect, ER is mainly used to study thermal cycling and ageing. Recently, measures of electrical resistance have been coupled to mechanical tests during shape memory effect phenomena. Most of publications using ER at constant temperature in the stress-strain domain was done in polycrystalline alloys of Ti-Ni and Ti-Ni-Cu. In this work, single crystals of copper-based samples were tested at different temperatures to analyse the behaviour of stress and resistivity variation versus strain. During superelasticity test, ER variation presents a linear behaviour and an absence of hysteresis with strain. Mechanical tests are performed at different temperatures and with different orientations of the tensile axis. These results show that the martensite variants present an electrical anisotropy.

The charge-density-wave transition in Lu5Ir4Si10 under uniaxial pressure

An uniaxial pressure cell for low temperature use is described in detail. Then we present data of the electrical resistance of single crystals of Lu5Ir4Si10, which is known to show a charge-density-wave transition around 83 K and to become superconducting near 3.8 K, both phenomena being anticorrelated under pressure. Since the CDW in Lu5Ir4Si10 is a quasi one-dimensional phenomenon because of a chain-like structure, it responds to uniaxial pressure in a specific way.

Crystal growth and the influence of oxygen stoichiometry on electrical resistivity of single crystals

This paper presents the results of an analysis of the effects of reduction and oxidation processes on single crystals of (NCCO). It is experimentally shown that when the oxidation process is cyclically repeated the associated reduction process increases the of NCCO single crystals. The influence of the gassy atmosphere and the rate of the temperature change during thermal treatment on the electrical resistivity of single crystals is widely discussed.

Resistive relaxation processes in oxygen-deficient single crystals of YBa2Cu3O7−δ

The effect of low-temperature annealing on the superconducting transition temperature and electrical resistance of single crystals of YBa2Cu3O7−δ with an oxygen deficiency δ=0.5–0.6 quenched from temperatures of 620–650 °C is considered. The transition temperature increases during annealing, while the resistance decreases. The isothermal relaxation of resistance is measured and used for estimating the activation energy of the relaxation process, which coincides with the activation energy of oxygen diffusion. The obtained results are attributed to oxygen ordering in Cu-O planes without changing its concentration. The observed step form of resistive transitions to the superconducting state is interpreted as the formation of clusters characterized by different oxygen concentrations and ordering. The cluster size is estimated.

Pressure dependence of superconducting critical temperature ofSr2RuO4

We studied electrical resistivity of single crystals of an oxide superconductor Sr{sub 2}RuO{sub 4} under hydrostatic pressure up to 12 kbar. The midpoint T{sub c} decreases at the rate of 3{percent}/kbar. Anomalous increase of resistivity along the c axis is observed at room temperature with increasing pressure, whereas that in the ab plane decreased with pressure as normally expected. {copyright} {ital 1997} {ital The American Physical Society}

Anisotropy of the mixed‐state resistance of Tl2Ba2CaCu2O8 single crystals

AbstractThe electrical resistance of single crystals of the high‐temperature superconductor Tl2Ba2CaCu2O8 has been measured as a function of the angle θ between the direction of the magnetic field and the current‐carrying CuO2‐planes. The resistance is maximal for θ = 90° (B⟂CuO2‐planes) and decreases to a minimum at θ = 0°. For small angles an anomalous enhancement of the resistance is found. While the general shape of the resistance is generated by the motion of “pancake vortices” in the CuO2‐planes, the anomaly is due to “Josephson vortices” moving perpendicular to the planes.

Weakly increasing anisotropy in Zn doped YBa2Cu3O7−δ

The electrical resistivity of single crystals of YBa2Cu3O7−δ with 1 and 3.5% Zn replacing copper has been studied in magnetic field up to 12 T parallel to thec-axis. From the onset ofc-axis resistance, ocurring at a higher temperature than for the in-plane resistivity, the phase diagram can be determined which separates the region of intact vortex tubes from that of decorrelated vortex segments moving independently in differentab-planes of the crystal. This phase separation occurs at a larger magnetic field for comparable temperatures and concentrations when compared to Fe-doped Y-123. This result and a quantitative description in terms of a published model for Josephson tunneling between parallel planes, show that Zn-doping increases anisotropy only weakly in contrast to Fe-doped Y-123.

Magnetic and thermal properties of U xLa 1− xPd 2Al 3

We present the experimental results of the specific heat, magnetic susceptibility and electrical resistivity of single crystals of U x La 1− x Pd 2Al 3. As the uranium atom is replaced by the lanthanum atom, the Néel tem x = 0.5, the ferromagnetic phase transition occurs and the feature is similar to a weak itinerant ferromagnet. It is found that both the electrical resistivity and the magnetic susceptibility cannot be scaled with uranium concentration. The temperature dependence of the electrical resistivity suggests the local nature of the spin fluctuations.

In situ electrical resistivity measurements during the sulphuration of pyrite and Fe thin films

A cell has been built to measure the electrical resistivity of single crystals and thin films in a sulphur atmosphere. Resistivity variations during the sulphuration of pyrite samples have been investigated as a function of temperature ( approximately 450-723 K) and of time at constant temperature. The transformation of Fe thin films into pyrite films has been followed through their electrical resistivity changes up to approximately 623 K. Results are briefly discussed by considering the stoichiometric and crystallographic transformations undergone by the films. After these preliminary results some open questions are presented.

Zone Refining of High-Purity Aluminum

Zone refining has been tried on high-purity aluminum produced by a combination of the three-layer electrolytic refining process and the segregation process. The cropping procedure was effective in increasing the efficiency of zone refining. The highest residual resistance ratio R(300 K)/R(4.2 K) obtained was about 90000 in the bulk value, corresponding to 99.99999% aluminum. In the region of very high purities, it has been found that the residual electrical resistivity in single crystals of aluminum exhibits strong anisotropy, not yet predicted for a normal metal with cubic symmetry. The resistivity increases in the order of the 〈110〉, 〈111〉 and 〈100〉 directions.

Electrical resistivity of single crystals and thin films of SnSe

Electrical resistivity of single crystals and thin films of SnSe

Anisotropy of Residual Electrical Resistivity in High-Purity Aluminum Single Crystals

Measurements have been made on the residual electrical resistivity in single crystals of high-purity aluminum ( R R R ≃ 50000) at 4.2 K. The samples were cut from single-crystal plates with {110} surfaces. The axes of the samples were oriented parallel with the principal axes <100>, <111> and <110>. The results show strong anisotropy, previously not predicted for a normal metal with cubic symmetry. The resistivity increases in the order of the <110>, <111> and <100> directions; the value along <100> is significantly larger than those of the other two directions.