Angular Dependence Of Resistivity Research Articles

Angular dependence of resistance and critical current of a Bi-2223 superconducting joint

Low resistance and high critical current are prerequisites for superconducting joints used in persistent-mode magnets. Herein, we use a joint resistance evaluation system, previously developed by us, to systematically evaluate the angular dependence of resistance and critical current of a Bi-2223 superconducting joint in a closed-loop sample. The current decay is measured by rotating the sample incrementally. The time dependence of the loop current is evaluated at 4 K, 0.15–0.28 T, and magnetic field angles ranging from 90° to 0, wherein 90° corresponds to the direction parallel to the tape surface. The results suggest that the resistance and critical current of the joint depend on the angle of the magnetic field. The evaluated critical current increases as the angle increases. The angular dependence of resistance can be divided into three regions: low-resistance, transition, and high-resistance regions. The low-resistance region exists at high angles close to 90°. In this region, the decay of the loop current is small, and the persistent current continues to flow. Furthermore, the joint resistance is less than 1.4 × 10−13 Ω. In the transition region, the joint resistance significantly increases by three orders of magnitude with sample rotation. This significant increase is attributed to an increase in the perpendicular component of the magnetic field, which decreases the critical current of the joint. At lower angles, the joint resistance remains high, ranging from 10−11 to 10−10 Ω. A significant decay in the loop current is observed in the high-resistance region. Based on these findings, we conclude that the design of a persistent-mode magnet must consider not only the magnitude but also the direction of the magnetic field applied to superconducting joints.

Anomalous symmetry breaking in the Weyl semimetal CeAlGe

CeAlGe, a proposed type-II Weyl semimetal, orders antiferromagnetically below 5 K. At 2 K, spin-flop and a spin-flip transitions to less than 1 $\mu_B$/Ce are observed in the $M(H)$ data below 30 kOe, ($\bf{H}\|\bf{a}$ and $\bf{b}$, and 4.3 kOe, $\bf{H}\|\langle110\rangle$, respectively, indicating a four-fold symmetry of the $M(H)$ data along the principal directions in the tetragonal $\it{ab}$ plane with $\langle110\rangle$ set of easy directions. However, anomalously robust and complex twofold symmetry is observed in the angular dependence of resistivity and magnetic torque data in the magnetically ordered state once the field is swept in the $\it{ab}$ plane. This twofold symmetry is independent of temperature and field hystereses and suggests a magnetic phase transition that separates two different magnetic structures in the $\it{ab}$ plane. The boundary of this magnetic phase transition and possibly the type of low-field magnetic structure can be tuned by an Al deficiency.

Microstructure and superconducting properties of high-rate PLD-derived GdBa2Cu3O7\u2212\u03b4 coated conductors with BaSnO3 and BaZrO3 pinning centers

The microstructure of GdBa2Cu3O7−δ based on superconducting tapes with BaSnO3 and BaZrO3 artificial pinning centers formed by high-rate pulse laser deposition in SuperOx Japan was studied by scanning/transmission electron microscopy. The artificial pinning centers have adopted columnar morphology with average diameter of about 8 nm (BaSnO3-doped sample) and 6.5 nm (BaZrO3-doped sample) and density of 500 μm−2 for the both samples. The average length of the BaSnO3 nanocolumns is about two times higher than the BaZrO3 nanocolumns. The angular dependences of critical current in magnetic field up to 1 Tesla at 77 and 65 K have been obtained. The critical current and its anisotropy depend on artificial pinning centers presence and their type. The angular dependence of resistivity in the field up to 9 Tesla was also studied and discussed.

Effect of Te-doping on the superconducting characteristics of FeSe single crystal

FeSe1-xTex (x = 0.5, 0.6 and 0.7) single crystals were prepared by the chemical reaction sealed in a small quartz tube with high vacuum. The angular dependence of resistance was measured in different magnetic field at a constant temperature, and scaled by the anisotropic Gingzburg-Landau theory, respectively, for these single crystals. The field dependences of critical temperature and flux pinning energy were obtained from resistance versus temperature curves measured in various magnetic fields perpendicular and parallel to the c-axis. The critical current density and the flux pinning force were calculated by the Bean model from the magnetization loops. The Te-doping had an obvious effect on the critical temperature Tc, the critical current density Jc and the flux pinning energy U; but there was a weak effect on the anisotropy of FeSe1-xTex single crystals. The flux pinning characteristics were also discussed.

Four-fold symmetry of resistivity and flux pinning energy in Ba0.67K0.33BiO3+δ single crystal

Ba0.67K0.33BiO3+δ single crystal with Tc ∼ 26.4 K has been prepared by the molten salt electrochemical method. We observed a four-fold symmetry in the angular dependence of ab-plane resistance R (θ) at H = 0.5 T and T = 25.5 K for the first time. The data can be scaled by R = [R1sin2(θ + 45°) + R2cos2(θ + 45°) − R(90°)]|sin2θ| + R(90°). Although dip structure appears in R(θ) when the angles between the magnetic field direction and c-axis are 0°, 90°, 180° and 270°, respectively, the maximal position of resistance tilted away θ = 45° and θ = 135°, namely the angle difference between two peaks is 79° or 101°. This result indicates the superconducting Ba0.67K0.33BiO3+δ single crystal is probably an orthorhombic structure with distorted Bi−O octahedron. We consider that the angular dependence of resistivity comes from the superconducting energy gap with pairing symmetry. The flux pinning energy for θ = 90° is higher than that for θ = 135° proves the existence of the anisotropic vortex pinning effect. The field dependence of flux pinning energy displays a power law, U ∝ H−α. The irreversibility line was also discussed.

Abnormal Behavior of the Angular Dependence of Resistivity in YBCO Thin Films

Careful investigation of the angular dependence of resistivity ρ(θ) (θ is the angle between the magnetic field and the ab-planes) as a function of the temperature within the superconducting transition in an applied magnetic field B up to 1 T for a series of YBa2Cu3O7−δ (YBCO) thin films revealed a large variation in the shape and width of the minimum displayed in the vicinity of θ=0°, from a flat to a very sharp behavior. The series of films studied included both optimally doped and underdoped samples of different Tc, critical current density Jc, film thickness, and preparation techniques. ρ(θ) measured for B close to θ=0° (B parallel to ab-planes) for both B‖J and B⊥J (J is the applied current density) showed two classes of samples; class of samples where ρ(θ) is independent of the direction of B relative to J and the other class where ρ(θ) depends on the orientation B relative to J. This unusual unique behavior motivated us to investigate its origin by looking at the scaling of ρ(θ) as a function of the reduced field. Scaling of ρ(θ)) with the reduced field B(γ−2cos 2θ+sin 2)1/2 allowed a quantitative determination of the value of γ (intrinsic anisotropy) which varies between 7 and 400, and is independent of film thickness and Jc. Analysis of the microstructure though XRD of the films studied showed that the anisotropy is related to microstrain of the films.

New Insights on the Intrinsic Anisotropy of YBCO Films

Careful investigation of the angular dependence of resistivity ρ(θ) (θ is the angle between the magnetic field and the ab-planes) and the temperature dependence of resistivity ρ(T) within the superconducting transition in an applied magnetic field B up to 1 T for a series of YBa2Cu3O7−δ (YBCO) thin films revealed a large variation of intrinsic anisotropy factor γ. The series of films studied included both optimally doped and underdoped samples of different Tc, critical current density Jc, film thickness, and preparation techniques. The variation in the shape and depth of the minimum measured for ρ(θ) near θ=0° could be directly correlated to the intrinsic anisotropy of the YBCO films. The results of fitting of ρ(θ) using Bardeen–Stephen theory allowed a quantitative determination of the value of γ which varies between 7 and 230, and is independent of Tc, film thickness, or Jc. The sharper the minimum in ρ(θ) around θ=0° the larger is the anisotropy. For highly anisotropic film, ρ(θ) showed an identical behavior for B∥J and B⊥J (i.e., ρ(θ) is independent of the angle θ between B and J for this film). The large variation in γ could be attributed to the “buckling” of the CuO2 planes.

Angular dependence of resistivity in the superconducting state ofNdFeAsO0.82F0.18 single crystals

We report the results of angle dependent resistivity ofNdFeAsO0.82F0.18 single crystals in the superconducting state. By doing the scaling of resistivitywithin the frame of the anisotropic Ginzburg–Landau theory, it is found that theangle dependent resistivity measured under different magnetic fields at a certaintemperature can be collapsed onto one curve. As a scaling parameter, the anisotropyΓ can be determined for different temperatures. It is found thatΓ(T) increases slowly with decreasing temperature, varying from at T = 50 K to at T = 44 K. This temperature dependence can be understood within the picture of multi-bandsuperconductivity.

Angular dependent transport properties of MgB 2 films with columnar grains

We studied the angular dependence of the transport properties of MgB 2 films with columnar grains grown by hybrid physical chemical vapor deposition method, one sample with unreacted boron in the volume and the other sample with no traceable impurity phase. The angular dependence of resistivity and critical current density in applied magnetic fields for both samples showed a flux pinning effect by the grain boundaries between columnar grains. The temperature dependence of the upper critical fields was analyzed by using the dirty-limit two-gap model. We found that the unreacted boron in the body of the film had negative effect on flux pinning and intraband electron diffusivities.

Phase-slip-like resistivity in underdopedYBa2Cu3O7

We investigated the anomalous peak resistivity below the onset ${T}_{c}$ in underdoped ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7},$ reminiscent of that observed in one-dimensional (1D) wires of conventional superconductors. We performed measurements of the angular dependence of resistivity $\ensuremath{\rho}(\ensuremath{\theta})$ in a magnetic field and the temperature dependence of resistivity $\ensuremath{\rho}(T),$ which exhibit a peak for $\mathbf{B}\ensuremath{\Vert}$ ab planes. This peak in $\ensuremath{\rho}(T)$ disappears for $\mathbf{B}\ensuremath{\Vert}$ c axis. The width of the corresponding maximum in $\ensuremath{\rho}(\ensuremath{\theta})$ at $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}$ $(\mathbf{B}\ensuremath{\Vert}$ ab planes) decreases with the increasing c-axis component of the field $(B\mathrm{sin}\ensuremath{\theta}).$ The maximum in $\ensuremath{\rho}(\ensuremath{\theta})$ and $\ensuremath{\rho}(T)$ decreases with an increasing applied transport current. We analyzed the data using three different models of resistivity based on a 2D resistor array, flux motion, and thermally activated phase slips. Numerical calculations suggest that in a filamentary underdoped system, the phase-slip events could produce an anomalous resistivity close to ${T}_{c}.$

QUANTUM OSCILLATIONS, TUNNELING MAGNETORESISTANCE AND ANGULAR DEPENDENCE OF MAGNETIZATION IN Ca3Ru2O7

Ca3Ru2O7 has a double Ru-O layered orthorhombic structure. It is a "bad" metal characterized by various abrupt magnetic and electronic transitions that are highly anisotropic. Ca3Ru2O7 undergoes antiferromagnetic ordering at TN = 56 K and a metal to poorer metal transition at TM = 48 K with a unique antiferromagnetic metallic phase intermediate between the paramagnetic and antiferromagnetic phases. Our recent study reveals a few more striking features: (1) Quantum oscillations, i.e., the Shubnikov-de Haas effect, of which the fast Fourier transform shows two frequencies F1 = 23.4 and F2 = 41 tesla, respectively; (2) Inter-plane tunneling magnetoresistance, whose ratio is more than 90% [ρ(0) - ρ(H)/ρ(0)]; (3) Anomalous angular dependence of magnetization, which leads to similar angular dependence of resistivity due to a strong spin-charge coupling. Ca3Ru2O7 is a rare system that possesses a wide range of interesting yet complex physical properties that very often do not coexist in other materials. The results and discussions will be presented along with comparisons with other related systems.

Angular dependence of resistivity and critical current in YBCO thin film

The anisotropic properties of c-axis oriented thin films of YBaCuO are studied using the angular dependence of V/I charateristics. The sample was rotated by mechanical rotator in magnetic field with angular resolution better than 0.06°. The angular dependence of critical current of our samples is well describes by the formula J c( θ)=J c(0)/| sinθ| μ . The classical thermally activated model was found appropriate for V/I characteristic description.

Intrinsic pinning and dissipation at high current density in epitaxial thin films of YBa 2Cu 2O 7− y

Dissipation in the mixed state of YBa 2Cu 3O 7− y under magnetic fields applied parallel and nearly parallel to the basal plane is studied by use of epitaxial thin film samples and a measurement system with angular precision of ∼0.02°. It is found that the dependence of resistivity on the relative angle between the field and current diminishes as the film thickness is decreased, indicating a tendency of approach to the two-dimensional limit. The anomalous peak in the angular dependence of resistivity at high current densities, which we reported in our previous paper, is further investigated. It is found that the phenomenon is most distinct in the transverse magnetoresistance geometry and high transport current densities, indicatiing that it is caused by a strong Lorentz force acting on the segment of a flux line parallel to the layers. We attribute the phenomenon to a thermally assisted depinning of flux line segment (parallel to the layers) out of the intrinsic pinning potential.

Anomalous angular dependence of dissipation in layered high-temperature superconductors

Resistive behavior of Bi 2Sr 2CaCu 2O 8+y and YBa 2Cu 3O 7−y in their mixed state has been investigated as a function of magnetic field angle, strength, transport current density and temperature. Striking novel features in the angular dependence of resistivity have been found at elevated transport current densities. In the case of YBa 2Cu 3O 7−y>, an anomalous enhancement of dissipation occurs in an angular range, 5° <θ<30° (θ being the field angle relative to the ab-plane). This is compared with a similar phenomenon we reported earlier for Bi 2Sr 2CaCu 2O 8+y which occurs in a much lower angle range, 0.1° <θ<0.5°. Possible origin of such anomalous angular dependences of dissipation are discussed in the context of flux structure and dynamics in layered high-temperature superconductors under tilted magnetic fields.