Hall Effect In Mixed State Research Articles

Mixed state odd Hall effect in YBa2Cu3O7?? with unidirectional twins

We have studied the mixed state Hall effect in YBa2Cu3O7−δ single crystals with unidirectional twins: ϱxy=f(H). An analysis of the Hall conductivity σxy in free flux flow regime reveals that σxy can be successfully described by two terms which are related to the quasiparticle excitations and the motion of free vortices respectively. We have discovered the strong twin dependence of the Hall conductivity σxy in the pinning (TAFF) regime and detected the sign reverse of the Hall conductivity σxy at changing angle α (+45 °→−45 °) between current and twin plane that indicated the presence of backflow of vortices. We have observed that σxy tends to -∞ while approaching the melting line. These results provide the evidence of strong planar pinning influence on the Hall conductivity.

Hall effect in detwinned single crystals of YBa2(Cu1?x Zn x )3O7 ??in the mixed state

The effect of zinc doping on the mixed-state Hall effect in detwinned single crystals of YBa2Cu3O7 −δ has been studied. We observe a sign reveral of the Hall effect in crystals with a superconducting transition temperature (Tc) as low as 71 K. The Hall conductivity in the mixed state follows theC1/H+C2H field dependence. The absolute value of the coefficientC1 increases faster than (1–T/Tc) with decreasing temperature.C2 increases rapidly asT falls belowTc. The temperature dependence of the ratioC1/C2 scales approximately asT/Tc for different levels of zinc doping.

Pinning strength dependence of mixed-state Hall effect in YBa2Cu3O7 crystals with columnar defects.

The mixed-state Hall effect of twinned YB${\mathrm{a}}_{2}$C${\mathrm{u}}_{3}$${\mathrm{O}}_{7}$ crystals after heavy-ion irradiation clearly showed that the strong pinning induced by columnar defects not only modifies the scaling behavior between the Hall resistivity and longitudinal resistivity, but affects the temperature dependence of the Hall conductivity. For the irradiated crystals, the scaling exponent at 4 T was found to be $1.5\ifmmode\pm\else\textpm\fi{}0.1$ compared to $2.0\ifmmode\pm\else\textpm\fi{}0.2$ for the unirradiated one. The temperature dependence of the Hall conductivity of the irradiated crystals exhibited a clear deviation from that of the unirradiated one at low temperatures.

Hall effect in RBa2Cu3O7 (R=Y,Yb) thin films in high magnetic fields

We report on the mixed state Hall effect of RBa2Cu3O7 (R=Y, Yb) thin films, in high magnetic fields parallel to thec-axis. Our main result is the observation of a direct influence of disorder on the Hall conductivity. The scaling relation ρxy ∝ ρ xx β is observed, with an exponent β that decreases with increasing pinning strength.

Anisotropy, pinning, and the mixed-state Hall effect.

We have studied the mixed-state Hall effect of the high-{ital T}{sub {ital c}} superconductors Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4} (NCCO), Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} (Tl2212), and YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO), and the isotropic low-{ital T}{sub {ital c}} superconductor amorphous Mo{sub 3}Si ({ital a}-Mo{sub 3}Si). We demonstrate the pinning independence of the Hall conductivity {sigma}{sub {ital xy}} and its consequent scaling in terms of the anisotropy of NCCO, Tl2212, and YBCO. In YBCO and {ital a}-Mo{sub 3}Si the Hall angle is enhanced as we reduce the effective pinning, yet {sigma}{sub {ital xy}} is unchanged. For all of these materials there is a vortex contribution {sigma}{sub {ital xy}}{similar_to}1/{ital H} at low fields while at high fields {sigma}{sub {ital xy}}{similar_to}{ital H}. These results provide evidence that beneath the effects of pinning and anisotropy a relatively simple and universal behavior of the mixed-state Hall effect exists.

The mixed-state Hall effect in YBa 2Cu 3O 7/PrBa 2Cu 3O 7 multilayers

Hall coefficient and longitudinal (ϱ xx) resistivities were examined to study the vortex dynamics in the YBa 2Cu 3O 7/PrBa 2Cu 3O 7 (YBCO/PBCO) multilayers. We find that the sign reversal of the Hall coefficient R H diminishes with a decreasing thickness of the individual YBCO layer or a increasing thickness of the individual PBCO layer. These effects suggest a strong correlation between the mechanism of the mixed-state Hall voltage and the coupling strength between the layers.

Hall effect in the mixed state of superconducting L1.85Ce0.15CuO4 (L=Nd,Sm) single crystals.

The temperature and field dependencies of the Hall voltage in the mixed and in the normal state of supeconducting ${\mathit{L}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4}$ (L=Nd and Sm) single crystals have been measured. Crystals having different critical temperatures (15${\mathit{T}}_{\mathit{c}}$20 K) and transition widths (0.5${\mathit{T}}_{\mathit{c}}$3 K) have been used in order to explore the effects of crystal quality on the controversial mixed-state Hall effect. In spite of the cerium doping, the normal-state Hall coefficient is found to be positive at low temperatures (T\ensuremath{\gtrsim}${\mathit{T}}_{\mathit{c}}$) for all measured crystals. At higher temperatures (T\ensuremath{\gg}${\mathit{T}}_{\mathit{c}}$), the Hall coefficient becomes negative. In the mixed state, the Hall resistivity displays an anomalous ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{y}}$(H) peak. However, in contrast to what has been found in other high-${\mathit{T}}_{\mathit{c}}$ superconductors, the polarity of the anomaly can have, depending on temperature, either the same sign or opposite to the Hall effect in the normal state, just above ${\mathit{T}}_{\mathit{c}}$. The appearance of the ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{y}}$(H) anomaly is not ubiquitous but is only observed in crystals of narrow transition widths. To account for these results we explore several of the possible explanations that have been already proposed.

Unified theory of mixed state Hall effect in type-II superconductors: Scaling behavior and sign reversal.

Based upon the normal core model of Bardeen and Stephen and by taking into account both the backflow effect and thermal fluctuations, we have developed a unified theory for the flux motion, particularly for the mixed state Hall effect in type-II superconductors. Both the puzzling scaling behavior and the anomalous sign reversal of the Hall effect have been demonstrated rigorously and naturally. We show that our results successfully explain all essential features of experiments on the mixed state Hall resistivity observed in high-[ital T][sub [ital c]] superconductors.

Hall effect in the mixed state of Y1-xPrxBa2Cu3O7- delta single crystals.

The magnetic field and the temperature dependence of the mixed-state Hall effect have been measured on single crystals in the system Y[sub 1[minus][ital x]]Pr[sub [ital x]]Ba[sub 2]Cu[sub 3]O[sub 7[minus][delta]] (0.0[le][ital x][le]0.3) with the magnetic field perpendicular to the [ital ab] plane and the current flowing in the [ital ab] plane. A sign change of the Hall resistivity is observed at low Pr concentrations, with the negative Hall resistivity disappearing between the concentrations of [ital x]=0.1 and [ital x]=0.2. The field dependence of the Hall resistivity for various Pr concentrations can be qualitatively explained by incorporating a finite pinning force [bold F][sub [ital p]] in the Nozieres and Vinen (NV) model.

Flux-flow Hall effect in superconducting Tl2Ba2CaCu2O8 films.

In both high-${\mathit{T}}_{\mathit{c}}$ and low-${\mathit{T}}_{\mathit{c}}$ superconductors, the Hall effect in the mixed state often shows a sign reversal below ${\mathit{T}}_{\mathit{c}}$ that contradicts standard theories for flux-vortex motion. We have measured the mixed-state Hall effect in high-quality superconducting films of ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$, and find that the Hall angle \ensuremath{\alpha} below ${\mathit{T}}_{\mathit{c}}$ consists of two components: A field-independent component exhibits a complicated temperature dependence, including a sign change near ${\mathit{T}}_{\mathit{c}}$, while a second component with very weak temperature dependence is linear in field and resembles the normal-state Hall angle. The field independence of the sign-reversing component is evidence for vortex motion, and can be understood in terms of simple drag forces acting on vortices.

Mixed-State Hall Effect in an Extreme Type-II Superconductor

Measurements of mixed-state transverse and longitudinal voltages at $T=1.2\ifmmode^\circ\else\textdegree\fi{}$K, $0lHl39$ kG, $0lJl800$ A/${\mathrm{cm}}^{2}$ on an extremely high-$\ensuremath{\kappa}$ type-II alloy superconductor Ti-16 at.% Mo ($\ensuremath{\kappa}=68$, ${T}_{c}=4.2\ifmmode^\circ\else\textdegree\fi{}$K, zero-temperature upper critical field ${H}_{c20}=63$ kG) show that the high-$J$, nearly $J$-independent, mixed-state Hall-angle tangent ${tan\ensuremath{\theta}}_{m}(H)$ is much larger than the normal-state value ${tan\ensuremath{\theta}}_{n}(H)$. At the highest applied magnetic field, the reduced Hall-angle tangent ${P}_{m}(\frac{H}{{H}_{k20}}=0.35)=\frac{[{tan\ensuremath{\theta}}_{m}(H=39 \mathrm{kG})]}{[{tan\ensuremath{\theta}}_{n}({H}_{k20})]}\ensuremath{\approx}0.6$, where ${H}_{k20}=111$ kG is determined by the measured reduced flux-flow resistivity $\frac{{\ensuremath{\rho}}_{f}(H)}{{\ensuremath{\rho}}_{n}}=\frac{H}{{H}_{k20}}$. This contrasts with previous results pertinent to pure or low-$\ensuremath{\kappa}$ materials where ${H}_{k20}\ensuremath{\approx}{H}_{c20}:{P}_{m}(0.35)\ensuremath{\approx}0.35$ (Bardeen-Stephen theory), (1) (Nozi\`eres-Vinen theory), 0.35 (Nb measurements of Fiory and Serin), (2) (Nb-Ta measurements of Niessen et al.).