Electric field effects on vortex dynamics in ultrathinYBa2Cu3

Abstract

The effects of charge-carrier density modulation on critical currents and vortex dynamics in ultrathin YBaaCuaO?-^ films were investigated through transport measurements in field-effect devices. Two distinct dissipation regions in resistive transitions in applied magnetic fields are identified by the electric field effect. A Kosterlitz-Thouless-like transition is observed in zero magnetic field, which can be tuned by the electric field. The importance of thermal fluctuations for the dissipation in high-7c superconductors is stressed. PACS numbers: 74.4a+k, 74.60.Jg, 74.70.Vy, 74.75.+tRecent work has shown that the properties of ultrathin films of YBa2Cu307-5 (YBCO) can be significantly modulated by the application of electric fields [1-5]. The electric field changes the charge-carrier density in a film without changing the chemical structure or composition, thus providing a powerful tool for understanding hightemperature superconductors. Mannhart et ai [4] studied the electric field effect on the critical current density and explained it by field-induced depinning. However, the consistency of this model with details of the effects remains to be proven. In this Letter we report the measurement of resistive transitions and the current-voltage characteristics of ultrathin YBCO films which are subjected to external electric and magnetic fields. It turns out that the electric field effect reveals details of the dissipation processes which are hard to access by other techniques. A transition from a high-temperature, high-dissipation state to a low-temperature, low-dissipation state is observed and identified by a different dependence on the charge-carrier density. The results provide evidence for a Kosterlitz-Thouless-type transition in zero magnetic field, and a transition from a low-temperature (solid or hexatic) to a high-temperature (liquid) vortex phase in magnetic fields.The sample in this work consisted of a c-axis-oriented YBCO film prepared by pulsed laser deposition with a nominal thickness of 5 nm, i.e., four unit cells. The thickness fluctuation of such films is generally of the order of one unit cell [6]. On top of the YBCO layer, a 400-nmthick SrTiOs dielectric layer was deposited in situ with the same technique, and then a gold gate electrode was evaporated. Details of the sample preparation and SrTiOs properties have been published earlier [5,7]. The charge-carrier density in the YBCO layer was modulated by applying a gate voltage between the gate electrode and the YBCO film. The total applied charge was measured by an electrometer. The maximum applied gate voltage is limited by the breakdown behavior of the dielectric. To avoid interference of leakage currents with the test currents, the gate voltage was kept low enough for the leakage current to not exceed 10 nA, while the measurement currents ranged from /iA to mA. Current-voltage

Finite-size effects and dynamical scaling in two-dimensional Josephson junction arrays

“…2 and Figs. [4][5][6][7] shows that this, indeed, is the case (at least in comparison to the quality of the scaling collapse in the lower curve of Fig. 2).…”

Persistent electrical doping of Bi2Sr2CaCu2OMotzkau1, Jacobs2, Katterwe3 et al. 2012Phys. Rev. B131100View full textAdd to dashboardCite

“…A persistent electrostatic field-effect due to net electric polarization or trapped charges can be realized at the interface between a superconductor and a ferroelectric [35] or polar insulator [36]. This is also a surface phenomenon, but in case of layered cuprates, which represent stacks of metallic CuO planes sandwiched between polar-insulating layers [37], electrostatic charging of insulating layers may in principle lead to the bulk persistent electrostatic field-effect.…”

“…The electrostatic charging of means by current injection takes place uniformly within the whole structure. Therefore, unlike the conventional electric field effect [20] and the electrostatic field effect at the interface between a superconductor and a ferroelectric material [35,36], the current injection may lead to a persistent bulk electrostatic field-effect doping of Bi-2212. Koval et.…”

Relationship between electrical transport and hole concentration in YBa2Cu3O7−x ultrathin films probed by electric fields

“…13 On the other side, the experimental I DS Ϫ V DS characteristics could be well described by a power law V ϳ I ␣ predicted by the Kosterlitz-Thouless theory of thermal fluctuations, and it was pointed out that the electric field primarily acts on the exponent ␣. 18,29 After our considerations in the previous sections based on the findings of a rather low hole concentration ͑1 ϫ 10 21 cm Ϫ3 ͒ and a strong field effect on T c ͑␤ϭ2.5͒ we do not exclude the influence of weak links in the ultrathin films on our j c modulation with ␥ϭ3. However, we have no clear evidence and the interpretation contradicts the findings in the j c versus magnetic field measurements mentioned above.…”