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We propose and demonstrate a spatial partition method for the high-frequency photo-response of superconducting devices correlated with inductive and resistive changes in microwave impedance. Using a laser scanning microscope, we show that resistive losses are mainly produced by local defects at microstrip edges and by intergrain weak links in the hightemperature superconducting material. These defects initiate nonlinear high-frequency response due to overcritical current densities and entry of vortices.

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“…(1) and (2). Figure 4(a) shows the distribution PR X (x,y) along the edge of an element of the resonator from Fig.…”

Section: ⎤ ⎥ ⎥ ⎦mentioning

confidence: 99%

“…Despite the voluminous work on the nature of NL effects in HTS, the causes are not completely clear and remain under debate [2]. It is widely accepted that sources of this problem have both resistive and inductive origins, and arise locally as a result of high current densities J RF (x,y) nonuniformly distributed in the cross-section of SC films.…”

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confidence: 99%

Measurement of local reactive and resistive photoresponse of a superconducting microwave device

Zhuravel

Anlage

Ustinov

2006

Applied Physics Letters

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“…Near-field microscopy has been successfully done at optical 2,3 and microwave 4,5 frequencies. In a typical experimental setup, the distance h between the probe and sample is much less than the free space wavelength λ.…”

Section: Introductionmentioning

confidence: 99%

Effect of tip geometry on contrast and spatial resolution of the near-field microwave microscope

Imtiaz

Anlage

2006

Journal of Applied Physics

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The Near-Field Scanning Microwave Microscope (NSMM) can quantitatively image materials properties at length scales far shorter than the free space wavelength (λ). Here we report a study of the effect of tip-geometry on the NSMM signals. This particular NSMM utilizes scanning tunneling microscopy (STM) for distance-following control. We systematically examined many commercially available STM tips, and find them to have a conical structure on the macroscopic scale, with an embedded sphere (of radius r sphere ) at the apex of the tip. The r sphere values used in the study ranged from 0.1 μm to 12.6 μm. Tips with larger r sphere show good signal contrast (as measured by the frequency shift (Δf) signal between tunneling height and 2 μm away from the sample) with NSMM. For example, the tips with r sphere = 8 μm give signal contrast of 1000 kHz compared to 85 kHz with a tip of r sphere = 0.55 μm. However, large r sphere tips distort the topographic features acquired through STM. A theoretical model is used to understand the tip-to-sample interaction. The model a email address: anlage@umd.edu 1 quantitatively explains the measured change in quality factor (Q) as a function of height over bulk Copper and Silicon samples.

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“…Indeed, using a scanning localized microwave source, 15 it would be possible to probe the ac dynamics of AJ on GB, minimizing the effect of pinned A vortices. For instance, the AJ core size and thus the local J b can be extracted from ac measurements of higher voltage harmonics, as described in the preceding section.…”

Section: Discussionmentioning

confidence: 99%

“…34,35 Many observable features of global current-voltage characteristics, magnetization, rf response, and flux creep of HTS polycrystal may be due to dynamics and pinning of vortices in easy-flow channels, rather than stronger pinned vortices in the grains. [36][37][38][39][40] By contrast, GBs in low-T c materials do not block macroscopic currents, but can enhance flux pinning 41,42 and play the role of ''hidden'' weak links that strongly affect the vortex mass and viscosity 19 crucial for transport and microwave response of superconductors, 14,15 The behavior of vortices in easy flow channels on GBs in polycrystal is mostly determined by the structure of vortex cores which depends on the local depairing current density J b through a GB at the nanoscale of few current channels between the dislocations. The extreme sensitivity of J b () to the misorientation angle makes GBs in HTS a unique tool to trace a fundamental transition between the Abrikosov ͑A͒ and Josephson ͑J͒ vortices.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear dynamics of vortices in easy flow channels along grain boundaries in superconductors

Gurevich

2002

Phys. Rev. B

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A theory of nonlinear dynamics of mixed Abrikosov vortices with Josephson cores ͑AJ vortices͒ on lowangle grain boundaries ͑GB͒ in superconductors is proposed. As the misorientation angle increases, vortices on low-angle GBs evolve from the Abrikosov vortices with normal cores to intermediate AJ vortices with Josephson cores, whose length l along GB is smaller that the London penetration depth , but larger than the coherence length . Dynamics and pinning of the AJ vortex structures determine the in-field current transport through GB and the microwave response of polycrystal in the crucial misorientation range Ͻ20-30°of the exponential drop of the local critical current density J b () through GB. An exact solution for an overdamped periodic AJ vortex structure driven along GB by an arbitrary time-dependent transport current in a dc magnetic field HϾH c1 is obtained. It is shown that the dynamics of the AJ vortex chain is parametrized by solutions of two coupled first-order nonlinear differential equations which describe self-consistently the time dependence of the vortex velocity and the AJ core length. Exact formulas for the dc flux flow resistivity R f (H), and the nonlinear voltage-current characteristics are obtained. Dynamics of the AJ vortex chain driven by superimposed ac and dc currents is considered, and general expressions for a linear complex resistivity R() and dissipation of the ac field are obtained. A flux flow resonance is shown to occur at large dc vortex velocities v for which the imaginary part of R() has peaks at the ''washboard'' ac frequency 0 ϭ2v/a, where a is the intervortex spacing. This resonance can cause peaks and portions with negative differential conductivity on the averaged dc voltage-current (V-I) characteristics. ac currents of large amplitude cause generation of higher voltage harmonics and phase locking effects which manifest themselves in steps on the averaged dc I-V curves at the Josephson voltages, nប/2e with nϭ1.2, . . . .

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Cited by 27 publications

References 51 publications

Measurement of local reactive and resistive photoresponse of a superconducting microwave device

Measurement of local reactive and resistive photoresponse of a superconducting microwave device

Effect of tip geometry on contrast and spatial resolution of the near-field microwave microscope

Nonlinear dynamics of vortices in easy flow channels along grain boundaries in superconductors

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