Strong pinning

For very strong pinning points at T = 0 K, dislocations can mechanically break away only when the dislocation segment is bowed enough to meet another segment on the other side of the pinning point (shown as the burst in Fig. 7.6). This will occur when... 

Strong pinning limit Exact ground state... 

For large values of u our flow equations break down. Qualitatively the flow is towards large u and small K. We can, however, find the asymptotic behavior in this phase by solving the initial model in the strong pinning limit exactly. To find this solution we will assume strong pinning centers and weak thermal fluctuations ... 

Fig. 4. Ground states in the strong pinning regime characterized by the integer number n°. The wavy lines show an excitation from one ground state forming an in-stanton configuration which could be a mechanism for quantum tunneling transport at low temperatures [35, 33],...

In the last region K = 0 for T -C c/(p2/imp) we come back to the strong pinning case, discussed in section 3.3 before, and calculate the pair correlation function exactly. Taking into account that the hi s are independent on different lattice sites, i.e., hihj oc the (discrete) phase correlation function is given... 

Figure 21. TAS MRAM cell using a weakly pinned low blocking temperature storage layer (thin Mnlr, low Tb), and a strongly pinned, high blocking temperature, reference layer (PtMn, thick Mnlr, high Tb) [89, 90].

In this paper, we concentrate on the /j+SR measurements and determine if YBa2Cu307 is a bulk. v-wave (nodeless) superconductor, as determined in Refs. 1-3, or a d-wave superconductor, whose order parameter A(k), changes sign as a function of k, as claimed in Ref. 8. In making this determination, we show that the features observed in the single-crystal data of Ref. 8 are actually due to temperature-activated fluxon de-pinning, an effect which is not readily observable in strongly pinned systems such as the early powder samples or the early heavily-twinned crystals. 

Under conditions of charge neutrality, n = N, the Fermi energy is midway between the le and 2e states and as n varies it departs very little from this position. For example, when = O.IA, the shift is less than 2kT, so that the Fermi energy is strongly pinned. In contrast, when the defect has a positive 7, the Fermi energy moves rapidly from the lower le level to the upper 2e level near n = N. The different behavior of E-g is shown in Fig. 4.5. 

The observed values of threshold fields are close to ones predicted by theoretical model of Maki and Viros ek (ref.9.). According to the expression (9) and taking Nq V=0.1, A (0) 10 eV and Uj /n a few ppm, one gets Ej (0)-10mV/cm. Furthermore, the temperature dependence of Ej is also qualitatively in accordance to a theoretical prediction (eq.(lO)). However, we find a stronger increase of Ej above Tc/2, namely (Tq)/Ej(1.7K)-2.5,if compared to a theoretically expected value of 1.33. Note that the latter value is calculated for a strong-pinning limit. 

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