Transient vortex states, created after a sudden exposure of a Bi2Sr2CaCu2O8+δ crystal to a steady magnetic field, are observed using a high-temporal resolution magneto-optical imaging system. The images reveal dynamic coexistence of a disordered phase near the sample edges and a quasi-ordered phase in the sample interior, prior to the establishment of a quasi-ordered state throughout the entire sample as dictated by the thermodynamic conditions. Different points on the borderline between these two phases move toward the sample edges at different rates, depending on the local induction.
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changei n their slope at x = x, (markedb y bold circles),i ndicatinga changein the bulk currentd ensity.A s evidentf rom the figure, the point xf movesp rogressivelwy ith time toward the sample edges and, simultaneouslyt,h e induction Bf at xr increases.T he point xr also signifies a remarkablec hangein magneticr elaxation characteristicTs.o illustratet his point we employt he Biot-Savarlta w to fit the data of Fig. 1, using surfacec urrenJts , and two bulk currentsJh and Jt as fitting parametersA.s showni n the log-logp lotin the insett o Fig. 1, the bulk currenJth , correspondintog the part of the profile near the edges, exhibits a power-law decay with time (Jh ~ 1/t°31), whereas deviationsf rom a power-lawa re evidenfto rJr. The break in the inductionp rofileat x, which marks a changei n the bulk current densitya nd in the relaxationch aracteristics, indicates a dynamic coexistenceo f two distinctv ortexs tateso n both sideso f xc The nature of these phases is explained as follows.T he sudden injectiono f vorticesin to the sample through its edges creates a transient disordereds tate of the vortex matter. A quasi-orderedt hermodynamic vortex state starts to nucleaten ear the samplec enterw herethe field is minimum, and expandtso wardt he samplee dgesx, f is a point on the borderb etweenth e expanding quasi-orderedp hase and the decaying transiendti sorderepdh ase. In order to constructt he borderline betweent he two phases,w e utilize their different relaxation characteristics.W e subtract consecutive2 D induction images and plot the differenceI.n the quasi-ordered state the decay is relativelyf ast and the differncesa re relativelyla rge( brighti n our gray scale).T he slow decayo f the disordered stater esultsi n a relativelys mall difference (dark color). Figure 2 illustratesa result of such a procedures, howinga clear border betweenth e two phasesT. his borderc an be viewed as the front of the growing quasi-orderedp haseT. he curveds hapeo f this front results from the dependencoef the growth rate on the local induction \[7\]T.h e 2D distributiono f the inductionfi eld for a thin rectangulasra mple\ [8\]l eads to the curved fronts howni n Fig. 2. This researchw as supportedb y The Israel Science Foundationf oundedb y the IsraelA cademyo f Sciencesa ndH umanitie-s Center of ExcellenceP rogram,a nd by the Heinrich Hertz Minerva Center for High Temperature Superconductivity. Y.Y. acknowledgessu pportf rom the U.S.-Israel Binational Science Foundation. D. G. acknowledgess upport from the Clore FoundationT.. T. acknowledgessu pporftr om a Grant-in-Aidf or ScientificR esearchfr om the Ministry of Education,S cience,S ports and Culturea, ndfrom CREST.