Dynamic and static properties of mesoscopic vortex matter

M. I. DOLZ; Y. FASANO; L. TOSI; A. B. KOLTON; H. PASTORIZA

Varsovia - Polonia

Congreso; CMD23 - 23rd General Conference of the Condensed Matter Division of the European Physical Society.; 2010

Instytut Problemów Jadrowych

p { margin-bottom: 0.21cm; } Vortex matter in type-II superconductors is a sand-box to study static and dynamic properties of soft condensed matter systems since the control parameters are easily tunable by changing temperature and magnetic field. Recently, the issue of the sensibility of the physical properties of soft condensed matter to the system size has gained a large attention in the community. In this work we study this issue by accessing to structural and dynamic properties of vortex matter. Vortices repel between each other and as a consequence form an elastic structure whose structural properties strongly depend on the interaction of vortices with thermal and static disorder. The latter is given by the pinning landscape of the samples provided they naturally present crystal defects where superconductivity is depleted. The competition between the elastic interaction between vortices and the vortex-quenched disorder interaction results in a typical lengthscale known as the Larkin length [1,2]. This is the minimal size that has to have a vortex structure in order to remain pinned by quenched disorder, namely that the system presents a finite barrier that inhibits its depinning when perturbative forces (currents) are applied. This Larkin lengthscale rises when the magnitude of quenched disorder decreases or alternatively the vortex-vortex interaction increases. For materials with a weak pinning potential such as the high-temperature superconductor Bi-2212, this length is within the range of microns, although it depends on temperature. Therefore, tailoring the sample size in the micron-sized range allows to get information of the dependence of the Larkin length with temperature providing the dynamic response of the mesoscopic sample becomes irreversible at the temperature TIL which this length becomes the size of the sample. We present here results on the dependence on the sample size of the irreversibility line, the temperature at which pinning becomes effective, obtained by means of micro-electro-mechanical torsional oscillators. The samples where engineered out of bulk as-grown-Bi-2212 samples by combining optical lithographic and etching techniques [3]. We combine this data with the analysis of the structural properties of mesoscopic vortex matter. Magnetic decoration experiments provide snapshots of the vortex structure, with single vortex resolution, at the irreversibility temperature [4]. The dependence of the positional order on the sample size is discussed in connection to the variation of the Larkin length with temperature. [1] T. Giamarchi and P. L. Doussal, "Elastic theory of pinned flux lattices", Phys. Rev. Lett. 72, 1530 (1994). [2] T. Giamarchi and P. L. Doussal, "Elastic theory of flux lattices in the presence of weak disorder", Phys. Rev. B. 52, 1242 (1995). [3] M. I. Dolz, A. B. Kolton and H. Pastoriza, "Direct determination of the collective pinning radius in the cuprate superconductor Bi2Sr2CaCu2O8+", Phy. Rev. B 81, 092502 (2010). [4] Y. Fasano and M. Menghini,"Magnetic-decoration imaging of structural transitions induced in vortex matter" review contribution inSuperconductors Science and Technology 21, 023001 (2008).