Utilizing a novel and exact inversion scheme, we determine the complex linear conductivity σ(ω) from the linear magnetic ac-susceptibility which has been measured from 3 mHz to 50 MHz in fields between 0.4 T and 4 T applied parallel to the c-axis of a 250 nm thin disk. The frequency derivative of the phase σ ′′ /σ ′ and the dynamical scaling of σ(ω) above and below Tg(B) provide clear evidence for a continuous phase transition at Tg to a generic superconducting state. Based on the vortexglass scaling model, the resulting critical exponents ν and z are close to those frequently obtained on films by other means and associated with an 'isotropic' vortex glass. The field effect on σ(ω) can be related to the increase of the glass coherence length, ξg ∼ B.

Dynamic scaling analyses of the ac conductivity measured between 1 and 190 kOe before and after heavy ion irradiation parallel to the c axis reveal continuous phase transitions to superconducting glassy vortex states. A first unambiguous evidence for the predicted Bose-glass (BG) behavior being stable up to the matching field H f 40 kOe is presented. The critical exponents differ significantly from those obtained for HЌc and those reported recently for twin-free crystals, suggesting that the inherent uncorrelated disorder in thin films reduces the vortex line wandering, and therefore enhances the BG transition.

The complex electrical conductivity o (u) is determined from the linear ac susceptibility between 3 Hz and 3 MHz measured in fields between 0.4 and 12T parallel and perpendicular to the c axis of a twinned crystal. Dynamical scaling of ] o [ and o "/o' reveals ordering temperatures Ts(B) and field-independent scaling functions by using the variable (T,z Ts)/ -[T Ts[. F-or B J c, the critical exponents v and z agree with values obtained on films indicating isotropic vortex-glass fluctuations, whereas those for B [[ c indicate elongated fluctuations in the c direction mediated by correlated pinning via the edges of twin boundaries. PACS numbers: 74.25.Nf, 74.60.ae, 74.72.Bk Based on early indications and suggestions for a glassy vortex state in a granular high-T, superconductor [1], Fisher et aL [2,3] argued that in the absence of a driving current j this state represents a thermodynamic equilibrium phase emerging from a vortex liquid below some transition line Ts(B). In clear distinction to the predictions of the flux creep [4] and thermally activated flux flow [5] models, which yield genuine superconductivity,i.e. , zero resistance p(j -+ 0), only at zero ternperature, the vortex glass (VG) is characterized by p = 0 for all temperatures below T~(B). Convincing evidence for the existence of this continuous phase transition has been provided by a number of scaling analyses of nonlinear voltage-current isotherms for YBazCus07 s (YBCO) [6 -14]. The principal scaling variable of the VG transition is the glass correlation length 8 ] T -Ts [ " describing the diverging size of glassy islands and of lakes of vortex fluid above and below Tg(B), respectively, and also the increasing lifetime of these fluctuations r P.The present physical interest in the VG transition is focused on the not yet well understood effect of the possible types of disorder. The original "isotropic" VG model of Fisher et aL [2,3] considered weak pinning to point defects which, due to charge doping, is intrinsic for all high-T, materials. According to subsequent mean-field (MF) work by Dorsey et al. [15], (i) the VG transition may arise from a random spatial distribution of T, and (ii) critical fluctuations lead to real exponents larger than the MF limits,~F = 1/2 and zMF = 4 . Fisher et aL [3] also indicated the possibility of anisotropic vortex fluctuations, characterized by a superdivergence of the correlation length parallel to B, E, Et/&, with 0.5 ( t, ' ( 1.More recently, Nelson and Vinokur [16] considered the case of columnar pinning, either implemented artificially or originating from the mosaic of twin planes intrinsically present in bulk YBCO. Based on the Bose glass (BG) model and ignoring point defects they predicted a transition at TBG to the vortex glass, characterized by ( = TABLE

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