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Detrital shocked minerals can provide valuable residual records of eroded impact structures. Recent studies have reported shocked minerals in modern alluvium in a subtropical climate from the deeply eroded 2.02 Ga Vredefort Dome impact basin in South Africa. To evaluate the detrital shocked mineral record at a large impact structure in a temperate setting with a Holocene glacial erosional history, we investigated ∼4000 detrital zircons and ∼20,000 quartz grains at the less-eroded 1.85 Ga Sudbury Basin in Ontario, Canada, for the presence of shocked sand grains. Modern alluvium from rivers within and outside the basin, and Holocene glaciofluvial sands (eskers and outwash deltas) across the basin were investigated for shocked minerals. Shocked zircon and/or quartz were found in all modern rivers and most Holocene glacial deposits within, but not outside, the basin. Petrography and scanning electron microscopy (SEM; backscattered electron [BSE]; cathodoluminescence [CL]) imaging and analysis (energy-dispersive X-ray spectroscopy [EDS], electron backscatter diffraction [EBSD]) were used to document shock microstructures. Of the total detrital zircons surveyed, ∼3% (118/3978) were identified as shocked; Holocene samples contained higher average percentages of shocked zircon (63/1361, or 4.6%, with a high of 29%) compared to modern alluvium (55/2617, or 2.1%, with a high of 6%). EBSD analysis revealed a range of shock microstructures, including planar fractures, deformation microtwins, and crystal plastic deformation. At Sudbury, detrital shocked quartz is rare compared to zircon; only 15 grains (∼0.08%) were identified, all with decorated planar deformation features (PDFs). These results demonstrate that a detrital shocked mineral record exists at a large impact basin that is in a "youthful" stage of erosion, despite its age. In addition to modern alluvium, our results also identify glaciofluvial eskers and deltas as reservoirs for detrital shocked minerals; glacial episodes thus enhance the dispersal and preservation of shocked detritus in sedimentary systems. Despite physical differences, the observation that the two largest Precambrian impact basins continue to contribute detrital shocked minerals 2 b.y. after impact suggests that a shocked mineral record of impacts on early Earth should reside in Precambrian siliciclastic rocks.

The record of meteorite impacts on Earth is incomplete due to the destruction of impact craters by erosion and burial. Shocked minerals residing in sediments may help further document the impact record. To evaluate the survival of shocked minerals in fluvial systems we investigated ∼10,000 sand grains from seven sites along the Vaal River in South Africa, ranging from 103 to 759 km downriver from the 2.020 Ga Vredefort impact structure, for the presence of detrital shocked minerals. Detailed observations were made of >7000 quartz grains by petrographic analysis, and >3300 zircon and monazite grains by scanning electron microscopy, using BSE, CL, and EBSD methods. Shock microstructures were identified in detrital quartz, monazite and zircon grains in all of the Vaal River sediment samples analyzed, from the Vredefort Dome to the confluence with the Orange River, 759 km downstream. Analysis of U–Th–Pb and REE compositions of detrital shocked zircon and monazite by SHRIMP-RG allows correlation of the grains to Archean basement exposed in the Vredefort impact structure. Three distinct detrital shocked zircon age populations at 3104 Ma, 3065 Ma and 2867 Ma were identified. Apparent ages of detrital shocked monazite range from 3044 Ma to 2157 Ma, including two groupings at 2640 Ma and 2454 Ma. The Vredefort impact event does not appear to have caused significant Pb-loss for the majority of the grains; Neoproterozoic lower concordia intercepts (1093–751 Ma) in the zircon populations indicate most Pb-loss occurred during the Kibaran orogeny in southern Africa. This study demonstrates that shocked minerals survive long distances (at least 750 km) of transport within fluvial environments, and can be correlated to known bedrock localities using U–Th–Pb dating. The implications of these results are: (1) detrital shocked minerals within modern sediments can be used to identify the existence of an impact structure; geochronology of shocked zircon and monazite can provide target bedrock ages and metamorphic history that can constrain the location of the structure. (2) The persistence of ancient shocked zircon in modern fluvial sedimentary systems suggests that a detrital shocked mineral record of early impact events on Earth may be preserved in siliciclastic sedimentary rocks.

Microstructural and geochronological analysis of shocked zircon has greatly advanced understanding the formation and evolution of impact structures. However, fundamental aspects of shock-produced planar microstructures in zircon remain poorly known, such as their deformation mechanisms, crystallographic orientations, and how planar microstructures visible at the grain scale by scanning electron microscopy correlate to microstructures visible at sub-micrometer scales by transmission electron microscopy and electron backscatter diffraction (EBSD). To unify observations of planar microstructures in zircon made at different scales into a consistent framework, we integrate the results of: (1) three-dimensional crystallographic modeling of planar microstructure orientations, with (2) 360° external prism backscattered electron imaging at the grain scale, and (3) polished section cathodoluminescence and EBSD analysis at the sub-micrometer scale for a suite of detrital shocked zircons eroded from the Vredefort Dome in South Africa. Our combined approach resulted in the documentation of seven planar microstructure orientations that can be correlated from grain to sub-micrometer scales of observation: (010), (100), (112), (112), (112), (1 12), and (011). All orientations of planar microstructures exhibit minor variations in style, however all are considered to be fractures; no amorphous ZrSiO4 lamellae were identified. We therefore favor the usage of “planar fracture” (PF) over “planar deformation feature” (PDF) for describing the observed planar microstructures in zircon based broadly on the nomenclature developed for shocked quartz. Some {112} PFs visible at the grain scale contain impact microtwins detectable by EBSD, and are the first report of polysynthetic twinning in zircon. The microtwins consist of parallel sets of thin lamellae of zircon oriented 65° about and occur in multiple crosscutting {112} orientations within single grains. Curviplanar fractures and injected melt are additional impact-related microstructures associated with PF formation. Crosscutting relations of shock microstructures reveal the following chronology: (1) Early development of c-axis parallel PFs in (010) and (100) orientations; (2) the development of up to four {112} PFs, including some with microtwins; (3) the development of curviplanar fractures and the injection of impact derived melt; (4) the development of (011) PFs associated with compressional deformation; and (5) grain-scale non-discrete crystal plastic deformation. Experimental constraints for the onset of PFs, together with the absence of reidite, suggest formation conditions from 20 to 40 GPa for all of the planar microstructures described here.

Using a Tunnel Diode Oscillator technique, we have measured the effect of a parallel magnetic field on the in-plane rf penetration depths in organic [α-(BEDT-TTF)2NH4Hg(SCN)4 and k-(BEDT-TTF)2Cu(NCS)2] and heavy fermion (CeCoIn5) superconductors. We show that in this particular geometry, the effects due to vortex activity are minimized. The penetration depth is then governed by the density of superconducting carriers. It is shown in many experiments including rf penetration depth measurement that α-(BEDT-TTF)2NH4Hg(SCN)4 and CeCoIn5 have s-wave and d-wave pairing symmetries, respectively. The pairing symmetry of k-(BEDT-TTF)2-Cu(NCS)2, however, is still an unsolved matter, showing inconsistent results. In this paper, the penetration depth of k-(BEDT-TTF)2Cu(NCS)2 is shown to be more similar to α-(BEDT-TTF)2NH4Hg(SCN)4 than to CeCoIn5, suggesting the pairing is nodeless.

We present torque magnetization measurements on the quasi-2D heavy fermion superconductor CeCoIn5 at temperatures down to 20 mK and magnetic fields up to 18 T. At orientations with the magnetic field perpendicular to the conducting planes, a prominent vortex lattice peak effect is present at around 0.5H c2. The peak effect gradually disappears upon rotating the field into the plane parallel orientation. We interpret the absence of the peak effect for the plane parallel case as a transformation of the Abrikosov lattice into a Josephson vortex state, favored by the Pauli paramagnetic limit in CeCoIn5 together with the unusually large condensation energy. Additionally, we do not observe flux avalanches as found in organic superconductors and suggest that the complete absence of vortex activity in the plane parallel field orientation is crucial for the formation of Fulde–Ferrell–Larkin–Ovchinnikov superconductivity in CeCoIn5.

We report angular dependent heat capacity, RF penetration depth, and magnetization studies on CeCoIn5, a clean quasi-2D strongly correlated superconductor in the paramagnetic limit. At temperatures below 350 mK and magnetic field applied parallel to the conducting planes, we find evidence for the inhomogeneous FFLO superconducting state close to the upper critical field. For small tilt angles, where both orbital and paramagnetic pair-breaking becomes important, the superconducting order parameter assumes higher Landau level states within the FFLO state. For applied field at an angle greater than 15° no FFLO signature is observed and a BCS-type superconducting state emerges.

We report penetration depth and resistivity measurements on a number of organic and heavy fermion superconductors in the Pauli paramagnetic limit using a self resonant tank circuit based on a tunnel diode oscillator (TDO). We call a superconductor Pauli limited when the interaction of the applied magnetic field with the electron spin limits the superconducting state, in contrast to orbital limiting, the traditional effect where vortices eventually destroy the superconducting state. In the Pauli limit, Hc2 can change from a second order to a first order phase transition at low temperatures, or in a very clean sample a new superconducting state with a spatially varying order parameter has been predicted, which we refer to as the FFLO state. We have done extensive experiments that show a range of Pauli limited behavior in anisotropic superconductors. Our results for α-(ET)2NH4Hg(SCN)4, κ-(ET)2Cu(NCS)2, and CeCoIn5 show that the nature of the Pauli limiting state is sensitive to the mean freepath in the sample. In CeCoIn5 we have observed clear evidence of the FFLO state using our TDO method, and our data agrees with specific heat and magnetization measurements. We also show that the application of pressure will suppress the Pauli limiting in κ-(ET)2Cu(NCS)2.

Since the discovery of superconductivity, there has been a drive to understand the mechanisms by which it occurs. The BCS (Bardeen-Cooper-Schrieffer) model successfully treats the electrons in conventional superconductors as pairs coupled by phonons (vibrational modes of oscillation) moving through the material, but there is as yet no accepted model for high-transition-temperature, organic or 'heavy fermion' superconductivity. Experiments that reveal unusual properties of those superconductors could therefore point the way to a deeper understanding of the underlying physics. In particular, the response of a material to a magnetic field can be revealing, because this usually reduces or quenches superconductivity. Here we report measurements of the heat capacity and magnetization that show that, for particular orientations of an external magnetic field, superconductivity in the heavy-fermion material CeCoIn(5) is enhanced through the magnetic moments (spins) of individual electrons. This enhancement occurs by fundamentally altering how the superconducting state forms, resulting in regions of superconductivity alternating with walls of spin-polarized unpaired electrons; this configuration lowers the free energy and allows superconductivity to remain stable. The large magnetic susceptibility of this material leads to an unusually strong coupling of the field to the electron spins, which dominates over the coupling to the electron orbits.

Local magnetic measurements utilizing a micro-Hall probe were performed on a superconducting heavy fermion CeCoIn5 single crystal. We show that the critical current follows a power law as predicted by Ginzburg–Landau theory. This behavior is found to be universal in different heavy fermion and high-Tc superconducting materials. Furthermore, we report on remanent magnetization relaxation showing a high relaxation rate with approximately linear temperature dependence. Although qualitatively similar to another undoped heavy fermion, UBe13, this relaxation rate is significantly higher, providing evidence that CeCoIn5 can be grown in the clean limit.

We measure the heat capacity of a UBe13 sample with an unusually low T c for a polycrystal. We find an upturn in the upper critical field H c2(T) below about T c/2, much as for higher-T c samples. Comparing the critical fields in our sample and in samples with higher T c's shows that the low temperature limit of H c2 is proportional to T c(H = 0), as expected if the upturn comes from an FFLO phase and strong coupling.

Magnetic measurements were performed on a ring patterned [YBa 2 Cu 3 O 7− δ ] 56 A /[PrBa 2 (Cu 3− x Ga x )O 7− δ ] 125 A superlattice with a transition temperature to superconductivity of T c =69 K. In this way, the critical current density j c ( T ), current–voltage characteristics E ( j ) and hysteresis M ( H ) were obtained. The normalized relaxation rate S ( T ) shows an anomalous drop for T ≥65 K pointing to a reduced dissipation. An additional scaling analysis according to the vortex-glass theory reveals a crossover from 3D to quasi-2D behavior. A related anomaly was also observed in j c ( T ) behavior showing an unusual kink, from which a corresponding H – T borderline can be constructed, which is suggested to be due to a crossover from 3D to 2D collective pinning in accordance with the collective creep theory.

By using a superconducting quantum interference device (SQUID), the temporal relaxation of the magnetization was determined for ring-shaped Tl 2 Ba 2 CaCu 2 O 8 thin films at various temperatures between 10 K and 80 K in magnetic fields ranging from 2 mT to 0.3 T. Based on these data, a detailed analysis has been performed related to the following methods or models: (1) Fitting the data to the thermally activated flux motion and collective pinning model; (2) Applying the Generalized Inversion Scheme to extract the temperature dependence of the unrelaxed critical current density j c ( T ) and pinning potential U c ( T ); (3) Testing a modified Maley's method to obtain the current dependent activation energy for flux motion; (4) 2D vortex glass scaling. It is found that, for low fields (2 mT, 10 mT, 40 mT) the experimental data can be described by an elastic flux motion, most probably due to 3D single vortex creep. At higher fields (0.1 T, 0.2 T, 0.3 T), the observed behavior can be interpreted in terms of plastic flux motion which is probably governed by dislocation mediated flux creep. These high field data can also be consistently described by the 2D vortex glass scaling with scaling parameters ν 2D , T 0 and p being consistent with those derived from corresponding transport measurement. Also, results are presented demonstrating the importance of optimizing the scan length of the sample in a moving sample SQUID magnetometer to avoid artifacts.

By analyzing I-V characteristics (E-j curves), which were experimentally determined on Tl2Ba2CaCu2O8 thin films in magnetic fields Be varying from 0 T to 5 T, we find that the transition of the linear resistivity ρlin = [E/j]j → 0 signaling superconductivity exhibits different criticalities for different magnetic fields. Starting with a Berezinskii-Kosterlitz-Thouless transition at TBKT = 103.7 K for Be = 0 T, one induces a crossover to a quasi-2D or 3D vortex-glass transition at a finite Tg for magnetic fields below a few kOe, and finally a "true" 2D vortex-glass with Tg = 0 K for higher fields. We argue that this field-induced crossover of criticalities is a general feature of all strongly anisotropic high-Tc superconductors.

The magnetic ac response of rectangles, squares, disks, and rings patterned from ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ films (typical thickness 200 nm) was determined as a function of temperature for the case of the exciting external magnetic ac field being directed perpendicular to the film plane. For this geometry strong demagnetizing effects are expected and corresponding theories describing the resulting real $({\ensuremath{\chi}}^{\ensuremath{'}})$ and imaginary $({\ensuremath{\chi}}^{\ensuremath{''}})$ parts of the magnetic susceptibility $\ensuremath{\chi}$ on the basis of critical state models have only recently been developed. Plotting ${\ensuremath{\chi}}^{\ensuremath{''}}$ versus ${\ensuremath{\chi}}^{\ensuremath{'}}$ turns out to be useful in order to test these theories with respect to different sample shapes without invoking a specific temperature dependence of the critical current density ${J}_{c}(T)$. In this way, the following results were found. The shape dependent differences of the susceptibility are only small (of the order of %) with the smallest difference between squares and disks as predicted by theory. The recent theories yield an improved description of the experimental $\ensuremath{\chi}$ data as compared to a conventional Bean model neglecting demagnetization effects. At temperatures just below the superconducting transition, however, these theories based on purely hysteretic losses fail to be quantitative. A systematic change of symmetry of the ${\ensuremath{\chi}}^{\ensuremath{''}}$ versus ${\ensuremath{\chi}}^{\ensuremath{'}}$ curves is observed if rings of decreasing widths are patterned from a disk. For a diameter to width ratio $D/wg20$ the experimental susceptibilities, including the temperature dependence of the third harmonic, approach the behavior as calculated for an ideal thin narrow ring. This result allows a quantitative determination of ${J}_{c}(T)$ on such rings as is demonstrated by additional dc magnetization measurements using a SQUID magnetometer.

We report penetration depth and resistivity measurements on the heavy fermion superconductor ${\mathrm{CeCoIn}}_{5}$ using a self-resonant tank circuit based on a tunnel diode oscillator. For magnetic fields applied near parallel to the $ab$ planes and temperatures below 250 mK, two phase transitions were found. The lower field transition, within the superconducting state, is of a second order and we identify it as the transition from the ordinary vortex state to the Fulde, Ferrell, Larkin, Ovchinnikov (FFLO) state. The higher field transition marks the change from the FFLO to the normal state. This higher field transition, ${H}_{c2}$, is of first order up to 900 mK, the highest temperature measured. Our normal-state resistivity measurements at temperatures between 100 and 900 mK suggest that the FFLO state is related to the change of the quasiparticle interaction strength, ${F}_{0}^{a}$.

Local magnetization measurements on 100 nm type-II superconducting Pb thin films show that flux penetration changes qualitatively with temperature. Small flux jumps at the lowest temperatures gradually increase in size, then disappear near T = 0.7Tc. Comparison with other experiments suggests that the avalanches correspond to dendritic flux protrusions. Reproducibility of the first flux jumps in a decreasing magnetic field indicates a role for defect structure in determining avalanches. We also find a temperature-independent final magnetization after flux jumps, analogous to the angle of repose of a sandpile., 6 pages, 5 figures

We irradiate the heavy fermion superconductors (U,Th)Be_13 with high-energy heavy ions. Damage from the ions affects both heat capacity and magnetization measurements, although much less dramatically than in other superconductors. From these data and from direct imaging, we conclude that the irradiation does not create the amorphous columnar defects observed in high-temperature superconductors and other materials. We also find that the damage suppresses the two superconducting transitions of U_0.97Th_0.03Be_13 by comparable amounts, unlike their response to other types of defects., Revisions/additions/cuts scattered throughout

For a quantitative determination of the magnetic response of HTSC thin films of various shapes (disks, rectangles etc.) in magnetic fields oriented perpendicular to the film plane by applying ac- or dc- techniques, the strong demagnetization effects have to be taken into account. It will be demonstrated that due to recent theoretical progress, such a quantitative analysis is now possible. It turns out that for determining critical currents, photolithographically patterned rings are especially useful. Using this technique, the intrinsic effect of dimensionality of a vortex system on its dynamics has been studied for ring patterned Tl-2212 films revealing a 3D to 2D transition induced by an external magnetic field.

Investigations on flux dynamics of ring-shaped T12Ba2CaCu2O8 superconducting thin films have been carried out by measuring the temperature dependent magnetization M(T) during field-cooling (FC) and zero-field-cooling (ZFC) processes. For a given magnetic field, from the magnetization behavior two distinct temperatures, Tkink and Tirr, can be defined. Below Tkink, a clear hysteretic behavior of M(T) is observed leading to a large irreversible signal ΔM = MFC − MZFC. Above Tkink, this irreversible signal, though being very small, is still non-zero until it eventually vanishes at a higher temperature Tirr. Above Tirr, both curves MFC(T) and MZFC(T) merge together and become temperature independent. We attribute the first region ( T< Tkink) to a 3D vortex-glass phase, the second region (Tkink < T < Tirr) to a vortex line liquid state and the third region (Tirr < T < Tc) to a pancake liquid state.

Movshovich et al. suggest that our calorimetric observation of the FFLO superconducting phase boundary1 and its angular dependence are inconsistent with their own data reporting the possible presence of an FFLO phase, and that we have incorrectly used magnetothermal measurements to identify the order of the FFLO transition. They also contest that the correlation of the magnetization steps with the calorimetrically identified FFLO superconducting phase of CeCoIn5 is coincidental. We consider each of these points in turn.