المؤلفون: Louden, E. R., Manni, S., Van Zandt, J. E., Leishman, A. W. D., Taufour, V., Bud'ko, S. L., DeBeer-Schmitt, L., Honecker, D., Dewhurst, C. D., Canfield, P. C., Eskildsen, M. R.

المصدر: J. Appl. Cryst. 55, 693 (2022)

مصطلحات موضوعية: Condensed Matter - Superconductivity

الوصف: Using small-angle neutron scattering we have studied the vortex lattice in superconducting MgB$_2$ with the magnetic field applied along the $c$-axis, doped with either manganese or carbon to achieve a similar suppression of the critical temperature. For Mn-doping, the vortex lattice phase diagram remains qualitatively similar to that of pure MgB$_2$, undergoing a field-and temperature-driven $30^{\circ}$ rotation transition, indicating only a modest effect on the vortex-vortex interaction. In contrast, the vortex lattice rotation transition is completely suppressed in the C-doped case, likely due to a change in the electronic structure which affects the two-band/two-gap nature of superconductivity in MgB2. The vortex lattice longitudinal correlation length shows the opposite behavior, remaining roughly unchanged between pure and C-doped MgB$_2$ while it is significantly reduced in the Mn-doped case. However, the extensive vortex lattice metastability and related activated behavior, observed in conjunction with the vortex lattice transition in pure MgB$_2$, is also seen in the Mn doped sample. This shows that the vortex lattice disordering is not associated with a substantially increased vortex pinning.
Comment: To appear in the Journal of Applied Crystallography for the special issue "Magnetic Small-Angle Neutron Scattering - from nanoscale magnetism to long-range magnetic structures"

الوصول الحر: http://arxiv.org/abs/2202.10490Test

المؤلفون: Louden, E. R., Leishman, A. W. D., Rastovski, C., Kuhn, S. J., DeBeer-Schmitt, L., Dewhurst, C. D., Zhigadlo, N. D., Eskildsen, M. R.

المصدر: New J. Phys. 21, 063003 (2019)

مصطلحات موضوعية: Condensed Matter - Superconductivity

الوصف: The vortex lattice in MgB2 is characterized by the presence of long-lived metastable states, which arise from cooling or heating across the equilibrium phase boundaries. A return to the equilibrium configuration can be achieved by inducing vortex motion. Here we report on small-angle neutron scattering studies of MgB2, focusing on the structural properties of the vortex lattice as it is gradually driven from metastable to equilibrium states by an AC magnetic field. Measurements were performed using initial metastable states obtained either by cooling or heating across the equilibrium phase transition. In all cases, the longitudinal correlation length remains constant and comparable to the sample thickness. Correspondingly, the vortex lattice may be considered as a system of straight rods, where the formation and growth of equilibrium state domains only occurs in the two-dimensional plane perpendicular to the applied field direction. Spatially resolved raster scans of the sample were performed with apertures as small as 80 microns, corresponding to only 1.2*10^6 vortices for an applied field of 0.5 T. These revealed spatial variations in the metastable and equilibrium vortex lattice populations, but individual domains were not directly resolved. A statistical analysis of the data indicates an upper limit on the average domain size of approximately 50 microns.
Comment: 13 pages, 9 figures

الوصول الحر: http://arxiv.org/abs/1902.08512Test

المؤلفون: Louden, E. R., Rastovski, C., DeBeer-Schmitt, L., Dewhurst, C. D., Zhigadlo, N. D., Eskildsen, M. R.

المصدر: Phys. Rev. B 99, 144515 (2019)

مصطلحات موضوعية: Condensed Matter - Superconductivity

الوصف: We have studied non-equilibrium phase transitions in the vortex lattice in superconducting MgB2, where metastable states are observed in connection with an intrinsically continuous rotation transition. Using small-angle neutron scattering and a stop-motion technique, we investigated the manner in which the metastable vortex lattice returns to the equilibrium state under the influence of an ac magnetic field. This shows a qualitative difference between the supercooled case which undergoes a discontinuous transition, and the superheated case where the transition to the equilibrium state is continuous. In both cases the transition may be described by an an activated process, with an activation barrier that increases as the metastable state is suppressed, as previously reported for the supercooled vortex lattice [E. R. Louden et al., Phys. Rev. B 99, 060502(R) (2019)]. Separate preparations of superheated metastable vortex lattices with different domain populations showed an identical transition towards the equilibrium state. This provides further evidence that the vortex lattice metastability, and the kinetics associated with the transition to the equilibrium state, is governed by nucleation and growth of domains and the associated domain boundaries.
Comment: 27 pages, 10 figures. arXiv admin note: text overlap with arXiv:1812.05970

الوصول الحر: http://arxiv.org/abs/1902.04565Test

المؤلفون: Louden, E. R., Rastovski, C., Kuhn, S. J., Leishman, A. W. D., DeBeer-Schmitt, L., Dewhurst, C. D., Zhigadlo, N. D., Eskildsen, M. R.

المصدر: Phys. Rev. B 99, 060502 (2019)

مصطلحات موضوعية: Condensed Matter - Superconductivity

الوصف: Using small-angle neutron scattering, we investigated the behavior of a metastable vortex lattice state in MgB2 as it is driven towards equilibrium by an AC magnetic field. This shows an activated behavior, where the AC field amplitude and cycle count are equivalent to, respectively, an effective "temperature" and "time". The activation barrier increases as the metastable state is suppressed, corresponding to an aging of the vortex lattice. Furthermore, we find a cross-over from a partial to a complete suppression of metastable domains depending on the AC field amplitude, which may empirically be described by a single free parameter. This represents a novel kind of collective vortex behavior, most likely governed by the nucleation and growth of equilibrium vortex lattice domains.
Comment: 5 pages plus 3 pages of supplemental material

الوصول الحر: http://arxiv.org/abs/1812.05970Test

المؤلفون: Smylie, M. P., Claus, H., Kwok, W. -K., Louden, E. R., Eskildsen, M. R., Sefat, A. S., Zhong, R. D., Schneeloch, J., Gu, G. D., Bokari, E., Niraula, P. M., Kayani, A., Dewhurst, C. D., Snezhko, A., Welp, U.

المصدر: Phys. Rev. B 97, 024511 (2018)

مصطلحات موضوعية: Condensed Matter - Superconductivity

الوصف: The temperature dependence of the London penetration depth $\Delta\lambda(T)$ in the superconducting doped topological crystalline insulator Sn$_{1-x}$In$_x$Te was measured down to 450 mK for two different doping levels, x $\approx$ 0.45 (optimally doped) and x $\approx$ 0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. The introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance $T_c$, indicating that ferroelectric interactions do not compete with superconductivity.
Comment: 6 pages, 7 figures

الوصول الحر: http://arxiv.org/abs/1711.09862Test

المؤلفون: Kuhn, S. J., Morgenlander, W., Louden, E. R., Rastovski, C., Gannon, W. J., Takatsu, H., Peets, D. C., Maeno, Y., Dewhurst, C. D., Gavilano, J., Eskildsen, M. R.

المصدر: Phys. Rev. B 96, 174507 (2017)

مصطلحات موضوعية: Condensed Matter - Superconductivity

الوصف: Despite numerous studies the exact nature of the order parameter in superconducting Sr2RuO4 remains unresolved. We have extended previous small-angle neutron scattering studies of the vortex lattice in this material to a wider field range, higher temperatures, and with the field applied close to both the <100> and <110> basal plane directions. Measurements at high field were made possible by the use of both spin polarization and analysis to improve the signal-to-noise ratio. Rotating the field towards the basal plane causes a distortion of the square vortex lattice observed for H // <001>, and also a symmetry change to a distorted triangular symmetry for fields close to <100>. The vortex lattice distortion allows us to determine the intrinsic superconducting anisotropy between the c-axis and the Ru-O basal plane, yielding a value of ~60 at low temperature and low to intermediate fields. This greatly exceeds the upper critical field anisotropy of ~20 at low temperature, reminiscent of Pauli limiting. Indirect evidence for Pauli paramagnetic effects on the unpaired quasiparticles in the vortex cores are observed, but a direct detection lies below the measurement sensitivity. The superconducting anisotropy is found to be independent of temperature but increases for fields > 1 T, indicating multiband superconductvity in Sr2RuO4. Finally, the temperature dependence of the scattered intensity provides further support for gap nodes or deep minima in the superconducting gap.
Comment: 14 pages, 8 figures

الوصول الحر: http://arxiv.org/abs/1710.10310Test

المؤلفون: Bermúdez, M. Marziali, Louden, E. R., Eskildsen, M. R., Dewhurst, C. D., Bekeris, V., Pasquini, G.

مصطلحات موضوعية: Condensed Matter - Superconductivity

الوصف: We studied thermal and dynamic history effects in the vortex lattice (VL) near the order-disorder transition in clean NbSe$_2$ single crystals. Comparing the evolution of the effective vortex pinning and the bulk VL structure, we observed metastable superheated and supercooled VL configurations that coexist with a hysteretic effective pinning response due to thermal cycling of the system. A novel scenario, governed by the interplay between (lower) elastic and (higher) plastic energy barriers, is proposed as an explanation for our observations: Plastic barriers, which prevent the annihilation or creation of topological defects, require dynamic assistance to be overcome and to achieve a stable VL at each temperature. Conversely, thermal hysteresis in the pining response is ascribed to low energy barriers, which inhibit rearrangement within a single VL correlation volume and are easily overcome as the relative strength of competing interactions changes with temperature.
Comment: 9 pages, 5 figures. To be published in Physical Review B

الوصول الحر: http://arxiv.org/abs/1701.08798Test

المؤلفون: Louden, E R, Leishman, A W D, Rastovski, C, Kuhn, S J, DeBeer-Schmitt, L, Dewhurst, C D, Zhigadlo, N. D., Eskildsen, M R

المصدر: Louden, E R; Leishman, A W D; Rastovski, C; Kuhn, S J; DeBeer-Schmitt, L; Dewhurst, C D; Zhigadlo, N. D.; Eskildsen, M R (2019). Structural studies of metastable and equilibrium vortex lattice domains in MgB2. New journal of physics, 21(6), 063003. Institute of Physics Publishing IOP 10.1088/1367-2630/ab20eb

مصطلحات موضوعية: 570 Life sciences, biology, 540 Chemistry

وصف الملف: application/pdf

العلاقة: https://boris.unibe.ch/140676Test/

الإتاحة: https://doi.org/10.1088/1367-2630/ab20ebTest
https://boris.unibe.ch/140676/1/Louden_2019_New_J._Phys._21_063003.pdfTest
https://boris.unibe.ch/140676Test/

المؤلفون: Louden, E. R., Rastovski, C., Kuhn, S. J., Leishman, A. W. D., DeBeer-Schmitt, L., Dewhurst, C. D., Zhigadlo, N. D., Eskildsen, M. R.

المساهمون: U.S. Department of Energy, Oak Ridge National Laboratory

المصدر: Physical Review B ; volume 99, issue 6 ; ISSN 2469-9950 2469-9969

الإتاحة: https://doi.org/10.1103/physrevb.99.060502Test

المؤلفون: Puscheck, E., Perez, G., Dutta, S., Abdulhasan, M., Louden, E., Rappolee, D.A.

المصدر: Fertility and Sterility ; volume 110, issue 4, page e173-e174 ; ISSN 0015-0282

مصطلحات موضوعية: Obstetrics and Gynecology, Reproductive Medicine

الإتاحة: https://doi.org/10.1016/j.fertnstert.2018.07.515Test
https://api.elsevier.com/content/article/PII:S0015028218311075?httpAccept=text/xmlTest
https://api.elsevier.com/content/article/PII:S0015028218311075?httpAccept=text/plainTest