[{"type":"speech","title":"Opening of the superconducting energy gap observed with neutron spectroscopy","issued":{"date-parts":[["2007"]]},"author":[{"family":"Weber","given":"F."},{"family":"Kreyssig","given":"A."},{"family":"Pintschovius","given":"L."},{"family":"Reichardt","given":"W."},{"family":"Stockert","given":"O."},{"family":"Heid","given":"R."},{"family":"Reznik","given":"D."},{"family":"Hradil","given":"K."}],"note":"71.Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Fr\u00fchjahrstagung des Arbeitskreises Festk\u00f6rperphysik, Fachverband Tiefe Temperaturen, Regensburg, 26.-30.M\u00e4rz 2007 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.42(2007) TT 10.1","abstract":"Section Low Temperature Physics (TT)\nTuesday\nTT 10: Superconductivity - Properties, Electronic Structure, Order Parameter\nTime: Tuesday 9:30\u201313:00\nLocation: H18\nTT 10.1\nTue 9:30\nH18\nwith Neutron Spectroscopy \u2014 \u2022Frank Weber1,2 , Andreas\nOliver Stockert5 , Rolf Heid1 , Dmitry Reznik1 , and Klaudia\nWe present inelastic neutron scattering data on YNi2 B2 C (Tc = 15 K).\nWe made a systematic study of the already known phonon anomaly in\nthe (100)-direction [1] as well as of a so far unexplored anomaly at the\nzone boundary in the (110)-direction (M-point). Our data unambiguously show that the superconductivity-induced changes of the spectral\nfunction of phonons with a strong electron-phonon coupling can extremely well be understood in the framework of a theory proposed by\nAllen et al. [2]. The analysis yields the temperature dependent SC energy gap with high accuracy. As a consequence, even deviations from\nBCS like behavior can be assessed with con\ufb01dence. Further, we found\nthat the SC gap extracted from the phonon data for q=(0.5,0,0) and\nq=(0.5,0.5,0), respectively, di\ufb00ers by a factor 1.4. This is a direct proof\nfor the long discussed anisotropy of the SC energy gap in borocarbides.\n[1] Kawano et al., PRL. 77, 4628 (1996), [2] Allen et al., PRB 56,\n5552 (1997)\nTT 10.2\nTue 9:45\nH18\nElectron Spin Dynamics of the Novel Superconductor CaC6\n\u00b4\nprobed by ESR \u2014 \u2022Ferenc Muranyi, Grzegorz Urbanik,\n\u00a8\nVladislav Kataev, and Bernd Buchner \u2014 Leibniz Institute for\nSolid State and Materials Research Dresden, 01171 Dresden, PO BOX\n270116, Germany\nThe Conduction Electron Spin Resonance (CESR) was measured on a\nthick slab of polycrystalline CaC6 in the normal and superconducting\nstate. The measurements characterize the metallic properties in the\nnormal state and indicates the description of superconductivity in the\ndirty limit. Magnetic \ufb01eld dependent nonlinear absorption in the superconducting state evidenced the anisotropy of Hc2 . Superconducting\nstate measurements revealed the increase of e\ufb00ective skin depth below\nTc .\nTT 10.3\nTue 10:00\nH18\nPhonon anomalies in detwinned YBa2 Cu3 O7\u2212x : Strong abanisotropy in the phonon vibrations \u2014 \u2022M. Bakr, C. Ulrich,\nJ. Unterhinninghofen, D. Manske, C. Lin, and B. Keimer \u2014 MaxPlanck-Institute for Solid State Research, Stuttgart, Germany\nWe have used Raman light scattering to investigate the electronic signal and phonon anomalies in detwinned optimally doped\nYBa2 Cu3 O7\u2212x single crystals. Within the experimental error bar, no\nchanges in the electronic gaps was observed with respect to the a and b\naxes. This is in contrast to previous experimental results observed by\nARPES data and Josephson current measurements. All phonons show\na pronounced asymmetry, i.e. Fano-pro\ufb01le, which indicates a strong\nelectron-phonon interaction. A pronounced anisotropy in the asymmetry is observed with respect to the crystallographic a and b axes.\nThis anisotropy appears for example for the 340 cm\u22121 phonon, but\nthe 501 cm\u22121 phonon shows the largest di\ufb00erence. It is interesting to\nnote that this phonon is right at the energy of the 2\u2206max gap. The\nanisotropy of the asymmetry parameter, 1\/q, is already present in the\nnormal state. Below Tc , the 1\/q changes drastically and in a characteristic way for the a and b axes. Finally, we compare our results\nwith Fermi-liquid based calculations. Our results provide further insight into the electron-phonon interaction and therefore the electronic\nsystem of high Tc superconductors.\nTT 10.4\nTue 10:15\nH18\nTheory for ultrafast dynamics in cuprates: Role of electronphonon coupling \u2014 \u2022Julia Unterhinninghofen1 , Dirk Manske1 ,\nand Andreas Knorr2 \u2014 1 Max-Planck-Institut f\u00a8 r Festk\u00a8rperu\nWe present a theory for ultrafast nonequilibrium dynamics in cuprate\nsuperconductors. In a typical time-resolved spectroscopy experiment,\nthe sample is exited with an intense laser pulse, creating nonequilibrium quasiparticles which subsequently can relax via various scattering\nprocesses, restoring the superconducting state. We use the method of\ndensity matrix theory to study the optical excitation and relaxation\ndynamics in cuprates from a microscopical viewpoint. In particular,\nwe consider scattering with optical phonons, looking at the interplay\nbetween relaxation of the excited quasiparticles and the creation of\nnonequilibrium phonon distributions; the superconducting state is restored on a 10 picosecond timescale, while the phonons have longer\nrelaxation times. Time-resolved pump-probe spectra are calculated\nand compared both to quasi-equilibrium models and experimental results.\nTT 10.5\nTue 10:30\nH18\nCharge(re)distribution at YBCO\/metal interfaces: screened\n\u00a8\n\u2014 Institut f\u00a8 r Physik, Universit\u00a8t Augsburg, 86135 Augsburg\nThe functionality of nanoscale devices depends crucially on the transport properties across the interfaces. Especially, the transport mechanism in electronic devices based on high-Tc -superconductors is of\nspecial interest, in particular the charge density within the superconducting CuO2 planes in the vicinity of an interface or grain boundary.\nMain questions in this context are interface charging, band bending,\nor contact resistivity. We calculate the local electronic structure of\nan YBCO\/metal interface using density functional theory (using the\nWien2k code) in two di\ufb00erent geometries (where the interface is either\nparallel or perpendicular to the CuO2 planes), including an optimization of the atomic positions near the interface. We consider supercells\nwith 4 metal and 2 YBCO or 6 metal and 3 YBCO units, respectively.\nFor the parallel contact we \ufb01nd a transfer of holes out of the CuO2\nplanes resulting in shift to the underdoped regime of the high-Tc phase\ndiagram. Thus, this geometry re\ufb02ects the properties of a grain boundary. The results are neither dependent on contact geometry, nor the\ncontact metal, or interface plane.\nTT 10.6\nTue 10:45\nH18\nFirst principles Thermodynamics of YBa2 Cu3 O7 \u2014 Volker\nPankoke1,2 , \u2022Rolf Heid1 , and Klaus-Peter Bohnen1 \u2014\nnen\nModern density-functional based methods nowadays allow for an accurate calculation of phonon spectra and their dependence on structural\nparameters, which is a prerequisite for the study of \ufb01nite temperature\nproperties based on the free energy. Due to the large numerical costs,\nhowever, ab initio studies of thermodynamic properties have been restricted in most cases to crystals with simple lattice structures.\nWe will present an application of this ab initio approach to the\ncuprate superconductor YBa2 Cu3 O7 with its rather complex crystal structure. Thermodynamical properties are calculated within the\nquasiharmonic approximation using phonon spectra obtained by density functional perturbation theory. We will discuss results for the\nanisotropic thermal expansion and speci\ufb01c heat in comparison with\nexperiment to assess the accuracy of this approach.\nTT 10.7\nTue 11:00\nH18\nTerahertz spectroscopy of electron-doped superconductors in magnetic \ufb01eld \u2014 \u2022Artem V. Pronin1 , Andrei\nPimenov2,3 , Alois Loidl2 , Akio Tsukada4,5 , and Micho Naito4 \u2014\nV, EKM, Universit\u00a8t Augsburg, 86135 Augsburg, Germany \u2014\n3 Experimentelle Physik 4, Universit\u00a8t W\u00a8 rzburg, 97074 W\u00a8 rzburg,\nGermany \u2014 4 Department of Applied Physics, Tokyo University of\nAgriculture and Technology, 2-24-16, Naka-cho, Kog","kit-publication-id":"230067487"}]