[{"type":"speech","title":"High-temperature echo of the quantum phase transition in CeCu\u2086\u208b\u2093Au\u2093","issued":{"date-parts":[["2007"]]},"author":[{"family":"Klein","given":"M."},{"family":"Nuber","given":"A."},{"family":"L\u00f6hneysen","given":"H. von"},{"family":"Reinert","given":"F."}],"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 2.10","abstract":"Section Low Temperature Physics (TT)\nMonday\n[1] T. Lorenz et al., cond-mat\/0609348 (2006), B.C. Watson et al.,\nPRL 86, 5168 (2001). [2] L.J. Zhu et al., PRL 91, 066404 (2003), M.\nGarst and A. Rosch , PRB 72, 205129 (2005).\nTT 2.5\nMon 10:30\nH19\nHigh pressure quantum phase transition in the weakly\n\u00a8\nStockholm Univ., Stockholm, Sweden\nTetragonal Cu2 Te2 O5 Br2 contains clusters of four Cu2+ (S = 1\/2) in\na planar coordination. These tetrahedra form weakly coupled sheets\nwithin the crystallographic a-b plane. Therefore, this system is ideal to\nstudy the interplay between the spin frustration on a tetrahedron with\nlocalized low-energy excitations and collective magnetism induced by\ninter-tetrahedra couplings. In this material a strongly reduced magnetic transition temperature TN = 11.4 K in comparison with a dominant magnetic exchange of 40 K is found.\nWe examined the quantum critical behaviour of polycrystalline\nCu2 Te2 O5 Br2 in ZF muSR experiments under external pressures. We\nobserved a continuous decrease of the magnetic phase volume and of\nthe sublattice magnetization, studied via the spontaneous muon spin\nprecession frequency, with increasing pressure. The measurements at\n6 kbar did not show any sign of static magnetic correlations down to\n0.3 Kelvin. We conclude that this system shows a quantum critical\npoint at 6 kbar where the magnetic ordered phase disappears and a\nspin liquid ground state is formed.\nTT 2.6\nMon 10:45\nH19\nQuantum phase transitions and dimensional reduction in an\u00a8\ntiferromagnets with inter-layer frustration \u2014 \u2022Oliver Rosch,\nInga Fischer, and Matthias Vojta \u2014 Institut f\u00a8 r Theoretische\nWe discuss phase transitions of quasi-two-dimensional antiferromagnets with a fully frustrated inter-layer interaction. Using symmetry\narguments in a perturbation expansion for the order parameter theory and applying the bond-operator method beyond the harmonic approximation, we calculate the magnetic excitation spectrum in di\ufb00erent parameter regimes. We consider various crossovers in the vicinity\nof the quantum critical points and the \ufb01nite-temperature transitions.\nWe also discuss the relation of our results to recent experiments on\nBaCuSi2 O6 which indicated the possibilty of dimensional reduction\nthrough geometric frustration.\n15 min. break\nTT 2.7\nMon 11:15\nH19\nInterplay between chiral symmetry breaking and spinon con\ufb01nement in Mott insulators \u2014 \u2022Flavio Nogueira and Hagen\nIt is well known that compact quantum electrodynamics in 2+1 dimensions (QED3 ) is an e\ufb00ective theory Mott insulators near the so called\nresonating valence-bond (RVB) \ufb02ux phase. We have recently demonstrated the stability of the spin liquid for a large enough number of\nspinon species [1]. However, the e\ufb00ect of chiral symmetry breaking\n(CSB), which leads to the appearence of spin density wave, was not\nconsidered. CSB is known to occur in noncompact QED3 . In this work\nwe discuss the interplay between CSB and con\ufb01nement in the compact\ncase and point out the consequences for the stability of spin liquids for\nthe physically relevant number of spinon species, N=2.\n[1] F. S. Nogueira and H. Kleinert, Phys. Rev. Lett. 95, 176406 (2005)\ntuned close to van Hove \ufb01lling by the magnetic \ufb01eld. The transition is\nsecond order for high temperature (T ) and changes into \ufb01rst order for\nlow T . The \ufb01rst order transition is accompanied by a metamagnetic\ntransition. The uniform magnetic susceptibility and the speci\ufb01c heat\ndivided by temperature show strong T dependence, especially logT divergence at van Hove \ufb01lling. The Fermi surface instability then cuts\no\ufb00 these non-Fermi liquid behaviors and gives rise to a speci\ufb01c heat\njump and a cusp in the susceptibility at Tc .\nTT 2.9\nMon 11:45\nH19\nLogarithmic Fermi-liquid breakdown in Nb1.02 Fe1.98 \u2014\n\u2022Manuel Brando1 , Dennis Moroni-Klementowicz2 , Carsten\nStrasse 40, D-01187 Dresden, Germany \u2014 2 Dept.\nof Physics,\nRoyal Holloway, University of London, Egham TW20 0EX, UK \u2014\n3 Laboratoire Louis N\u00b4el, CNRS, B.P. 166, 38042 Grenoble Cedex\n9, France \u2014 4 Commissariat ` l\u2019Energie Atomique, D\u00b4partement de\nRecherche Fondamentale sur la Mati`re Condens\u00b4e, SPSMS, 38054\nGrenoble, France\nWe report measurements of the heat capacity C and of the resistivity \u03c1\nin stoichiometric and slightly Nb-rich NbFe2 samples, including a single\ncrystal with the composition Nb1.02 Fe1.98 , which on the phase diagram\nis located very close to the quantum critical point (TN\n2.8K). Both\nthe resistivity and the heat capacity of the nearly quantum-critical\nsingle crystal display striking, robust non-Fermi liquid temperature\ndependences: while the heat capacity coe\ufb03cient \u03b3 = C\/T diverges\nweakly as C\/T \u223c log T from 4K down to 0.1K, in line with theoretical\npredictions for 3-D ferromagnetic quantum criticality, the resistivity\nfollows a T 3\/2 power-law, familiar from the case of MnSi and naively\npredicted for the proximity of an antiferromagnetic quantum critical\npoint.\nTT 2.10\nMon 12:00\nH19\n\u00a8\nCeCu6\u2212x Aux \u2014 \u2022M. Klein1 , A. Nuber1 , H. v. Lohneysen2,3 , and\nF. Reinert1 \u2014 1 Universit\u00a8t W\u00a8 rzburg, Experimentelle Physik II, Am\nHubland, 97074 W\u00a8 rzburg \u2014 2 Universit\u00a8t Karlsruhe, Physikalisches\nDuring the last years many experiments and theoretical investigations\nhave been performed to explain the nature of quantum critical points\n(QCP) in heavy-fermion compounds. One important candidate of\nthese compounds is CeCu6\u2212x Aux which goes from a paramagnetic\nmetal to an antiferromagnetic metal as x increases. The QCP appears\nwhen the critical value of xc \u223c 0.1 is reached.\nWe have performed high-resolution photoemission experiments(\u2206E <\n5 meV) on single crystals with di\ufb00erent gold concentrations at temperatures in the range from T = 15 K to 60 K. Though these temperatures\nwere much higher than the characteristic temperatures we see a signi\ufb01cant jump in the spectral weight of the Kondo-resonance at xc implying\na sudden change in the correlation between localized 4f-electrons and\nconduction electrons. A comparison with NCA calculations allows a\nquantitative determination of the Kondo temperature and the crystal\n\ufb01eld energies. This \ufb01nite temperature signatur is a further key to solve\nthe question about the nature of the QCP in this system.\nTT 2.11\nMon 12:15\nH19\nSpontaneous Fermi surface symmetry breaking in Sr3 Ru2 O7\n\u2014 \u2022Hiroyuki Yamase and Andrey Katanin \u2014 Max-Planck-Institute\nMultiple energy scales at a quantum critical point \u2014 \u2022P.\nPhysics of Solids, 01187 Dresden \u2014 3 Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA \u2014 4 Institute for Solid\nState Physics, Vienna University of Technology, 1004 Vienna, Austria \u2014 5 Center for Materials Theory, Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08855, USA \u2014\n6 Department of Physics & Astronomy, Rice University, Houston, TX\n77005, USA\nThe most salient features observed around a metamagnet","kit-publication-id":"230067473"}]