Competing orders in the cuprate superconductors
Subir Sachdev
Department of Physics, Yale University, P.O. Box 208120, New Haven CT 06520-8120, USA.
Recent observations support the proposal that ground state correlations in the cuprates can be described by a common theory of competing order parameters in the doped Mott insulator, and of proximity to quantum phase transitions associated with them. The competing orders can be tuned by an applied magnetic field: theoretical predictions1 for the phase diagram as a function of doping concentration and magnetic field strength, and for the structure of the field-induced vortices in the superconductor will be presented. The microstructure of the charge order observed in STM will also be related to theoretical predictions arising from studies of magnetic transitions in Mott insulators and in superconductors.
Antiferromagnetic vortex core studied by spatially-resolved NMR
K. Kumagaia, K. Kakuyanagia, Y. Matsudab, T. Hasegawac
aDivision of Physics, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
bISSP, University of Tokyo, Kashiwa 277-8581, Japan
cInstitute for Materials Research, Tohoku University, Sendai, 980-8577, Japan
Recent experimental studies have established that the spatially-resolved NMR in the vortex state serves as a powerful probe for locally different electronic state. We provide local information on antiferromagnetic (AF) correlations in the different regions of the vortex state by 205Tl-NMR imaging in nearly optimal-doped Tl2Ba2CuO6. 205Tl-1 in the vortex core is enhanced almost by two orders larger than that of the superconducting region, and the T-dependence of T1-1 shows a peak at T=20 K well below Tc=85 K, indicating clearly that in the core region Cu spins show a local AF ordering. These results indicate that the suppression of the d-wave SC order parameter leads to the nucleation of islands with local AF order.
Doping and field dependence of vortex core states in Bi2Sr2CaCu2O8+d
B. W. Hoogenbooma, K. Kadowakib, B. Revaza, M. Lic, Ch. Rennerd, Ø. Fischera
aDPMC, Université de Genève, 24 Quai Ernest-Ansermet, 1211 Genève 4, Switzerland
bInstitute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
cKamerlingh Onnes Lab., Leiden University, P/A Niels Bohrweg 2, 2342 CA Leiden, The Netherlands
dNEC Research Institute, 4 Independence Way, Princeton, New Jersey 08540, USA
Using scanning tunneling spectroscopy, we show that for slightly overdoped Bi2Sr2CaCu2O8+d samples a high degree of electronic homogeneity can be obtained, depending on the superconducting transition width. Such homogeneous samples are ideally suited for the study of vortex cores. The energy of quasiparticle states in the vortex cores is shown to scale with the superconducting gap, and independent of the magnetic field between 1 and 6 T. These observations allow a discussion on the discrete nature of quasiparticle states in vortex cores in high-Tc superconductors.
High Magnetic Field NMR Microscopy of Vortices in High-Tc Superconductors
V. F. Mitrovi\' ca, E. E. Sigmundb, W. P. Halperinb, A. P. Reyesc, P. Kuhnsc, W. G. Moultonc
aPresent Address: Grenoble High Magnetic Field Laboratory, 38042 Grenoble Cedex 9, France
bNorthwestern University, Evanston, Illinois 60208, U.S.A.
cNational High Magnetic Field Laboratory, Tallahassee, Florida 32310, U.S.A.
We present spatially resolved NMR measurements of the vortex structure of HTS, including a spatially resolved measurement of the spin-lattice relaxation rate, which is sensitive to the local density of electronic states (DOS). With this tool we have investigated the electronic excitations both inside and outside the vortex cores. In the regions outside the vortex core we observe the vortex currents shifting the quasiparticle excitation spectrum through a Doppler effect. In the vortex core region we find the evidence for the existance of antiferromagnetic fluctuations.
Possible Antiferromagnetic Vortex Cores in La2-xSrxCuO4 Probed by mSR
R. Kadonoa, W. Higemotoa, A. Kodaa, M. I. Larkinb, G. M. Lukeb, A. T. Savicib, Y. J. Uemurab, K. M. Kojimac, T. Okamotoc, T. Kakeshitac, S. Uchidac, T. Itod, K. Okad
aInstitute of Materials Structure Science, KEK, Tsukuba, Ibaraki 305-0801, Japan
bPhysics Department, Columbia University, New York, NY10027, USA
cDepartment of Superconductivity, University of Tokyo, Tokyo 113-8656, Japan
dNational Institute of Advanced Industrial Science and Technology, Tsukuba 305-8562, Japan
The spatial field distribution in the flux line lattice (FLL) state of La2-xSrxCuO4 (LSCO) has been studied by muon spin rotation (mSR). In a single crystalline LSCO with nominally optimal doping (x=0.15), we have observed two mSR signals at high fields where one signal exhibits strong broadening unexpected for the field profile of conventional FLL state. The possibility to attribute such a field-induced component to the antiferromagnetic vortex cores suggested by neutron diffraction is discussed.