Quantum spin excitations through the metal-to-insulator crossover in YBa₂Cu₃O_6+y

Journal Article · Tue Jan 01 04:00:00 EST 2008 · Physical Review B

DOI:https://doi.org/10.1103/PhysRevB.77.014523· OSTI ID:939660

Li, Shiliang ^[1]; Yamani, Zahra ^[2]; Kang, Hye Jung ^[3]; Segawa, Kouji ^[4]; Ando, Y. ^[4]; Yao, Xin ^[5]; Mook, Jr, Herbert A ^[6]; Dai, Pengcheng ^[6]

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1. University of Tennessee, Knoxville (UTK)
2. Canadian Neutron Beam Centre, National Research Council, Chalk River Laboratorie
3. National Institute of Standards and Technol/University of Maryland, College Park
4. Central Research Institute of Electric Power Industry, Japan
5. Shanghai Jiao Tong University, Shanghai
6. ORNL

We use inelastic neutron scattering to study the temperature dependence of the spin excitations of a detwinned superconducting YBa{sub 2}Cu{sub 3}O{sub 6.45} (T{sub c} = 48 K). In contrast to earlier work on YBa{sub 2}Cu{sub 3}O{sub 6.5} (T{sub c} = 58 K), where the prominent features in the magnetic spectra consist of a sharp collective magnetic excitation termed 'resonance' and a large ({h_bar} {omega} {approx} 15 meV) superconducting spin gap, we find that the spin excitations in YBa{sub 2}Cu{sub 3}O{sub 6.45} are gapless and have a much broader resonance. Our detailed mapping of magnetic scattering along the a*/b*-axis directions at different energies reveals that spin excitations are unisotropic and consistent with the 'hourglasslike' dispersion along the a*-axis direction near the resonance, but they are isotropic at lower energies. Since a fundamental change in the low-temperature normal state of YBa{sub 2}Cu{sub 3}O{sub 6+y} when superconductivity is suppressed takes place at y {approx} 0.5 with a metal-to-insulator crossover (MIC), where the ground state transforms from a metallic to an insulating like phase, our results suggest a clear connection between the large change in spin excitations and the MIC. The resonance therefore is a fundamental feature of metallic ground state superconductors and a consequence of high-T{sub c} superconductivity.

• Research Organization: Oak Ridge National Laboratory (ORNL); High Flux Isotope Reactor
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 939660
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 014524 Vol. 77
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
EXCITATION
GROUND STATES
NEUTRONS
RESONANCE
SCATTERING
SPECTRA
SPIN
SUPERCONDUCTIVITY
SUPERCONDUCTORS
TEMPERATURE DEPENDENCE