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

OSTI ID:939659

Mook, Jr, Herbert A ^[1]

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1. 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: 939659
• 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