Measurement of the London moment in two high-temperature superconductors

Abstract

THE well-known London equations dictate that the magnetic field inside a stationary superconductor vanishes. The same equations, however, predict that the superconductor generates a magnetic field when it is put into uniform rotation. The associated magnetic moment is known as the London moment. Here we show that high-transition-temperature (high-T_c) superconducting oxides indeed possess this fundamental property, and when rotated, develop a London moment of the same magnitude as that of conventional superconductors, provided that the signal is scaled to the shielded volume fraction. This confirms that high-T_c superconductivity corresponds to a superfluid phase in the London sense, and that the mass of the carriers that appears in the expression of the London moment is the free-electron mass, irrespective of the nature of the carriers in the normal state.