Abstract
We discuss collective spin-wave excitations in triplet superconductors with an easy axis anisotropy for the order parameter. Using a microscopic model for interacting electrons, we estimate the frequency of such excitations in Bechgaard salts and ruthenate superconductors to be 1 and 20 GHz, respectively. We introduce an effective bosonic model to describe spin-wave excitations and calculate their contribution to the nuclear spin-lattice relaxation rate. We find that, in the experimentally relevant regime of temperatures, this mechanism leads to the power law scaling of 1/T1 with temperature. For two- and three-dimensional systems, the scaling exponents are 3 and 5, respectively. We discuss experimental manifestations of the spin-wave mechanism of the nuclear spin-lattice relaxation.
Highlights
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In the experimentally relevant regime of temperatures, this mechanism leads to the power law scaling of 1=T1 with temperature
Nuclear magnetic resonance (NMR) experiments have been useful for analyzing the symmetry of the superconducting order parameter [6] and for clarifying the structure of the phase diagram in systems with competing orders [7]
Summary
Spin-Wave Contribution to the Nuclear Spin-Lattice Relaxation in Triplet Superconductors. We introduce an effective bosonic model to describe spin-wave excitations and calculate their contribution to the nuclear spin-lattice relaxation rate. A common feature of the NMR experiments in certain families of triplet superconductors (TSC) is the power law temperature dependence of the nuclear spin-lattice relaxation rate (NRR). In this Letter, we consider a mechanism of the nuclear spin-lattice relaxation that is not due to Bogoliubov quasiparticles but due to collective spin-wave (SW) excitations of the TSC order parameter. We estimate the value of !0 to be tens of millidegrees Kelvin for Bechgaard salts and hundreds of millidegrees Kelvin for the ruthenates This is much larger than the nuclear Larmor frequency !N but smaller than the typical temperature used in experiments. In the Hamiltonian (2), we replace a0 by its expectation value, take the terms quadratic in a , and perform the Bogoliubov rotap P
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