Low lying spin excitation in the spin ice, Ho₂Ti ₂O₇

The high flux and low background of the new backscattering spectrometer at the SNS combine to produce an excellent signal to noise ratio, allowing us to investigate a low lying weak excitation never seen before in the spin ice, Ho₂Ti₂O₇. This non-dispersive excitation has been observed at E = 26.3 μeV below 100 K but is resolution limited only below ∼ 65 K. It is indifferent to magnetic fields below μ₀H = 4.5 T, at 1.6 K. These characteristics help us to identify the excitation as due to the nuclear spin system.