Pressure effect on hydrogen tunneling in alpha-Mn with the use of diamond anvils*

Recently, we have studied the pressure effect on the tunneling mode and vibrational spectra of hydrogen in alpha-MnH0.07 by using inelastic neutron scattering (INS) [1]. Applying hydrostatic pressure up to 30 kbar was shown to shift both the hydrogen optical modes and the tunneling peak to higher energies. First-principles calculations reveal that the potential for hydrogen in alpha-Mn becomes overall steeper with increasing pressure. At the same time, the barrier height and its extent in the direction of tunneling decrease and the calculations predict significant changes of the dynamics of hydrogen in alpha-Mn at 100 kbar, when the estimated tunneling splitting of the hydrogen ground state exceeds the barrier height. In the present work, using our high-pressure polycrystalline diamond anvils cell for ~1 mm3 sample, recently developed at SNS [2], we confirmed the previous INS results at 30 kbar, and observed the disappearence of the tunneling peak at 70 kbar, in agreement with the prediction.

 

[1] A.I. Kolesnikov et al. Phys. Rev. B 94 (2016) 134301.

[2] H. Haberl et al. Rev. Sci. Instr. 89 (2018) 092902.