20. July 2018

Gesara Bimashofer wins best poster prize at the 2018 PNCMI

Gesara Bimashofer, PhD student of the Laboratory for Neutron Scattering and Imaging at PSI, was awarded the best poster prize at the 2018 Polarized Neutrons in Condensed Matter Investigations Conference held in Abingdon, UK. Supervised by Dr. Jochen Stahn and in collaboration with Prof. Dr. Thomas Lippert, she studies reversible magnetoelectric switching by electrochemical lithium intercalation for La_1-xSr_xMnO₃ using the reflectometer Amor at the SINQ facility at PSI. This work is funded by the Swiss National Science Foundation SNF.

2. June 2018

Imaging the inside of injection needles with neutrons

Researchers from the Paul Scherrer Institute PSI, the University of Basel and the company F. Hoffmann-La Roche have found out why proper storage is crucial for syringes which are pre-filled with a liquid medication. Thanks to the special, well established neutron imaging capability at the neutron source SINQ at PSI, it's clear: The liquid medication can inadvertently get from the syringe cylinder into the metal needle prior to administration when the pre-filled syringe is stored at adversely high temperatures. This study has once again demonstrated that neutron imaging is a powerful tool. The technique has furthered the understanding of needle clogging phenomena. It thus contributes to the future development and the reliable use of pre-filled syringes as drug containers. PSI Media Release

10. May 2018

Experimental signatures of emergent quantum electrodynamics in Pr₂Hf₂O₇

R. Sibille et al., Nature Physics, adv. online publication (April 2018). In a quantum spin liquid, the magnetic moments of the constituent electron spins evade classical long-range order to form an exotic state that is quantum entangled and coherent over macroscopic length scales. Such phases offer promising perspectives for device applications in quantum information technologies, and their study can reveal new physics in quantum matter. Here we report neutron scattering measurements of the rare-earth pyrochlore magnet Pr₂Hf₂O₇ that provide evidence for a quantum spin ice ground state. We find a quasi-elastic structure factor with pinch points - a signature of a classical spin ice - that are partially suppressed, as expected in the quantum-coherent regime of the lattice field theory at finite temperature. Our result allows an estimate for the speed of light associated with magnetic photon excitations. We also reveal a continuum of inelastic spin excitations, which resemble predictions for the fractionalized, topological excitations of a quantum spin ice. Taken together, these two signatures suggest that the low-energy physics of Pr₂Hf₂O₇ can be described by emergent quantum electrodynamics. If confirmed, the observation of a quantum spin ice ground state would constitute a concrete example of a three-dimensional quantum spin liquid - a topical state of matter that has so far mostly been explored in lower dimensionalities.

3. April 2018

Dipolar Spin Ice States with a Fast Monopole Hopping Rate in CdEr₂X₄ (X = Se, S)

S. Gao et al., Physical Review Letters 120, 137201 (2018). Excitations in a spin ice behave as magnetic monopoles, and their population and mobility control the dynamics of a spin ice at low temperature. CdEr₂Se₄ is reported to have the Pauling entropy characteristic of a spin ice, but its dynamics are three orders of magnitude faster than the canonical spin ice Dy₂Ti₂O₇. In this Letter we use diffuse neutron scattering to show that both CdEr₂Se₄ and CdEr₂S₄ support a dipolar spin ice state—the host phase for a Coulomb gas of emergent magnetic monopoles. These Coulomb gases have similar parameters to those in Dy₂Ti₂O₇, i.e., dilute and uncorrelated, and so cannot provide three orders faster dynamics through a larger monopole population alone. We investigate the monopole dynamics using ac susceptometry and neutron spin echo spectroscopy, and verify the crystal electric field Hamiltonian of the Er³⁺ ions using inelastic neutron scattering. A quantitative calculation of the monopole hopping rate using our Coulomb gas and crystal electric field parameters shows that the fast dynamics in CdEr₂X₄ (X = Se, S) are primarily due to much faster monopole hopping. Our work suggests that CdEr₂X₄ offer the possibility to study alternative spin ice ground states and dynamics, with equilibration possible at much lower temperatures than the rare earth pyrochlore examples.