Quantum fluctuations in the Kagome spin ice state of Pr$_{\mathrm{2}}$Zr$_{\mathrm{2}}$O$_{\mathrm{7}}$

While water ice and spin ice compounds such as Dy$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$ and Ho$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$ are semi-classical, low spin pyrochlores where exchange interactions prevail over dipole-dipole interactions can have substantial quantum fluctuations and perhaps realize quantum spin ice [1-3] where emergent magnetic monopoles have quantum dynamics and an artificial electromagnetism is manifest in low energy photon-like excitations. Pr$_{\mathrm{2}}$Zr$_{\mathrm{2}}$O$_{\mathrm{7}}$ was recently found to be an excellent candidate for quantum spin ice [2]. Strong quantum fluctuations were detected in Pr$_{\mathrm{2}}$Zr$_{\mathrm{2}}$O$_{\mathrm{7}}$ [3] but also a very strong sample variability, which is tied to the non-Kramers nature of the J$=$4 Pr3$+$ multiplet and an underlying structural instability. We have conducted neutron scattering experiments new high quality crystals to study quantum fluctuations in Pr$_{\mathrm{2}}$Zr$_{\mathrm{2}}$O$_{\mathrm{7}}$, with fields along [111]. At Q$=$ (2/3, 2/3, -4/3) where classical spin ice Ho$_{\mathrm{2}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$ shows a pinch point, we found a peak in Pr$_{\mathrm{2}}$Zr$_{\mathrm{2}}$O$_{\mathrm{7}}$. The quantum kagome ice state thus appears to be quite different from the classical case. [1] K. A. Ross et al., Phys. Rev. X 1 (2011) 021002. [2] K. Kimura et al., JPS Conf. Proc. 3 (2014) 014027. [3] K. Kimura et al., Nat. Commun. 4 (2013) 1934.