Quantum fluctuations in spin-ice-like Pr2Zr2O7

Abstract

Spin ice is a magnetic analog of H 2 O ice that harbors dense static disorder. Dipolar interactions between classical spins yield a frozen frustrated state with residual configurational Pauling entropy and emergent magnetic monopolar quasiparticles. Introducing quantum fluctuations is of great interest as this could melt spin ice and allow coherent propagation of monopoles. Here, we report experimental evidence for quantum dynamics of magnetic monopolar quasiparticles in a new class of spin ice based on exchange interactions, Pr 2 Zr 2 O 7 . Narrow pinch point features in otherwise diffuse elastic neutron scattering reflects adherence to a divergence-free constraint for disordered spins on long time scales. Magnetic susceptibility and specific heat data correspondingly show exponentially activated behaviors. In sharp contrast to conventional ice, however, 490% of the neutron scattering is inelastic and devoid of pinch points furnishing evidence for magnetic monopolar quantum fluctuations.

Magnetic and Thermal Properties of the Single Crystalline Pr2Zr2O7 in a [111] Field

“…Figure 1(a) shows the temperature (T ) dependence of the inverse magnetic susceptibility 1/χ(T ) for the magnetic field (H) along the [111] direction below 10 K. The data follows Curie-Weiss law χ(T ) = C/(T − θ CW ), and the fit yields the effective moment µ eff = 2.5µ B and Weiss-temperature θ CW = −0.4 K (antiferromagnetic). The negative, antiferromagnetic Weiss temperature is consistent with the previous reports [14,15]. Dy, Ho) becomes the so-called "three-in, one-out" structure when the magnetic field is applied along the 111 direction [16].…”

“…The fact that the calculated values largely exceeds the experimental data excludes a fully-frozen state of 4 f moment, but instead suggests the possibility of a dynamic liquid state, leading to the reduction of the nuclear Schottky anomaly as observed in our experiment [19]. The dynamic state of the 4 f moments is fully consistent with the strong quantum fluctuations probed by our neutron scattering experiments [14].…”

“…Here, the lattice contribution was estimated from the specific heat of the non-magnetic analog La 2 Zr 2 O 7 and the CEF contribution was calculated using the CEF scheme determined in Ref. 14 Fig. 2), the broad peak was found at T ∼ 1.5 K indicates the evolution of spin-ice correlation.…”

“…Very recently, we have reported that Pr 2 Zr 2 O 7 is a new member of the exchange spin ice [14]. The Pr moment has a 111 Ising anisotropy similarly to the dipolar spin ice.…”

A two-dimensional spin liquid in quantum kagome ice

“…The effects of certain types of quantum fluctuations on the spin ice state have been investigated theoretically 12 and numerically 13,14 , where they have been demonstrated to lift the classical degeneracy and promote a three-dimensional (3D) QSL phase with low-energy gapless excitations that behave like photons 12,13 [15][16][17] . In an attempt to elucidate the microscopic underpinnings of these and related materials, recent theoretical studies have produced a general low-energy effective spin-1/2 model for magnetism in rare earth pyrochlores [18][19][20] .…”