Emergent Fine Structure Constant of Quantum Spin Ice Is Large

Abstract

Condensed matter systems provide alternative 'vacua' exhibiting emergent low-energy properties drastically different from those of the standard model. A case in point is the emergent quantum electrodynamics (QED) in the fractionalized topological magnet known as quantum spin ice, whose magnetic monopoles set it apart from the familiar QED of the world we live in. Here, we show that the two greatly differ in their fine-structure constant α, which parametrizes how strongly matter couples to light: αQSI is more than an order of magnitude greater than αQED ≈ 1/137. Furthermore, αQSI, the emergent speed of light, and all other parameters of the emergent QED, are tunable by engineering the microscopic Hamiltonian. We find that αQSI can be tuned all the way from zero up to what is believed to be the strongest possible coupling beyond which QED confines. In view of the small size of its constrained Hilbert space, this marks out quantum spin ice as an ideal platform for studying exotic quantum field theories and a target for quantum simulation. The large αQSI implies that experiments probing candidate condensed-matter realizations of quantum spin ice should expect to observe phenomena arising due to strong interactions.

Probing emergent QED in quantum spin ice via Raman scattering of phonons: shallow inelastic scattering and pair production

“…The above application of the mean-field approach to calculate the Raman vertex can be invalidated via strong gauge fluctuations, which couple to the electric charges and the magnetic monopoles. The relevant fine-structure coupling constant for the emergent quantum electrody-namics of quantum spin ice has recently been numerically estimated to be 0.1 [92]. This suggests that the perturbative expansion may provide a leading estimate of the effect of the gauge fluctuations for the magnetic monopoles with their large gap.…”

“…The bare band structure of monopoles gets further renormalised due to the gauge fluctuations [92]. However, in the following discussion, we will assume the monopole-gauge coupling constant to be small, so that these only lead to a sub-leading corrections of the GMFT results (see Sec.…”

Exceptional dynamics of interacting spin liquids

“…Much recent work has focused on realizing new types of spin liquids and understanding their implications in dynamics and experiments through mean-field approaches. Interactions and disorder are prominent in many experimental settings, however, and can affect the dynamics and thermodynamics [6][7][8][9][10][11][12][13][14][15][16][17][18]. A common expectation is that such effects either renormalize the properties of quasiparticles (and give them finite lifetimes), or open a gap if they violate certain symmetries.…”

Dynamics in the planar pyrochlore lattice: bow-tie flat band and mixed 't Hooft anomaly

“…As a paradigmatic example, the pyrochlore quantum spin ice manifesting emergent U(1) gauge structure [4,5], and the corresponding effective field theory is QED 4 . In the past decades, many exotic phenomena in spin ice have been discovered, such as magnetic monopole [6], gauge photon [7], Coulomb phase [8] and the large emergent fine structure constant [9].…”