NMR Relaxation in Ising Spin Chains

January 31, 2019

Crossover phase diagram of the Ising chain in a transverse field h

The quantum Ising chain in a transverse magnetic field is the paradigm of a quantum phase transition, displaying universal quantum criticality at low temperatures. Insights from this model have informed studies of quantum criticality in numerous modern correlated-electron materials. There have been a number of experimental studies of the quantum Ising chain, most notably in the material CoNb2O6. It has recently become clear that there was a surprising discrepancy between the observations: the energy gap in the quantum disordered regime as measured by nuclear magnetic resonance was approximately twice that measured by other methods. In a new paper in PHysics Review B, grad student Julia Steinberg, Prof. Subir Sachdev, and colleagues from the Johns Hopkins University and Rudolf Peierls Centre for Theoretical Physics (UK) show via careful analysis of the low-temperature excitations that this is not a discrepancy, nut rather, it is in fact to be expected from the subtle interactions between the excitations. Although the underlying spin excitations are bosonic, their interactions transmute them into fermions, and this is a key ingredient in understanding the experiments.

Read Julia Steinberg, N. P. Armitage, Fabian H. L. Essler, and Subir Sachdev, "NMR relaxation in Ising spin chains," Phys. Rev. B 99 (29 January 2019) https://doi.org/10.1103/PhysRevB.99.035156.