Condensed Matter

Jammed Spin Liquid in the Bond-Disordered Kagome Antiferromagnet
Thomas Bilitewski, Mike E. Zhitomirsky, Roderich Moessner

We study a class of continuous spin models with bond disorder including the kagome Heisenberg antiferromagnet. For weak disorder strength, we find discrete ground states whose number grows exponentially with system size. These states do not exhibit zero-energy excitations characteristic of highly frustrated magnets but instead are local minima of the energy landscape. This represents a spin liquid version of the phenomenon of jamming familiar from granular media and structural glasses. Correlations of this jammed spin liquid, which upon increasing the disorder strength gives way to a conventional spin glass, may be algebraic (Coulomb type) or exponential.

Phys. Rev. Lett. 119, 247201 (2017)

Disorder-Free Localization
A. Smith, J. Knolle, D. L. Kovrizhin, R. Moessner

The venerable phenomena of Anderson localization, along with the much more recent many- body localization, both depend crucially on the presence of disorder. The latter enters either in the form of quenched disorder in the parameters of the Hamiltonian, or through a special choice of a disordered initial state. Here, we present a model with localization arising in a very simple, completely translationally invariant quantum model, with only local interactions between spins and fermions. By identifying an extensive set of conserved quantities, we show that the system generates purely dynamically its own disorder, which gives rise to localization of fermionic degrees of freedom. Our work gives an answer to a decades old question whether quenched disorder is a necessary condition for localization. It also offers new insights into the physics of many-body localization, lattice gauge theories, and quantum disentangled liquids.

Phys. Rev. Lett. 118, 266601 (2017)

Equilibration and order in quantum Floquet matter
R. Moessner, S. L. Sondhi

Equilibrium thermodynamics is characterized by two fundamental ideas: thermalization-that systems approach a late time thermal state; and phase structure-that thermal states exhibit singular changes as various parameters characterizing the system are changed. We summarize recent progress that has established generalizations of these ideas to periodically driven, or Floquet, closed quantum systems. This has resulted in the discovery of entirely new phases which exist only out of equilibrium, such as the π-spin glass/Floquet time crystal.

Nature Physics 13, 424 (2017)