Pumping approximately integrable systems

• Published in: Nature communications Vol. 8; no. 1; p. 15767
• Main Authors: Lange, Florian, Lenarčič, Zala, Rosch, Achim
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 09.06.2017; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/483/640; 639/766/530/2803; 639/766/530/2804; Approximation; Conservation laws; Equilibrium; Heat; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms15767

Weak perturbations can drive an interacting many-particle system far from its initial equilibrium state if one is able to pump into degrees of freedom approximately protected by conservation laws. This concept has for example been used to realize Bose–Einstein condensates of photons, magnons and excitons. Integrable quantum systems, like the one-dimensional Heisenberg model, are characterized by an infinite set of conservation laws. Here, we develop a theory of weakly driven integrable systems and show that pumping can induce large spin or heat currents even in the presence of integrability breaking perturbations, since it activates local and quasi-local approximate conserved quantities. The resulting steady state is qualitatively captured by a truncated generalized Gibbs ensemble with Lagrange parameters that depend on the structure but not on the overall amplitude of perturbations nor the initial state. We suggest to use spin-chain materials driven by terahertz radiation to realize integrability-based spin and heat pumps. Integrable models have an infinite number of conserved quantities but most realizations suffer from integrability breaking perturbations. Here the authors show that weakly driving such a system by periodic perturbations leads to large nonlinear responses governed by the approximate conservation laws.