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TT: Fachverband Tiefe Temperaturen

TT 6: Focused Session: Frontiers in Classical and Quantum Spin Liquids

TT 6.5: Topical Talk

Montag, 14. März 2011, 17:15–18:00, HSZ 03

Quantum Criticality and E8 symmetry in an Ising Chain — •Alan Tennant — Helmholtz Zentrum Berlin

Quantum phase transitions take place between distinct phases of matter at zero temperature. Near the transition point, exotic quantum symmetries can emerge that govern the excitation spectrum of the system. A symmetry described by the E-8 Lie group with a spectrum of eight particles was long predicted to appear near the critical point of an Ising chain. We realize this system experimentally by using strong transverse magnetic fields to tune the quasi-one-dimensional Ising ferromagnet CoNb$_2$O$_6$ (cobalt niobate) through its critical point. Spin excitations are observed to change character from pairs of kinks in the ordered phase to spin-flips in the paramagnetic phase. Just below the critical field, the spin dynamics shows a fine structure with two sharp modes at low energies, in a ratio that approaches the golden mean predicted for the first two meson particles of the E-8 spectrum. Our results demonstrate the power of symmetry to describe complex quantum behaviors. \newline Science 327, 177 (2010)