The Helical Liquid and the Edge of Quantum Spin Hall Systems
Abstract
Edge states of the recently proposed quantum spin Hall systems constitutes a new symmetry class of one-dimensional liquids dubbed the 'helical liquid', where the direction of the right or left motion is determined by the spin direction. A no-go theorem shows that a helical liquid with an odd number of components cannot be constructed in a purely 1D lattice system. In a helical liquid with an odd number of components, an uniform gap can only appear when the time-reversal (TR) symmetry is spontaneously broken by the interaction. On the other hand, a correlated two-particle backscattering by an impurity can cause insulating behavior while keeping the TR invariance. The Kondo effect of a magnetic impurity is also studied in the helical liquid.Keywords
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