Possible spiral structure in the pseudogap phase of cuprates.

 

Victor Yakovenko

 

Dept. of Physics, University of Maryland, College Park

 

We propose a novel chiral order parameter to explain recent experimental developments concerning the polar Kerr effect in underdoped cuprates.  Originally, experimental observation of the polar Kerr effect in the pseudogap phase of cuprates was interpreted as a signature of a ferromagnetic-like time-reversal symmetry breaking.  However, more recent measurements suggest that this interpretation is not correct, and the polar Kerr effect is more likely to originate from a chiral and inversion symmetry breaking, which results in handedness and spatial dispersion with gyrotropy.  Our theoretical scenario is based on the loop-current model by Varma, which is characterized by the in-plane anapole moment N and exhibits the magnetoelectric effect.  We propose a helical structure where the vector N(n) in the layer n is twisted by the angle pi/2 relative to N(n-1), thus breaking inversion symmetry.  As a result, the magnetic field lines produced by the loop currents get twisted in a double-helix manner reminiscent of DNA.  We show that coupling between magnetoelectric terms in the neighboring layers for this structure produces optical gyrotropy, which results in circular and linear dichroism and the polar Kerr effect.

 

Reference:

S. S. Pershoguba, K. Kechedzhi, and V. M. Yakovenko, PRL 111, 047005 (2013),

also in Physics Synopsis, http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.111.047005

 

Host: Prof. G. Kotliar