Correlations at PT-symmetric quantum critical point

Rövid cím: 
Correlations at PT-symmetric q-critical point
2022. 05. 13. 10:15
BME building F, seminar room of the Dept. of Theoretical Physics & Online
Balázs Dóra (BME)
We consider a PT-symmetric Fermi gas with an exceptional point, 
representing the critical point between PT-symmetric and symmetry 
broken phases. The low energy spectrum remains linear in momentum 
and is identical to that of a hermitian Fermi gas. The fermionic Green's 
function decays in a power law fashion for large distances, as expected 
from gapless excitations, albeit the exponent is reduced from −1 due to 
the quantum Zeno effect. In spite of the gapless nature of the excitations, 
the ground state entanglement entropy saturates to a finite value, 
independent of the subsystem size due to the non-hermitian correlation 
length intrinsic to the system. Attractive or repulsive interaction drives 
the system into the PT-symmetry broken regime or opens up a gap and 
protects PT-symmetry, respectively. Our results challenge the concept of 
universality in non-hermitian systems, where quantum criticality can be 
masked due to non-hermiticity.
[1]: B Dóra, D Sticlet, CP Moca: Phys. Rev. Lett. 128, 146804 (2022)