Spin impurities coupled to quantum critical systems
K. Chen, Y. Komijani, Even-odd effect of an spin-S impurity coupled to a quantum critical system, Phys. Rev. B 100, 094514 (2019).
A potential trap in a superfluid--Mott insulator transition of Bose-Hubbard model can be described by a spin-1/2 XY-coupled to the Wilson-Fisher fixed point of a phi^4 theory. This the XY Bose-Kondo universality class and the spin will be partially screened at the infrared fixed point.
Here, we were motivated by interplay between two/few of such potential traps, which can be described by two-impurity Bose-Kondo model. It turns out that at low-energies such a system can be described by a spin-S coupled to the critical system.
- For the case of S=1, we used renormalization group with dimensional and cut=-off regularization in combination with quantum Monte carlo to study various critical exponents which showed good agreements.
Moreover, we found out that depending on whether 2S is even or odd the system can behave differently. Either full lifting of all 2S+1 degeneracies or a residual degeneracy leading to partial screening.