TY  - JOUR
A1  - Assaad, Fakher F.
A1  - Herbut, Igor F.
T1  - Pinning the Order: The Nature of Quantum Criticality in the Hubbard Model on Honeycomb Lattice
JF  - Physical Review X
N2  - In numerical simulations, spontaneously broken symmetry is often detected by computing two-point correlation functions of the appropriate local order parameter. This approach, however, computes the square of the local order parameter, and so when it is small, very large system sizes at high precisions are required to obtain reliable results. Alternatively, one can pin the order by introducing a local symmetrybreaking field and then measure the induced local order parameter infinitely far from the pinning center. The method is tested here at length for the Hubbard model on honeycomb lattice, within the realm of the projective auxiliary-field quantum Monte Carlo algorithm. With our enhanced resolution, we find a direct and continuous quantum phase transition between the semimetallic and the insulating antiferromagnetic states with increase of the interaction. The single-particle gap, measured in units of Hubbard U, tracks the staggered magnetization. An excellent data collapse is obtained by finite-size scaling, with the values of the critical exponents in accord with the Gross-Neveu universality class of the transition.
KW  - strongly correlated materials
KW  - mesoscopics
KW  - computational physics
Y1  - 2013
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-129829
VL  - 3
IS  - 031010
ER  - 
TY  - JOUR
A1  - Engel, Volker
A1  - Albert, Julian
A1  - Schubert, Alexander
T1  - Two-dimensional vibronic spectroscopy of molecular predissociation
JF  - New Journal of Physics
N2  - We calculate two-dimensional (2D) spectra reflecting the time-dependent electronic predissociation of a diatomic molecule. The laser-excited electronic state is coupled non-adiabatically to a fragment channel, leading to the decay of the prepared quasi-bound states. This decay can be monitored by the three-pulse configuration employed in optical 2D spectroscopy. It is shown that in this way it is possible to state-selectively characterize the time-dependent population of resonance states with different lifetimes. A model of the NaI molecule serves as a numerical example.
KW  - computational physics
KW  - atomic physics
KW  - molecular physics
Y1  - 2013
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-96199
ER  -