TY - JOUR
AB - We study the effect of a linear tunneling coupling between two-dimensional systems, each separately
exhibiting the topological Berezinskii-Kosterlitz-Thouless (BKT) transition. In the uncoupled limit, there
are two phases: one where the one-body correlation functions are algebraically decaying and the other with
exponential decay. When the linear coupling is turned on, a third BKT-paired phase emerges, in which one-body correlations are exponentially decaying, while two-body correlation functions exhibit power-law
decay. We perform numerical simulations in the paradigmatic case of two coupled XY models at finite
temperature, finding evidences that for any finite value of the interlayer coupling, the BKT-paired phase is
present. We provide a picture of the phase diagram using a renormalization group approach.
AU - Bighin, Giacomo
AU - Defenu, Nicolò
AU - Nándori, István
AU - Salasnich, Luca
AU - Trombettoni, Andrea
ID - 6940
IS - 10
JF - Physical Review Letters
SN - 0031-9007
TI - Berezinskii-Kosterlitz-Thouless paired phase in coupled XY models
VL - 123
ER -
TY - JOUR
AB - We study few-body bound states of charged particles subject to attractive zero-range/short-range plus repulsive Coulomb interparticle forces. The characteristic length scales of the system at zero energy are set by the Coulomb length scale D and the Coulomb-modified effective range r eff. We study shallow bound states of charged particles with D >> r eff and show that these systems obey universal scaling laws different from neutral particles. An accurate description of these states requires both the Coulomb-modified scattering length and the effective range unless the Coulomb interaction is very weak (D -> ). Our findings are relevant for bound states whose spatial extent is significantly larger than the range of the attractive potential. These states enjoy universality – their character is independent of the shape of the short-range potential.
AU - Schmickler, C.H.
AU - Hammer, H.-W.
AU - Volosniev, Artem
ID - 6955
JF - Physics Letters B
SN - 0370-2693
TI - Universal physics of bound states of a few charged particles
VL - 798
ER -
TY - JOUR
AB - Recently it was shown that a molecule rotating in a quantum solvent can be described in terms of the “angulon” quasiparticle [M. Lemeshko, Phys. Rev. Lett. 118, 095301 (2017)]. Here we extend the angulon theory to the case of molecules possessing an additional spin-1/2 degree of freedom and study the behavior of the system in the presence of a static magnetic field. We show that exchange of angular momentum between the molecule and the solvent can be altered by the field, even though the solvent itself is non-magnetic. In particular, we demonstrate a possibility to control resonant emission of phonons with a given angular momentum using a magnetic field.
AU - Rzadkowski, Wojciech
AU - Lemeshko, Mikhail
ID - 415
IS - 10
JF - The Journal of Chemical Physics
TI - Effect of a magnetic field on molecule–solvent angular momentum transfer
VL - 148
ER -
TY - JOUR
AB - We introduce a Diagrammatic Monte Carlo (DiagMC) approach to complex molecular impurities with rotational degrees of freedom interacting with a many-particle environment. The treatment is based on the diagrammatic expansion that merges the usual Feynman diagrams with the angular momentum diagrams known from atomic and nuclear structure theory, thereby incorporating the non-Abelian algebra inherent to quantum rotations. Our approach works at arbitrary coupling, is free of systematic errors and of finite size effects, and naturally provides access to the impurity Green function. We exemplify the technique by obtaining an all-coupling solution of the angulon model, however, the method is quite general and can be applied to a broad variety of quantum impurities possessing angular momentum degrees of freedom.
AU - Bighin, Giacomo
AU - Tscherbul, Timur
AU - Lemeshko, Mikhail
ID - 417
IS - 16
JF - Physical Review Letters
TI - Diagrammatic Monte Carlo approach to rotating molecular impurities
VL - 121
ER -
TY - JOUR
AB - We analyze the theoretical derivation of the beyond-mean-field equation of state for two-dimensional gas of dilute, ultracold alkali-metal atoms in the Bardeen–Cooper–Schrieffer (BCS) to Bose–Einstein condensate (BEC) crossover. We show that at zero temperature our theory — considering Gaussian fluctuations on top of the mean-field equation of state — is in very good agreement with experimental data. Subsequently, we investigate the superfluid density at finite temperature and its renormalization due to the proliferation of vortex–antivortex pairs. By doing so, we determine the Berezinskii–Kosterlitz–Thouless (BKT) critical temperature — at which the renormalized superfluid density jumps to zero — as a function of the inter-atomic potential strength. We find that the Nelson–Kosterlitz criterion overestimates the BKT temperature with respect to the renormalization group equations, this effect being particularly relevant in the intermediate regime of the crossover.
AU - Bighin, Giacomo
AU - Salasnich, Luca
ID - 420
IS - 17
JF - International Journal of Modern Physics B
TI - Renormalization of the superfluid density in the two-dimensional BCS-BEC crossover
VL - 32
ER -