152 research outputs found
Dissipative Preparation of Antiferromagnetic Order in the Fermi-Hubbard Model
The Fermi-Hubbard model is one of the key models of condensed matter physics,
which holds a potential for explaining the mystery of high-temperature
superconductivity. Recent progress in ultracold atoms in optical lattices has
paved the way to studying the model's phase diagram using the tools of quantum
simulation, which emerged as a promising alternative to the numerical
calculations plagued by the infamous sign problem. However, the temperatures
achieved using elaborate laser cooling protocols so far have been too high to
show the appearance of antiferromagnetic and superconducting quantum phases
directly. In this work, we demonstrate that using the machinery of dissipative
quantum state engineering, one can efficiently prepare antiferromagnetic order
in present-day experiments with ultracold fermions. The core of the approach is
to add incoherent laser scattering in such a way that the antiferromagnetic
state emerges as the dark state of the driven-dissipative dynamics. In order to
elucidate the development of the antiferromagnetic order we employ two
complementary techniques: Monte Carlo wave function simulations for small
systems and a recently proposed variational method for open quantum systems,
operating in the thermodynamic limit. The controlled dissipation channels
described in this work are straightforward to add to already existing
experimental setups.Comment: 9 pages, 5 figure
Gutzwiller Wave-Function Solution for Anderson Lattice Model: Emerging Universal Regimes of Heavy Quasiparticle States
The recently proposed diagrammatic expansion (DE) technique for the full
Gutzwiller wave function (GWF) is applied to the Anderson lattice model (ALM).
This approach allows for a systematic evaluation of the expectation values with
GWF in the finite dimensional systems. It introduces results extending in an
essential manner those obtained by means of standard Gutzwiller Approximation
(GA) scheme which is variationally exact only in infinite dimensions. Within
the DE-GWF approach we discuss principal paramagnetic properties of ALM and
their relevance to heavy fermion systems. We demonstrate the formation of an
effective, narrow -band originating from atomic -electron states and
subsequently interpret this behavior as a mutual intersite -electron
coherence; a combined effect of both the hybridization and the Coulomb
repulsion. Such feature is absent on the level of GA which is equivalent to the
zeroth order of our expansion. Formation of the hybridization- and
electron-concentration-dependent narrow effective -band rationalizes common
assumption of such dispersion of levels in the phenomenological modeling of
the band structure of CeCoIn. Moreover, we show that the emerging
-electron coherence leads in a natural manner to three physically distinct
regimes within a single model, that are frequently discussed for 4- or 5-
electron compounds as separate model situations. We identify these regimes as:
(i) mixed-valence regime, (ii) Kondo-insulator border regime, and (iii)
Kondo-lattice limit when the -electron occupancy is very close to the
electrons half-filling, . The non-Landau
features of emerging correlated quantum liquid state are stressed.Comment: Submitted to Phys. Rev.
Coexistence of Nematic Order and Superconductivity in the Hubbard Model
We study the interplay of nematic and superconducting order in the
two-dimensional Hubbard model and show that they can coexist, especially when
superconductivity is not the energetically dominant phase. Due to a breaking of
the symmetry, the coexisting phase inherently contains admixture of the
-wave pairing components. As a result, the superconducting gap exhibits very
non-standard features including changed nodal directions. Our results also show
that in the optimally doped regime the superconducting phase is typically
unstable towards developing nematicity (breaking of the symmetry). This
has implications for the cuprate high- superconductors, for which in this
regime the so-called intertwined orders have recently been observed. Namely,
the coexisting phase may be viewed as a precursor to such more involved
patterns of symmetry breaking.Comment: 5 pages, 3 figure
High-temperature superconductivity in the two-dimensional t-J model: Gutzwiller wavefunction solution
A systematic diagrammatic expansion for Gutzwiller wavefunctions (DE-GWFs) proposed very recently is used for the description of the superconducting (SC) ground state in the two-dimensional square-lattice t–J model with the hopping electron amplitudes t (and ) between nearest (and next-nearest) neighbors. For the example of the SC state analysis we provide a detailed comparison of the methodʼs results with those of other approaches. Namely, (i) the truncated DE-GWF method reproduces the variational Monte Carlo (VMC) results and (ii) in the lowest (zeroth) order of the expansion the method can reproduce the analytical results of the standard Gutzwiller approximation (GA), as well as of the recently proposed 'grand-canonical Gutzwiller approximation' (called either GCGA or SGA). We obtain important features of the SC state. First, the SC gap at the Fermi surface resembles a wave only for optimally and overdoped systems, being diminished in the antinodal regions for the underdoped case in a qualitative agreement with experiment. Corrections to the gap structure are shown to arise from the longer range of the real-space pairing. Second, the nodal Fermi velocity is almost constant as a function of doping and agrees semi-quantitatively with experimental results. Third, we compare the doping dependence of the gap magnitude with experimental data. Fourth, we analyze the k-space properties of the model: Fermi surface topology and effective dispersion. The DE-GWF method opens up new perspectives for studying strongly correlated systems, as it (i) works in the thermodynamic limit, (ii) is comparable in accuracy to VMC, and (iii) has numerical complexity comparable to that of the GA (i.e., it provides the results much faster than the VMC approach).Foundation for Polish Science (FNP)/TEAM programNational Science Centre (NCN)/MAESTR
High-temperature superconductivity in the two-dimensional t–J model : Gutzwiller wavefunction solution
A systematic diagrammatic expansion for Gutzwiller wavefunctions (DE-GWFs) proposed very recently is used for the description of the superconducting (SC) ground state in the two-dimensional square-lattice t–J model with the hopping electron amplitudes t (and t') between nearest (and next-nearest) neighbors. For the example of the SC state analysis we provide a detailed comparison of the methodʼs results with those of other approaches. Namely, (i) the truncated DE-GWF method reproduces the variational Monte Carlo (VMC) results and (ii) in the lowest (zeroth) order of the expansion the method can reproduce the analytical results of the standard Gutzwiller approximation (GA), as well as of the recently proposed 'grand-canonical Gutzwiller approximation' (called either GCGA or SGA). We obtain important features of the SC state. First, the SC gap at the Fermi surface resembles a d_{x^{2}-y^{2}} wave only for optimally and overdoped systems, being diminished in the antinodal regions for the underdoped case in a qualitative agreement with experiment. Corrections to the gap structure are shown to arise from the longer range of the real-space pairing. Second, the nodal Fermi velocity is almost constant as a function of doping and agrees semi-quantitatively with experimental results. Third, we compare the doping dependence of the gap magnitude with experimental data. Fourth, we analyze the k-space properties of the model: Fermi surface topology and effective dispersion. The DE-GWF method opens up new perspectives for studying strongly correlated systems, as it (i) works in the thermodynamic limit, (ii) is comparable in accuracy to VMC, and (iii) has numerical complexity comparable to that of the GA (i.e., it provides the results much faster than the VMC approach)
Laser-induced rotation of iodine molecules in He-nanodroplets: revivals and breaking-free
Rotation of molecules embedded in He nanodroplets is explored by a
combination of fs laser-induced alignment experiments and angulon quasiparticle
theory. We demonstrate that at low fluence of the fs alignment pulse, the
molecule and its solvation shell can be set into coherent collective rotation
lasting long enough to form revivals. With increasing fluence, however, the
revivals disappear -- instead, rotational dynamics as rapid as for an isolated
molecule is observed during the first few picoseconds. Classical calculations
trace this phenomenon to transient decoupling of the molecule from its He
shell. Our results open novel opportunities for studying non-equilibrium
solute-solvent dynamics and quantum thermalization.Comment: 6+7 pages; 4+1 figures; 1 tabl
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