9 research outputs found
Higher-order spin-hole correlations around a localized charge impurity
Analysis of higher-order correlation functions has become a powerful tool for investigating interacting many-body systems in quantum simulators, such as quantum gas microscopes. Experimental measurements of mixed spin-charge correlation functions in the 2D Hubbard have been used to study equilibrium properties of magnetic polarons and to identify coherent and incoherent regimes of their dynamics. In this paper we consider theoretically an extension of this technique to systems which use a pinning potential to reduce the mobility of a single dopant in the Mott insulating regime of the 2D Hubbard model. We find that localization of the dopant has a dramatic effect on its magnetic dressing. The connected third order spin correlations are weakened in the case of a mobile hole but strengthened near an immobile hole. In the case of the fifth-order correlation function, we find that its bare value has opposite signs in cases of the mobile and of fully pinned dopant, whereas the connected part is similar for both cases.We study suppression of higher-order correlators by thermal fluctuations and demonstrate that they can be observed up to temperatures comparable to the spin-exchange energy J. We discuss implications of our results for understanding the interplay of spin and charge in doped Mott insulators
Imaging magnetic polarons in the doped Fermi-Hubbard model
Polarons are among the most fundamental quasiparticles emerging in
interacting many-body systems, forming already at the level of a single mobile
dopant. In the context of the two-dimensional Fermi-Hubbard model, such
polarons are predicted to form around charged dopants in an antiferromagnetic
background in the low doping regime close to the Mott insulating state.
Macroscopic transport and spectroscopy measurements related to high
materials have yielded strong evidence for the existence of such quasiparticles
in these systems. Here we report the first microscopic observation of magnetic
polarons in a doped Fermi-Hubbard system, harnessing the full single-site spin
and density resolution of our ultracold-atom quantum simulator. We reveal the
dressing of mobile doublons by a local reduction and even sign reversal of
magnetic correlations, originating from the competition between kinetic and
magnetic energy in the system. The experimentally observed polaron signatures
are found to be consistent with an effective string model at finite
temperature. We demonstrate that delocalization of the doublon is a necessary
condition for polaron formation by contrasting this mobile setting to a
scenario where the doublon is pinned to a lattice site. Our work paves the way
towards probing interactions between polarons, which may lead to stripe
formation, as well as microscopically exploring the fate of polarons in the
pseudogap and bad metal phase
Microscopic evolution of doped Mott insulators from polaronic metal to Fermi liquid
The competition between antiferromagnetism and hole motion in two-dimensional
Mott insulators lies at the heart of a doping-dependent transition from an
anomalous metal to a conventional Fermi liquid. Condensed matter experiments
suggest charge carriers change their nature within this crossover, but a
complete understanding remains elusive. We observe such a crossover in
Fermi-Hubbard systems on a cold-atom quantum simulator and reveal the
transformation of multi-point correlations between spins and holes upon
increasing doping at temperatures around the superexchange energy. Conventional
observables, such as spin susceptibility, are furthermore computed from the
microscopic snapshots of the system. Starting from a magnetic polaron regime,
we find the system evolves into a Fermi liquid featuring incommensurate
magnetic fluctuations and fundamentally altered correlations. The crossover is
completed for hole dopings around . Our work benchmarks theoretical
approaches and discusses possible connections to lower temperature phenomena
Robust Bilayer Charge-Pumping for Spin- and Density-Resolved Quantum Gas Microscopy
Quantum gas microscopy has emerged as a powerful new way to probe quantum
many-body systems at the microscopic level. However, layered or efficient
spin-resolved readout methods have remained scarce as they impose strong
demands on the specific atomic species and constrain the simulated lattice
geometry and size. Here we present a novel high-fidelity bilayer readout, which
can be used for full spin- and density-resolved quantum gas microscopy of
two-dimensional systems with arbitrary geometry. Our technique makes use of an
initial Stern-Gerlach splitting into adjacent layers of a highly-stable
vertical superlattice and subsequent charge pumping to separate the layers by
m. This separation enables independent high-resolution images of each
layer. We benchmark our method by spin- and density-resolving two-dimensional
Fermi-Hubbard systems. Our technique furthermore enables the access to advanced
entropy engineering schemes, spectroscopic methods or the realization of
tunable bilayer systems
Direct observation of incommensurate magnetism in Hubbard chains
The interplay between magnetism and doping is at the origin of exotic
strongly correlated electronic phases and can lead to novel forms of magnetic
ordering. One example is the emergence of incommensurate spin-density waves
with a wave vector that does not match the reciprocal lattice. In one dimension
this effect is a hallmark of Luttinger liquid theory, which also describes the
low energy physics of the Hubbard model. Here we use a quantum simulator based
on ultracold fermions in an optical lattice to directly observe such
incommensurate spin correlations in doped and spin-imbalanced Hubbard chains
using fully spin and density resolved quantum gas microscopy. Doping is found
to induce a linear change of the spin-density wave vector in excellent
agreement with Luttinger theory predictions. For non-zero polarization we
observe a decrease of the wave vector with magnetization as expected from the
Heisenberg model in a magnetic field. We trace the microscopic origin of these
incommensurate correlations to holes, doublons and excess spins which act as
delocalized domain walls for the antiferromagnetic order. Finally, when
inducing interchain coupling we observe fundamentally different spin
correlations around doublons indicating the formation of a magnetic polaron
Measuring the polarization of electromagnetic fields using Rabi-rate measurements with spatial resolution: Experiment and theory
ISSN:1094-1622ISSN:0556-2791ISSN:1050-294
Higher-order spin-hole correlations around a localized charge impurity
Analysis of higher-order correlation functions has become a powerful tool for investigating interacting many-body systems in quantum simulators, such as quantum gas microscopes. Experimental measurements of mixed spin-charge correlation functions in the 2D Hubbard have been used to study equilibrium properties of magnetic polarons and to identify coherent and incoherent regimes of their dynamics. In this paper we consider theoretically an extension of this technique to systems which use a pinning potential to reduce the mobility of a single dopant in the Mott insulating regime of the 2D Hubbard model. We find that localization of the dopant has a dramatic effect on its magnetic dressing. The connected third order spin correlations are weakened in the case of a mobile hole but strengthened near an immobile hole. In the case of the fifth-order correlation function, we find that its bare value has opposite signs in cases of the mobile and of fully pinned dopant, whereas the connected part is similar for both cases. We study suppression of higher-order correlators by thermal fluctuations and demonstrate that they can be observed up to temperatures comparable to the spin-exchange energy J. We discuss implications of our results for understanding the interplay of spin and charge in doped Mott insulators.ISSN:2643-156