
4
gion of momentum space, the bare meson dispersion ap-
proaches the meson-magnon scattering continuum most
closely, as indicated by the dashed and solid black lines
in Fig. 2. Without meson-magnon interactions and for
sufficiently weak fields ht, J, we find that they can
even cross, leading to a decaying bare meson state inside
the meson-magnon scattering continuum. However, in
Sec. V B we analyze our effective meson-magnon Hamil-
tonian and find indications that meson-magnon interac-
tions in the 1D chain are strong enough to avoid such
quasiparticle decay [44]. Namely, the meson and magnon
bands repel and an isolated quasiparticle band of the
mesonic magnetic polaron survives even around k= 0.
This prediction is further supported by td-MPS simula-
tions at small fields where the effect is most pronounced.
Methodologically, we deviate from the standard ap-
proach typically used to describe magnetic polaron for-
mation in an AFM [45–47]. As mentioned above, we first
take into account how the mobile hole distorts the N´eel
background with pure Ising interactions. This allows us
to make a direct connection to the Z2LGT and identify
the parton content of the meson. Moreover, we can rela-
tively easily capture the competition between the tunnel-
ing term tand the linear string tension ∝h, to all orders
in t/h. This is achieved within a strong-coupling theory.
Next we introduce generalized Holstein-Primakoff bosons
(loosely speaking, magnons) by expanding around the al-
ready distorted N´eel state (we refer to this approach as
the generalized 1/S approximation [22]). This yields ad-
ditional couplings of the meson to the magnons; impor-
tantly, the strength of these couplings is only of order
J, and a fraction of tfor some further corrections we
identify. Hence, perturbative or simple variational ap-
proaches are sufficient to capture the additional meson-
magnon interactions. This should be contrasted with
the traditional 1/S approximation [45–47] where the hole
hopping titself leads to magnon creation: as a result, the
effective Hamiltonian is strongly coupled when t>hand
direct analytical insights are harder to obtain.
C. Possible experimental realizations
Experimentally, the model in Eq. (1) we study can be
realized in different ultracold atom setups. We propose
to use ultracold fermionic Lithium or Potassium atoms
which have very successfully explored the SU(2)-invariant
2D Fermi-Hubbard model [28]. The main obstacle in
these systems is to implement the staggered magnetic
field, which requires local addressability on the scale of
an optical wavelength, see e.g. [48], and sizable magnetic
moments in order to distinguish different spin states, in a
regime close to an atomic Feshbach resonance to realize
super-exchange couplings.
A first option is to use Potassium atoms in a quantum
gas microscope [49] which have a sizable magnetic mo-
ment [50], allowing for a local modulation of the magnetic
field. A second option is to work in a mixed-dimensional
setting where tunneling is strongly suppressed by strong
gradients along all but one lattice direction [29]. More-
over, we assume that nearest-neighbor AFM Ising cou-
plings between all spins are present, which dominate over
the weak super-exchange couplings along the gradient di-
rections. This can be realized in an optical lattice by
adding Rydberg dressing [51]. When doping only the
central chain with one hole and keeping all neighboring
chains at half filling, the surrounding spin chains can gen-
erate an effective staggered field term ±hif they are suffi-
ciently cold. Here we assumed, in a mean-field spirit, that
the wavefunctions of the different chains approximately
factorize. Similarly, in mixed-dimensional settings with
SU (2) invariant spin-exchange interactions [29,30] we
expect a ground state with broken SU (2) symmetry in
qualitatively very similar physics.
Finally, we note that the 1D model in Eq. (1) can be
equally realized with bosons as long as one ensures to
have AFM Heisenberg couplings between the spins [52,
53]. The statistics of the dopants is irrelevant, as can be
shown by a Jordan-Wigner transformation. Hence the
model in Eq. (1) can also be simulated in qubit arrays
or digital quantum computers [54], without the need to
incorporate fermionic statistics.
III. NUMERICAL DMRG SPECTRA
In this section we present our numerical results, largely
based on td-MPS simulations [55], which support our
main findings about the structure and interactions of
doped holes in the 1D spin chain with a staggered field.
We already compare our numerical results to predictions
by the semi-analytical strong-coupling meson-magnon
theory introduced in the subsequent sections. This the-
ory provides a unified understanding of all our key nu-
merical observations.
Detailed descriptions of the numerical td-MPS simu-
lations we performed can be found in Refs. [21,23]; our
algorithm builds upon the earlier works [56–58]. To en-
sure proper convergence of the MPS calculations, we per-
formed the same convergence checks, in time and bond-
dimension, as described in [21,23].
A. Ground state: Dressed hole
In Fig. 3we start by showing the standard one-hole
angle-resolved photoemission spectrum (ARPES), de-
fined by
S(k, ω) = −1
πImZ∞
0
dtei(ω−E0)t
√LX
j
eikj Gj(t),(5)
with the Green’s function
Gj(t) = X
σhΨ0|ˆc†
j,σe−iˆ
Htˆc0,σ|Ψ0i(6)