Title: Flux-Stabilized Majorana Zero Modes in Coupled One-Dimensional Fermi Wires,
Abstract: One promising avenue to study one-dimensional ($1$D) topological phases is to
realize them in synthetic materials such as cold atomic gases. Intriguingly, it
is possible to realize Majorana boundary modes in a $1$D number-conserving
system consisting of two fermionic chains coupled only by pair-hopping
processes. It is commonly believed that significant interchain single-particle
tunneling necessarily destroys these Majorana modes, as it spoils the
$\mathbb{Z}_2$ fermion parity symmetry that protects them. In this Letter, we
present a new mechanism to overcome this obstacle, by piercing a (synthetic)
magnetic $\pi$-flux through each plaquette of the Fermi ladder. Using
bosonization, we show that in this case there exists an exact leg-interchange
symmetry that is robust to interchain hopping, and acts as fermion parity at
long wavelengths. We utilize density matrix renormalization group and exact
diagonalization to verify that the resulting model exhibits Majorana boundary
modes up to large single-particle tunnelings, comparable to the intrachain
hopping strength. Our work highlights the unusual impacts of different
topologically trivial band structures on these interaction-driven topological
phases, and identifies a distinct route to stabilizing Majorana boundary modes
in $1$D fermionic ladders.