  Octupole correlations in the low-energy collective states of neutron-rich
nuclei with the neutron number $N\approx56$ are studied within the interacting
boson model (IBM) that is based on the nuclear density functional theory. The
constrained self-consistent mean-field (SCMF) calculations using a universal
energy density functional and a pairing interaction provide the potential
energy surfaces in terms of the axially-symmetric quadrupole and octupole
deformations for the even-even nuclei $^{86-94}$Se, $^{88-96}$Kr, $^{90-98}$Sr,
$^{92-100}$Zr, and $^{94-102}$Mo. The SCMF energy surface is then mapped onto
the energy expectation value of a version of the IBM in the boson condensate
state, which consists of the neutron and proton monopole $s$, quadrupole $d$,
and octupole $f$ bosons. This procedure determines the strength parameters of
the IBM Hamiltonian, which is used to compute relevant spectroscopic
properties. At the SCMF level, no octupole deformed ground state is obtained,
while the energy surface is generally soft in the octupole deformation at
$N\approx56$. The predicted negative-parity yrast bands with the bandhead state
$3^-_1$ weakly depend on $N$ and become lowest in energy at $N=56$ in each of
the considered isotopic chains. The model further predicts finite electric
octupole transition rates between the lowest negative- and the positive-parity
ground-state bands.
