  Spatial confinement of electronic topological surface states (TSS) in
topological insulators poses a formidable challenge because TSS are protected
by time-reversal symmetry. In previous works formation of a gap in the
electronic spectrum of TSS has been successfully demonstrated in topological
insulator/magnetic material heterostructures, where ferromagnetic exchange
interactions locally lifts the time-reversal symmetry. Here we report an
experimental evidence of exchange interaction between a topological insulator
Bi2Se3 and a magnetic insulator EuSe. Spin-polarized neutron reflectometry
reveals a reduction of the in-plane magnetic susceptibility within a 2 nm
interfacial layer of EuSe, and the combination of SQUID magnetometry and Hall
measurements points to the formation of an antiferromagnetic layer with at
least five-fold enhancement of N\'eel's temperature. Abrupt resistance changes
in high magnetic fields indicate interfacial exchange coupling that affects
transport in a TSS. High temperature local control of TSS with zero net
magnetization unlocks new opportunities for the design of electronic,
spintronic and quantum computation devices, ranging from quantization of Hall
conductance in zero fields to spatial localization of non-Abelian excitations
in superconducting topological qubits.
