  Topological insulators (TIs) are a new class of quantum materials that
exhibit spin momentum locking (SML) of massless Dirac fermions in the surface
states. Usually optical methods, such as angle and spin-resolved photoemission
spectroscopy, have been employed to observe the helical spin polarization in
the surface states of three-dimensional (3D) TIs up to room temperatures.
Recently, spin polarized surface currents in 3D TIs were detected by electrical
methods using ferromagnetic (FM) contacts in a lateral spin-valve measurement
geometry. However, probing the spin texture with such electrical approaches is
so far limited to temperatures below 125K, which restricts its application
potential. Here we demonstrate the room temperature electrical detection of the
spin polarization on the surface of Bi$_2$Se$_3$ due to SML by employing spin
sensitive FM tunnel contacts. The current-induced spin polarization on the
Bi$_2$Se$_3$ surface is probed at room temperature by measuring a spin-valve
signal while switching the magnetization direction of the FM detector. The spin
signal increases linearly with current bias, reverses sign with current
direction, exhibits a weak temperature dependence and decreases with higher TI
thickness, as predicted theoretically. Our results demonstrate the electrical
detection of the spin polarization on the surface of 3D TIs, which could lead
to innovative spin-based quantum information technology at ambient
temperatures.
