Inverse Spin-Galvanic Effect in the Interface between a Topological Insulator and a Ferromagnet

Abstract

When a ferromagnet is deposited on the surface of a topological insulator (TI) the topologically protected surface state develops a gap and becomes a 2-dimensional quantum Hall liquid. We demonstrate that the Hall current in such a liquid, induced by an external electric field, can have a large effect on the magnetization dynamics of the ferromagnet by changing the effective anisotropy field. This change is dissipationless and may be substantial even in weakly spin-orbit coupled ferromagnets. We study the possibility of dissipationless current-induced magnetization reversal in monolayer-thin, insulating ferromagnets with a soft perpendicular anisotropy and discuss possible applications of this effect.

Hedgehog spin texture and Berry’s phase tuning in a magnetic topological insulator

“…Such spin configuration simultaneous with the chemical potential placed within the magnetic gap ( Fig. 5d) is the fundamental requirement for most of the theoretical proposals relevant to the utilization of magnetic topological insulators in novel devices [4, [9][10][11][12]. Furthermore, if the bulk bandgap of the Mn-Bi 2 Se 3 film is tuned to zero at the critical point of the topological phase transition [29], a new topologically protected Weyl semimetal phase [31,32] with yet more exotic but undiscovered state of matter is also predicted to take place, which is among the most exciting future frontiers to be enabled by our achievement of a sample that features a TR broken hedgehog-like spin texture with a GP = 0 state [31,32].…”

“…We further show that an insulating gap induced by quantum tunneling between surfaces exhibits spin texture modulation at low energies but respects time-reversal invariance. These spin phenomena and the control of their Fermi surface geometrical phase first demonstrated in our experiments pave the way for future realization of many predicted exotic magnetic phenomena of topological origin.Since the discovery of three dimensional topological insulators [1][2][3][4][5], topological order proximity to ferromagnetism has been considered as one of the core interests of the field [6][7][8][9][10][11][12][13][14][15][16]. Such interest is strongly motivated by the proposed time-reversal (TR) breaking topological physics such as quantized anomalous chiral Hall current, spin current, axion electrodynamics, and inverse spin-galvanic effect [9][10][11][12], all of which critically rely on finding a way to break TR symmetry on the surface and utilize the unique TR broken spin texture for applications.…”

“…Such interest is strongly motivated by the proposed time-reversal (TR) breaking topological physics such as quantized anomalous chiral Hall current, spin current, axion electrodynamics, and inverse spin-galvanic effect [9][10][11][12], all of which critically rely on finding a way to break TR symmetry on the surface and utilize the unique TR broken spin texture for applications. Since quantum coherence is essential in many of these applications, devices need to be engineered into thin films in order to enhance or de-enhance surface-tosurface coupling or the quantum tunneling of the electrons.…”

Antidamping spin-orbit torque driven by spin-flip reflection mechanism on the surface of a topological insulator: A time-dependent nonequilibrium Green function approach

“…For example, very recent experiments [14][15][16] have replaced HM with threedimensional topological insulators (3D TIs) [17]. The TIs enhance [18][19][20] (by a factor v F /α R , where v F is the Fermi velocity on the surface of TI and α R is the Rashba SOC strength [21,22] at the F/HM interface) the transverse nonequilibrium spin density driven by the longitudinal charge current, which is responsible for the large fieldlike SOT component [20,23] observed experimentally [14][15][16].…”

Signatures of Dirac fermion-mediated magnetic order

“…Prominent systems showing novel properties associated with the spin degree of freedom are magnetic skyrmions 1 and the recently discovered topological insulators (TIs) 2,3 . TIs, in particular, offer an ideal platform to explore several exotic phenomena which, in addition to being relevant to both condensed matter and highenergy physics [4][5][6] , are expected to have direct applications in devices with unique functionalities [7][8][9] . The promise of this new class of materials is related to their unconventional electronic properties.…”