Scaling behavior of the quantum phase transition from a quantum-anomalous-Hall insulator to an axion insulator

Abstract

The phase transitions from one plateau to the next plateau or to an insulator in quantum Hall and quantum anomalous Hall (QAH) systems have revealed universal scaling behaviors. A magnetic-field-driven quantum phase transition from a QAH insulator to an axion insulator was recently demonstrated in magnetic topological insulator sandwich samples. Here, we show that the temperature dependence of the derivative of the longitudinal resistance on magnetic field at the transition point follows a characteristic power-law that indicates a universal scaling behavior for the QAH to axion insulator phase transition. Similar to the quantum Hall plateau to plateau transition, the QAH to axion insulator transition can also be understood by the Chalker–Coddington network model. We extract a critical exponent κ ~ 0.38 ± 0.02 in agreement with recent high-precision numerical results on the correlation length exponent of the Chalker–Coddington model at ν ~ 2.6, rather than the generally-accepted value of 2.33.

Recent Progress in Proximity Coupling of Magnetism to Topological Insulators

“…[ 213 ] Subsequently, there were several other reports of QAHE in similar heterostructures. [ 29,197,214–217 ]…”

Surface charge induced Dirac band splitting in a charge density wave material (TaSe4)2I

“…Below Tc, the CDW gap of hundreds of meV can drive (TaSe4)2I into an axion insulator state [15][16][17]. Unlike the axion insulator state realized in molecular beam epitaxy grown magnetic topological insulator sandwich heterostructures, where the gap opening at Dirac point is induced by internal magnetization [21][22][23], the axion insulator realized here arises from the formation of the CDW order in a Weyl semimetal [24][25][26]. One recent transport study on (TaSe4)2I claimed that the axion insulator state appears at low temperatures [17].…”

Any Axion Insulator Must be a Bulk Three-Dimensional Topological Insulator

“…All of the individual layers in the hetero-structure stacks reported in [16][17][18] fall into a 2D regime if compared directly to our 2D-3D transition scale. Moreover recent measurements of the temperature dependence in the same trilayers reveals a critical exponent consistent with that of a (2D) integer quantum Hall effect [42]. All of this implies that quantum Hall systems exhibiting the zero Hall plateau state have fundamentally 2D electrodynamic properties, thus lack a 3D bulk and cannot host axion properties.…”

“…It is worth noting that in the 2D limit, we find that the peak two-terminal resistance of the 5.3 nm thick layer exceeds 10GΩ (an estimated lower bound on the sample resistance, see suppl. material [22] for more details), which is one order of magnitude larger than the value recently reported in a magnetic heterostructure (trilayer), and attributed to unconventional insulating properties providing evidence of an axion insulator [42].…”