Large discrete jumps observed in the transition between Chern states in a ferromagnetic Topological Insulator

TL;DR

This study observes large, discrete jumps in the transition between Chern states in a ferromagnetic topological insulator, revealing temperature-dependent escape dynamics influenced by dissipation and quantum tunneling effects.

Contribution

It provides the first detailed experimental analysis of rapid Chern state transitions and their dependence on dissipation and temperature in ferromagnetic topological insulators.

Findings

Large resistance jumps occur at ultralow dissipation levels.

Escape rates are strongly suppressed by increasing temperature.

Jumps are spatially correlated over large sample regions.

Abstract

A striking prediction in topological insulators is the appearance of the quantized Hall resistance when the surface states are magnetized. The surface Dirac states become gapped everywhere on the surface, but chiral edge states remain on the edges. In an applied current, the edge states produce a quantized Hall resistance that equals the Chern number C = +1 or -1 (in natural units), even in zero magnetic field. This quantum anomalous Hall effect was observed by Chang et al. With reversal of the magnetic field, the system is trapped in a metastable state because of magnetic anisotropy. Here we investigate how the system escapes the metastable state at low temperatures (10-200 mK). When the dissipation (measured by the longitudinal resistance) is ultralow, we find that the system escapes by making a few, very rapid transitions, as detected by large jumps in the Hall and longitudinal resistances. Using the field at which the initial jump occurs to estimate the escape rate, we find that raising the temperature strongly suppresses the rate. From a detailed map of the resistance vs. gate voltage and temperature, we show that dissipation strongly affects the escape rate. We compare the observations with dissipative quantum tunneling predictions. In the ultralow dissipation regime, there exist two temperature scales T1 = 70 mK and T2 = 145 mK between which jumps can be observed. The jumps display a spatial correlation that extends over a large fraction of the sample.