title: Large discrete jumps observed in the transition between Chern states in a ferromagnetic topological insulator.
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 (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. We investigate how the system escapes the metastable state at low temperatures (10 to 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 versus 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, two temperature scales (T 1 ~ 70 mK and T 2 ~ 145 mK) exist, between which jumps can be observed. The jumps display a spatial correlation that extends over a large fraction of the sample.
authors.affiliation: Department of Physics, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Minhao
authors.initials: M
authors.lastname: Liu
authors.affiliation: Department of Physics, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Wudi
authors.identifier: 0000-0002-2609-133X
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Physics, Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Richardella
authors.affiliation: Department of Physics, Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Abhinav
authors.initials: A
authors.lastname: Kandala
authors.affiliation: Department of Physics, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Jian
authors.identifier: 0000-0003-0297-6528
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Physics, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Ali
authors.identifier: 0000-0003-4996-8904
authors.initials: A
authors.lastname: Yazdani
authors.affiliation: Department of Physics, Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Nitin
authors.identifier: 0000-0003-2599-346X
authors.initials: N
authors.lastname: Samarth
authors.affiliation: Department of Physics, Princeton University, Princeton, NJ 08544, USA.
authors.forename: N Phuan
authors.initials: NP
authors.lastname: Ong
mesh_terms: D059346:Magnets; D011789:Quantum Theory; D012666:Semiconductors; D013696:Temperature
keywords: Topological insulators; chern number; chiral edge states; dissipationless transport; dissipative quantum tunneling; metastability; quantization of hall resistance; quantum anomalous hall effect