scholarly journals Direct visualization of edge state in even-layer MnBi2Te4 at zero magnetic field

2021 ◽  
Author(s):  
Weiyan Lin ◽  
Yang Feng ◽  
Yongchao Wang ◽  
Zichen Lian ◽  
Hao Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Time Reversal ◽  
Edge State ◽  
Quantum Spin ◽  
Zero Magnetic Field ◽  
Zero Field ◽  
Topological Phases ◽  
Edge States ◽  
Direct Visualization ◽  
Translation Symmetry

Abstract Being the first intrinsic antiferromagnetic (AFM) topological insulator, MnBi2Te4 is argued to be a topological axion state in its even-layer form due to the antiparallel magnetization between the top and bottom layers. Here we combine both transport and scanning microwave impedance microscopy (sMIM) to investigate such axion state in atomically thin MnBi2Te4 with even-layer thickness at zero magnetic field. While transport measurements show a zero Hall plateau signaturing the axion state, sMIM uncovers an unexpected edge state raising questions regarding the nature of the “axion state”. Based on our model calculation, we propose that the even-layer MnBi2Te4 at zero field is in an AFM quantum spin Hall (QSH) state hosting a pair of helical edge states. Such novel AFM QSH is originated from the combination of half translation symmetry and time-reversal symmetry in MnBi2Te4. Our finding thus signifies the richness of topological phases in MnB2Te4 that has yet to be fully explored.

scholarly journals Observation of backscattering induced by magnetism in a topological edge state

2020 ◽  
Vol 117 (28) ◽  
pp. 16214-16218 ◽  
Author(s):  
Berthold Jäck ◽  
Yonglong Xie ◽  
B. Andrei Bernevig ◽  
Ali Yazdani
Keyword(s):  
Time Reversal ◽  
Edge State ◽  
Quantum Spin ◽  
Scanning Tunneling ◽  
Edge States ◽  
Quantum Spin Hall Effect ◽  
Quasiparticle Interference ◽  
Spin Polarized ◽  
Ferromagnetic Iron ◽  
Bilayer Edge

The boundary modes of topological insulators are protected by the symmetries of the nontrivial bulk electronic states. Unless these symmetries are broken, they can give rise to novel phenomena, such as the quantum spin Hall effect in one-dimensional (1D) topological edge states, where quasiparticle backscattering is suppressed by time-reversal symmetry (TRS). Here, we investigate the properties of the 1D topological edge state of bismuth in the absence of TRS, where backscattering is predicted to occur. Using spectroscopic imaging and spin-polarized measurements with a scanning tunneling microscope, we compared quasiparticle interference (QPI) occurring in the edge state of a pristine bismuth bilayer with that occurring in the edge state of a bilayer, which is terminated by ferromagnetic iron clusters that break TRS. Our experiments on the decorated bilayer edge reveal an additional QPI branch, which can be associated with spin-flip scattering across the Brioullin zone center between time-reversal band partners. The observed QPI characteristics exactly match with theoretical expectations for a topological edge state, having one Kramer’s pair of bands. Together, our results provide further evidence for the nontrivial nature of bismuth and in particular, demonstrate backscattering inside a helical topological edge state induced by broken TRS through local magnetism.

scholarly journals Topological gaps by twisting

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Matheus I. N. Rosa ◽  
Massimo Ruzzene ◽  
Emil Prodan
Keyword(s):  
Magnetic Field ◽  
Quantum Hall Effect ◽  
Twist Angle ◽  
Quantum Hall ◽  
Topological Phases ◽  
Edge States ◽  
Layered Systems ◽  
Virtual Laboratories ◽  
Higher Dimensional ◽  
Chern Numbers

AbstractTwisted bilayered systems such as bilayered graphene exhibit remarkable properties such as superconductivity at magic angles and topological insulating phases. For generic twist angles, the bilayers are truly quasiperiodic, a fact that is often overlooked and that has consequences which are largely unexplored. Herein, we uncover that twisted n-layers host intrinsic higher dimensional topological phases, and that those characterized by second Chern numbers can be found in twisted bi-layers. We employ phononic lattices with interactions modulated by a second twisted lattice and reveal Hofstadter-like spectral butterflies in terms of the twist angle, which acts as a pseudo magnetic field. The phason provided by the sliding of the layers lives on 2n-tori and can be used to access and manipulate the edge states. Our work demonstrates how multi-layered systems are virtual laboratories for studying the physics of higher dimensional quantum Hall effect, and can be employed to engineer topological pumps via simple twisting and sliding.

scholarly journals Large discrete jumps observed in the transition between Chern states in a ferromagnetic topological insulator

2016 ◽  
Vol 2 (7) ◽  
pp. e1600167 ◽  
Author(s):  
Minhao Liu ◽  
Wudi Wang ◽  
Anthony R. Richardella ◽  
Abhinav Kandala ◽  
Jian Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Metastable State ◽  
Large Fraction ◽  
Surface States ◽  
Anomalous Hall Effect ◽  
Escape Rate ◽  
Zero Magnetic Field ◽  
Hall Resistance ◽  
Edge States ◽  
Longitudinal Resistance

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 numberC= ±1 (in natural units), even in zero magnetic field. This quantum anomalous Hall effect was observed by Changet 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 (T1~ 70 mK andT2~ 145 mK) exist, between which jumps can be observed. The jumps display a spatial correlation that extends over a large fraction of the sample.

Multiplets at zero magnetic field: The geometry of zero-field NMR

2013 ◽  
Vol 138 (18) ◽  
pp. 184202 ◽  
Author(s):  
Mark C. Butler ◽  
Micah P. Ledbetter ◽  
Thomas Theis ◽  
John W. Blanchard ◽  
Dmitry Budker ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Zero Magnetic Field ◽  
Zero Field

Magnetic Prehistory in the Heat Capacity of the Low-Temperature Superconductors

2015 ◽  
Vol 233-234 ◽  
pp. 741-744
Author(s):  
Sergey Mikhailovich Podgornykh
Keyword(s):  
Magnetic Field ◽  
Heat Capacity ◽  
External Magnetic Field ◽  
Low Temperature ◽  
Temperature Dependence ◽  
Zero Magnetic Field ◽  
Zero Field ◽  
Ring Specimen ◽  
Trapped Flux ◽  
The Magnetic Field

Effect of the magnetic prehistory on the temperature dependence of the heat capacity of the superconducting Pb, La, Sn. has been studied. As soon as the external magnetic field riches the valueHext=HCthe superconductivity is completely destroyed. The trapped flux was produced in the ring specimen after the magnetic field was turned off atT<TC. We observed a difference of the value of the heat capacity between zero field cooled (ZFC) and field cooled (FC) states in zero magnetic field for the ring specimen. It is found that the FC heat capacity is smaller than the heat capacity both in the normal and in superconducting states.

scholarly journals Non-local terahertz photoconductivity in the topological phase of Hg1−xCdxTe

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
A. S. Kazakov ◽  
A. V. Galeeva ◽  
A. I. Artamkin ◽  
A. V. Ikonnikov ◽  
L. I. Ryabova ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Laser Pulses ◽  
Zero Magnetic Field ◽  
Zero Field ◽  
Topological Phase ◽  
Non Local ◽  
Dark Signal ◽  
The Magnetic Field

AbstractWe report on observation of strong non-local photoconducitivity induced by terahertz laser pulses in non-zero magnetic field in heterostructures based on Hg1−xCdxTe films being in the topological phase. While the zero-field non-local photoconductivity is negligible, it is strongly enhanced in magnetic fields ~ 0.05 T resulting in appearance of an edge photocurrent that exceeds the respective dark signal by orders of magnitude. This photocurrent is chiral, and the chirality changes every time the magnetic field or the electric bias is reversed. Appearance of the non-local terahertz photoconductivity is attributed to features of the interface between the topological film and the trivial buffer.

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