Precision measurement of the quantized anomalous Hall resistance at zero magnetic field

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.

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Intrinsic quantized anomalous Hall effect in a moiré heterostructure

Science ◽

10.1126/science.aay5533 ◽

2019 ◽

Vol 367 (6480) ◽

pp. 900-903 ◽

Cited By ~ 117

Author(s):

M. Serlin ◽

C. L. Tschirhart ◽

H. Polshyn ◽

Y. Zhang ◽

J. Zhu ◽

...

Keyword(s):

Magnetic Field ◽

Energy Gap ◽

Hexagonal Boron Nitride ◽

Magnetic Ordering ◽

Anomalous Hall Effect ◽

Zero Magnetic Field ◽

Strong Interactions ◽

Hall Resistance ◽

Magnetic Memory ◽

Electrical Currents

The quantum anomalous Hall (QAH) effect combines topology and magnetism to produce precisely quantized Hall resistance at zero magnetic field. We report the observation of a QAH effect in twisted bilayer graphene aligned to hexagonal boron nitride. The effect is driven by intrinsic strong interactions, which polarize the electrons into a single spin- and valley-resolved moiré miniband with Chern number C = 1. In contrast to magnetically doped systems, the measured transport energy gap is larger than the Curie temperature for magnetic ordering, and quantization to within 0.1% of the von Klitzing constant persists to temperatures of several kelvin at zero magnetic field. Electrical currents as small as 1 nanoampere controllably switch the magnetic order between states of opposite polarization, forming an electrically rewritable magnetic memory.

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Quantum anomalous Hall edge channels survive up to the Curie temperature

Nature Communications ◽

10.1038/s41467-021-25912-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Kajetan M. Fijalkowski ◽

Nan Liu ◽

Pankaj Mandal ◽

Steffen Schreyeck ◽

Karl Brunner ◽

...

Keyword(s):

Magnetic Field ◽

Curie Temperature ◽

Careful Analysis ◽

Zero Magnetic Field ◽

Hall Resistance ◽

Thermally Activated ◽

Open Questions ◽

Channel Transport ◽

Potential Applications ◽

Non Local

AbstractAchieving metrological precision of quantum anomalous Hall resistance quantization at zero magnetic field so far remains limited to temperatures of the order of 20 mK, while the Curie temperature in the involved material is as high as 20 K. The reason for this discrepancy remains one of the biggest open questions surrounding the effect, and is the focus of this article. Here we show, through a careful analysis of the non-local voltages on a multi-terminal Corbino geometry, that the chiral edge channels continue to exist without applied magnetic field up to the Curie temperature of bulk ferromagnetism of the magnetic topological insulator, and that thermally activated bulk conductance is responsible for this quantization breakdown. Our results offer important insights on the nature of the topological protection of these edge channels, provide an encouraging sign for potential applications, and establish the multi-terminal Corbino geometry as a powerful tool for the study of edge channel transport in topological materials.

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Experimental signatures of nodeless multiband superconductivity in a $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ single crystal

Scientific Reports ◽

10.1038/s41598-021-92709-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Chanhee Kim ◽

Dilip Bhoi ◽

Yeahan Sur ◽

Byung-Gu Jeon ◽

Dirk Wulferding ◽

...

Keyword(s):

Magnetic Field ◽

Single Crystal ◽

Zero Magnetic Field ◽

Anisotropy Ratio ◽

Strong Temperature Dependence ◽

Critical Fields ◽

Band Theory ◽

Plane Field ◽

Low Field ◽

Out Of Plane

AbstractIn order to understand the superconducting gap nature of a $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ 2H-Pd 0.08 TaSe 2 single crystal with $$T_{c} = 3.13 \text { K}$$ T c = 3.13 K , in-plane thermal conductivity $$\kappa $$ κ , in-plane London penetration depth $$\lambda _{\text {L}}$$ λ L , and the upper critical fields $$H_{c2}$$ H c 2 have been investigated. At zero magnetic field, it is found that no residual linear term $$\kappa _{0}/T$$ κ 0 / T exists and $$\lambda _{\text {L}}$$ λ L follows a power-law $$T^n$$ T n (T: temperature) with n = 2.66 at $$T \le \frac{1}{3}T_c$$ T ≤ 1 3 T c , supporting nodeless superconductivity. Moreover, the magnetic-field dependence of $$\kappa _{0}$$ κ 0 /T clearly shows a shoulder-like feature at a low field region. The temperature dependent $$H_{c2}$$ H c 2 curves for both in-plane and out-of-plane field directions exhibit clear upward curvatures near $$T_c$$ T c , consistent with the shape predicted by the two-band theory and the anisotropy ratio between the $$H_{c2}$$ H c 2 (T) curves exhibits strong temperature-dependence. All these results coherently suggest that $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ 2H-Pd 0.08 TaSe 2 is a nodeless, multiband superconductor.

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Imaging the formation and surface phase separation of the CE phase

npj Quantum Materials ◽

10.1038/s41535-021-00353-2 ◽

2021 ◽

Vol 6 (1) ◽

Author(s):

Haibiao Zhou ◽

Qiyuan Feng ◽

Yubin Hou ◽

Masao Nakamura ◽

Yoshinori Tokura ◽

...

Keyword(s):

Magnetic Field ◽

Phase Transitions ◽

Charge Ordering ◽

Zero Magnetic Field ◽

Ferromagnetic Phase ◽

Emergent Properties ◽

Orbital Ordering ◽

Strong Electron ◽

Antiferromagnetic Correlation ◽

Ordering Transitions

AbstractThe CE phase is an extraordinary phase exhibiting the simultaneous spin, charge, and orbital ordering due to strong electron correlation. It is an ideal platform to investigate the role of the multiple orderings in the phase transitions and discover emergent properties. Here, we use a cryogenic high-field magnetic force microscope to image the phase transitions and properties of the CE phase in a Pr0.5Ca0.5MnO3 thin film. In a high magnetic field, we observed a clear suppression of magnetic susceptibility at the charge-ordering insulator transition temperature (TCOI), whereas, at the Néel temperature (TN), no significant change is observed. This observation favors the scenario of strong antiferromagnetic correlation developed below TCOI but raises questions about the Zener polaron paramagnetic phase picture. Besides, we discoverd a phase-separated surface state in the CE phase regime. Ferromagnetic phase domains residing at the surface already exist in zero magnetic field and show ultra-high magnetic anisotropy. Our results provide microscopic insights into the unconventional spin- and charge-ordering transitions and revealed essential attributes of the CE phase, highlighting unusual behaviors when multiple electronic orderings are involved.

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Lower bounds for the first eigenvalue of the Laplacian with zero magnetic field in planar domains

Journal of Functional Analysis ◽

10.1016/j.jfa.2021.108999 ◽

2021 ◽

pp. 108999

Author(s):

Bruno Colbois ◽

Alessandro Savo

Keyword(s):

Magnetic Field ◽

Lower Bounds ◽

Zero Magnetic Field ◽

First Eigenvalue ◽

The First Eigenvalue ◽

Planar Domains

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Colossal anomalous Nernst effect in a correlated noncentrosymmetric kagome ferromagnet

Science Advances ◽

10.1126/sciadv.abf1467 ◽

2021 ◽

Vol 7 (13) ◽

pp. eabf1467

Author(s):

T. Asaba ◽

V. Ivanov ◽

S. M. Thomas ◽

S. Y. Savrasov ◽

J. D. Thompson ◽

...

Keyword(s):

Magnetic Field ◽

Electronic Structure ◽

Theoretical Calculations ◽

Zero Magnetic Field ◽

Nernst Effect ◽

Nodal Lines ◽

Transverse Response ◽

Narrow Bands ◽

Strong Spin ◽

Anomalous Nernst Effect

The transverse voltage generated by a temperature gradient in a perpendicularly applied magnetic field, termed the Nernst effect, has promise for thermoelectric applications and for probing electronic structure. In magnetic materials, an anomalous Nernst effect (ANE) is possible in a zero magnetic field. We report a colossal ANE in the ferromagnetic metal UCo0.8Ru0.2Al, reaching 23 microvolts per kelvin. Uranium’s 5f electrons provide strong electronic correlations that lead to narrow bands, a known route to producing a large thermoelectric response. In addition, uranium’s strong spin-orbit coupling produces an intrinsic transverse response in this material due to the Berry curvature associated with the relativistic electronic structure. Theoretical calculations show that in UCo0.8Ru0.2Al at least 148 Weyl nodes, and two nodal lines, exist within 60 millielectron volt of the Fermi level. This work demonstrates that magnetic actinide materials can host strong Nernst and Hall responses due to their combined correlated and topological nature.

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TRANSPORT PROPERTIES OF 2D ELECTRON GAS IN AN n-InGaAs/GaAs DQW IN A VICINITY OF LOW MAGNETIC-FIELD-INDUCED HALL INSULATOR–QUANTUM HALL LIQUID TRANSITION

International Journal of Nanoscience ◽

10.1142/s0219581x07004523 ◽

2007 ◽

Vol 06 (03n04) ◽

pp. 173-177

Author(s):

YU. G. ARAPOV ◽

S. V. GUDINA ◽

G. I. HARUS ◽

V. N. NEVEROV ◽

N. G. SHELUSHININA ◽

...

Keyword(s):

Magnetic Field ◽

Electron Gas ◽

Quantum Hall ◽

Zero Magnetic Field ◽

Double Quantum ◽

Ballistic Regime ◽

2D Electron Gas ◽

Double Quantum Well ◽

Liquid Transition ◽

Low Magnetic Field

The resistivity (ρ) of low mobility dilute 2D electron gas in an n- InGaAs / GaAs double quantum well (DQW) exhibits the monotonic "insulating-like" temperature dependence (dρ/dT < 0) at T = 1.8–70 K in zero magnetic field. This temperature interval corresponds to a ballistic regime (kBTτ/ħ > 0.1–3.5) for our samples, and the electron density is on an "insulating" side of the so-called B = 0 2D metal–insulator transition. We show that the observed features of localization and Landau quantization in a vicinity of the low magnetic-field-induced insulator–quantum Hall liquid transition is due to the σxy(T) anomalous T-dependence.

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