The quantized version of the anomalous Hall effect has been predicted to occur in magnetic topological insulators, but the experimental realization has been challenging. Here, we report the observation of the quantum anomalous Hall (QAH) effect in thin films of chromium-doped (Bi,Sb)2Te3, a magnetic topological insulator. At zero magnetic field, the gate-tuned anomalous Hall resistance reaches the predicted quantized value of h/e2, accompanied by a considerable drop in the longitudinal resistance. Under a strong magnetic field, the longitudinal resistance vanishes, whereas the Hall resistance remains at the quantized value. The realization of the QAH effect may lead to the development of low-power-consumption electronics.

Experimental Observation of the Quantum Anomalous Hall Effect in a Magnetic Topological Insulator

This paper gives the 2010 self-consistent set of values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use. The 2010 adjustment takes into account the data considered in the 2006 adjustment as well as the data that became available from 1 January 2007, after the closing date of that adjustment, until 31 December 2010, the closing date of the new adjustment. Further, it describes in detail the adjustment of the values of the constants, including the selection of the final set of input data based on the results of least-squares analyses. The 2010 set replaces the previously recommended 2006 CODATA set and may also be found on the World Wide Web at physics.nist.gov/constants.

/pdf/codata-recommended-values-of-the-fundamental-physical-4bsdant71c.pdf

CODATA Recommended Values of the Fundamental Physical Constants: 2006

The quantum Hall effect (QHE), one example of a quantum phenomenon that occurs on a truly macroscopic scale, has attracted intense interest since its discovery in 1980 and has helped elucidate many important aspects of quantum physics. It has also led to the establishment of a new metrological standard, the resistance quantum. Disappointingly, however, the QHE has been observed only at liquid-helium temperatures. We show that in graphene, in a single atomic layer of carbon, the QHE can be measured reliably even at room temperature, which makes possible QHE resistance standards becoming available to a broader community, outside a few national institutions.

/pdf/room-temperature-quantum-hall-effect-in-graphene-4g4wtfiglq.pdf

Room-Temperature Quantum Hall Effect in Graphene

http://absimage.aps.org/image/MAR07/MWS_MAR07-2006-005868.pdf

Room Temperature Quantum Hall Effect in Graphene

The robustness of edge states against external influence is a phenomenon that has been successfully applied to electron transport. A study now predicts that the same concept can also lead to improved optical devices. Topological protection might, for example, reduce the deleterious influence of disorder on coupled-resonator optical waveguides.

/pdf/robust-optical-delay-lines-with-topological-protection-2e2guxbv33.pdf

Robust optical delay lines with topological protection

The quantum Hall effect (QHE) provides an invariant reference for resistance linked to natural constants It is used worldwide to maintain and compare the unit of resistance The reproducibility reached today is almost two orders of magnitude better than the uncertainty of the determination of the ohm in the international system of units SI In this article, mainly the aspects of the QHE relevant for its metrological application are reviewed After a short introduction of the theoretical models describing the integer QHE, the properties of the devices used in metrology and the measurement techniques are described A detailed summary is given on the measurements carried out to demonstrate the universality of the quantized Hall resistance and to assess all the effects leading to deviations of the Hall resistance from the quantized value In addition, the present and future role of the QHE in the SI and the field of natural constants is discussed

https://iopscience.iop.org/article/10.1088/0034-4885/64/12/201/pdf

The quantum Hall effect as an electrical resistance standard

Over the last 30 years, metrology laboratories have used the quantum behavior of the Josephson effect to greatly improve voltage metrology. The following article reviews the history and present status of the research and development for Josephson voltage standards. Specifically, the technology and performance of voltage standards that have quantum accuracy is explained in detail, as is their impact on a wide range of electrical metrology applications, primarily those for dc and ac voltage measurements. The physics of the Josephson effect will be presented and the importance of quantum-based electrical standards will be discussed. A detailed explanation of the operation of the conventional Josephson voltage standard and its use for dc applications will be presented, including a description of the most important results. The latter sections of this paper describe recent efforts to apply the Josephson effect to ac voltage and other electrical metrology applications. Advanced voltage standard systems have been developed that provide new features such as stable, programmable dc voltages and quantum-accurate ac waveform synthesis. The superconducting technology and integrated circuit designs for these systems will be described. Two different systems have dramatically improved precision measurements for audio-frequency voltages and for electric power metrology.

/pdf/application-of-the-josephson-effect-in-electrical-metrology-3pftntbc5u.pdf

Application of the Josephson effect in electrical metrology

The METAS watt balance project was initiated slightly more than a decade ago. Over this time, the apparatus has been through an uninterrupted series of upgrades that have improved its reliability to a point where continuous series of measurements can be taken fully automatically over periods of several months. A comprehensive analysis of possible systematic errors has now been completed and a large set of data has been analysed to calculate a value for the Planck constant h. This paper describes the watt balance in detail, explains the data acquisition and analysis thoroughly and presents the uncertainty budget. The value of the Planck constant determined with our apparatus is h = 6.626?069?1(20) ? 10?34?J?s with a relative standard uncertainty of 0.29 ? 10?6. This value differs from the 2006 CODATA adjustment by 0.024??W?W?1.

https://iopscience.iop.org/article/10.1088/0026-1394/48/3/007/pdf

Determination of the Planck constant with the METAS watt balance

A two‐coil mutual‐inductance technique for measuring the complex ac response of a two‐dimensional (2‐D) superconductor to a weak ac magnetic field is described. Analytical and numerical methods are presented which allow extraction of the complex ac conductance of the superconductor from the signal voltage induced in the detection coil by the screening currents flowing in the sample. The method is illustrated by measurements of the ac conductance of a square network of aluminum wires from which the penetration depths of both the network and (granular) aluminum are deduced. It is shown that the method provides a powerful tool to observe characteristic features associated with critical phenomena in 2‐D superconducting systems.

Blaise Jeanneret

Papers

The quantum Hall effect as an electrical resistance standard

Application of the Josephson effect in electrical metrology

Determination of the Planck constant with the METAS watt balance

Inductive conductance measurements in two-dimensional superconducting systems

High-precision measurements of the quantized Hall resistance:Experimental conditions for universality