The phase diagram is characterized by the phase boundaries, BAFM (T) and BQH (T). News. If the 3D bulk states cannot be depleted entirely, they also have a trivial quantum Hall effect. DOI: 10.4236/jmp.2013.411A1003 3,240 Downloads 4,702 Views Citations This article belongs to the Special Issue on Advances in Quantum Physics. The discrepancy is possibly caused by the surface/interface effects that are not theoretically considered. A fundamental question is whether the observed quantized Hall resistance plateau is caused by Landau level quantization, as the ordinary QHE with LLs can also give rise to quantized Hall resistance plateaus and vanishing Rxx. Theoretical calculations of 9-SL FM MnBi2Te4. abstract = "We review recent results concerning the spectrum of edge states in the quantum. With further application of a perpendicular magnetic field, the sample is supposed to enter the perfectly aligned FM state [19]. (f) B-T phase diagram of s3. Typically, the DFT+U method was applied in previous studies of MnBi2Te4 [11,21]. To obtain flakes with thickness down to several nanometers, we heated the substrate after covering the scotch tape at 393 K (120°C) for one minute. The back gate voltages were applied by a Kethiley 2912A source meter. S9). increases by 1 for every |$\Delta N = 4$| (Fig. The green and orange arrowed lines depict the edge states of the 3D quantum Hall effect. Figure 1d and e displays the gate-dependent magneto-transport properties of s6 under perpendicular magnetic field at T = 2 K. Two sharp transitions at around 3 T and 5 T can be clearly observed on both Rxx and Ryx in Fig. (f) If there were only one surface, as shown in (g), an electron could not be driven by B to perform a complete cyclotron motion, because it cannot take all the momentum angle from 0 to 2π. kx stands for (kx, ky) for the bulk and kx for the surface, respectively. The quantization can be observed in two dimensions because the bulk states in the interior of the sample can be gapped. 3b and e) at various temperatures (the cyan spheres) and the peak value of the Rxx (T) curve (Fig. The main conditions for this phenomenon to be observed are extremely low temperatures and the presence of a … Thouless DJ, Kohmoto M, Nightingale MP et al. Figure 2 shows the temperature evolution of the high-Chern-number QHE without LLs with the Vbg = −19 V. As the temperature increases to 13 K, the height of the Hall resistance plateau stays above 0.97 h/2e2 and Rxx remains below 0.026 h/2e2. The quantum anomalous Hall effect is defined as a quantized Hall effect realized in a system without an external magnetic field. If there were only the top surface (Fig. 1g), the Fermi-arc surface states could not support a complete cyclotron motion in real space (Fig. 1f); then there would be no Landau levels, edge states, or quantum Hall effect. S8) at zero magnetic field (the pink sphere). Temperature dependence of the high-Chern-number QHE without LLs in s6. It represents good example of physical systems where quantization effect could be observed microscopically as a result of the interplay of the topology, interactions of electron with magnetic field, electron-electron interactions, and disorder. The basics are described well but there’s nothing about Chern-Simons theories or the importance of the edge modes. These observations unambiguously demonstrate that the observed quantized Hall resistance plateau has nothing to do with LLs and the quantized Ryx originates from Chern insulator state. More research will be necessary to verify the mechanism and realize the 3D quantum Hall effect in the future. The Fermi surface of the surface states is known as the Fermi arcs (red and blue curves in Fig. 1a–d). Obviously, one would never obtain high Chern number C > 1 in AFM MnBi2Te4. Nevertheless, several questions still hold. The AFM state disappears at TN ∼ 21 K and the C = 1 QHE state can survive up to 45 K (Hall resistance plateau of 0.904 h/e2), much higher than TN. The conventional quantum Hall effect is a particular example of the general relation if one views the electric field as a rate of change of the vector potential. The fractional quantum Hall effect offers an experimental system where this possibility is realized. The carrier Hall mobility of hexagonal boron nitride (hBN) encapsulated InSe flakes can be up to 5000 cm 2 V −1 s −1 at 1.5 K, enabling to observe the quantum Hall effect in a synthesized van der Waals semiconductor. (b) Optical image of the 10-SL MnBi2Te4 device s6. Electrical transport measurements were conducted in a 16T-Physical Property Measurement System (PPMS-16T) from Quantum Design with base temperature T = 1.9 K and magnetic field up to 16 T. Stanford Research Systems SR830 lock-in amplifiers were used to measure longitudinal resistance and Hall signals of the device with an AC bias current of 100 nA at a frequency of 3.777 Hz. 4b, the 9-SL film is a high-Chern-number band insulator with |$C = 2$|⁠. Explore the latest full-text research PDFs, articles, conference papers, preprints and more on QUANTUM HALL EFFECT. 4d), which confirms |$C = 2$|⁠. The red and blue arrows denote magnetic moment directions of Mn ions. The black spots stand for the Weyl nodes. When further increasing Vbg to 10 V, the quantized Hall resistance plateaus remain robust as shown in Fig. Figure 1b shows an optical image of the MnBi2Te4 device (s6) with Hall bar geometry. The quantum anomalous Hall effect is defined as a quantized Hall effect realized in a system without external magnetic field. analyzed the data. Weyl points (WPs) with topological charge of +1 and −1 are denoted by blue and red circles in the top panel, respectively. Here, we construct a different type of fractional quantum Hall system, which has the special property that it lives in fractal dimensions. Furthermore, for the C = 2 devices, the quantized Ryx plateau in device s6 with n-type carriers (Fig. The mobility values range from 100 to 300 cm2 V−1 s−1, which are typically below the critical value for formation of LLs up to 15 T [28]. Remarkably, the magnetic transition results in a topological phase transition from an AFM TI to a ferromagnetic Weyl semimetal in the bulk [11,12], leading to a physical scenario in which Chern insulators with C > 1 are designed [21,25–27]. 3a and b. Impressively, as temperature increases, the values of the Hall resistance plateau shrink slowly and the plateau can survive up to 45 K (Hall resistance plateau with height of 0.904 h/e2), much higher than the Néel temperature TN ∼ 21 K of s2 (Fig. S1f). This book is a compilation of major reprint articles on one of the most intriguing phenomena in modern physics: the quantum Hall effect. The use of the quantum Hall effect was reviewed for the precise measurement of electrical resistance. We show that when modulated into the insulating regime by a small back gate voltage, the nine-layer and ten-layer MnBi2Te4 devices can be driven to Chern insulator with C = 2 at moderate perpendicular magnetic field. Efforts on high-Chern-number and high-temperature QHE without LLs are still highly desired for exploring emergent physics and low-power-consumption electronics [10]. The 3D quantum Hall effect may be realized in other systems with novel surface states. The substrates were pre-cleaned in oxygen plasma for five minutes with ∼60 mtorr pressure. S9), and finally decided to use the experimental value |${c_0} = 13.6$| Å. Y.X. In particular, a special attention is payed to the derivation of the conditions under which gapless edge states exist in the spectrum, of … Therefore, first-principles calculations indicate that high-Chern-number band insulators can be realized in the FM Weyl semimetal MnBi2Te4 by means of quantum confinement. International Center for Quantum Materials, School of Physics, Peking University. The band structure of a topological semimetal looks like a 3D graphene [9–12], with the conduction and valence bands touching at the Weyl nodes (Fig. 1a). Magnetic-Field-Induced Phase Transition and a Possible Quantum Hall Effect in the Quasi-One-Dimensional CDW Organic Conductor HMTSF-TCNQ Standard electron beam lithography in a FEI Helios NanoLab 600i Dual Beam System was used to define electrodes after spin-coating PMMA resist. J.G. 3d and e, Ryx of s3 is 0.997 h/e2 at 1.9 K (Rxx ∼ 0.00006 h/e2), 8 V, and even at 30 K (above Néel temperature TN = 22.5 K), Ryx can reach 0.967 h/e2 (Rxx ∼ 0.0023 h/e2). Quantized Hall resistance h/2e2 accompanied by vanishing longitudinal resistance with the temperature as high as 13 K is observed in the ten-layer device. H.L. 1d) and s7 with p-type carriers (Fig. (Right) The quantum anomalous Hall effect has quantum Hall features without an applied field. The discovery of the Josephson effect and the integer quantum Hall effect (QHE) led to the realization of reproducible and universal voltage and resistance standards directly linked to Planck’s constant and the electron charge. However, in the above-mentioned QHE systems without LLs, only a Hall resistance plateau with C = 1 can be obtained by coupling topological surface states with magnetism. The AFM state disappears at TN ∼ 22.5 K and the well-defined quantization can stay till 30 K (Hall resistance plateau of 0.967 h/e2). 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