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Superhard semiconductors have been long sought after for electronic device applications enduring extreme conditions, such as astronautics, due to their intrinsic toughness, high thermal and chemical stability. Here, we report the superhard p-type semiconductor Al2.69B50 single crystal with the determined Vickers hardness of ~ 40.5 GPa under the load of 0.49 N, being one of the hardest semiconductor compounds that have been ever found. With the direct band gap of 2.3 eV, Al2.69B50 exhibits excellent optical transmittance (> 90%,) covering the visible range from 459 nm to 760 nm and part of infrared range, and also shows high intensity of photon emission in the visible light. Al2.69B50 is very stable, thermally and chemically, with ultra-low density of ～2.52 g/cm3, allowing for further extension of its applications. Such an assembly of various excellent properties within one material has great implication for high power electronic design and applications.

Strongly correlated oxides with a broken symmetry could exhibit various phase transitions, such as superconductivity, magnetism and ferroelectricity. Construction of superlattices using these materials is effective to design crystal symmetries at atomic scale for emergent orderings and phases. Here, antiferromagnetic Ruddlesden-Popper Sr2IrO4 and perovskite paraelectric (ferroelectric) SrTiO3 (BaTiO3) are selected to epitaxially fabricate superlattices for symmetry engineering. An emergent magnetoelectric phase transition is achieved in Sr2IrO4/SrTiO3 superlattices with artificially designed ferroelectricity, where an observable interfacial Dzyaloshinskii-Moriya interaction driven by non-equivalent interface is considered as the microscopic origin. By further increasing the polarization namely interfacial Dzyaloshinskii-Moriya interaction via replacing SrTiO3 with BaTiO3, the transition temperature can be enhanced from 46 K to 203 K, accompanying a pronounced magnetoelectric coefficient of ~495 mV/cm·Oe. This interfacial engineering of Dzyaloshinskii-Moriya interaction provides a strategy to design quantum phases and orderings in correlated electron systems., A controllable magnetoelectric phase based on symmetry engineering is challenge in natural bulk crystals. Here, via engineering of interfacial Dzyaloshinskii-Moriya interaction, the authors design a magnetoelectric phase transition in oxide superlattices of correlated electron systems.

Pedestrian dead reckoning (PDR) is widely used in handheld indoor positioning systems. However, low-cost inertial sensors built into smartphones provide poor-quality measurements, resulting in cumulative error which consists of heading estimation error caused by gyroscope and step length estimation error caused by an accelerometer. Learning more motion features through limited measurements is important to improve positioning accuracy. This paper proposes an improved PDR system using smartphone sensors. Using gyroscope, two motion patterns, walking straight or turning, can be recognised based on dynamic time warp (DTW) and thus improve heading estimation from an extended Kalman filter (EKF). Joint quasi-static field (JQSF) detection is used to avoid bad magnetic measurements due to magnetic disturbances in an indoor environment. In terms of periodicity of angular rate while walking, peak–valley angular velocity detection and zero-cross detection is combined to detect steps. A step-length estimation method based on deep belief network (DBN) is proposed. Experimental results demonstrate that the proposed PDR system can achieve more accurate indoor positioning.

Topologically nontrivial electronic states are recently found in a family of noncentrosymmetric transition metal pnictides TRuX ( T = Zr, Hf; X = P, As), presenting a unique platform for superconductivity to interplay with topological electronic states and asymmetric spin–orbit coupling. Here, we investigate the superconducting order parameter of HfRuP and ZrRuAs by measuring the magnetic penetration depth change Δ λ ( T ) using a method based on the tunnel-diode oscillator. Both compounds show clear exponential temperature dependence in Δ λ ( T ) at low temperatures, suggesting fully-gapped superconductivity. Moreover, the superfluid densities in both HfRuP and ZrRuAs can be reasonably described by an s-wave superconducting model.

5d族过渡金属氧化物具有强自旋轨道耦合作用, 可以衍生出诸多量子现象, 例如, Sr2IrO4是强自旋轨道耦合导致的Mott绝缘体. 为了研究Sr2IrO4新奇的电子结构和伴随的功能性, 亟待调控其Mott能带. 本文中, 我们利用激光辅助分子束外延, 在单晶SrTiO3 衬底上外延制备了高质量的Sr2IrO4薄膜和Sr2IrO4/SrTiO3超晶格. 电输运测试表明, 热激发和Mott可变程跃迁两种传导机制分别适用于Sr2IrO4薄膜和Sr2IrO4/SrTiO3超晶格. 这种传导机制的转变表明Sr2IrO4/SrTiO3界面电子结构发生了重构. 此外, Sr2IrO4/SrTiO3 超晶格的带隙从270.7–81.4 meV的显著调控可能源自Ir–O–Ti界面 电子去局域化导致的能带展宽. 本研究表明, 超晶格界面工程可在原子尺度上有效地调控强关联氧化物的电子结构.

Superhard semiconductors have been long sought after for electronic device applications enduring extreme conditions, such as astronautics, due to their intrinsic toughness, high thermal and chemical stability. Here, we report the superhard p-type semiconductor Al

Single crystals of PrFe

All van der Waals (vdW) Fe3GeTe2/Cr2Ge2Te6/graphite magnetic heterojunctions have been fabricated via mechanical exfoliation and stacking, and their magnetotransport properties are studied in detail. At low bias voltages large negative junction magnetoresistances have been observed and are attributed to spin-conserving tunneling transport across the insulating Cr2Ge2Te6 layer. With increasing bias, a crossover to Fowler-Nordheim tunneling takes place. The negative sign of the tunneling magnetoresistance (TMR) suggests that the bottom of conduction band in Cr2Ge2Te6 belongs to minority spins, opposite to the findings of some first-principles calculations. This work shows that the vdW heterostructures based on 2D magnetic insulators are a valuable platform to gain further insight into spin polarized tunneling transport, which is the basis for pursuing high performance spintronic devices and a large variety of quantum phenomena., 17 pages, 4 figures. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing

Topological crystalline insulators (TCIs) are insulating electronic states with nontrivial topology protected by crystalline symmetries. Recently, theory has proposed new classes of TCIs protected by rotation symmetries $$\hat C_n$$ C ̂ n , which have surface rotation anomaly evading the fermion doubling theorem, i.e., n instead of 2n Dirac cones on the surface preserving the rotation symmetry. Here, we report the first realization of the $$\hat C_2$$ C ̂ 2 rotation anomaly in a binary compound SrPb. Our first-principles calculations reveal two massless Dirac fermions protected by the combination of time-reversal symmetry $$\hat T$$ T ̂ and $$\hat C_{2y}$$ C ̂ 2 y on the (010) surface. Using angle-resolved photoemission spectroscopy, we identify two Dirac surface states inside the bulk band gap of SrPb, confirming the $$\hat C_2$$ C ̂ 2 rotation anomaly in the new classes of TCIs. The findings enrich the classification of topological phases, which pave the way for exploring exotic behavior of the new classes of TCIs.

Quantum spin Hall (QSH) effect with great promise for the potential application in spintronics and quantum computing has attracted extensive research interest from both theoretical and experimental researchers. Here, we predict monolayer ${\mathrm{Ta}}_{2}{\mathrm{Pd}}_{3}{\mathrm{Te}}_{5}$ can be a QSH insulator based on first-principles calculations. The interlayer binding energy in the layered van der Waals compound ${\mathrm{Ta}}_{2}{\mathrm{Pd}}_{3}{\mathrm{Te}}_{5}$ is $19.6\phantom{\rule{0.16em}{0ex}}\mathrm{meV}/{\AA{}}^{2}$; thus, its monolayer/thin-film structures could be readily obtained by exfoliation. The band inversion near the Fermi level (${E}_{F}$) is an intrinsic characteristic, which happens between $\mathrm{Ta}\text{\ensuremath{-}}5d$ and $\mathrm{Pd}\text{\ensuremath{-}}4d$ orbitals without spin-orbit coupling (SOC). The SOC effect opens a global gap and makes the system a QSH insulator. With the $d\text{\ensuremath{-}}d$ band-inverted feature, the nontrivial topology in monolayer ${\mathrm{Ta}}_{2}{\mathrm{Pd}}_{3}{\mathrm{Te}}_{5}$ is characterized by the time-reversal topological invariant ${\mathbb{Z}}_{2}=1$, which is computed by the one-dimensional (1D) Wilson loop method as implemented in our first-principles calculations. The helical edge modes are also obtained using surface Green's function method. Our calculations show that the QSH state in ${\mathrm{Ta}}_{2}{M}_{3}{\mathrm{Te}}_{5}$ ($M=\mathrm{Pd}$, Ni) can be tuned by external strain. These monolayers and thin films provide feasible platforms for realizing QSH effect as well as related devices.

Single crystals of PrFe2Ga8 were successfully grown by using Ga self-flux. PrFe2Ga8 crystallizes in the CaCo2Al8-type orthorhombic structure with the space group Pbam (no. 55). By combining the results from the magnetic-susceptibility, specific-heat, and resistivity measurements, we show that PrFe2Ga8 exhibits a magnetic order at 14 K. For H // c, the antiferromagnetic order can be suppressed by magnetic fields. However, the magnetic order is robust against magnetic fields for H ⊥ c. Our results provide basic physical properties of PrFe2Ga8 and will help to further understand the magnetism in this system.

We report the experimental and theoretical studies of a magnetic topological nodal line semimetal candidate HoSbTe. Single crystals of HoSbTe are grown from Sb flux, crystallizing in a tetragonal layered structure (space group: P4/nmm, no.129), in which the Ho-Te bilayer is separated by the square-net Sb layer. The magnetization and specific heat present distinct anomalies at 4 K related to an antiferromagnetic (AFM) phase transition. Meanwhile, with applying magnetic field perpendicular and parallel to the crystallographic c axis, an obvious magnetic anisotropy is observed. Electrical resistivity undergoes a bad-metal-like state below 200 K and reveals a plateau at about 8 K followed by a drop due to the AFM transition. In addition, with the first-principle calculations of band structure, we find that HoSbTe is a topological nodal line semimetal or a weak topological insulator with or without taking the spin-orbit coupling into account, providing a platform to investigate the interplay between magnetic and topological fermionic properties., 7 pages, 6 figures, 2tables

Based on the first-principles calculations and theoretical analysis, we investigate the electronic structures, topological phase transition (TPT), and topological properties of the layered magnetic compound ${\mathrm{MnSb}}_{2}{\mathrm{Te}}_{4}$. We have synthesized a ${\mathrm{MnSb}}_{2}{\mathrm{Te}}_{4}$ sample and determined its crystal structure. It has a crystal similar to that of the magnetic topological insulator ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ but has Mn and Sb site mixing. For the ideal case without such site mixing, our calculation indicates ${\mathrm{MnSb}}_{2}{\mathrm{Te}}_{4}$ is antiferromagnetic (AFM), and there is no band inversion at $\mathrm{\ensuremath{\Gamma}}$. The band inversion can be realized by increasing the spin-orbit coupling (SOC) of Sb by more than $30%$, and this results in a TPT from a trivial AFM insulator to an AFM topological insulator or an axion insulator. The compressive uniaxial strain can also drive a similar TPT if the interlayer distance is shortened by more than $5%$. For the ferromagnetic (FM) case without Mn and Sb site mixing, it is a normal FM insulator. The band inversion can happen when SOC is enhanced by $10%$ or the interlayer distance is decreased by more than $1%$. Thus, FM ${\mathrm{MnSb}}_{2}{\mathrm{Te}}_{4}$ can be tuned to be the simplest type-I Weyl semimetal with only one pair of Weyl nodes on the threefold rotational axis, which is different from the proposal that Mn and Sb site mixing can result in a ferrimagnetic state and a type-II Weyl semimetal state.

We report on low-temperature electron transport properties of MnSb 2 Te 4, a candidate of ferrimagnetic Weyl semimetal. Long-range magnetic order is manifested as a nearly square-shaped hysteresis loop in the anomalous Hall resistance, as well as sharp jumps in the magnetoresistance. At temperatures below 4 K, a lnT-type upturn appears in the temperature dependence of longitudinal resistance, which can be attributed to the electron-electron interaction (EEI), since the weak localization can be excluded by the temperature dependence of magnetoresistance. Although the anomalous Hall resistance exhibits a similar lnT-type upturn in the same temperature range, such correction is absent in the anomalous Hall conductivity. Our work demonstrates that MnSb 2 Te 4 microflakes provide an ideal system to test the theory of EEI correction to the anomalous Hall effect.

We report the synthesis of single-crystal NbC, a transition metal carbide with various unusual properties. Transport, magnetic susceptibility, and specific heat measurements demonstrate that NbC is a conventional superconductor with a superconducting transition temperature ($T_c$) of 11.5 K. Our theoretical calculations show that NbC is a type-II Dirac semimetal with strong Fermi surface nesting, which is supported by our ARPES measurement results. We also observed the superconducting gaps of NbC using angle-resolved photoemission spectroscopy (ARPES) and found some unconventional behaviors. These intriguing superconducting and topological properties, combined with the high corrosion resistance, make NbC an ideal platform for both fundamental research and device applications., Comment: to appear in Physical Review B

Two-dimensional topological insulators (2DTIs), which host the quantum spin Hall (QSH) effect, are one of the key materials in next-generation spintronic devices. To date, experimental evidence of the QSH effect has only been observed in a few materials, and thus, the search for new 2DTIs is at the forefront of physical and materials science. Here, we report experimental evidence of a 2DTI in the van der Waals material Ta$_2$Pd$_3$Te$_5$. First-principles calculations show that each monolayer of Ta$_2$Pd$_3$Te$_5$ is a 2DTI with weak interlayer interactions. Combined transport, angle-resolved photoemission spectroscopy, and scanning tunneling microscopy measurements confirm the existence of a band gap at the Fermi level and topological edge states inside the gap. These results demonstrate that Ta$_2$Pd$_3$Te$_5$ is a promising material for fabricating spintronic devices based on the QSH effect., Comment: 6 pages, 3 figures

In magnetic topological insulators (TIs), the interplay between magnetic order and nontrivial topology can induce fascinating topological quantum phenomena, such as the quantum anomalous Hall effect, chiral Majorana fermions, and axion electrodynamics. Recently, a great deal of attention has been focused on the intrinsic magnetic TIs, where disorder effects can be eliminated to a large extent, which is expected to facilitate the emergence of topological quantum phenomena. Despite intensive efforts, experimental evidence of the topological surface states (SSs) remains elusive. Here, by combining first-principles calculations and angle-resolved photoemission spectroscopy (ARPES) experiments, we reveal that EuSn2As2 is an antiferromagnetic TI with the observation of Dirac SSs consistent with our prediction. We also observe nearly gapless Dirac SSs in antiferromagnetic TIs MnBi2nTe3n+1 (n=1 and 2), which are absent in previous ARPES results. These results provide clear evidence for nontrivial topology of these intrinsic magnetic TIs. Furthermore, we find that the topological SSs show no observable changes across the magnetic transition within the experimental resolution, indicating that the magnetic order has a quite small effect on the topological SSs, which can be attributed to weak hybridization between the localized magnetic moments, from either 4f or 3d orbitals, and the topological electronic states. This finding provides insights for further research that the correlations between magnetism and topological states need to be strengthened to induce larger gaps in the topological SSs, which will facilitate the realization of topological quantum phenomena at higher temperatures.

Recently rare-earth chalcogenides have been revealed as a family of quantum spin liquid (QSL) candidates hosting a large number of members. In this paper we report the crystal growth and magnetic measurements of KErTe$_2$, which is the first member of telluride in the family. Compared to its cousins of oxides, sulfides and selenides, KErTe$_2$ retains the high symmetry of $R\overline{3}m$ and Er$^{3+}$ ions still sit on a perfect triangular lattice. The separation between adjacent magnetic layers is expectedly increased, which further enhances the two dimensionality of the spin system. Specific heat and magnetic susceptibility measurements on KErTe$_2$ single crystals reveal no structural and magnetic transition down to 1.8 K. Most interestingly, the absorption spectrum shows that the charge gap of KErTe$_2$ is roughly 0.93$\pm$0.35 eV, which is the smallest among all the reported members in the family. This immediately invokes the interest towards metallization even superconductivity using the compound.

Topological materials harbor topologically protected boundary states. Recently, TaIrTe

The intertwined charge, spin, orbital, and lattice degrees of freedom could endow 5d compounds with exotic properties. Current interest is focused on electromagnetic interactions in these materials, whereas the important role of lattice geometry remains to be fully recognized. For this sake, we investigate pressure-induced phase transitions in the spin-orbit Mott insulator Sr3Ir2O7 with Raman, electrical resistance, and x-ray diffraction measurements. We reveal an interesting magnetic transition coinciding with a structural transition at 14.4 GPa, but without a concurrent insulator-metal transition. The conventional correlation between magnetic and Mott insulating states is thereby absent. The observed softening of the one-magnon mode can be explained by a reduced tetragonal distortion, while the actual magnetic transition is associated with tilting of the IrO6 octahedra. This work highlights the critical role of lattice frustration in determining the high-pressure phases of Sr3Ir2O7. The ability to control electromagnetic properties via manipulating the crystal structure with pressure promises a new way to explore new quantum states in spin-orbit Mott insulators., 6 pages, 5 figures

Since the discovery of extremely large nonsaturating magnetoresistance (MR) in WTe

Since the discovery of extremely large non-saturating magnetoresistance (MR) in WTe2, much effort has been devoted to understanding the underlying mechanism, which is still under debate. Here, we explicitly identify the dominant physical origin of the large non-saturating MR through in-situ tuning of the magneto-transport properties in thin WTe2 film. With an electrostatic doping approach, we observed a non-monotonic gate dependence of the MR. The MR reaches a maximum (10600%) in thin WTe2 film at certain gate voltage where electron and hole concentrations are balanced, indicating that the charge compensation is the dominant mechanism of the observed large MR. Besides, we show that the temperature dependent magnetoresistance exhibits similar tendency with the carrier mobility when the charge compensation is retained, revealing that distinct scattering mechanisms may be at play for the temperature dependence of magneto-transport properties. Our work would be helpful for understanding mechanism of the large MR in other nonmagnetic materials and offers an avenue for achieving large MR in the non-magnetic materials with electron-hole pockets., 16 pages, 3 figures, accepted by Nano Letters

ZrCo

Exotic properties in single or few layers of van der Waals materials carry great promise for applications in nanoscaled electronics, optoelectronics and flexible devices. The established, distinct examples include extremely high mobility and superior thermal conductivity in graphene, a large direct band gap in monolayer MoS2 and quantum spin Hall effect in WTe2 monolayer, etc. All these exotic properties arise from the electron quantum confinement effect in the two-dimensional limit. Here we report a novel phenomenon due to one-dimensional (1D) confinement of carriers in a layered van der Waals material NbSi0.45Te2 revealed by angle-resolved photoemission spectroscopy, i.e. directional massless Dirac fermions. The 1D behavior of the carriers is directly related to a stripe-like structural modulation with the long-range translational symmetry only along the stripe direction, as perceived by scanning tunneling microscopy experiment. The four-fold degenerated node of 1D Dirac dispersion is essential and independent on band inversion, because of the protection by nonsymmorphic symmetry of the stripe structure. Our study not only provides a playground for investigating the striking properties of the essential directional massless Dirac fermions, but also introduces a unique monomer with 1D long-range order for engineering nano-electronic devices based on heterostructures of layered van der Waals materials., Comment: A revised version published in Nature Materials (2019); 20 pages, 4 figures

Weyl semimetals exhibit exceptional quantum electronic transport due to the presence of topologically-protected band crossings called Weyl nodes. The nodes come in pairs with opposite chirality, but their number and location in momentum space is otherwise material specific. Following the initial discoveries there is now a need for better material realizations, ideally comprising a single pair of Weyl nodes located at or very close to the Fermi level and in an energy window free from other overlapping bands. Here we propose the layered intermetallic EuCd$_2$As$_2$ to be such a system. We show that Weyl nodes in EuCd$_2$As$_2$ are magnetically-induced via exchange coupling, emerging when the Eu spins are aligned by a small external magnetic field. The identification of EuCd$_2$As$_2$ as a model magnetic Weyl semimetal, evidenced here by ab initio calculations, photoemission spectroscopy, quantum oscillations and anomalous Hall transport measurements, opens the door to fundamental tests of Weyl physics.

Barlowite ${\mathrm{Cu}}_{4}{(\mathrm{OH})}_{6}\mathrm{FBr}$ shows three-dimensional (3D) long-range antiferromagnetism, which is fully suppressed in ${\mathrm{Cu}}_{3}\mathrm{Zn}{(\mathrm{OH})}_{6}\mathrm{FBr}$ with a kagome quantum spin liquid ground state. Here we report systematic studies on the evolution of magnetism in the ${\mathrm{Cu}}_{4\ensuremath{-}x}{\mathrm{Zn}}_{x}{(\mathrm{OH})}_{6}\mathrm{FBr}$ system as a function of $x$ to bridge the two limits of ${\mathrm{Cu}}_{4}{(\mathrm{OH})}_{6}\mathrm{FBr}\phantom{\rule{0.28em}{0ex}}(x=0)$ and ${\mathrm{Cu}}_{3}\mathrm{Zn}{(\mathrm{OH})}_{6}\mathrm{FBr}\phantom{\rule{0.28em}{0ex}}(x=1)$. Neutron-diffraction measurements reveal a hexagonal-to-orthorhombic structural change with decreasing temperature in the $x=0$ sample. While confirming the 3D antiferromagnetic nature of low-temperature magnetism, the magnetic moments on some ${\mathrm{Cu}}^{2+}$ sites on the kagome planes are found to be vanishingly small, suggesting strong frustration already exists in barlowite. Substitution of interlayer ${\mathrm{Cu}}^{2+}$ with ${\mathrm{Zn}}^{2+}$ with gradually increasing $x$ completely suppresses the bulk magnetic order at around $x=0.4$ but leaves a local secondary magnetic order up to $x\ensuremath{\sim}0.8$ with a slight decrease in its transition temperature. The high-temperature magnetic susceptibility and specific-heat measurements further suggest that the intrinsic magnetic properties of kagome spin liquid planes may already appear from $xg0.3$ samples. Our results reveal that the ${\mathrm{Cu}}_{4\ensuremath{-}x}{\mathrm{Zn}}_{x}{(\mathrm{OH})}_{6}\mathrm{FBr}$ may be the long-thought experimental playground for the systematic investigations of the quantum phase transition from a long-range antiferromagnet to a topologically ordered quantum spin liquid.

We report the synthesis and physical properties of the single crystals of TaC, which are proposed to hold topological band structure as a topological superconductor (TSC) candidate. Magnetization, resistivity and specific heat measurements are performed and indicate that TaC is bulk superconductor with critical temperature of 10.3 K. TaC is a strongly coupled type-II superconductor and the superconducting state can be well described by s-wave Bardeen–Cooper–Schrieffer theory with a single gap. The upper critical field (H c2) of TaC shows linear temperature dependence, which is quite different from most conventional superconductors and isostructural NbC, which is proposed to manifest topological nodal-loops or type-II Dirac points as well as superconductivity. Our results suggest that TaC would be a new candidate for further research of TSCs.

Being parent materials of two-dimensional (2D) crystals, van der Waals layered materials have received revived interest. In most 2D materials, the interaction between electrons is negligible. Introducing the interaction can give rise to a variety of exotic properties. Here, via intercalating a van der Waals layered compound VS2, we find evidence for electron correlation by extensive magnetic, thermal, electrical, and thermoelectric characterizations. The low temperature Sommerfeld coefficient is 64 mJ⋅K−2⋅mol−1 and the Kadowaki–Woods ratio r KW ∼ 0.20a 0. Both supports an enhancement of the electron correlation. The temperature dependences of the resistivity and thermopower indicate an important role played by the Kondo effect. The Kondo temperature T K is estimated to be around 8 K. Our results suggest intercalation as a potential means to engineer the electron correlation in van der Waals materials, as well as 2D materials.

We report the physical properties, crystalline and magnetic structures of singe crystals of a new layered antiferromagnetic (AFM) material PrPd0.82Bi2. The measurements of magnetic properties and heat capacity indicate an AFM phase transition at T N ∼ 7 K. A large Sommerfeld coefficient of 329.23 mJ⋅mol−1⋅K−2 is estimated based on the heat capacity data, implying a possible heavy-fermion behavior. The magnetic structure of this compound is investigated by a combined study of neutron powder and single-crystal diffraction. It is found that an A-type AFM structure with magnetic propagation wavevector k = (0 0 0) is formed below T N. The Pr3+ magnetic moment is aligned along the crystallographic c-axis with an ordered moment of 1.694(3) μ B at 4 K, which is smaller than the effective moment of the free Pr3+ ion of 3.58 μ B. PrPd0.82Bi2 can be grown as large as 1 mm×1 cm in area with a layered shape, and is very easy to be cleaved, providing a unique opportunity to study the interplay between magnetism, possible heavy fermions, and superconductivity.

A WiFi-received signal strength index (RSSI) fingerprinting-based indoor positioning system (WiFi-RSSI IPS) is widely studied due to advantages of low cost and high accuracy, especially in a complex indoor environment where performance of the ranging method is limited. The key drawback that limits the large-scale deployment of WiFi-RSSI IPS is time-consuming offline site surveys. To solve this problem, we developed a method using multi-mounted devices to construct a lightweight site-survey radio map (LSS-RM) for WiFi positioning. A smartphone was mounted on the foot (Phone-F) and another on the waist (Phone-W) to scan WiFi-RSSI and simultaneously sample microelectromechanical system inertial measurement-unit (MEMS-IMU) readings, including triaxial accelerometer, gyroscope, and magnetometer measurements. The offline site-survey phase in LSS-RM is a client&ndash, server model of a data collection and preprocessing process, and a post calibration process. Reference-point (RP) coordinates were estimated using the pedestrian dead-reckoning algorithm. The heading was calculated with a corner detected by Phone-W and the preassigned site-survey trajectory. Step number and stride length were estimated using Phone-F based on the stance-phase detection algorithm. Finally, the WiFi-RSSI radio map was constructed with the RP coordinates and timestamps of each stance phase. Experimental results show that our LSS-RM method can reduce the time consumption of constructing a WiFi-RSSI radio map from 54 min to 7.6 min compared with the manual site-survey method. The average positioning error was below 2.5 m with three rounds along the preassigned site-survey trajectory. LSS-RM aims to reduce offline site-survey time consumption, which would cut down on manpower. It can be used in the large-scale implementation of WiFi-RSSI IPS, such as shopping malls, hospitals, and parking lots.

Growth of high-quality single crystals is of great significance for research of condensed matter physics. The exploration of suitable growing conditions for single crystals is expensive and time-consuming, especially for ternary compounds because of the lack of ternary phase diagram. Here we use machine learning (ML) trained on our experimental data to predict and instruct the growth. Four kinds of ML methods, including support vector machine (SVM), decision tree, random forest and gradient boosting decision tree, are adopted. The SVM method is relatively stable and works well, with an accuracy of 81% in predicting experimental results. By comparison, the accuracy of laboratory reaches 36%. The decision tree model is also used to reveal which features will take critical roles in growing processes.