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<jats:p>We report the experimental production of degenerate Fermi gases of <jats:sup>6</jats:sup>Li atoms in an optical dipole trap. The gray-molasses technique is carried out to decrease the atomic temperature to 57 μK, which facilitates the efficient loading of cold atoms into the optical dipole trap. The Fermi degeneracy is achieved by evaporative cooling of a two-spin mixture of <jats:sup>6</jats:sup>Li atoms on the Feshbach resonance. The degenerate atom number per spin is 3.5 × 10<jats:sup>4</jats:sup>, and the reduced temperature <jats:italic>T</jats:italic>/<jats:italic>T</jats:italic> <jats:sub>F</jats:sub> is as low as 0.1, where <jats:italic>T</jats:italic> <jats:sub>F</jats:sub> is the Fermi temperature of the non-interacting Fermi gas. We also observe the anisotropic expansion of the atom cloud in the strongly interacting regime.</jats:p>

<jats:p>The Magnus Hall effect (MHE) is a new type of linear-response Hall effect, recently proposed to appear in two-dimensional (2D) nonmagnetic systems at zero magnetic field in the ballistic limit. The MHE arises from a self-rotating Bloch electron moving under a gradient-electrostatic potential, analogous to the Magnus effect in the macrocosm. Unfortunately, the MHE is usually accompanied by a trivial transverse signal, which hinders its experimental observation. We systematically investigate the material realization and experimental measurement of the MHE, based on symmetry analysis and first-principles calculations. It is found that both the out-of-plane mirror and in-plane two-fold symmetries can neutralize the trivial transverse signal to generate clean MHE signals. We choose two representative 2D materials, monolayer MoS<jats:sub>2</jats:sub>, and bilayer WTe<jats:sub>2</jats:sub>, to study the quantitative dependency of MHE signals on the direction of the electric field. The results are qualitatively consistent with the symmetry analysis, and suggest that an observable MHE signal requires giant Berry curvatures. Our results provide detailed guidance for the future experimental exploration of MHE.</jats:p>

<jats:p>It has recently been demonstrated that various topological states, including Dirac, Weyl, nodal-line, and triple-point semimetal phases, can emerge in antiferromagnetic (AFM) half-Heusler compounds. However, how to determine the AFM structure and to distinguish different topological phases from transport behaviors remains unknown. We show that, due to the presence of combined time-reversal and fractional translation symmetry, the recently proposed second-order nonlinear Hall effect can be used to characterize different topological phases with various AFM configurations. Guided by the symmetry analysis, we obtain expressions of the Berry curvature dipole for different AFM configurations. Based on the effective model, we explicitly calculate the Berry curvature dipole, which is found to be vanishingly small for the triple-point semimetal phase, and large in the Weyl semimetal phase. Our results not only put forward an effective method for the identification of magnetic orders and topological phases in AFM half-Heusler materials, but also suggest these materials as a versatile platform for engineering the nonlinear Hall effect.</jats:p>

<jats:p>We report an experimental study of electron transport properties of MnSe/(Bi,Sb)<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub> heterostructures, in which MnSe is an antiferromagnetic insulator, and (Bi,Sb)<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub> is a three-dimensional topological insulator (TI). Strong magnetic proximity effect is manifested in the measurements of the Hall effect and longitudinal resistances. Our analysis shows that the gate voltage can substantially modify the anomalous Hall conductance, which exceeds 0.1 <jats:italic>e</jats:italic> <jats:sup>2</jats:sup>/<jats:italic>h</jats:italic> at temperature <jats:italic>T</jats:italic> = 1.6 K and magnetic field <jats:italic>μ</jats:italic> <jats:sub>0</jats:sub> <jats:italic>H</jats:italic> = 5 T, even though only the top TI surface is in proximity to MnSe. This work suggests that heterostructures based on antiferromagnetic insulators provide a promising platform for investigating a wide range of topological spintronic phenomena.</jats:p>

<jats:p>Atomically thin two-dimensional (2D) materials are the building bricks for next-generation electronics and optoelectronics, which demand plentiful functional properties in mechanics, transport, magnetism and photoresponse. For electronic devices, not only metals and high-performance semiconductors but also insulators and dielectric materials are highly desirable. Layered structures composed of 2D materials of different properties can be delicately designed as various useful heterojunction or homojunction devices, in which the designs on the same material (namely homojunction) are of special interest because preparation techniques can be greatly simplified and atomically seamless interfaces can be achieved. We demonstrate that the insulating pristine ZnPS<jats:sub>3</jats:sub>, a ternary transition-metal phosphorus trichalcogenide, can be transformed into a highly conductive metal and an n-type semiconductor by intercalating Co and Cu atoms, respectively. The field-effect-transistor (FET) devices are prepared via an ultraviolet exposure lithography technique. The Co-ZnPS<jats:sub>3</jats:sub> device exhibits an electrical conductivity of 8 × 10<jats:sup>4</jats:sup> S/m, which is comparable to the conductivity of graphene. The Cu-ZnPS<jats:sub>3</jats:sub> FET reveals a current ON/OFF ratio of 10<jats:sup>5</jats:sup> and a mobility of 3 × 10<jats:sup>−2</jats:sup> cm<jats:sup>2</jats:sup>⋅V<jats:sup>−1</jats:sup>⋅s<jats:sup>−1</jats:sup>. The realization of an insulator, a typical semiconductor and a metallic state in the same 2D material provides an opportunity to fabricate n-metal homojunctions and other in-plane electronic functional devices.</jats:p>

<jats:p>The modulation of electrical properties of MoS<jats:sub>2</jats:sub> has attracted extensive research interest because of its potential applications in electronic and optoelectronic devices. Herein, interfacial charge transfer induced electronic property tuning of MoS<jats:sub>2</jats:sub> are investigated by <jats:italic>in situ</jats:italic> ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy measurements. A downward band-bending of MoS<jats:sub>2</jats:sub>-related electronic states along with the decreasing work function, which are induced by the electron transfer from Cs overlayers to MoS<jats:sub>2</jats:sub>, is observed after the functionalization of MoS<jats:sub>2</jats:sub> with Cs, leading to n-type doping. Meanwhile, when MoS<jats:sub>2</jats:sub> is modified with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (<jats:italic>F</jats:italic> <jats:sub>4</jats:sub>-TCNQ), an upward band-bending of MoS<jats:sub>2</jats:sub>-related electronic states along with the increasing work function is observed at the interfaces. This is attributed to the electron depletion within MoS<jats:sub>2</jats:sub> due to the strong electron withdrawing property of <jats:italic>F</jats:italic> <jats:sub>4</jats:sub>-TCNQ, indicating p-type doping of MoS<jats:sub>2</jats:sub>. Our findings reveal that surface transfer doping is an effective approach for electronic property tuning of MoS<jats:sub>2</jats:sub> and paves the way to optimize its performance in electronic and optoelectronic devices.</jats:p>

<jats:p>Recent experiments have demonstrated the realization of the three-dimensional quantum Hall effect in highly anisotropic crystalline materials, such as ZrTe<jats:sub>5</jats:sub> and BaMnSb<jats:sub>2</jats:sub>. Such a system supports chiral surface states in the presence of a strong magnetic field, which exhibit a one-dimensional metal-insulator crossover due to suppression of surface diffusion by disorder potential. We study the nontrivial surface states in a lattice model and find a wide crossover of the level-spacing distribution through a semi-Poisson distribution. We also discover a nonmonotonic evolution of the level statistics due to the disorder-induced mixture of surface and bulk states.</jats:p>

<jats:p>Twisting the stacking of layered materials leads to rich new physics. A three-dimensional topological insulator film hosts two-dimensional gapless Dirac electrons on top and bottom surfaces, which, when the film is below some critical thickness, will hybridize and open a gap in the surface state structure. The hybridization gap can be tuned by various parameters such as film thickness and inversion symmetry, according to the literature. The three-dimensional strong topological insulator Bi(Sb)Se(Te) family has layered structures composed of quintuple layers (QLs) stacked together by van der Waals interaction. Here we successfully grow twistedly stacked Sb<jats:sub>2</jats:sub>Te<jats:sub>3</jats:sub> QLs and investigate the effect of twist angels on the hybridization gaps below the thickness limit. It is found that the hybridization gap can be tuned for films of three QLs, which may lead to quantum spin Hall states. Signatures of gap-closing are found in 3-QL films. The successful <jats:italic>in situ</jats:italic> application of this approach opens a new route to search for exotic physics in topological insulators.</jats:p>

<jats:p>The electronic and superconducting properties of Fe<jats:sub>1–<jats:italic>δ</jats:italic> </jats:sub>Se single-crystal flakes grown hydrothermally are studied by the transport measurements under zero and high magnetic fields up to 38.5 T. The results contrast sharply with those previously reported for nematically ordered FeSe by chemical-vapor-transport (CVT) growth. No signature of the electronic nematicity, but an evident metal-to-nonmetal crossover with increasing temperature, is detected in the normal state of the present hydrothermal samples. Interestingly, a higher superconducting critical temperature <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> of 13.2 K is observed compared to a suppressed <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> of 9 K in the presence of the nematicity in the CVT FeSe. Moreover, the upper critical field in the zero-temperature limit is found to be isotropic with respect to the field direction and to reach a higher value of ∼42 T, which breaks the Pauli limit by a factor of 1.8.</jats:p>

<jats:p>We present the superconducting (SC) property and high-robustness of structural stability of kagome CsV<jats:sub>3</jats:sub>Sb<jats:sub>5</jats:sub> under <jats:italic>in situ</jats:italic> high pressures. For the initial SC-I phase, its <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> is quickly enhanced from 3.5 K to 7.6 K and then totally suppressed at <jats:italic>P</jats:italic> ∼ 10 GPa. With further increasing pressure, an SC-II phase emerges at <jats:italic>P</jats:italic> ∼ 15 GPa and persists up to 100 GPa. The <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> rapidly increases to the maximal value of 5.2 K at <jats:italic>P</jats:italic> = 53.6 GPa and slowly decreases to 4.7 K at <jats:italic>P</jats:italic> = 100 GPa. A two-dome-like variation of <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> in CsV<jats:sub>3</jats:sub>Sb<jats:sub>5</jats:sub> is concluded here. The Raman measurements demonstrate that weakening of <jats:italic>E</jats:italic> <jats:sub>2g</jats:sub> mode and strengthening of <jats:italic>E</jats:italic> <jats:sub>1g</jats:sub> mode occur without phase transition in the SC-II phase, which is supported by the results of phonon spectra calculations. Electronic structure calculations reveal that exertion of pressure may bridge the gap of topological surface nontrivial states near <jats:italic>E</jats:italic> <jats:sub>F</jats:sub>, i.e., disappearance of <jats:italic>Z</jats:italic> <jats:sub>2</jats:sub> invariant. Meanwhile, the Fermi surface enlarges significantly, consistent with the increased carrier density. The findings here suggest that the change of electronic structure and strengthened electron-phonon coupling should be responsible for the pressure-induced reentrant SC.</jats:p>