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<jats:p>Thermoelectric materials are critical parts in thermal electric devices. Here, Zintl phase BaAgSb in space group of P6<jats:sub>3</jats:sub>/mmc is reported as a promising thermoelectric material in density function theory. The anisotropic lattice thermal conductivity and phonon transport properties are investigated in theory. The strong phonon-phonon scattering in BaAgSb exhibits ultra-low lattice thermal conductivity of 0.59 W⋅m<jats:sup>−1</jats:sup>⋅K<jats:sup>−1</jats:sup> along <jats:italic>c</jats:italic>-axis at 800 K, and high thermoelectric performance ZT = 0.94 at 400 K. The mix of covalent and ionic bond supports high carrier mobility and low thermal conductivity. The unusual features make BaAgSb a potential thermoelectric material.</jats:p>

<jats:p>Tunable carrier density plays a key role in the investigation of novel transport properties in three-dimensional topological semimetals. We demonstrate that the carrier density, as well as the mobility, of Dirac semimetal Cd<jats:sub>3</jats:sub>As<jats:sub>2</jats:sub> nanoplates can be effectively tuned via <jats:italic>in situ</jats:italic> thermal treatment at 350 K for one hour, resulting in non-monotonic evolution by virtue of the thermal cycling treatments. The upward shift of Fermi level relative to the Dirac nodes blurs the surface Fermi-arc states, accompanied by an anomalous phase shift in the oscillations of bulk states, due to a change in the topology of the electrons. Meanwhile, the oscillation peaks of bulk longitudinal magnetoresistivity shift at high fields, due to their coupling to the oscillations of the surface Fermi-arc states. Our work provides a thermal control mechanism for the manipulation of quantum states in Dirac semimetal Cd<jats:sub>3</jats:sub>As<jats:sub>2</jats:sub> at high temperatures, via their carrier density.</jats:p>

<jats:p>Twisting two layers into a magic angle (MA) of ∼1.1° is found essential to create low energy flat bands and the resulting correlated insulating, superconducting, and magnetic phases in twisted bilayer graphene (TBG). While most of previous works focus on revealing these emergent states in MA-TBG, a study of the twist angle dependence, which helps to map an evolution of these phases, is yet less explored. Here, we report a magneto-transport study on one non-magic angle TBG device, whose twist angle <jats:italic>θ</jats:italic> changes from 1.25° at one end to 1.43° at the other. For <jats:italic>θ</jats:italic> = 1.25° we observe an emergence of topological insulating states at hole side with a sequence of Chern number | <jats:italic>C</jats:italic> | = 4 – | <jats:italic>v</jats:italic> |, where <jats:italic>v</jats:italic> is the number of electrons (holes) in moiré unite cell. When <jats:italic>θ</jats:italic> &gt; 1.25°, the Chern insulator from flat band disappears and evolves into fractal Hofstadter butterfly quantum Hall insulator where magnetic flux in one moiré unite cell matters. Our observations will stimulate further theoretical and experimental investigations on the relationship between electron interactions and non-trivial band topology.</jats:p>

<jats:p>The newly discovered superconductivity in infinite-layer nickelate superconducting films has attracted much attention, largely because their crystalline and electronic structures are similar to those of high-<jats:italic>T</jats:italic> <jats:sub>c</jats:sub> cuprate superconductors. The upper critical field can provide a great deal of information on the subject of superconductivity, but detailed experimental data are still lacking for these films. We present the temperature- and angle-dependence of resistivity, measured under different magnetic fields <jats:italic>H</jats:italic> in Nd<jats:sub>0.8</jats:sub>Sr<jats:sub>0.2</jats:sub>NiO<jats:sub>2</jats:sub> thin films. The onset superconducting transition occurs at about 16.2 K at 0 T. Temperature-dependent upper critical fields, determined using a criterion very close to the onset transition, show a clear negative curvature near the critical transition temperature, which can be explained as a consequence of the paramagnetically limited effect on superconductivity. The temperature-dependent anisotropy of the upper critical field is obtained from resistivity data, which yields a value decreasing from 3 to 1.2 with a reduction in temperature. This can be explained in terms of the variable contribution from the orbital limit effect on the upper critical field. The angle-dependence of resistivity at a fixed temperature, and at different magnetic fields, cannot be scaled to a curve, which deviates from the prediction of the anisotropic Ginzburg–Landau theory. However, at low temperatures, the resistance difference can be scaled via the parameter <jats:italic>H<jats:sup>β</jats:sup> </jats:italic> |cos<jats:italic>θ</jats:italic>| (<jats:italic>β</jats:italic> = 6–1), with <jats:italic>θ</jats:italic> being the angle enclosed between the <jats:italic>c</jats:italic>-axis and the applied magnetic field. As the first detailed study of the upper critical field of nickelate thin films, our results clearly indicate a small anisotropy, and a paramagnetically limited effect, in terms of superconductivity, in nickelate superconductors.</jats:p>

<jats:p>Superconductivity below 0.3 K and a charge-density-wave-like (CDW-like) anomaly at 280 K were observed in EuBiS<jats:sub>2</jats:sub>F recently. Here we report a systematic study of structural and transport properties in Eu<jats:sub>0.5</jats:sub>Ln<jats:sub>0.5</jats:sub>BiS<jats:sub>2</jats:sub>F (<jats:italic>Ln</jats:italic> = La, Ce, Pr, Nd, Sm) by electrical resistivity, magnetization, and specific heat measurements. The lattice constants have a significant change upon rare earth substitution for Eu, suggesting an effective doping. As <jats:italic>Ln</jats:italic> is changed from Sm to La, the superconducting transition temperature <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> increases from 1.55 K to 2.8 K. In contrast to the metallic parent compound, the temperature dependence of electrical resistivity displays semiconducting-like behavior for all the Eu<jats:sub>0.5</jats:sub> <jats:italic>Ln</jats:italic> <jats:sub>0.5</jats:sub>BiS<jats:sub>2</jats:sub>F samples. Meanwhile, the CDW-like anomaly observed in EuBiS<jats:sub>2</jats:sub>F is completely suppressed. Unlike the mixed valence state in the undoped compound, Eu ions in these rare-earth-doped samples are mainly divalent. A specific anomaly at 1.3 K resembling that in EuBiS<jats:sub>2</jats:sub>F suggests the coexistence of superconductivity and spin glass state for Eu<jats:sub>0.5</jats:sub>La<jats:sub>0.5</jats:sub>BiS<jats:sub>2</jats:sub>F. Coexistence of ferromagnetic order and superconductivity is found below 2.2 K in Eu<jats:sub>0.5</jats:sub>Ce<jats:sub>0.5</jats:sub>BiS<jats:sub>2</jats:sub>F samples. Our results supplies a rich diagram showing that many interesting properties can be induced in BiS<jats:sub>2</jats:sub>-based compounds.</jats:p>

<jats:p>Artificial spin ice (ASI) structures have significant technological potential as reconfigurable metamaterials and magnetic storage media. We investigate the field/frequency-dependent magnetic dynamics of a kagome ASI made of 25-nm-thick permalloy nanomagnet elements, combining magnetoresistance (MR) and microscale ferromagnetic resonance (FMR) techniques. Our FMR spectra show a broadband absorption spectrum from 0.2 GHz to 3 GHz at <jats:italic>H</jats:italic> below 0.3 kOe, where the magnetic configuration of the kagome ASI is in the multidomain state, because the external magnetic field is below the obtained coercive field <jats:italic>H</jats:italic> <jats:sub>c</jats:sub> ∼ 0.3 kOe, based on both the low-field range MR loops and simulations, suggesting that the low-field magnetization dynamics of kagome ASI is dominated by a multimode resonance regime. However, the FMR spectra exhibit five distinctive resonance modes at the high-field quasi-uniform magnetization state. Furthermore, our micromagnetic simulations provide additional spatial resolution of these resonance modes, identifying the presence of two high-frequency primary modes, localized in the horizontal and vertical bars of the ASI, respectively; three other low-frequency modes are mutually exclusive and separately pinned at the corners of the kagome ASI by an edge-induced dipolar field. Our results suggest that an ASI structural design can be adopted as an efficient approach for the development of low-power filters and magnonic devices.</jats:p>

<jats:p>The Kitaev spin liquid (KSL) system has attracted tremendous attention in recent years because of its fundamental significance in condensed matter physics and promising applications in fault-tolerant topological quantum computation. Material realization of such a system remains a major challenge in the field due to the unusual configuration of anisotropic spin interactions, though great effort has been made before. Here we reveal that rare-earth chalcohalides REChX (RE = rare earth; Ch = O, S, Se, Te; X = F, Cl, Br, I) can serve as a family of KSL candidates. Most family members have the typical SmSI-type structure with a high symmetry of <jats:inline-formula> <jats:tex-math><?CDATA $R\bar{3}m$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>R</mml:mi> <mml:mover accent="true"> <mml:mn>3</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>m</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_38_4_047502_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, and rare-earth magnetic ions form an undistorted honeycomb lattice. The strong spin-orbit coupling of 4<jats:italic>f</jats:italic> electrons intrinsically offers anisotropic spin interactions as required by the Kitaev model. We have grown the crystals of YbOCl and synthesized the polycrystals of SmSI, ErOF, HoOF and DyOF, and made careful structural characterizations. We carry out magnetic and heat capacity measurements down to 1.8 K and find no obvious magnetic transition in all the samples but DyOF. The van der Waals interlayer coupling highlights the true two-dimensionality of the family which is vital for the exact realization of Abelian/non-Abelian anyons, and the graphene-like feature will be a prominent advantage for developing miniaturized devices. The family is expected to act as an inspiring material platform for the exploration of KSL physics.</jats:p>

<jats:p>Pinched <jats:italic>P</jats:italic>–<jats:italic>E</jats:italic> hysteresis loops have been observed in filled tungsten bronze Ba<jats:sub>4</jats:sub>Eu<jats:sub>2</jats:sub>Ti<jats:sub>4</jats:sub>Nb<jats:sub>6</jats:sub>O<jats:sub>30</jats:sub>, indicating the presence of novel polarization mechanisms. We investigate the evolution of polar order in filled tungsten bronze Ba<jats:sub>4</jats:sub>Eu<jats:sub>2</jats:sub>Ti<jats:sub>4</jats:sub>Nb<jats:sub>6</jats:sub>O<jats:sub>30</jats:sub>, together with its dielectric properties over a wide temperature range, from 50 K to 773 K. The temperature dependences of the dielectric properties exhibit two low-temperature dielectric relaxations, at around 300 K (P1), and 100 K (P2), and a high temperature peak at 588 K with no frequency dispersion, indicating the ferroelectric transition temperature <jats:italic>T</jats:italic> <jats:sub>c</jats:sub>. Pinched <jats:italic>P</jats:italic>–<jats:italic>E</jats:italic> loops are observed in the temperature range between the low temperature relaxation at P1, and the ferroelectric transition. On cooling, the pinched <jats:italic>P</jats:italic>–<jats:italic>E</jats:italic> hysteresis loops open gradually, with increasing remnant polarization (<jats:italic>P</jats:italic> <jats:sub>r</jats:sub>). Two pairs of reversal electric fields indicate two types of polar reversal mechanisms, with an activated energy of 1.41 eV (<jats:italic>E</jats:italic> <jats:sub>1</jats:sub>), and 0.94 eV (<jats:italic>E</jats:italic> <jats:sub>2</jats:sub>), respectively. One corresponds to the field-induced transition from a nonpolar to a polar state, which dominates at a high temperature close to <jats:italic>T</jats:italic> <jats:sub>c</jats:sub>, while the other relates to the reversal of ferroelectric domains which stabilize gradually on cooling. At temperatures below 300 K, the polarization exhibits an evident decrease, probably related to the disruption of the polar order due to the dielectric relaxation at P1.</jats:p>

<jats:p>Kinetic energy (KE) functional is crucial to speed up density functional theory calculation. However, deriving it accurately through traditional physics reasoning is challenging. We develop a generally applicable KE functional estimator for a one-dimensional (1D) extended system using a machine learning method. Our end-to-end solution combines the dimensionality reduction method with the Gaussian process regression, and simple scaling method to adapt to various 1D lattices. In addition to reaching chemical accuracy in KE calculation, our estimator also performs well on KE functional derivative prediction. Integrating this machine learning KE functional into the current orbital free density functional theory scheme is able to provide us with expected ground state electron density.</jats:p>

<jats:p>The non-Hermitian <jats:italic>PT</jats:italic>-symmetric system can live in either unbroken or broken <jats:italic>PT</jats:italic>-symmetric phase. The separation point of the unbroken and broken <jats:italic>PT</jats:italic>-symmetric phases is called the <jats:italic>PT</jats:italic>-phase-transition point. Conventionally, given an arbitrary non-Hermitian <jats:italic>PT</jats:italic>-symmetric Hamiltonian, one has to solve the corresponding Schrödinger equation explicitly in order to determine which phase it is actually in. Here, we propose to use artificial neural network (ANN) to determine the <jats:italic>PT</jats:italic>-phase-transition points for non-Hermitian <jats:italic>PT</jats:italic>-symmetric systems with short-range potentials. The numerical results given by ANN agree well with the literature, which shows the reliability of our new method.</jats:p>