Publications by authors named "Qihang Liu"

To generate and manipulate spin-polarized electronic states in solids are crucial for modern spintronics. The textbook routes employ quantum well states or Shockley/topological type surface states whose spin degeneracy is lifted by strong spin-orbit coupling and inversion symmetry breaking at the surface/interface. The resultant spin polarization is usually truncated because of the intertwining between multiple orbitals.

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  • Recent research has identified unconventional antiferromagnets that allow for spin splitting of electronic states, which could significantly advance antiferromagnetic spintronics due to their unique magnetic symmetries.
  • * The study focuses on CrSb, a promising metallic antiferromagnet with a high Néel temperature of 703 K, using techniques like angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) to analyze its electronic structure.
  • * Findings disclose a notable, k-dependent spin splitting of up to 0.8 eV, surpassing traditional spin-orbit coupling effects, suggesting CrSb could contribute to the development of efficient spintronic devices that work at room temperature.
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Background: Studies about the combined effects of gaseous air pollutants and particulate matters are still rare.

Objectives: This study was performed based on baseline survey of the Diverse Life-Course Cohort in the Beijing-Tianjin-Hebei (BTH) Region of North China to evaluate the association of long-term air pollutants with blood pressure and the combined effect of the air pollutants mixture among 32821 natural han population aged 20 years or above.

Methods: Three-year average exposure to air pollutants (PM, PM, PM, O, SO, NO, and CO) and PM components [black carbon (BC), ammonium (NH), nitrate (NO), sulfate (SO), and organic matter (OM)] of residential areas were calculated based on well-validated models.

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Background: The fat-to-muscle mass ratio (FMR), integrating the antagonistic effects of fat and muscle mass, has been suggested as a valuable indicator to assess cardiometabolic health independent of overall adiposity. However, the specific associations of total and regional FMR with cardiometabolic risk are poorly understood. We aimed to examine sex-specific associations of total and regional FMR with single and clustered cardiometabolic risk factors (CRFs).

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  • The kagome spin ice can exhibit frustrated magnetic excitations when local spins are flipped, which can be studied using scanning tunneling microscopy (STM).
  • Applying this technique to the kagome metal HoAgGe, distinct dips in the local tunneling spectrum indicate a strong correlation with the spin ice's magnetic properties, disappearing above the spin ice formation temperature.
  • A two-level spin-flip model is proposed to explain these tunneling dips, highlighting the role of spin-orbit coupling in the emergent excitations of spin ice magnetism in this material.
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In solid state systems, group representation theory is powerful in characterizing the behavior of quasiparticles, notably the energy degeneracy. While conventional group theory is effective in answering yes-or-no questions related to symmetry breaking, its application to determining the magnitude of energy splitting resulting from symmetry lowering is limited. Here, we propose a theory on quasisymmetry and near degeneracy, thereby expanding the applicability of group theory to address questions regarding large-or-small energy splitting.

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Aims: The evidence for joint and independent associations of low muscle mass and low muscle strength with diabetes is limited and mixed. The study aimed to determine the associations of muscle parameters (muscle mass, strength, quality, and sarcopenia) and sarcopenia obesity with diabetes, and the previously unstudied mediating effect of inflammation.

Materials And Methods: A total of 13,420 adults from the 2023 China National Health Survey (CNHS) and 5,380 adults from the 2011-2014 National Health and Nutrition Examination Survey (NHANES) were included in this study.

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  • Photon-photon correlations are crucial for understanding optical coherence, which involves how light waves interact with each other.
  • A new type of quantum light state called photonic dimers has been introduced, where the basic units are pairs of bound photons rather than solo photons like in traditional lasers.
  • This study examines the coherence properties of these photonic-dimer states and their interference patterns in a double-slit experiment, comparing them to those of standard lasers and thermal light sources.
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Spatial, momentum and energy separation of electronic spins in condensed-matter systems guides the development of new devices in which spin-polarized current is generated and manipulated. Recent attention on a set of previously overlooked symmetry operations in magnetic materials leads to the emergence of a new type of spin splitting, enabling giant and momentum-dependent spin polarization of energy bands on selected antiferromagnets. Despite the ever-growing theoretical predictions, the direct spectroscopic proof of such spin splitting is still lacking.

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We review recent progress in the electronic structure study of intrinsic magnetic topological insulators (MnBiTe) · (BiTe) ([Formula: see text]) family. Specifically, we focus on the ubiquitously (nearly) gapless behavior of the topological Dirac surface state observed by photoemission spectroscopy, even though a large Dirac gap is expected because of surface ferromagnetic order. The dichotomy between experiment and theory concerning this gap behavior is perhaps the most critical and puzzling question in this frontier.

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Nontrivial electronic states are attracting intense attention in low-dimensional physics. Though chirality has been identified in charge states with a scalar order parameter, its intertwining with charge density waves (CDW), film thickness, and the impact on the electronic behaviors remain less well understood. Here, using scanning tunneling microscopy, we report a 2 × 2 chiral CDW as well as a strong suppression of the Te-5 hole-band backscattering in monolayer 1-TiTe.

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The long-sought Chern insulators that manifest a quantum anomalous Hall effect are typically considered to occur in ferromagnets. Here, we theoretically predict the realizabilities of Chern insulators in antiferromagnets, in which the magnetic sublattices are connected by symmetry operators enforcing zero net magnetic moment. Our symmetry analysis provides comprehensive magnetic layer point groups that allow antiferromagnetic (AFM) Chern insulators, revealing that an in-plane magnetic configuration is required.

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Background: Studies comparing the effects of different sizes and concentrations of ambient particulate matter (PM) on pulmonary function in different regions and sexes remain sparse.

Objectives: To investigate the associations of different sizes and levels of long-term ambient PM exposure with pulmonary function among people of different sexes in typical areas of South and North China.

Methods: In 2021, a total of 1,592 participants aged 20-73 years were recruited to participate in the pulmonary function test from the baseline survey of the Diverse Life-Course Cohort (DLCC) in typical areas of Guangdong Province and Hebei Province.

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The century-long development of surface sciences has witnessed the discoveries of a variety of quantum states. In the recently proposed "obstructed atomic insulators", symmetric charges are pinned at virtual sites where no real atoms reside. The cleavage through these sites could lead to a set of obstructed surface states with partial electronic occupation.

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Background: Variations in the prevalence and pattern of multimorbidity might be attributable to lifestyle and environmental factors. This study was performed to determine the prevalence of common chronic diseases and to reveal multimorbidity patterns among adults in Guangdong province with Chaoshan, Hakka, and island cultures.

Methods: We used data collected at the baseline survey (April-May 2021) of the Diverse Life-Course Cohort study and included 5,655 participants aged ≥20 years.

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The discovery of hidden spin polarization (HSP) in centrosymmetric nonmagnetic crystals, i.e., spatially distributed spin polarization originated from local symmetry breaking, has promised an expanded material pool for future spintronics.

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Heterostructures composed of the intrinsic magnetic topological insulator MnBiTe and its nonmagnetic counterpart BiTe host distinct surface electronic band structures depending on the stacking order and exposed termination. Here, we probe the ultrafast dynamical response of MnBiTe and MnBiTe following near-infrared optical excitation using time- and angle-resolved photoemission spectroscopy and disentangle surface from bulk dynamics based on density functional theory slab calculations of the surface-projected electronic structure. We gain access to the out-of-equilibrium charge carrier populations of both MnBiTe and BiTe surface terminations of MnBiTe, revealing an instantaneous occupation of states associated with the BiTe surface layer followed by carrier extraction into the adjacent MnBiTe layers with a laser fluence-tunable delay of up to 350 fs.

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An interplay of geometrical frustration and strong quantum fluctuations in a spin-1/2 triangular-lattice antiferromagnet (TAF) can lead to exotic quantum states. Here, we report the neutron-scattering, magnetization, specific heat, and magnetocaloric studies of the recently discovered spin-1/2 TAF NaBaCo(PO), which can be described by a spin-1/2 easy axis XXZ model. The zero-field neutron diffraction experiment reveals an incommensurate antiferromagnetic ground state with a significantly reduced ordered moment of about 0.

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Dirac semimetal is a phase of matter whose elementary excitation is described by the relativistic Dirac equation. In the limit of zero mass, its parity-time symmetry enforces the Dirac fermion in the momentum space, which is composed of two Weyl fermions with opposite chirality, to be non-chiral. Inspired by the flavor symmetry in particle physics, we theoretically propose a massless Dirac-like equation yet linking two Weyl fields with the identical chirality by assuming isospin symmetry, independent of the space-time rotation exchanging the two fields.

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Photonic Fock states are the most basic quantum states of a radiation field, but arbitrary number states are still difficult to produce. Here we propose to use superradiant atoms in a chiral waveguide to generate multi-photon Fock states deterministically. We calculate the explicit forms of the output quantum photonic states and their correlation functions.

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The layer Hall effect describes electrons spontaneously deflected to opposite sides at different layers, which has been experimentally reported in the MnBiTe thin films under perpendicular electric fields. Here, we reveal a universal origin of the layer Hall effect in terms of the so-called hidden Berry curvature, as well as material design principles. Hence, it gives rise to zero Berry curvature in momentum space but non-zero layer-locked hidden Berry curvature in real space.

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The topological magnetoelectric effect (TME) is a hallmark response of the topological field theory, which provides a paradigm shift in the study of emergent topological phenomena. However, its direct observation is yet to be realized due to the demanding magnetic configuration required to gap all surface states. Here, we theoretically propose that axion insulators with a simple ferromagnetic configuration, such as the MnBiTe/(BiTe) family, provide an ideal playground to realize the TME.

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The Diverse Life-Course Cohort (DLCC) is a large-scale prospective study including around 130,000 participants in mainland China. The primary aims of DLCC include contributing to knowledge on noncommunicable chronic disease determinants, particularly cardiometabolic diseases, and exploring the long-term effect of ambient air pollutants or other environmental risk factors on health among all-age populations. The cohort consists of several sub-populations that cover the whole life-course and diverse resources: from premarital to adolescents, adults from workplace and communities ranged from 18 to 93 years old.

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Breaking time reversal symmetry in a topological insulator may lead to quantum anomalous Hall effect and axion insulator phase. MnBiTe is a recently discovered antiferromagnetic topological insulator with ∼ 12.5 K, which is composed of an alternatively stacked magnetic layer (MnBiTe) and nonmagnetic layer (BiTe).

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