We investigate polarization-dependent ultrafast photocurrents in the Weyl semimetal TaAs using terahertz (THz) emission spectroscopy. Our results reveal that highly directional, transient ...photocurrents are generated along the noncentrosymmetric c axis regardless of incident light polarization, while helicity-dependent photocurrents are excited within the ab plane. This is consistent with earlier static photocurrent experiments, and demonstrates on the basis of both the physical constraints imposed by symmetry and the temporal dynamics intrinsic to current generation and decay that optically induced photocurrents in TaAs are inherent to the underlying crystal symmetry of the transition metal monopnictide family of Weyl semimetals.
Although topological artificial systems, like acoustic and photonic crystals and cold atoms in optical lattices were initially motivated by simulating topological phases of electronic systems, they ...have their own unique features such as the spinless time-reversal symmetry and tunable Z2 gauge fields. Hence, it is fundamentally important to explore new topological phases based on these features. Here, we point out that the Z2 gauge field leads to two fundamental modifications of the conventional k ⋅ p method: (i) The little co-group must include the translations with nontrivial algebraic relations. (ii) The algebraic relations of the little co-group are projectively represented. These give rise to higher-dimensional irreducible representations and therefore highly degenerate Fermi points. Breaking the primitive translations can transform the Fermi points to interesting topological phases. We demonstrate our theory by two models: a rectangular π -flux model exhibiting graphenelike semimetal phases, and a graphite model with interlayer π flux that realizes the real second-order nodal-line semimetal phase with hinge helical modes. Their physical realizations with a general bright-dark mechanism are discussed. Our finding opens a new direction to explore novel topological phases unique to crystalline systems with gauge fields and establishes the approach to analyze these phases.
Summary
Deficiency of CARD9 (caspase recruitment domain‐containing protein 9) has been reported in individuals with recurrent and invasive fungal infections. We report on a patient who first had ...Trichosporon asahii affecting the skin then Candida albicans infections involving the digestive tract and knee joint, along with elevated serum IgE. After stimulation with C. albicans, peripheral blood mononuclear cells of this patient produced less tumour necrosis factor‐α, interferon‐γ and interleukin‐17 than those of healthy controls. Furthermore, the serum IgE levels of this patient were positively correlated with the severity of fungal infection during the course of treatment. Sanger sequencing identified one homozygous frameshift mutation (p.D274fsX60) in CARD9. We further performed a review including 48 cases with CARD9 deficiency. According to the data published previously, CARD9‐deficient patients demonstrated obviously elevated IgE in serum (median 1300 IU mL−1), which could distinguish them from otherwise healthy people with fungal infections (area under the curve 0·94, P < 0·001). Patients carrying the mutations Q289X and Q295X had a higher mortality rate (24% vs. 0%, P < 0·05). Patients with the mutations R18W, R35Q, R70W, G72S or Y91H in the CARD domain, and the nonsense mutation Q295X in the coiled‐coil domain, seemed to be more prone to Candida infections (90% vs. 20%, P < 0·005) and central nervous system infections (60% vs. 12%, P < 0·005).
What's already known about this topic?
CARD9 deficiency is a rare autosomal recessive genetic defect in T helper 17 immunity, resulting in susceptibility to recurrent and invasive fungal infections.
Patients with genetic defects in T helper 17 immunity are prone to hyper‐IgE syndrome.
What does this study add?
We report a patient with CARD9 p.D274fsX60 mutation manifested as multiple organs infections by Trichosporon asahii and Candida albicans.
This study enriches the phenotypic spectrum of CARD9 deficiency.
IgE level seems to be a possible clue for diagnosis or therapeutic effect of fungal infection in CARD9‐deficient patients.
Rockburst is a sudden and violent failure of rocks and it often occurs in hard rocks in highly stressed ground. Strainburst is classified as one type of rockburst and it often occurs in rocks near or ...at the excavation boundary. Deep insight into the strainburst phenomenon is essential for safe underground construction at depth. In this paper, an experimental laboratory study on the strainburst behavior of Beishan granite is presented. Based on in-situ stress measurement data from the Beishan area in China, a series of tests under different unloading rates were performed to investigate the strainburst process using a true-triaxial strainburst test system which was equipped with an acoustic emission (AE) monitoring system. In addition, a high-speed video camera was used to record and visualize the initiation and ejection of rock fragments as well as the sudden dynamic failure (strainburst) of the test samples. AE characteristics associated with the cumulative energy and frequency–amplitude distributions were analyzed. Characteristics of the microscopic structure of a fragment generated from one test were observed using a scanning electron microscope. The experimental results indicate that the degree of violence during failure and the associated AE energy release in the strainburst process are dependent on the unloading rate. When the unloading rate is high, the rock is prone to strainburst. On the other hand, as the unloading rate decreases, the failure mode changes from strainburst to spalling. In addition, the cumulative AE energy is not sensitive to unloading rates greater than 0.05 MPa/s. When the unloading rate is less than 0.05 MPa/s, the cumulative AE energy shows a marked decreasing trend during rock failure.
Abstract
A recent focus of quantum spin liquid (QSL) studies is how disorder/randomness in a QSL candidate affects its true magnetic ground state. The ultimate question is whether the QSL survives ...disorder or the disorder leads to a “spin-liquid-like” state, such as the proposed random-singlet (RS) state. Since disorder is a standard feature of most QSL candidates, this question represents a major challenge for QSL candidates. YbMgGaO
4
, a triangular lattice antiferromagnet with effective spin-1/2 Yb
3+
ions, is an ideal system to address this question, since it shows no long-range magnetic ordering with Mg/Ga site disorder. Despite the intensive study, it remains unresolved as to whether YbMgGaO
4
is a QSL or in the RS state. Here, through ultralow-temperature thermal conductivity and magnetic torque measurements, plus specific heat and DC magnetization data, we observed a residual
κ
0
/
T
term and series of quantum spin state transitions in the zero temperature limit for YbMgGaO
4
. These observations strongly suggest that a QSL state with itinerant excitations and quantum spin fluctuations survives disorder in YbMgGaO
4
.
Abstract
The most fascinating feature of certain two-dimensional (2D) gapless quantum spin liquid (QSL) is that their spinon excitations behave like the fermionic carriers of a paramagnetic metal. ...The spinon Fermi surface is then expected to produce a linear increase of the thermal conductivity with temperature that should manifest via a residual value (
κ
0
/
T
) in the zero-temperature limit. However, this linear in
T
behavior has been reported for very few QSL candidates. Here, we studied the ultralow-temperature thermal conductivity of an effective spin-1/2 triangular QSL candidate Na
2
BaCo(PO
4
)
2
, which has an antiferromagnetic order at very low temperature (
T
N
~ 148 mK), and observed a finite
κ
0
/
T
extrapolated from the data above
T
N
. Moreover, while approaching zero temperature, it exhibits series of quantum spin state transitions with applied field along the
c
axis. These observations indicate that Na
2
BaCo(PO
4
)
2
possibly behaves as a gapless QSL with itinerant spin excitations above
T
N
and its strong quantum spin fluctuations persist below
T
N
.
A copper-based catalyst supported on carbon microspheres prepared by using the spray drying method has exhibited interesting Fenton-like catalytic properties for the degradation of Methyl Orange, ...Methyl Blue, and Rhodamine B in aqueous solution. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) data suggested that the catalyst consisted of copper particles covered by cuprous oxide. The influence of initial pH, reaction temperature, dosage of catalyst, and H2O2 concentration on the catalyst performance were investigated. Under optimum reaction conditions, the Behnajady–Modirshahla–Ghanbery kinetics model was observed to fit well with the experimental data. It was also observed that hydroxyl radical (HO•) formed from the reaction between hydrogen peroxide (H2O2) and cuprous (Cu+) species was responsible for the dye degradation under acidic conditions. This work provides new insights into the mechanism and kinetics of low-valence copper–carbon composite Fenton-like catalyst for degrading organic dyes.
Symmetry plays a key role in modern physics, as manifested in the revolutionary topological classification of matter in the past decade. So far, we seem to have a complete theory of topological ...phases from internal symmetries as well as crystallographic symmetry groups. However, an intrinsic element, i.e., the gauge symmetry in physical systems, has been overlooked in the current framework. Here, we show that the algebraic structure of crystal symmetries can be projectively enriched due to the gauge symmetry, which subsequently gives rise to new topological physics never witnessed under ordinary symmetries. We demonstrate the idea by theoretical analysis, numerical simulation, and experimental realization of a topological acoustic lattice with projective translation symmetries under a Z_{2} gauge field, which exhibits unique features of rich topologies, including a single Dirac point, Möbius topological insulator, and graphenelike semimetal phases on a rectangular lattice. Our work reveals the impact when gauge and crystal symmetries meet together with topology and opens the door to a vast unexplored land of topological states by projective symmetries.
The application of semiconductors in water treatment via photocatalysis of various pollutants has attracted much attention from researchers. In this work, photocatalytic degradation of methylene blue ...by P25 titanium dioxide was studied experimentally and then via modeling. The effects of lamp choice, concentration of catalyst, and methylene blue were analyzed. Desorption of methylene blue at the start of light radiation was observed, and analyzed in detail for the first time. Both desorption and degradation processes were modeled, and experimental data was fitted to a pseudo-first-order model with sufficient accuracy. The effects of catalyst and initial dye concentration on reaction rate constants were discussed.
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