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    Transport properties of topological nodal-line semimetal candidate CaAs3 under hydrostatic pressure
    Jing Li(李婧), Ling-Xiao Zhao(赵凌霄), Yi-Yan Wang(王义炎), Xin-Min Wang(王欣敏), Chao-Yang Ma(麻朝阳), Wen-Liang Zhu(朱文亮), Mo-Ran Gao(高默然), Shuai Zhang(张帅), Zhi-An Ren(任治安), Gen-Fu Chen(陈根富)
    Chin. Phys. B, 2019, 28 (4): 046202.   DOI: 10.1088/1674-1056/28/4/046202
    Abstract565)   HTML    PDF (1518KB)(260)      

    We report the transport properties of the CaAs3 single crystal, which has been predicted to be a candidate for topological nodal-line semimetals. At ambient pressure, CaAs3 exhibits semiconducting behavior with a small gap, while in some crystals containing tiny defects or impurities, a large “hump” in the resistivity is observed around 230 K. By applying hydrostatic pressure, the samples appear to a tendency towards metallic behavior, but not fully metallized up to 2 GPa. Further high pressure studies are needed to explore the topological characteristics for CaAs3.

    Optical investigation of topological semimetal SrMnSb2
    Zi-Yang Qiu(邱子阳), Zhi-Yu Liao(廖知裕), Xiang-Gang Qiu(邱祥冈)
    Chin. Phys. B, 2019, 28 (4): 047801.   DOI: 10.1088/1674-1056/28/4/047801
    Abstract530)   HTML    PDF (777KB)(182)      

    We investigate the temperature-dependent infrared spectroscopy of SrMnSb2, which is a semimetal with multiple Fermi surfaces. A notable blue shift of the plasma minimum in reflectivity upon cooling indicates that the carrier density varies with temperature. In the real part of the optical conductivity σ1(ω), a linearly-increased component which extrapolates to zero conductivity at finite frequency has been identified, which suggests dispersion of gapped Dirac band structures near the Fermi level. A two-Drude model, representing two different types of carriers, is introduced to describe the real part of optical conductivity. We separate the contributions of two-Drude model in dc conductivity, and demonstrate that the transport properties of SrMnSb2 are mainly affected by the narrow-Drude quasiparticles. Compared with the similar phenomena observed in CaMnSb2 and SrMnBi2, we can infer that the two-Drude model is an appropriate approach to investigate the multiband materials in AMnSb2 and AMnBi2 families.

    Tunable Weyl fermions and Fermi arcs in magnetized topological crystalline insulators
    Junwei Liu(刘军伟), Chen Fang(方辰), Liang Fu(傅亮)
    Chin. Phys. B, 2019, 28 (4): 047301.   DOI: 10.1088/1674-1056/28/4/047301
    Abstract513)   HTML    PDF (3560KB)(325)      

    Based on k·p analysis and realistic tight-binding calculations, we find that time-reversal-breaking Weyl semimetals can be realized in magnetically-doped (Mn, Eu, Cr, etc.) Sn1-xPbx(Te, Se) class of topological crystalline insulators. All the Weyl points are well separated in momentum space and possess nearly the same energy due to high crystalline symmetry. Moreover, both the Weyl points and Fermi arcs are highly tunable by varying Pb/Sn composition, pressure, magnetization, temperature, surface potential, etc., opening up the possibility of manipulating Weyl points and rewiring the Fermi arcs.

    Local evolutions of nodal points in two-dimensional systems with chiral symmetry
    Peiyuan Fu(符培源), Zhesen Yang(杨哲森), Jiangping Hu(胡江平)
    Chin. Phys. B, 2019, 28 (7): 077101.   DOI: 10.1088/1674-1056/28/7/077101
    Abstract351)   HTML    PDF (1736KB)(215)      

    Two-dimensional systems with chiral symmetry allow stable discrete band crossings (nodal points) in Brillouin zones. Here we study the local evolutions of these nodal points under chiral symmetry preserving perturbations. We find that these evolutions can be classified by different types of local k·p models around the nodal points. Several concrete examples are calculated to illustrate our results.

    Structural, elastic, and electronic properties of topological semimetal WC-type MX family by first-principles calculation
    Sami Ullah, Lei Wang(王磊), Jiangxu Li(李江旭), Ronghan Li(李荣汉), Xing-Qiu Chen(陈星秋)
    Chin. Phys. B, 2019, 28 (7): 077105.   DOI: 10.1088/1674-1056/28/7/077105
    Abstract466)   HTML    PDF (1649KB)(241)      

    Recently, the non-centrosymmetric WC-type materials (i.e., MoP, ZrTe, TaN, etc) have attracted extensive interest due to the discovery of their topological properties. By means of the first-principles calculations, here we have investigated the structural, thermodynamic, elastic, and electronic properties of the WC-type MX compounds (TiS, TiSe, TiTe, ZrS, ZrSe, ZrTe, HfS, HfSe, and HfTe). Among these nine compounds, five of them (TiS, ZrS, ZrSe0.9, ZrTe, and Hf0.92Se) have been experimentally synthesized to crystallize in the WC-type structure and other four members have never been reported. Our calculations demonstrated that they are all structurally, thermodynamically, and dynamically stable, indicating that all of them should be possibly synthesized. We have also derived their elastic constants of single crystalline and their bulk and shear moduli in terms of the R. Hill approximations. Furthermore, in similarity to ZrTe, all these compounds have been theoretically derived to be topological semimetals. Whereas TiS is unique because of the coexistence of the Dirac nodal lines (DNLs) and sixfold degenerate nodal points (sixfold DNPs), the other eight members are revealed to exhibit coexisted Weyl nodes (WPs) and triply degenerate nodal points (TDNPs). Their electronic and topological properties have been further discussed.

    Scanning tunneling microscopic investigation on morphology of magnetic Weyl semimetal YbMnBi2
    Zhen Zhu(朱朕), Dong Yan(严冬), Xiao-Ang Nie(聂晓昂), Hao-Ke Xu(徐豪科), Xu Yang(杨旭), Dan-Dan Guan(管丹丹), Shiyong Wang(王世勇), Yao-Yi Li(李耀义), Canhua Liu(刘灿华), Jun-Wei Liu(刘军伟), Hui-Xia Luo(罗惠霞), Hao Zheng(郑浩), Jin-Feng Jia(贾金锋)
    Chin. Phys. B, 2019, 28 (7): 077302.   DOI: 10.1088/1674-1056/28/7/077302
    Abstract562)   HTML    PDF (1491KB)(254)      

    YbMnBi2 is a recently discovered time-reversal-symmetry breaking type-Ⅱ Weyl semimetal. However, as a representation of the new category of topological matters, the scanning tunneling microcopy (STM) results on such important material are still absent. Here, we report the STM investigations on the morphology of vacuum cleaved single crystalline YbMnBi2 samples. A hill and valley type of topography is observed on the YbMnBi2 surface, which is consistent with the non-layer nature of its crystal structure. Analysis of STM images yields the information of the index of the vicinal surface. Our results here lay a playground of future atomic scale research on YbMnBi2.

    Electronic structure of correlated topological insulator candidate YbB6 studied by photoemission and quantum oscillation
    T Zhang(张腾), G Li(李岗), S C Sun(孙淑翠), N Qin(秦娜), L Kang(康璐), S H Yao(姚淑华), H M Weng(翁红明), S K Mo, L Li(李璐), Z K Liu(柳仲楷), L X Yang(杨乐仙), Y L Chen(陈宇林)
    Chin. Phys. B, 2020, 29 (1): 017304.   DOI: 10.1088/1674-1056/ab6206
    Abstract448)   HTML    PDF (1772KB)(239)      
    Angle-resolved photoemission spectroscopy (ARPES) and torque magnetometry (TM) measurements have been carried out to study the electronic structures of a correlated topological insulator (TI) candidate YbB6. We observed clear surface states on the [001] surface centered at the Γ and M points of the surface Brillouin zone. Interestingly, the fermiology revealed by the quantum oscillation of TM measurements agrees excellently with ARPES measurements. Moreover, the band structures we observed suggest that the band inversion in YbB6 happens between the Yb5d and B2p bands, instead of the Yb5d and Yb4f bands as suggested by previous theoretical investigation, which will help settle the heavy debate regarding the topological nature of samarium/ytterbium hexaborides.
    Single crystal growth, structural and transport properties of bad metal RhSb2
    D S Wu(吴德胜), Y T Qian(钱玉婷), Z Y Liu(刘子懿), W Wu(吴伟), Y J Li(李延杰), S H Na(那世航), Y T Shao(邵钰婷), P Zheng(郑萍), G Li(李岗), J G Cheng(程金光), H M Weng(翁红明), J L Luo(雒建林)
    Chin. Phys. B, 2020, 29 (3): 037101.   DOI: 10.1088/1674-1056/ab696e
    Abstract537)   HTML    PDF (1974KB)(386)      
    We have successfully grown an arsenopyrite marcasite type RhSb2 single crystal, and systematically investigated its crystal structure, electrical transport, magnetic susceptibility, heat capacity, and thermodynamic properties. We found that the temperature-dependent resistivity exhibits a bad metal behavior with a board peak around 200 K. The magnetic susceptibility of RhSb2 shows diamagnetism from 300 K to 2 K. The low-temperature specific heat shows a metallic behavior with a quite small electronic specific-heat coefficient. No phase transition is observed in both specific heat and magnetic susceptibility data. The Hall resistivity measurements show that the conduction carriers are dominated by electrons with ne = 8.62×1018 cm-3 at 2 K, and the electron carrier density increases rapidly above 200 K without change sign. Combining with ab-initio band structure calculations, we showed that the unusual peak around 200 K in resistivity is related to the distinct electronic structure of RhSb2. In addition, a large thermopower S(T) about -140 μV/K is observed around 200 K, which might be useful for future thermoelectric applications.