# H. Ding - Jefferson Lab Hall A Collaboration

## Contact Details

NameH. Ding |
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AffiliationJefferson Lab Hall A Collaboration |
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Location |
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## Pubs By Year |
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## Pub CategoriesPhysics - Superconductivity (18) Physics - Materials Science (14) Physics - Strongly Correlated Electrons (13) Physics - Mesoscopic Systems and Quantum Hall Effect (9) High Energy Physics - Lattice (5) High Energy Physics - Phenomenology (4) Nuclear Theory (3) Computer Science - Computer Vision and Pattern Recognition (2) Nuclear Experiment (2) Mathematics - Numerical Analysis (2) Nonlinear Sciences - Chaotic Dynamics (2) Physics - Soft Condensed Matter (1) Physics - Statistical Mechanics (1) Computer Science - Networking and Internet Architecture (1) High Energy Physics - Theory (1) Physics - Accelerator Physics (1) Computer Science - Computational Geometry (1) Computer Science - Data Structures and Algorithms (1) Computer Science - Learning (1) Statistics - Machine Learning (1) |

## Publications Authored By H. Ding

Analyzing the structure of multiple point process observations provides insight into the understanding of complex networks and human activities. In this work, we present Bayesian nonparametric Poisson process allocation (BNPPA), a generative model to automatically infer the number of latent groups in temporal data based on the previous point estimation model, latent Poisson process allocation (LPPA). We derive a variational inference algorithm when incorporating a Dirichlet process prior and adding an integral constraint. Read More

We performed a Raman scattering study of thin films of LiTi$_2$O$_4$ spinel oxide superconductor. We detected four out of five Raman active modes, with frequencies in good accordance with our first-principles calculations. Three T$_{2g}$ modes show a Fano lineshape from 5 K to 295 K, which suggests an electron-phonon coupling in LiTi$_2$O$_4$. Read More

Being a task of establishing spatial correspondences, medical image registration is often formalized as finding the optimal transformation that best aligns two images. Since the transformation is such an essential component of registration, most existing researches conventionally quantify the registration uncertainty, which is the confidence in the estimated spatial correspondences, by the transformation uncertainty. In this paper, we give concrete examples and reveal that using the transformation uncertainty to quantify the registration uncertainty is inappropriate and sometimes misleading. Read More

**Authors:**Wencan Jin, Suresh Vishwanath, Jianpeng Liu, Lingyuan Kong, Rui Lou, Zhongwei Dai, Jerzy T. Sadowski, Xinyu Liu, Huai-Hsun Lien, Alexander Chaney, Yimo Han, Micheal Cao, Junzhang Ma, Tian Qian, Jerry I. Dadap, Shancai Wang, Malgorzata Dobrowolska, Jacek Furdyna, David A. Muller, Karsten Pohl, Hong Ding, Huili Grace Xing, Richard M. Osgood, Jr

**Category:**Physics - Materials Science

Topological crystalline insulators have been recently predicted and observed in rock-salt structure SnSe $\{111\}$ thin films. Previous studies have suggested that the Se-terminated surface of this thin film with hydrogen passivation, has a reduced surface energy and is thus a preferred configuration. In this paper, synchrotron-based angle-resolved photoemission spectroscopy, along with density functional theory calculations, are used to demonstrate conclusively that a rock-salt SnSe $\{111\}$ thin film epitaxially-grown on \ce{Bi2Se3} has a stable Sn-terminated surface. Read More

Real-world relations among entities can often be observed and determined by different perspectives/views. For example, the decision made by a user on whether to adopt an item relies on multiple aspects such as the contextual information of the decision, the item's attributes, the user's profile and the reviews given by other users. Different views may exhibit multi-way interactions among entities and provide complementary information. Read More

The problem of constrained $k$-center clustering has attracted significant attention in the past decades. In this paper, we study balanced $k$-center cluster where the size of each cluster is constrained by the given lower and upper bounds. The problem is motivated by the applications in processing and analyzing large-scale data in high dimension. Read More

Link-flooding attack (LFA) has emerged as a serious threat to Internet which cuts off connections between legitimate hosts and targeted servers by flooding only a few links (e.g., target links). Read More

Ratchet effect can give rise to nonzero mass flux under a zero-mean time-dependent drive. In this paper, we propose a new class of two-dimensional nano-ratchet: multilayer graphene with truncated-cone nanopores (GTCN). By performing molecular dynamics simulations, we find air molecules spontaneously transport to the small pores side of GTCN and form a remarkable pressure difference between the two sides of GTCN. Read More

We report a polarized Raman scattering study of non-symmorphic topological insulator KHgSb with hourglass-like electronic dispersion. Supported by theoretical calculations, we show that the lattice of the previously assigned space group $P6_3/mmc$ (No. 194) is unstable in KHgSb. Read More

In recent years, the capacitated center problems have attracted a lot of research interest. Given a set of vertices $V$, we want to find a subset of vertices $S$, called centers, such that the maximum cluster radius is minimized. Moreover, each center in $S$ should satisfy some capacity constraint, which could be an upper or lower bound on the number of vertices it can serve. Read More

**Authors:**N. Xu, G. Autes, C. E. Matt, B. Q. Lv, M. Y. Yao, F. Bisti, V. N. Strocov, D. Gawryluk, E. Pomjakushina, K. Conder, N. C. Plumb, M. Radovic, T. Qian, O. V. Yazyev, J. Mesot, H. Ding, M. Shi

The Weyl semimetal phase is a recently discovered topological quantum state of matter characterized by the presence of topologically protected degeneracies near the Fermi level. These degeneracies are the source of exotic phenomena, including the realization of chiral Weyl fermions as quasiparticles in the bulk and the formation of Fermi arc states on the surfaces. Here, we demonstrate that these two key signatures show distinct evolutions with the bulk band topology by performing angle-resolved photoemission spectroscopy, supported by first-principle calculations, on transition-metal monophosphides. Read More

We present updated studies on the chiral phase transition in $N_{f}=2+1$ QCD. Simulations have been carried out using Highly Improved Staggered Quarks (HISQ) on lattices with temporal extent $N_{\tau} = 6$ at vanishing baryon chemical potential. We updated our previous study \cite{Ding:2015pmg} by extending the temperature window from (140 MeV, 150 MeV) to (140 MeV, 170 MeV). Read More

In this talk I review the current status of lattice QCD calculations at nonzero temperature and density. I focus on the QCD phase structure and bulk QCD thermodynamics at zero and nonzero chemical potentials. Read More

This paper deals with the energy transport properties of charged particles with time-dependent damping force. Based on the proposed nonlinear dimensionless mapping,the stability and dynamical evolution of the particle system is analyzed with the help of manifold-based analysis approach.It has been found that the particle system possesses two types of energy asymptotic behaviors. Read More

We have performed an angle-resolved photoemission spectroscopy study of BaCr$_2$As$_2$, which has the same crystal structure as BaFe$_2$As$_2$, a parent compound of Fe-based superconductors. We determine the Fermi surface of this material and its band dispersion over 5 eV of binding energy. Very moderate band renormalization (1. Read More

**Authors:**Xun Shi, Zhiqing Han, Pierre Richard, Xianxin Wu, Xiliang Peng, Tian Qian, Shancai Wang, Jiangping Hu, Yujie Sun, Hong Ding

We performed angle-resolved photoemission spectroscopy studies on a series of FeTe$_{1-x}$Se$_{x}$ monolayer films grown on SrTiO$_{3}$. The superconductivity of the films is robust and rather insensitive to the variations of the band position and effective mass caused by the substitution of Se by Te. However, the band gap between the electron- and hole-like bands at the Brillouin zone center decreases towards band inversion and parity exchange, which drive the system to a nontrivial topological state predicted by theoretical calculations. Read More

We calculated the QCD equation of state using Taylor expansions that include contributions from up to sixth order in the baryon, strangeness and electric charge chemical potentials. Calculations have been performed with the Highly Improved Staggered Quark action in the temperature range $T\in [135~{\rm MeV}, 330~{\rm MeV}]$ using up to four different sets of lattice cut-offs corresponding to lattices of size $N_\sigma^3\times N_\tau$ with aspect ratio $N_\sigma/N_\tau=4$ and $N_\tau =6-16$. The strange quark mass is tuned to its physical value and we use two strange to light quark mass ratios $m_s/m_l=20$ and $27$, which in the continuum limit correspond to a pion mass of about $160$ MeV and $140$ MeV espectively. Read More

The Dragon-II linear induction accelerator is able to provide triple-pulse electron beams with an adjustable pulse spacing at the minimum of 300 ns. As a main determinant of the image quality, the X-ray spot size is usually quoted as an evaluation of the resolving power. The pinhole imaging method is applied to measure the two-dimensional spatial distribution of the triple-pulse X-ray source, by which the azimuthal asymmetry of the source can be analyzed. Read More

We investigate the phase structure of QCD with 3 degenerate quark flavors as function of the degenerate quark masses at vanishing baryon number density. We use the Highly Improved Staggered Quarks on lattices with temporal extent $N_{t}=6$ and perform calculations for six values of quark masses, which in the continuum limit correspond to pion masses in the range $80~{\rm MeV} \lesssim m_{\pi} \lesssim 230~$MeV. By analyzing the volume and temperature dependence of the chiral condensate and chiral susceptibility we find no direct evidence for a first order phase transition in this range of pion mass values. Read More

**Authors:**R. Lou, B. -B. Fu, Q. N. Xu, P. -J. Guo, L. -Y. Kong, L. -K. Zeng, J. -Z. Ma, P. Richard, C. Fang, Y. -B. Huang, S. -S. Sun, Q. Wang, L. Wang, Y. -G. Shi, H. C. Lei, K. Liu, H. M. Weng, T. Qian, H. Ding, S. -C. Wang

By employing angle-resolved photoemission spectroscopy combined with first-principles calculations, we performed a systematic investigation on the electronic structure of LaBi, which exhibits extremely large magnetoresistance (XMR), and is theoretically predicted to possess band anticrossing with nontrivial topological properties. Here, the observations of the Fermi-surface topology and band dispersions are similar to previous studies on LaSb [Phys. Rev. Read More

Single monolayer (ML) FeSe films grown on Nb-doped SrTiO3(001) substrates show the highest superconducting transition temperature (TC ~ 100 K) among the iron-based superconductors (iron-pnictide), while TC of bulk FeSe is only ~ 8 K. Antiferromagnetic (AFM) spin fluctuations were proposed to be crucial in iron-pnictides, which has inspired several proposals to understand the FeSe/SrTiO3 system. Although bulk FeSe does not show AFM order, calculations suggest that the parent FeSe/SrTiO3 films are AFM and the AFM interaction could be enhanced at the interface. Read More

**Authors:**B. Q. Lv, Z. -L. Feng, Q. -N. Xu, J. -Z. Ma, L. -Y. Kong, P. Richard, Y. -B. Huang, V. N. Strocov, C. Fang, H. -M. Weng, Y. -G. Shi, T. Qian, H. Ding

Condensed matter systems can host quasiparticle excitations that are analogues to elementary particles such as Majorana, Weyl, and Dirac fermions. Recent advances in band theory have expanded the classification of fermions in crystals, and revealed crystal symmetry-protected electron excitations that have no high-energy counterparts. Here, using angle-resolved photoemission spectroscopy, we demonstrate the existence of a triply degenerate point in the electronic structure of MoP crystal, where the quasiparticle excitations are beyond the Majorana-Weyl-Dirac classification. Read More

**Authors:**D. Rhodes, D. A. Chenet, B. E. Janicek, C. Nyby, Y. Lin, W. Jin, D. Edelberg, E. Mannebach, N. Finney, A. Antony, T. Schiros, T. Klarr, A. Mazzoni, M. Chin, Y. -c Chiu, W. Zheng, Q. R. Zhang, F. Ernst, J. I. Dadap, X. Tong, J. Ma, R. Lou, S. Wang, T. Qian, H. Ding, R. M. Osgood Jr, D. W. Paley, A. M. Lindenberg, P. Y. Huang, A. N. Pasupathy, M. Dubey, J. Hone, L. Balicas

MoTe$_2$ is an exfoliable transition metal dichalcogenide (TMD) which crystallizes in three symmetries, the semiconducting trigonal-prismatic $2H-$phase, the semimetallic $1T^{\prime}$ monoclinic phase, and the semimetallic orthorhombic $T_d$ structure. The $2H-$phase displays a band gap of $\sim 1$ eV making it appealing for flexible and transparent optoelectronics. The $T_d-$phase is predicted to possess unique topological properties which might lead to topologically protected non-dissipative transport channels. Read More

**Authors:**X. Yan, K. Allada, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, P. Bosted, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, W. Chen, K. Chirapatpimol, E. Chudakov, E. Cisbani, J. C. Cornejo, F. Cusanno, M. M. Dalton, W. Deconinck, C. W. de Jager, R. De Leo, X. Deng, A. Deur, H. Ding, P. A. M. Dolph, C. Dutta, D. Dutta, L. El Fassi, S. Frullani, H. Gao, F. Garibaldi, D. Gaskell, S. Gilad, R. Gilman, O. Glamazdin, S. Golge, L. Guo, D. Hamilton, O. Hansen, D. W. Higinbotham, T. Holmstrom, J. Huang, M. Huang, H. F Ibrahim, M. Iodice, X. Jiang, G. Jin, M. K. Jones, J. Katich, A. Kelleher, W. Kim, A. Kolarkar, W. Korsch, J. J. LeRose, X. Li, Y. Li, R. Lindgren, T. Liu, N. Liyanage, E. Long, H. -J. Lu, D. J. Margaziotis, P. Markowitz, S. Marrone, D. McNulty, Z. -E. Meziani, R. Michaels, B. Moffit, C. Munoz Camacho, S. Nanda, A. Narayan, V. Nelyubin, B. Norum, Y. Oh, M. Osipenko, D. Parno, J. -C. Peng, S. K. Phillips, M. Posik, A. J. R. Puckett, X. Qian, Y. Qiang, A. Rakhman, R. Ransome, S. Riordan, A. Saha, B. Sawatzky, E. Schulte, A. Shahinyan, M. H. Shabestari, S. Sirca, S. Stepanyan, R. Subedi, V. Sulkosky, L. -G. Tang, W. A. Tobias, G. M. Urciuoli, I. Vilardi, K. Wang, B. Wojtsekhowski, Y. Wang, X. Yan, H. Yao, Y. Ye, Z. Ye, L. Yuan, X. Zhan, Y. Zhang, Y. -W. Zhang, B. Zhao, Y. X. Zhao, X. Zheng, L. Zhu, X. Zhu, X. Zong

**Category:**Nuclear Experiment

The unpolarized semi-inclusive deep-inelastic scattering (SIDIS) differential cross sections in $^3$He($e,e^{\prime}\pi^{\pm}$)$X$ have been measured for the first time in Jefferson Lab experiment E06-010 performed with a $5.9\,$GeV $e^-$ beam on a $^3$He target. The experiment focuses on the valence quark region, covering a kinematic range $0. Read More

Emergence of collective dynamical chirality (CDC) at mesoscopic scales plays a key role in many formation processes of chiral structures in nature, which may also provide possible routines for people to fabricate complex chiral architectures. So far, most of reported CDCs are found in systems of active objects with individual structure chirality or/and dynamical chirality, and whether CDC can arise from simple and achiral units is still an attractive mystery. Here, we report a spontaneous formation of CDC in a system of both dynamically and structurally achiral particles motivated by active motion of cells. Read More

We aim to study thermodynamical effect of anomalous diffusion on a two-particle system using non-extensive statistics. We consider double two-particle systems, $A$ and $B$, whose q-entropy are $S_{q}$ and\ $% S_{q^{\prime }}$ correspondingly. They both are at temperature $T$. Read More

Relatively small data sets available for expression recognition research make the training of deep networks for expression recognition very challenging. Although fine-tuning can partially alleviate the issue, the performance is still below acceptable levels as the deep features probably contain redun- dant information from the pre-trained domain. In this paper, we present FaceNet2ExpNet, a novel idea to train an expression recognition network based on static images. Read More

**Authors:**S. -F. Wu, P. Richard, H. Ding, H. -H. Wen, Guotai Tan, Meng Wang, Chenglin Zhang, Pengcheng Dai, G. Blumberg

Using polarization-resolved electronic Raman scattering we study under-doped, optimally-doped and over-doped Ba$_{1-x}$K$_{x}$Fe$_2$As$_2$ samples in the normal and superconducting states. We show that low-energy nematic fluctuations are universal for all studied doping range. In the superconducting state, we observe two distinct superconducting pair breaking peaks corresponding to one large and one small superconducting gaps. Read More

**Authors:**W. -L. Zhang, P. Richard, A. van Roekeghem, S. -M. Nie, N. Xu, P. Zhang, H. Miao, S. -F. Wu, J. -X. Yin, B. B. Fu, L. -Y. Kong, T. Qian, Z. -J. Wang, Z. Fang, A. S. Sefat, S. Biermann, H. Ding

We performed an angle-resolved photoemission spectroscopy study of BaMn$_2$As$_2$ and BaMn$_2$Sb$_2$, which are isostructural to the parent compound BaFe$_2$As$_2$ of the 122 family of ferropnictide superconductors. We show the existence of a strongly $k_z$-dependent band gap with a minimum at the Brillouin zone center, in agreement with their semiconducting properties. Despite the half-filling of the electronic 3$d$ shell, we show that the band structure in these materials is almost not renormalized from the Kohn-Sham bands of density functional theory. Read More

It is well known that using high-order numerical algorithms to solve fractional differential equations leads to almost the same computational cost with low-order ones but the accuracy (or convergence order) is greatly improved, due to the nonlocal properties of fractional operators. Therefore, developing some high-order numerical approximation formulas for fractional derivatives play a more important role in numerically solving fractional differential equations. This paper focuses on constructing (generalized) high-order fractional-compact numerical approximation formulas for Riesz derivatives. Read More

We discover a pair of spin-polarized surface bands on the (111) face of grey arsenic by using angle-resolved photoemission spectroscopy (ARPES). In the occupied side, the pair resembles typical nearly-free-electron Shockley states observed on noble-metal surfaces. However, pump-probe ARPES reveals that the spin-polarized pair traverses the bulk band gap and that the crossing of the pair at $\bar\Gamma$ is topologically unavoidable. Read More

**Authors:**Yan-Feng Lv, Wen-Lin Wang, Yi-Min Zhang, Hao Ding, Wei Li, Lili Wang, Ke He, Can-Li Song, Xu-Cun Ma, Qi-Kun Xue

Using a cryogenic scanning tunneling microscopy, we report the observation of topologically nontrivial superconductivity on a single material of \beta-Bi2Pd films grown by molecular beam epitaxy. The superconducting gap associated with spinless odd-parity pairing opens on the surface and appears much larger than the bulk one due to the Dirac-fermion enhanced parity mixing of surface pair potential. Majorana zero modes (MZMs), supported by such superconducting states, are identified at magnetic vortices. Read More

We use electronic Raman scattering to study the low-energy excitations in BaFe$_2$(As$_{0.5}$P$_{0.5}$)$_2$ ($T_c \approx 16$ K) samples. Read More

Fe-K$_{\beta}$ X-ray emission spectroscopy measurements reveal an asymmetric doping dependence of the magnetic moments $\mu_\text{bare}$ in electron- and hole-doped BaFe$_{2}$As$_{2}$. At low temperature, $\mu_\text{bare}$ is nearly constant in hole-doped samples, whereas it decreases upon electron doping. Increasing temperature substantially enhances $\mu_\text{bare}$ in the hole-doped region, which is naturally explained by the theoretically predicted crossover into a spin-frozen state. Read More

Topological Kondo insulators are a new class of topological insulators in which metallic surface states protected by topological invariants reside in the bulk band gap at low temperatures. Unlike other three-dimensional topological insulators, a truly insulating bulk state, which is critical for potential applications in next-generation electronic devices, is guaranteed by many-body effects in the topological Kondo insulator. Furthermore, the system has strong electron correlations that can serve as a testbed for interacting topological theories. Read More

**Authors:**H. Miao, Z. P. Yin, S. F. Wu, J. M. Li, J. Ma, B. -Q. Lv, X. P. Wang, T. Qian, P. Richard, L. -Y. Xing, X. -C. Wang, C. Q. Jin, K. Haule, G. Kotliar, H. Ding

In the iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dxy orbital than on the dxz/yz orbital yield quasi-particles with dxy} orbital character having larger mass renormalization and abnormal temperature evolution. However, the physical origin of this orbital differentiation is debated between the Hund's coupling induced unbinding of spin and orbital degrees of freedom and the Hubbard interaction instigated orbital selective Mott transition. Here we use angle-resolved photoemission spectroscopy to identify an orbital-dependent correlation-induced quasi-particle (QP) anomaly in LiFeAs. Read More

The pairing mechanism of high-temperature superconductivity in cuprates remains the biggest unresolved mystery in condensed matter physics. To solve the problem, one of the most effective approaches is to investigate directly the superconducting CuO2 layers. Here, by growing CuO2 monolayer films on Bi2Sr2CaCu2O8+{\delta} substrates, we identify two distinct and spatially separated energy gaps centered at the Fermi energy, a smaller U-like gap and a larger V-like gap on the films, and study their interactions with alien atoms by low-temperature scanning tunneling microscopy. Read More

The angle-resolved photoemission spectra of the superconductor (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ have been investigated both experimentally and theoretically. Our results explain the previously obscured origins of all salient features of the ARPES response of this paradigm pnictide compound and reveal the origin of the Lifshitz transition. Comparison of calculated ARPES spectra with the underlying DMFT band structure shows an important impact of final state effects, which results for three-dimensional states in a deviation of the ARPES spectra from the true spectral function. Read More

Heteroepitaxial structures based on Bi$_{2}$Te$_{3}$-type topological insulators (TIs) exhibit exotic quantum phenomena. For optimal characterization of these phenomena, it is desirable to control the interface structure during film growth on such TIs. In this process, adatom mobility is a key factor. Read More

**Authors:**X. Shi, Z. -Q. Han, X. -L. Peng, P. Richard, T. Qian, X. -X. Wu, M. -W. Qiu, S. C. Wang, J. P. Hu, Y. -J. Sun, H. Ding

The origin of enhanced superconductivity over 50 K in the recently discovered FeSe monolayer films grown on SrTiO$_{3}$ (STO), as compared to 8 K in bulk FeSe, is intensely debated. As with the ferrochalcogenides A$_{x}$Fe$_{2-y}$Se$_{2}$ and potassium doped FeSe, which also have a relatively high superconducting critical temperature ($T_c$), the Fermi surface (FS) of the FeSe/STO monolayer films is free of hole-like FS, suggesting that a Lifshitz transition by which these hole FSs vanish may help increasing $T_c$. However, the fundamental reasons explaining this increase of $T_c$ remain unclear. Read More

We performed a comprehensive angle-resolved photoemission spectroscopy study of the electronic band structure of LaOFeAs single crystals. We found that samples cleaved at low temperature show an unstable and highly complicated band structure, whereas samples cleaved at high temperature exhibit a stable and clearer electronic structure. Using \emph{in-situ} surface doping with K and supported by first-principles calculations, we identify both surface and bulk bands. Read More

**Authors:**J. -Z. Ma, C. -J. Yi, B. Q. Lv, Z. J. Wang, S. -M. Nie, L. Wang, L. -Y. Kong, Y. -B. Huang, P. Richard, H. -M. Weng, B. A. Bernevig, Y. -G. Shi, T. Qian, H. Ding

Topological insulators (TIs) host novel states of quantum matter, distinguished from trivial insulators by the presence of nontrivial conducting boundary states connecting the valence and conduction bulk bands. Up to date, all the TIs discovered experimentally rely on the presence of either time reversal or symmorphic mirror symmetry to protect massless Dirac-like boundary states. Very recently, it has been theoretically proposed that several materials are a new type of TIs protected by nonsymmorphic symmetry, where glide-mirror can protect novel exotic surface fermions with hourglass-shaped dispersion. Read More

Compared to the the classical first-order Gr\"unwald-Letnikov formula at time $t_{k+1} (\textmd{or}\, t_{k})$, we firstly propose a second-order numerical approximate scheme for discretizing the Riemann-Liouvile derivative at time $t_{k+\frac{1}{2}}$, which is very suitable for constructing the Crank-Niclson technique applied to the time-fractional differential equations. The established formula has the following form $$ \begin{array}{lll} \displaystyle \,_{\mathrm{RL}}{{{\mathrm{D}}}}_{0,t}^{\alpha}u\left(t\right)\left|\right._{t=t_{k+\frac{1}{2}}}= \tau^{-\alpha}\sum\limits_{\ell=0}^{k} \varpi_{\ell}^{(\alpha)}u\left(t_k-\ell\tau\right) +\mathcal{O}(\tau^2),\,\,k=0,1,\ldots, \alpha\in(0,1), \end{array} $$ where the coefficients $\varpi_{\ell}^{(\alpha)}$ $(\ell=0,1,\ldots,k)$ can be determined via the following generating function $$ \begin{array}{lll} \displaystyle G(z)=\left(\frac{3\alpha+1}{2\alpha}-\frac{2\alpha+1}{\alpha}z+\frac{\alpha+1}{2\alpha}z^2\right)^{\alpha},\;|z|<1. Read More

In CaFe2As2, superconductivity can be achieved by applying a modest c-axis pressure of several kbar. Here we use scanning tunneling microscopy/spectroscopy (STM/S) to explore the STM tip pressure effect on single crystals of CaFe2As2. When performing STM/S measurements, the tip-sample interaction can be controlled to act repulsive with reduction of the junction resistance, thus to apply a tip pressure on the sample. Read More

**Authors:**L. -K. Zeng, R. Lou, D. -S. Wu, Q. N. Xu, P. -J. Guo, L. -Y. Kong, Y. -G. Zhong, J. -Z. Ma, B. -B. Fu, P. Richard, P. Wang, G. T. Liu, L. Lu, Y. -B. Huang, C. Fang, S. -S. Sun, Q. Wang, L. Wang, Y. -G. Shi, H. M. Weng, H. -C. Lei, K. Liu, S. -C. Wang, T. Qian, J. -L. Luo, H. Ding

By combining angle-resolved photoemission spectroscopy and quantum oscillation measurements, we performed a comprehensive investigation on the electronic structure of LaSb, which exhibits near-quadratic extremely large magnetoresistance (XMR) without any sign of saturation at magnetic fields as high as 40 T. We clearly resolve one spherical and one intersecting-ellipsoidal hole Fermi surfaces (FSs) at the Brillouin zone (BZ) center $\Gamma$ and one ellipsoidal electron FS at the BZ boundary $X$. The hole and electron carriers calculated from the enclosed FS volumes are perfectly compensated, and the carrier compensation is unaffected by temperature. Read More

**Authors:**N. R. Davies, R. D. Johnson, A. J. Princep, L. A. Gannon, J. -Z. Ma, T. Qian, P. Richard, H. Li, H. Nowell, P. J. Baker, Y. G. Shi, H. Ding, J. Luo, Y. F. Guo, A. T. Boothroyd

**Category:**Physics - Superconductivity

We report single crystal X-ray diffraction measurements on Na$_2$Ti$_{2}Pn_{2}$O ($Pn$ = As, Sb) which reveal a charge superstructure that appears below the density wave transitions previously observed in bulk data. From symmetry-constrained structure refinements we establish that the associated distortion mode can be described by two propagation vectors, ${\bf q}_{1} = (1/2, 0, l)$ and ${\bf q}_{2} = (0, 1/2, l)$, with $l=0$ (Sb) or $l = 1/2$ (As), and primarily involves in-plane displacements of the Ti atoms perpendicular to the Ti--O bonds. The results provide direct evidence for phonon-assisted charge density wave order in Na$_2$Ti$_{2}Pn_{2}$O and identify a proximate ordered phase that could compete with superconductivity in doped BaTi$_{2}$Sb$_{2}$O. Read More

We investigate the temperature dependence of the thermal dilepton rate and the electrical conductivity of the gluon plasma at temperatures of $1.1T_c$, $1.3T_c$ and $1. Read More

We performed an angle-resolved photoemission spectroscopy study of the Ni-based superconductor SrNi$_2$As$_2$. Electron and hole Fermi surface pockets are observed, but their different shapes and sizes lead to very poor nesting conditions. The experimental electronic band structure of SrNi$_2$As$_2$ is in good agreement with first-principles calculations after a slight renormalization (by a factor 1. Read More

**Authors:**L. Y. Xing, X. Shi, P. Richard, X. C. Wang, Q. Q. Liu, B. Q. Lv, J. -Z. Ma, B. B. Fu, L. -Y. Kong, H. Miao, T. Qian, T. K. Kim, M. Hoesch, H. Ding, C. Q. Jin

We synthesized a series of V-doped LiFe$_{1-x}$V$_x$As single crystals. The superconducting transition temperature $T_c$ of LiFeAs decreases rapidly at a rate of 7 K per 1\% V. The Hall coefficient of LiFeAs switches from negative to positive with 4. Read More

**Authors:**N. Xu, Z. J. Wang, A. P. Weber, A. Magrez, P. Bugnon, H. Berger, C. E. Matt, J. Z. Ma, B. B. Fu, B. Q. Lv, N. C. Plumb, M. Radovic, E. Pomjakushina, K. Conder, T. Qian, J. H. Dil, J. Mesot, H. Ding, M. Shi

A new type of Weyl semimetal state, in which the energy values of Weyl nodes are not the local extrema, has been theoretically proposed recently, namely type II Weyl semimetal. Distinguished from type I semimetal (e.g. Read More