NMR Evidence of Antiferromagnetic Spin Fluctuations in Nd_(0.85)Sr_(0.15)NiO_(2)

Despite the recent discovery of superconductivity in Nd_(1-x)Sr_(x)NiO_(2) thin films,the absence of superconductivity and antiferromagnetism in their bulk materials remains a puzzle.Here we report the 1H NMR measurements on powdered Nd0.85Sr0.15NiO2 samples by taking advantage of the enriched proton concentration after hydrogen annealing.We find a large full width at half maximum of the spectrum,which keeps increasing with decreasing the temperature T and exhibits an upturn behavior at low temperatures.The spin-lattice relaxation rate ^(1)T_(1)^(-1) is strongly enhanced when lowering the temperature,developing a broad peak at about 40 K,then decreases following a spin-wave-like behavior ^(1)T_(1)^(-1)∝T^(2) at lower temperatures.These results evidence a short-range glassy antiferromagnetic ordering of magnetic moments below 40 K and dominant antiferromagnetic fluctuations extending to much higher temperatures.Our findings reveal the strong electron correlations in bulk Nd_(0.85)Sr_(0.15)NiO_(2),and shed light on the mechanism of superconductivity observed in films of nickelates.

Hybridization Effects Revealed by Angle-Resolved Photoemission Spectroscopy in Heavy-Fermion Ce2IrIn8

We utilize high-resolution resonant angle-resolved photoemission spectroscopy(ARPES)to study the band structure and hybridization effect of the heavy-fermion compound Ce2 IrIn8.We observe a nearly flat band at the binding energy of 7 meV below the coherent temperature Tcoh^40 K,which characterizes the electrical resistance maximum and indicates the onset temperature of hybridization.However,the Fermi vector and the Fermi surface volume have little change around Tcoh,which challenges the widely believed evolution from a hightemperature small Fermi surface to a low-temperature large Fermi surface.Our experimental results of the band structure fit well with the density functional theory plus dynamic mean-field theory calculations.

Nonlinear uniaxial pressure dependence of the resistivity in Sr_(1-x)Ba_xFe_(1.97)Ni_(0.03)As_2

Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr1 _xBaxFel.97Nio.03As2, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Srl xBaxFe2As2 is determined by the strength of the magnetic-elastic coupling.

Brillouin gain spectrum characterization in Ge-doped large-mode-area fibers

The dependence of Brillouin gain spectrum(BGS)characteristics,including the Brillouin frequency shift(BFS)and the BGS bandwidth,on germanium concentration in large-mode-area Ge-doped passive fibers is investigated theoretically and experimentally.The simulation results show that the BFS is inversely proportional to GeO_(2)concentration,and the BGS bandwidth initially increases with the augment of GeO_(2)concentration,and then decreases.The BGSs of four fibers with core diameters of 10μm and 20μm for different GeO_(2)concentrations are compared experimentally.Experimental results demonstrate that with the same core diameter,the variations of BFS and BGS bandwidths with GeO_(2)concentration accord with the simulation results.Additionally,the BGS characteristics of three large-mode-area passive fibers with diameters of 10μm,25μm,and 30μm are measured,which confirm that the increasing of the fiber diameters will cause the BGS bandwidth to broaden.We believe that these results can provide valuable references for modulating the high-power narrowlinewidth fiber lasers and Brillouin fiber amplifiers.

Possible nodeless s~±-wave superconductivity in twisted bilayer graphene

The recent discovery of superconductivity in the twisted bilayer graphene has stimulated numerous theoretical proposals concerning its exact gap symmetry.Among them, the d + id or p + ip-wave was believed to be the most plausible solution.Here, considering that the superconductivity emerges near a correlated insulating state and may be induced by antiferromagnetic spin fluctuations, we apply the strong-coupling Eliashberg theory with both inter-and intraband quantum critical pairing interactions and discuss the possible gap symmetry in an effective low-energy four-orbital model.Our calculations reveal a nodeless s~±-wave as the most probable candidate for the superconducting gap symmetry in the experimentally relevant parameter range.This solution is distinctly different from previous theoretical proposals.It highlights the multi-gap nature of the superconductivity and puts the twisted bilayer graphene in the same class as the iron-pnictide,electron-doped cuprate, and some heavy fermion superconductors.

Pressure effect in the Kondo semimetal CeRu4Sn6 with nontrivial topology

Kondo semimetal CeRu4Sn6 is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport properties of single- and poly-crystalline samples. The electrical resistivity p （T） is gradually enhanced by applying pressure over a wide temperature range from room temperature down to 25 mK. Two thermal activation gaps estimated from high- and low-temperature windows are found to increase with pressure. A flat p（T） observed at the lowest temperatures below 300 mK appears to be robust against both pressure and field. This feature as well as the increase of the energy gaps calls for more intensive investigations with respect to electron correlations and band topology.

In-Plane Anisotropic Response to Uniaxial Pressure in the Hidden Order State of URu_(2)Si_(2)

We investigate the uniaxial-pressure dependence of resistivity for URu_(2−x)Fe_(x)Si_(2)samples with x=0 and 0.2,which host a hidden order(HO)and a large-moment antiferromagnetic(LMAFM)phase,respectively.For both samples,the elastoresistivityζshows a seemingly divergent behavior above the transition temperature T_(0)and a quick decrease below it.We find that the temperature dependence ofζfor both samples can be well described by assuming the uniaxial pressure effect on the gap or certain energy scale except forζ(110)of the x=0 sample,which exhibits a nonzero residual value at 0 K.We show that this provides a qualitative difference between the HO and LMAFM phases.Our results suggest that there is an in-plane anisotropic response to the uniaxial pressure that only exists in the hidden order state without necessarily breaking the rotational lattice symmetry.

Evolution of Topological End States in the One-Dimensional Kondo–Heisenberg Model with Site Modulation

We investigate interplay of topological and Kondo effects in a one-dimensional Kondo-Heisenberg model with nontrivial conduction band using the density matrix renormalization group method.By analyzing the density profile,the local hybridization,and the spin/charge gap,we find that the Kondo effect can be destructed at edges of the chain by the topological end state below a finite critical Kondo coupling J_(K)^(C).We construct a phase diagram characterizing the transition of the end states.

Spectroscopic data de-noising via training-set-free deep learning method

De-noising plays a crucial role in the post-processing of spectra.Machine learning-based methods show good performance in extracting intrinsic information from noisy data,but often require a high-quality training set that is typically inaccessible in real experimental measurements.Here,using spectra in angle-resolved photoemission spectroscopy(ARPES)as an example,we develop a de-noising method for extracting intrinsic spectral information without the need for a training set.This is possible as our method leverages the self-correlation information of the spectra themselves.It preserves the intrinsic energy band features and thus facilitates further analysis and processing.Moreover,since our method is not limited by specific properties of the training set compared with previous ones,it may well be extended to other fields and application scenarios where obtaining high-quality multidimensional training data is challenging.

Dynamic prediction of moving trajectory in pipe jacking: GRU-based deep learning framework

The moving trajectory of the pipe-jacking machine(PJM),which primarily determines the end quality of jacked tunnels,must be controlled strictly during the entire jacking process.Developing prediction models to support drivers in performing rectifications in advance can effectively avoid considerable trajectory deviations from the designed jacking axis.Hence,a gated recurrent unit(GRU)-based deep learning framework is proposed herein to dynamically predict the moving trajectory of the PJM.In this framework,operational data are first extracted from a data acquisition system;subsequently,they are preprocessed and used to establish GRU-based multivariate multistep-ahead direct prediction models.To verify the performance of the proposed framework,a case study of a large pipe-jacking project in Shanghai and comparisons with other conventional models(i.e.,long short-term memory(LSTM)network and recurrent neural network(RNN))are conducted.In addition,the effects of the activation function and input time-step length on the prediction performance of the proposed framework are investigated and discussed.The results show that the proposed framework can dynamically and precisely predict the PJM moving trajectory during the pipe-jacking process,with a minimum mean absolute error and root mean squared error(RMSE)of 0.1904 and 0.5011 mm,respectively.The RMSE of the GRU-based models is lower than those of the LSTM-and RNN-based models by 21.46%and 46.40%at the maximum,respectively.The proposed framework is expected to provide an effective decision support for moving trajectory control and serve as a foundation for the application of deep learning in the automatic control of pipe jacking.

A novel variant in TBX20 （p.DI76N） identified by whole-exome sequencing in combination with a congenital heart disease related gene filter is associated with familial atrial septal defect

Congenital heart disease （CHD） is the leading cause of birth defects, and its etiology is not completely understood. Atrial septal defect （ASD） is one of the most common defects of CHD. Previous studies have demonstrated that mutations in the transcription factor T-box 20 （TBX20） contribute to congenital ASD. Whole-exome sequencing in combination with a CHD-related gene filter was used to detect a family of three generations with ASD. A novel TBX20 mutation, c.526G〉A （p.D176N）, was identified and co-segregated in all affected members in this family. This mutation was predicted to be deleterious by bioinformatics programs （SIFT, Polyphen2, and MutationTaster）. This mutation was also not presented in the current Single Nucleotide Polymorphism Database （dbSNP） or National Heart, Lung, and Blood Institute （NHLBI） Exome Sequencing Project （ESP）. In conclusion, our finding expands the spectrum of TBX20 mutations and provides additional support that TBX20 plays important roles in cardiac development. Our study also provided a new and cost-effective analysis strategy for the genetic study in small CHD pedigree.

Impurity-induced bound states as a signature of pairing symmetry in multiband superconducting CeCu2Si2

The notion of multiband superconductivity with dominant two-gap features has been recently applied to the unconventional superconductor CeCu2Si2 for challenging the previously accepted concept of nodal d-wave pairing. In the proposed study, the realistic multiband Fermi surface topology of CeCu2Si2 was obtained through first-principles calculations, and analysis was conducted with an effective two-band hybridization model including detailed band structure. Within the T-matrix approximation, the obtained calculation results show that different pairing candidates, including fully gapped s-wave, loop-nodal s-wave, and d-wave pairings, could yield qualitatively distinct features characterized by impurity-induced bound states. These features can be verified through high-resolution scanning tunneling microscopy or spectroscopy and provide corroborative justification that would be beneficial for the ongoing research regarding the superconducting gap symmetry of CeCu2Si2 at ambient pressure.

Heavy fermion quantum criticality: The party is just beginning

Recently,Nature reported the discovery of a ferromagnetic quantum critical point(FM QCP)in the heavy fermion compound CeRh6Ge4[1].This is the first discovery of such kind in a stoichiometric compound.The FM order is suppressed at a critical pressure of 0.8 GPa,beyond which the ground state turns into a Fermi liquid.Previously,Science had also reported the observation of a FM QCP,albeit in the doped compound YbNi4(P0.92As0.08)2[2].

Quantum phase transition and destruction of Kondo effect in pressurized SmB6

SmB_6 has been a well-known Kondo insulator for decades, but recently attracts extensive new attention as a candidate topological system. Studying SmB_6 under pressure provides an opportunity to acquire the much-needed understanding about the effect of electron correlations on both the metallic surface state and bulk insulating state. Here we do so by studying the evolution of two transport gaps(low temperature gap E_l and high temperature gap E_h) associated with the Kondo effect by measuring the electrical resistivity under high pressure and low temperature(0.3 K) conditions. We associate the gaps with the bulk Kondo hybridization, and from their evolution with pressure we demonstrate an insulator-tometal transition at ~4 GPa. At the transition pressure, a large change in the Hall number and a divergence tendency of the electron-electron scattering coefficient provide evidence for a destruction of the Kondo entanglement in the ground state. Our results raise the new prospect for studying topological electronic states in quantum critical materials settings.

A unified theory of ferromagnetic quantum phase transitions in heavy fermion metals

Motivated by the recent discovery of a continuous ferromagnetic quantum phase transition in Ce Rh_(6)Ge_(4) and its distinction from other U-based heavy fermion metals such as UGe_(2),we develop a unified explanation of their different ground state properties based on an anisotropic ferromagnetic Kondo-Heisenberg model.We employ an improved large-N Schwinger boson approach and predict a full phase diagram containing both a continuous ferromagnetic quantum phase transition for large magnetic anisotropy and first-order transitions for relatively small anisotropy.Our calculations reveal three different ferromagnetic phases including a half-metallic spin selective Kondo insulator with a constant magnetization.The Fermi surface topologies are found to change abruptly between different phases,consistent with that observed in UGe_(2).At finite temperatures,we predict the development of Kondo hybridization well above the ferromagnetic long-range order and its relocalization near the phase transition,in good agreement with band measurements in Ce Rh_(6)Ge_(4).Our results highlight the importance of magnetic anisotropy and provide a unified theory for understanding the ferromagnetic quantum phase transitions in heavy fermion metals.

Spin current Kondo effect in frustrated Kondo systems

Magnetic frustrations can enhance quantum fluctuations in spin systems and lead to exotic topological insulating states.When coupled to mobile electrons,they may give rise to unusual non-Fermi liquid or metallic spin liquid states whose nature has not been well explored.Here,we propose a spin current Kondo mechanism underlying a series of non-Fermi liquid phases on the border of Kondo and magnetic phases in a frustrated three-impurity Kondo model.This mechanism is confirmed by renormalization group analysis and describes movable Kondo singlets called"holons"induced by an effective coupling between the spin current of conduction electrons and the vector chirality of localized spins.Similar mechanisms may widely exist in all frustrated Kondo systems and be detected through spin current noise measurements.

Mutant CARD10 in a family with progressive immunodeficiency and autoimmunity

Autoimmunity and immunodeficiency were previously considered to be mutually exclusive conditions.However,an increased understanding of the complex immune regulatory systems and signaling mechanisms,coupled with the application of genetic analysis,has demonstrated the complex relationships between the two kinds of diseases.1 In recent years,several mild forms of primary immunodeficiencies have been discovered,presenting with opportunistic infections overlapping autoimmunity and/or allergy late in life.

Haploinsufficiency of syncoilin leads to hypertrophic cardiomyopathy

Here we reported a SYNC nonsense variant in a Chinese family with hypertrophic cardiomyopathy(HCM)and firstly linked syncoilin(SYNC)to HCM.HCM is an inherited cardiovascular disease,affecting approximately 1:500 people,that is characterized by thickening of left ventricle(LV),especially the interventricular septum(IVS),and diastolic ventricular failure.1 To date,more than 15 genes of two groups underlying HCM have been identified.1 About 35%e60%HCM patients present autosomal dominant inheritance and carry a pathogenic variant in sarcomeric protein genes,such as b-myosin heavy chain(MYH7),myosin binding protein C(MYBPC3),and Troponin T(TNNT2).1 In addition,non-sarcomeric genetic causes of disease have also been observed in about 25%HCM patients,mainly related to metabolic storage diseases,mitochondrial cardiomyopathies,inborn errors of metabolism etc.