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, , Shamik Chakrabarti, Sajib Biswas, Amal Kumar Das
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac3039

Abstract:
Tunability of structural, magnetic and electronic properties of Co2FeGe Heusler alloy is experimentally demonstrated by doping Ti in the Fe site (i.e. Co2Fe1-xTixGe), followed by in-depth first principle calculations. Co2FeGe in its pure phase shows very high saturation magnetization, Curie temperature and spin-wave stiffness constant which were reported in our earlier work. With gradual increase in Ti doping concentration (x= 0.5 and 0.75), the experimental saturation magnetization is found to be decreased to 4.3 µB/f.u and 3.1 µB/f.u respectively as compared to the parent alloy (x=0) having the saturation magnetization of 6.1µB/f.u. Variation of spinwave stiffness constant is also studied for different x and found to be decreasing from peak value of 10.4 nm2- meV (for x=0) to the least value of 2.56 nm2-meV for x=0.5. Justification of the experimental results is given with first principle calculations. Computational phase diagram of the alloys is found in terms of formation energy showing that the doping in Fe site (i.e. Co2Fe1-xTixGe) is more stable rather than in Co site (i.e. Co2−xFeTixGe). The change in magnetic moment and halfmetallicity with Ti doping concentration is better explained under GGA+U approach as compared to GGA approach signifying that the electron-electron correlation (U) has a distinct role to play in the alloys. Effect of variation of U for Ti atom is studied and optimized with reference to the experimental results. The dynamical stability of the Co2Fe1-xTixGe alloy crystal structure is explained in terms of phonon dispersion relations and the effect of U on the phonon density of states is also explored. Close agreement between the experimental and theoretical results is observed.
Jeffrey Kaaret, Guru Khalsa,
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac3038

Abstract:
We use theory and first-principles calculations to investigate how structural changes induced by ultrafast optical excitation of infrared-active phonons change with hydrostatic pressure in LaAlO3. Our calculations show that the observed structural changes are sensitive to pressure, with the largest changes occurring at pressures near the boundary between the cubic perovskite and rhombohedral phases. We rationalize our findings by defining a figure of merit that depends only on intrinsic materials quantities, and show that the peak response near the phase boundary is dictated by different microscopic materials properties depending on the particular phonon mode being excited. Our work demonstrates how it is possible to systematically identify materials that may exhibit particularly large changes in structure and properties due to optical excitation of infrared-active phonons.
, Jonas Fransson,
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac303a

Abstract:
Quantum shape effect appears under the size-invariant shape transformations of strongly confined structures. Such a transformation distinctively influences the thermodynamic properties of confined particles. Due to their characteristic geometry, core-shell nanostructures are good candidates for quantum shape effects to be observed. Here we investigate the thermodynamic properties of non-interacting degenerate electrons confined in core-shell nanowires consisting of an insulating core and a GaAs semiconducting shell. We derive the expressions of shape-dependent thermodynamic quantities and show the existence of a new type of quantum oscillations due to shape dependence, in chemical potential, internal energy, entropy and specific heat of confined electrons. We provide physical understanding of our results by invoking the quantum boundary layer concept and evaluating the distributions of quantized energy levels on Fermi function and in state space. Besides the density, temperature and size, the shape per se also becomes a control parameter on the Fermi energy of confined electrons, which provides a new mechanism for fine tuning the Fermi level and changing the polarity of semiconductors.
, Bashab Dey, Tarun Kanti Ghosh
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2fd4

Abstract:
We study the magnetoelectric and magnetothermal transport properties of noncentrosymmetric metals using semiclassical Boltzmann transport formalism by incorporating the effects of Berry curvature and orbital magnetic moment. These effects impart quadratic-B dependence to the magnetoelectric and magnetothermal conductivities, leading to intriguing phenomena such as planar Hall effect, negative magnetoresistance, planar Nernst effect and negative Seebeck effect. The transport coefficients associated with these effects show the usual oscillatory behavior with respect to the angle between the applied electric field and magnetic field. The bands of noncentrosymmetric metals are split by Rashba spin-orbit coupling except at a band touching point. For Fermi energy below (above) the band touching point, giant (diminished) negative magnetoresistance is observed. This difference in the nature of magnetoresistance is related to the magnitudes of the velocities, Berry curvature and orbital magnetic moment on the respective Fermi surfaces, where the orbital magnetic moment plays the dominant role. The absolute magnetoresistance and planar Hall conductivity show a decreasing (increasing) trend with Rashba coupling parameter for Fermi energy below (above) the band touching point.
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2f6d

Abstract:
The short-range nature of the repulsive Weeks–Chandler–Anderson potential can create free particles/rattlers in a condensed system. The presence of rattlers complicates the analysis of the energy landscape due to extra zero-frequency normal modes. By employing a long-range gaussian tail modification, we remove the rattlers without changing the structure and the dynamics of the system, and successfully describe the potential energy landscape in terms of minima and transition states. This coarse-grained description of the landscape and the dynamical properties of the modified potential exhibit characteristic signatures of glass-forming liquids. However, we show that despite having qualitatively similar behaviour, the modified WCA potential is less frustrated compared to its attractive counterpart.
, Maria Calamiotou, Maurizio Polentarutti, Giorgio Bais, Annette Bussmann-Holder, Efthimios Liarokapis
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2f11

Abstract:
The influence of an external static magnetic field (up to 480mT) on the structural properties of EuTiO3 (ETO) polycrystalline samples was examined by powder XRD at the Elettra synchrotron facilities in the temperature range 100-300K. While the cubic to tetragonal structural phase transition temperature in this magnetic field range remains almost unaffected, significant lattice effects appear at two characteristic temperatures (~200 Κ and ~250 K), which become more pronounced at a critical threshold field. At ~200 Κ a change in the sign of magnetostriction is detected attributed to a modification of the local magnetic properties from intrinsic ferromagnetism to intrinsic antiferromagnetism. These data are a clear indication that strong spin-lattice interactions govern also the high temperature phase of ETO and trigger the appearance of magnetic domain formation and phase transitions.
, Wen-Chao Chen,
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2ed7

Abstract:
In this work, we propose a ferromagnetic Bi2Se3 as a candidate to hold the coexistence of Weyland nodal-line semimetal phases, which breaks the time reversal symmetry. We demonstrate that the type-I Weyl semimetal phase, type-I-, type-II- and their hybrid nodal-line semimetal phases can arise by tuning the Zeeman exchange field strength and the Fermi velocity. Their topological responses under U(1) gauge field are also discussed. Our results raise a new way for realizing Weyl and nodal-line semimetals and will be helpful in understanding the topological transport phenomena in three-dimensional material systems.
, , Yueshao Zheng, , Yexin Feng,
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2f10

Abstract:
The nitrogen-rich compounds are promising candidates for high-energy-density applications, owing to the large difference in the bonding energy between triple and single/double nitrogen bonds. The exploration of stable copper-nitrogen (Cu-N) compounds with high-energy-density has been challenging for a long time. Recently, through a combination of high temperatures and pressures, a new copper diazenide compound (P63/mmc-CuN2) has been synthesized [J. Phys. Chem. Lett. 2019, 10, 1109−1114]. But the pressure-composition phase diagram of Cu-N compounds at different temperatures is still highly unclear. Here, by combining first-principles calculations with crystal structure prediction method, the Cu-N compounds with different stoichiometric ratios were searched within the pressure range of 0-150 GPa. Four Cu-N compounds are predicted to be thermodynamically stable at high pressures, Pnnm-CuN2, two CuN3 compounds with the P-1 space group (named as I-CuN3 and II-CuN3) and P21/m-CuN5 containing cyclo-N5-. Finite temperature effects (vibrational energies) play a key role in stabilizing experimentally synthesized P63/mmc-CuN2 at ~55 GPa, compared to our predicted Pnnm-CuN2. These new Cu-N compounds show great promise for potential applications as high-energy-density materials with the energy densities of 1.57-2.74 kJ/g.
Zhibin Liang, Yuchuan Jiang, Xing Gong, Haoran Gong
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2e8e

Abstract:
An analytical bond-order potential (BOP) of Fe-Bi has been constructed and has been validated to have a better performance than the Fe-Bi potentials already published in the literature. Molecular dynamics simulations based on this BOP has been then conducted to investigate the ground-state properties of Bi, structural stability of the Fe-Bi binary system, and the effect of Bi on mechanical properties of BCC Fe. It is found that the present BOP could accurately predict the ground-state A7 structure of Bi and its structural parameters, and that a uniform amorphous structure of Fe100-xBix could be formed when Bi is located in the composition range of 26≤x<70. In addition, simulations also reveal that the addition of a very small percentage of Bi would cause a considerable decrease of tensile strength and critical strain of BCC Fe upon uniaxial tensile loading. The obtained results are in nice agreement with similar experimental observations in the literature.
Michela Pauletti, ,
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2e8f

Abstract:
In this work we assess and extend strategies for calculating surface tension of complex liquids from molecular dynamics simulations: the mechanical route and the instantaneous liquid interface approach. The former employs the connection between stress tensor and surface tension, whereas the latter involves computation of instantaneous density field. Whereas the mechanical route is general, the instantaneous liquid interface method involves system-dependent parameters restricting its original application to liquid water only. Here we generalize the approach to complex molecular liquids using atomic van der Waals radii. The performance of the approaches is evaluated on two liquid systems: acetonitrile and water-methanol mixture. In addition, we compare the effect of the computational models for interaction potentials based on semi-empirical electronic structure theory and classical force fields on the estimate of the surface tension within both stress tensor and instantaneous liquid interface approaches.
Bin Qian, Jinyu Liu, F. M. Zhang, F. J. Kong, W. Zhou, Q.C. Gu, , Z.D. Han, X.F. Jiang, Y. L. Zhu, et al.
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2db9

Yinze Qin, Shidong Zhang, Sijie Zhang, Matthew G Tucker, David A Keen, Guanqun Cai, , Martin T Dove
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2db8

Abstract:
We report a study of the orientational order and phase transitions in crystalline deuterated methane, carried out using neutron total scattering and the Reverse Monte Carlo (RMC) method. The resultant atomic configurations are consistent with the average structures obtained from Rietveld refinement of the powder diffraction data, but additionally enable us to determine the C–D bond orientational distribution functions (ODF) for the disordered molecules in the high-temperature phase, and for both ordered and disordered molecules in the intermediate-temperature phase. We show that this approach gives more accurate information than can been obtained from fitting a bond ODF to diffraction data. Given the resurgence of interest in orientationally-disordered crystals, we argue that the approach of total scattering with the RMC method provides a unique quantification of orientational order and disorder.
Chaebin Kim, Heung-Sik Kim,
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2d5d

Abstract:
The realization of Kitaev's honeycomb magnetic model in real materials has become one of the most pursued topics in condensed matter physics and materials science. If found, it is expected to host exotic quantum phases of matter and offers potential realizations of fault-tolerant quantum computations. Over the past years, much effort was made on 4d- or 5d- heavy transition metal compounds because of their intrinsic strong spin-orbit coupling. But more recently, there have been growing shreds of evidence that the Kitaev model could also be realized in 3d-transition metal systems with much weaker spin-orbit coupling. This review intends to serve as a guide to this fast-developing field focusing on systems with d7 transition metal occupation. It overviews the current theoretical and experimental progress on realizing the Kitaev model in those systems. We examine the recent experimental observations of candidate materials with Co2+ ions: e.g., CoPS3, Na3Co2SbO6, and Na2Co2TeO6, followed by a brief review of theoretical backgrounds. We conclude this article by comparing experimental observations with density functional theory (DFT) calculations. We stress the importance of inter-t2g hopping channels and Hund's coupling in the realization of Kitaev interactions in Co-based compounds, which has been overlooked in previous studies. This review suggests future directions in the search for Kitaev physics in 3d cobalt compounds and beyond.
Fei Chen, Hui Li, Hang Zhou, Ziyu Ye, Song Luo, Zheng Sun, Fenghao Sun, Jiawei Wang, , Hongxing Xu, et al.
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2d5e

Abstract:
In this work, by using femtosecond angle-resolved spectroscopic imaging technique, the ultrafast dynamics of confined exciton-polaritons in an optical induced potential well based on a ZnO whispering-gallery microcavity is explicitly visualized. The sub-picosecond transition between succeeding quantum harmonic oscillator states can be experimentally distinguished. The landscape of the potential well can be modified by the pump power, the spatial distance and the time delay of the two input laser pulses. Clarifying the underlying mechanism of the polariton harmonic oscillator is interesting for the applications of polariton-based optoelectronic devices and quantum information processing.
Nicole De March, Sandra Prado, Leon G Brunnet
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2cf0

Abstract:
The mechanism behind the high throughput rate in K+ channels is still an open problem. However, recent simulations have shown that the passage of potassium through the K+ channel core, the so-called selectivity filter, is water-free against models where the strength of Coulomb repulsion freezes ions conduction. Thus, it has been suggested that coherent quantum hopping might be relevant in mediating ion conduction. Within the quantum approach and the hypothesis of desolvated ions along the pathway, we start with several particles in a source to see how they go across a selectivity filter, modeled by a linear chain of sites, to be collected in a drain. We show that the average selectivity filter occupancy is three ions, and the ion transfer rate is ~ 108 ions/s, results which agree with the recent findings in the literature.
Suman Mondal, Pushpendra Yadav, Anan Bari Sarkar, Prabir Dutta, Saurav Giri, ,
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2cf1

Abstract:
The rare-earth intermetallic compound Ho5Sn3 demonstrates fascinating magnetic properties which include temperature-driven multiple magnetic transitions and field-driven metamagnetism. We address the magnetic character of this exciting compound through a combined experimental and theoretical studies. Ho5Sn3 orders antiferromagnetically below 28 K, and shows further spin reorientation transitions at 15 K and 12 K. We observe a sizable amount of low-temperature magnetocaloric effect in Ho5Sn3 with a maximum value of entropy change ∆S = -9.5 JKg−1K−1 for an applied field of H = 50 kOe at around 30 K. The field hysteresis is almost zero above 15 K where magneto-caloric effect is important. Interestingly, ∆S is found to change its sign from positive to negative as the temperature is increased above about 8 K, which can be linked to the multiple spin reorientation transitions. The signature of the metamagnetism is visible in the ∆S versus H plot. The magnetic ground state, obtained from the density functional theory based calculation, is susceptible to the effective Coulomb interaction (Ueff) between electrons. Depending upon the value of Ueff, the ground state can be ferromagnetic or antiferromagnetic. The compound shows large relaxation (14% change in magnetisation in 60 min) in the field cooled state with a logarithmic time variation, which may be connected to the competing magnetic ground states observed in our theoretical calculations. The competing magnetic ground states is equally evident from the small value of the paramagnetic Curie-Weiss temperature.
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2ca9

Abstract:
We investigate, numerically, the effects of externally imposed material flows on the structure and temporal evolution of liquid crystal skyrmions. The dynamics of a 2D system of skyrmions is modeled using the Ericksen-Leslie theory, which is based on two coupled equations, one for material flow and the other for the director field. As the time scales of the velocity and director fields differ by several orders of magnitude for realistic values of the system parameters, we have simplified the calculations by assuming that the velocity relaxes instantaneously when compared to the relaxation of the director field. Thus, we have used a finite-differences method known as artificial compressibility with adaptive time step to solve the velocity field and a fourth-order Runge-Kutta method for the director field. We characterized the skyrmion shape or configuration as a function of the time and the average velocity of the flow field. We found that for velocities above a certain threshold, the skyrmions stretch in the direction perpendicular to the flow, by contrast to the regime of weak flows where the skyrmions stretch along the streamlines of the flow field. These two regimes are separated by an abrupt (first-order) dynamical transition, which is robust with respect to e.g., the liquid crystal elastic anisotropy. Additionally, we have found how the presence of a second skyrmion affects the evolution of the shape of the skyrmions, by comparing the evolution of pairs of skyrmions to the evolution of a single-skyrmion.
Gia Huy Philipp Nguyen, , Hartmut Löwen
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2c3f

Abstract:
Self-propelled particles, which convert energy into mechanical motion, exhibit inertia if they have a macroscopic size or move inside a gaseous medium, in contrast to micron-sized overdamped particles immersed in a viscous fluid. Here we study an extension of the active Ornstein-Uhlenbeck model, in which self-propulsion is described by colored noise, to access these inertial effects. We summarize and discuss analytical solutions of the particle's mean-squared displacement and velocity autocorrelation function for several settings ranging from a free particle to various external influences, like a linear or harmonic potential and coupling to another particle via a harmonic spring. Taking into account the particular role of the initial particle velocity in a nonstationary setup, we observe all dynamical exponents between zero and four. After the typical inertial time, determined by the particle's mass, the results inherently revert to the behavior of an overdamped particle with the exception of the harmonically confined systems, in which the overall displacement is enhanced by inertia. We further consider an underdamped model for an active particle with a time-dependent mass, which critically affects the displacement in the intermediate time-regime. Most strikingly, for a sufficiently large rate of mass accumulation, the particle's motion is completely governed by inertial effects as it remains superdiffusive for all times.
Antonio Tavera-Vazquez, Natalia Rincón-Londoño, Ricky F López-Santiago,
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2c3e

Abstract:
This review paper presents a procedure for measuring the mesoscopic scales in micellar solutions embedded with giant cylindrical micelles using the mean square displacement determined with a quasi-elastic multiple light scattering method (Diffusing Wave Spectroscopy) and theory. The mesoscopic scales of interest are the micelles' total contour length, persistence and entanglement lengths, and the mesh size of the entangled micellar network. All of them depend on the physicochemical parameters of the solutions and determine the rheological behavior. We present an assessment of the whole procedure, the scattering experiments performance, the recovery of optical parameters, which includes dealing with the light absorption and its treatment, and how to develop the micro-rheology for obtaining the mesoscopic scales in these complex fluids.
, Anupam Saha
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2c40

Abstract:
We probe quantum oscillations in nodal line semimetals (NLSM) by considering a NLSM continuum model under strong magnetic field and report the characteristics of the Landau level spectra and the fluctuations in the Fermi level as the field in a direction perpendicular to the nodal plane is varied through. Based on the results on parallel magnetization, we demonstrate the growth of quantum oscillation with field strength as well as its constancy in period when plotted against 1/B. We find that the density of states which show series of peaks in succession, witness bifurcation of those peaks due to Zeeman effect. For field normal to nodal plane, such bifurcations are discernible only if the electron effective mass is considerably smaller than its free value, which usually happens in these systems. Though a reduced effective mass m* causes the Zeeman splitting to become small compared to Landau level spacings, experimental results indicate a manyfold increase in the Lande g factor which again amplifies the Zeeman contribution. We also consider magnetic field in the nodal plane for which the density of state peaks do not repeat periodically with energy anymore. The spectra become more spread out and the Zeeman splittings become less prominent. We find the low energy topological regime, that appears with such in-plane field set up, to shrink further with reduced m* values. However, such topological regime can be stretched out in case there are smaller Fermi velocities for electrons in the direction normal to the nodal plane.
Mao Xiujuan, , Ze Liu, Jiaxi Wang, Fuli He, Yafan Wang
Published: 30 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2bc5

Abstract:
Based on first-principles calculations, the unconventional Rashba- and Zeeman-type spin splitting can simultaneously coexist in the Pb-adsorbed monolayer WSe2 system. The first two adsorption configurations t1 and t2 show remarkable features under the spin-orbit coupling, in which two split energy branches show same spin states at the left or right side of Γ, and the spin polarization is reversed for both Rashba band branches. For the second adsorption configuration, an energy gap was observed near the unconventional spin polarization caused by the repelled Rashba bands for avoid crossing, and this gap can produce non-dissipative spin current by applying the voltage. The results for t2 configuration with spin reversal show that the repel band gap and Rashba parameter can be effectively regulated within the biaxial strain range of −8% to 6%. By changing the adsorption distance d between Pb and the neighboring Se atom layer, the reduced d caused the transfer from Rashba-type to Zeeman-type spin splitting. This predicted adsorption system would be promising for spintronic applications.
Published: 30 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2bc6

Abstract:
Using first-principles calculations for a few angstrom-sized pores (3-10\AA), we investigate pore-particle interaction. The translocation energy barrier changes for the angstrom-scale pores created in 2D-materials such as graphene which is calculated for the translocation of rare gases (He, Ne, Ar, Xe), diatomic molecules (H$_2$ and N$_2$), CO$_2$, and CH$_4$. For particles incident at 0$^o$ with a critical angle of 40$^o$ to the surface normal, the permeance through the pore is zero; which is different from the classical model's prediction of 19$^o$-37$^o$. The calculated translocation energy barrier ($\Delta$) and the surface diffusion energy barrier($\Delta'$) for the particles with small kinetic diameter (He, Ne and H$_2$), show that the direct flow is the dominant permeation mechanism ($\Delta\approx$0 and $\Delta'>30$\,meV). For the other particles with larger kinetic diameters (Ar, Kr, N$_2$, CH$_4$ and CO$_2$), we found that both surface diffusion and direct flow mechanisms are possible, i.e. $\Delta$ and $\Delta'\neq$0. This work provides important insights into the gas permeation theory and into the design and development of gas separation and filtration devices.
, , Kartik Panda, Sueli Hatsumi Masunaga, Leandro Rodrigues de Faria, L.E. Corre, F B Santos, , , T T Dorini, et al.
Published: 30 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2bc7

Abstract:
In the present work, we demonstrate that Zr$_{5}$Pt$_{3}$C$_{0.5}$ is an electron-phonon superconductor (with critical temperature $T_\mathrm{C}$ = 3.8\,K) with a nonsymmorphic topological Dirac nodal-line semimetal state, which we report here for the first time. The superconducting properties of Zr$_{5}$Pt$_{3}$C$_{0.5}$ have been investigated by means of magnetization, resistivity, specific heat, and muon spin rotation and relaxation ($\mu$SR) measurements. We find that at low temperatures, the depolarization rate is almost constant and it can be well described by a single-band $s-$wave model with a superconducting gap of $2\Delta(0)/k_\mathrm{B}T_\mathrm{C}$ = 3.84, in excellent agreement with the specific heat measurements. From the transverse field $\mu$SR analysis, we estimate the London penetration depth $\lambda_{L}$ = 469 nm, the superconducting carrier density $n_{s}$ = 1.83$\times$10$^{26}$ $m^{-3}$, and the effective mass $m^{*}$ = 1.428 $m_{e}$. The Zero field $\mu$SR confirms the absence of any spontaneous magnetic field in the superconducting ground state. In order to gain additional insights into the electronic ground state of C-doped Zr$_5$Pt$_3$, we also performed first-principles calculations within the framework of density functional theory (DFT). The observed homogenous electronic character of the Fermi surface as well as the mutual decrease of $T_\mathrm{C}$ and density of states at the Fermi level with the C doping are consistent with the experimental findings of this study. However, the band structure reveals the presence of robust, gapless fourfold-degenerate nodal lines protected by $6_{3}$ screw rotations and glide mirror planes. Therefore, Zr$_5$Pt$_3$ represents a novel, unprecedented condensed matter system to investigate the intricate interplay between superconductivity and topology.
Jie Mei, Xiyin Ye, , , XiaoMing Zhu
Published: 29 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2acf

Abstract:
In this work, we study the band structures and intrinsic anomalous Hall conductivity (AHC) of the ferromagnetic multiorbital tight-binding (TB) model derived from the transition metal compound Sr$_2$RuO$_4$ under periodic driving of monochromatic polarized light. Within the framework of the Floquet theory, we adopt the continued fraction technique to attain the effective Hamiltonian valid in the weak-driving and low-frequency regimes, and the related Green's functions which are further employed for the transport calculations based on the Kubo formalism. The high-frequency circularly and linearly polarized (LP) light has limited impacts on the band structures, while the low-frequency light with the photon energy smaller than the bandwidth of the system opens up bandgaps at the edges of the Floquet-Brillouin zone (FBZ) since the transitions between Floquet sidebands become significant. For intrinsic AHC, the left-handed circularly polarized (LCP) light plays a distinct role on AHC compared to the right-handed circularly polarized (RCP) light. Furthermore, it reveals that the roles of LCP and RCP light can be interchanged by altering the incident plane of light. Finally, the intrinsic AHC with the interplay between the short-range disorder and circularly polarized light is also investigated.
Wen-Yuan Wang,
Published: 29 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2b68

Abstract:
We study the effects of non-Hermiticity on quantum coherence via a noisy quantum kicked rotor (NQKR). The random noise comes from the fluctuations in kick amplitude at each time. The non-Hermitian driving indicates the imaginary kicking potential, representing the environment-induced atom gain and loss. In the absence of gain and loss, the random noise destroys quantum coherence manifesting dynamical localization, leads to classical diffusion. Interestingly, in the presence of non-Hermitian kicking potential, the occurrence of dynamical localization is highly sensitive to the gain and loss, manifesting the restoration of quantum coherence. Using the inverse participation ratio arguments, we numerically obtain a phase diagram of the classical diffusion and dynamical localization on the parameter plane of noise amplitude and non-Hermitian driving strength. With the help of analysis on the corresponding quasieigenstates, we achieve insight into dynamical localization, and uncover that the origin of the localization is interference between multiple quasi-eigenstates of the quantum kicked rotor (QKR). We further propose an experimental scheme to realize the NQKR in a dissipative cold atomic gas, which paves the way for future experimental investigation of a NQKR and its anomalous non-Hermitian properties.
Lavudya Devendar, Methattel Raman Shijeesh, Tushar Sakorikar, Lakshmi Ganapathi Kolla,
Published: 29 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2ad0

Abstract:
The confinement of water between sub-nanometer bounding walls of layered two-dimensional materials has generated tremendous interest. Here, we examined the influence of confined water on the mechanical and electromechanical response of graphene oxide films, prepared with variable oxidative states, casted on polydimethylsiloxane (PDMS) substrates. These films were subjected to uniaxial strain under controlled humid environments (5 to 90 % RH), while dc transport studies were performed in tandem. Straining resulted in the formation of quasi-periodic linear crack arrays. The extent of water intercalation determined the density of cracks formed in the system thereby, governing the electrical conductance of the films under strain. The crack density at 5 % strain, varied from 0 to 3.5 cracks/mm for hydrated films and 8 to 22 cracks/mm for dry films, across films with different high oxidative states. Correspondingly, the overall change in the electrical conductance at 5 % strain was observed to be ~ 5 to 20 folds for hydrated films and ~ 20 to 35 folds for the dry films. The results were modeled with a decrease in the in-plane elastic modulus of the film upon water intercalation, which was attributed to the variation in the nature of hydrogen bonding network in graphene oxide lamellae.
, Zhongshui Ma
Published: 29 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2b6a

Abstract:
We establish a brief relation between spin current and spin torque, including spin-orbit torque and spin transfer torque in 2D Rashba ferromagnets with nonuniform magnetic texture. Both electrically and thermally induced charge, heat, and spin current are investigated by the Luttinger's mechanical method, and we derive the contributions of magnetization corresponding to the thermal spin current and the thermal spin torque. The novel transport currents are also found in this paper when the interplay between SOC and non-uniform magnetic texture is taken into account.
Vivekanand Shukla, Yang Jiao, Carl Mikael Frostenson,
Published: 29 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2ad2

Abstract:
Hybrid density functionals replace a fraction of an underlying generalized-gradient approximation (GGA) exchange description with a Fock-exchange component. Range-separated hybrids (RSHs) also effectively screen the Fock-exchange component and thus open the door for characterizations of metals and adsorption at metal surfaces. The RSHs are traditionally based on a robust GGA, such as PBE [PRL 77, 3865 (1996)], for example, as implemented in the HSE design [JCP 118, 8207 (2003)]. Here we define an analytical-hole (AH) [JCP 128, 194105 (2008)] consistent-exchange (AHCX) RSH extension to the van der Waals density functional (vdW-DF) method [ROPP 78, 066501 (2015)], launching vdW-DF-ahcx. We characterize the GGA-type exchange in the vdW-DF-cx version [PRB 89, 035412 (2014)], isolate the short-ranged exchange component, and define the new vdW-DF hybrid. We find that the performance vdW-DF-ahcx compares favorably to (dispersion-corrected) HSE for descriptions of bulk (broad molecular) properties. We also find that it provides accurate descriptions of noble-metal surface properties, including CO adsorption.
Xingyu Hao, Zhiying Guo, Li Haijing, Yu Gong, Dongliang Chen
Published: 29 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2ad1

Abstract:
In this work, we explore the atomic vibration and local structure in 2H-MoTe2 by using high-pressure X-ray absorption fine structure (XAFS) spectroscopy up to ~20 GPa. The discrepancy between the Mo-Te and Mo-Mo bond length in 2H-MoTe2 obtained from extended-XAFS (EXAFS) and other techniques shows abnormal increase at 7.3 and 14.8 GPa, which is mainly due to the abrupt enhancement of vibration perpendicular to the bond direction. Ab-initio calculations are performed to study the electronic structure of 2H-MoTe2 up to 20 GPa and confirm a semiconductor to semimetal transition around 10 GPa and a Lifshitz transition around 15 GPa. We attribute the anomalous enhancement of vibration perpendicular to the bond direction to electronic transitions. We find the electronic transition induced enhancement of local vibration for the first time. Our finding offers a novel insight into the local atomic vibration and provides a new platform for understanding the relationship between the electronic transition and atomic vibration.
Ajay Kumar, Priyam Kwatra, Harikesh Meena, , Ling Wang,
Published: 29 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2ace

Abstract:
Ferroelectric liquid crystals (FLCs) possess excellent electro-optical properties compared to nematic liquid crystals including lower threshold voltage, faster switching response, good optical contrast and bi-stable switching, memory effect, etc. Due to such characteristic features, FLCs are more promising for next generation high performance photonic applications. Moreover, the synergy of FLCs with nanoscience has clearly shown the enormous possibilities to improve upon their electro-optical properties. Over the past two decades, several investigations of nanomaterial (metal, metal oxide, ferroelectric, insulating, graphene, semiconducting etc.) dispersed FLC nanocomposites have been carried out. Semiconducting nanomaterials (SNMs), exhibiting quantum confinement effect, have been one of the most explored nanomaterials as dopants in FLCs leading to better molecular alignment, enhanced dielectric behavior, pronounced memory effect, power efficient, faster switching response and enhanced photoluminescence. Here, we present a focused review on SNMs-FLCs nanocomposites and propose future work to advance liquid crystal nanoscience.
, Piotr Gierłowski, Marek Kuzmiak, Ramon Ferreira de Jesus, Oleksandr Onufriienko, Pavol Szabó, Yakov Kopelevich
Published: 27 September 2021
Journal of Physics: Condensed Matter, Volume 33; https://doi.org/10.1088/1361-648x/ac24c5

, M. Faraji, , Hamad R. Jappor, Siavash Karbasizadeh, Mitra Ghergherehchi, Daniela Gogova
Published: 27 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2a7b

Abstract:
In a very recent accomplishment, the two-dimensional form of Biphenylene network (BPN) has been fabricated. Motivated by this exciting experimental result on 2D layered BPN structure, herein we perform detailed density functional theory-based first-principles calculations, in order to gain insight into the structural, mechanical, electronic and optical properties of this promising nanomaterial. Our theoretical results reveal the BPN structure is constructed from three rings of tetragon, hexagon and octagon, meanwhile the electron localization function shows very strong bonds between the C atoms in the structure. The dynamical stability of BPN is verified via the phonon band dispersion calculations. The mechanical properties reveal the brittle behavior of BPN monolayer. The Youngs modulus has been computed as 0.1 TPa, which is smaller than the corresponding value of graphene, while the Poissons ratio determined to be 0.26 is larger than that of graphene. The band structure is evaluated to show the electronic features of the material; determining the BPN monolayer as metallic with a band gap of zero. The optical properties (real and imaginary parts of the dielectric function, and the absorption spectrum) uncover BPN as an insulator along the zz direction, while owning metallic properties in xx and yy directions. We anticipate that our discoveries will pave the way to the successful implementation of this 2D allotrope of carbon in advanced nanoelectronics.
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