Showing papers in "Journal of Physics: Condensed Matter in 2023"

Dynamic heat and charge transports through double-quantum-dot-interferometer modulated by Majorana bound states and time-oscillating Aharonov-Bohm flux

Abstract: Abstract Dynamic properties of Majorana bound states (MBSs) coupled double-quantum-dot (DQD) interferometer threaded with ac magnetic flux are investigated, and the time-averaged thermal current formulas are derived. Photon-assisted local and nonlocal Andreev reflections contribute efficiently to the charge and heat transports. The modifications of source-drain electric, electric-thermal, thermal conductances ( G , ξ , κ e ), Seebeck coefficient ( S c ), and thermoelectric figure of merit ( ZT ) versus AB phase have been calculated numerically. These coefficients exhibit the shift of oscillation period from 2 π to 4 π distinctly due to attaching MBSs. The applied ac flux enhances the magnitudes of G , ξ , κ e obviously, and the detailed enhancing behaviors are relevant to the energy levels of DQD. The enhancements of S c and ZT are generated due to the coupling of MBSs, while the application of ac flux suppresses the resonant oscillations. The investigation provides a clue for detecting MBSs through measuring the photon-assisted S c and ZT versus AB phase oscillations.

Wafer-scale controlled growth of MoS₂ by magnetron sputtering: from in-plane to inter-connected vertically-aligned flakes

Abstract: Abstract Recently, Molybdenum disulfide (MoS 2 ) has attracted great attention due to its unique characteristics and potential applications in various fields. The advancements in the field have substantially improved at the laboratory scale however, a synthesis approach that produces large area growth of MoS 2 on a wafer scale is the key requirement for the realization of commercial two-dimensional (2D) technology. Herein, we report tunable MoS 2 growth with varied morphologies via radio frequency magnetron sputtering by controlling growth parameters. The controlled growth from in-plane to vertically-aligned (VA) MoS 2 flakes has been achieved on a variety of substrates (Si, Si/SiO 2 , sapphire, quartz, and carbon fiber). Moreover, the growth of VA MoS 2 is highly reproducible and is fabricated on a wafer scale. The flakes synthesized on the wafer show high uniformity, which is corroborated by the spatial mapping using Raman over the entire 2-inch Si/SiO 2 wafer. The detailed morphological, structural, and spectroscopic analysis reveals the transition from in-plane MoS 2 to VA MoS 2 flakes. This work presents a facile approach to directly synthesize layered materials by sputtering technique on wafer scale. This paves the way for designing mass production of high-quality 2D materials, which will advance their practical applications by integration into device architectures in various fields.

B-site order/disorder in A₂BB′O₆ and its correlation with their magnetic property

Abstract: The disorder in any system affects their physical behavior. In this scenario, we report the possibility of disorder in A2BB'O6oxides and their effect on different magnetic properties. These systems show anti-site disorder by interchanging B and B' elements from their ordered position and giving rise to an anti-phase boundary. The presence of disorder leads to a reduction in saturationMand magnetic transition temperature. The disorder prevents the system from sharp magnetic transition which originates short-range clustered phase (or Griffiths phase) in the paramagnetic region just above the long-range magnetic transition temperature. Further, we report that the presence of anti-site disorder and anti-phase boundary in A2BB'O6oxides give different interesting magnetic phases like metamagnetic transition, spin-glass, exchange bias, magnetocaloric effect, magnetodielectric, magnetoresistance, spin-phonon coupling, etc.

Exceptional degeneracies in non-Hermitian Rashba semiconductors

Abstract: Exceptional points (EPs) are spectral degeneracies of non-Hermitian (NH) systems where eigenvalues and eigenvectors coalesce, inducing unique topological phases that have no counterpart in the Hermitian realm. Here we consider an NH system by coupling a two-dimensional semiconductor with Rashba spin–orbit coupling (SOC) to a ferromagnet lead and show the emergence of highly tunable EPs along rings in momentum space. Interestingly, these exceptional degeneracies are the endpoints of lines formed by the eigenvalue coalescence at finite real energy, resembling the bulk Fermi arcs commonly defined at zero real energy. We then show that an in-plane Zeeman field provides a way to control these exceptional degeneracies although higher values of non-Hermiticity are required in contrast to the zero Zeeman field regime. Furthermore, we find that the spin projections also coalescence at the exceptional degeneracies and can acquire larger values than in the Hermitian regime. Finally, we demonstrate that the exceptional degeneracies induce large spectral weights, which can be used as a signature for their detection. Our results thus reveal the potential of systems with Rashba SOC for realizing NH bulk phenomena.

Possible enhancement of the superconducting Tc due to sharp Kohn-like soft phonon anomalies

Abstract: Phonon softening is a ubiquitous phenomenon in condensed matter systems which is often associated with charge density wave (CDW) instabilities and anharmonicity. The interplay between phonon softening, CDW and superconductivity is a topic of intense debate. In this work, the effects of anomalous soft phonon instabilities on superconductivity are studied based on a recently developed theoretical framework that accounts for phonon damping and softening within the Migdal-Eliashberg theory. Model calculations show that the phonon softening in the form of a sharp dip in the phonon dispersion relation, either acoustic or optical (including the case of Kohn-type anomalies typically associated with CDW), can cause a manifold increase of the electron-phonon coupling constant $\lambda$. This, under certain conditions, which are consistent with the concept of optimal frequency introduced by Bergmann and Rainer, can produce a large increase of the superconducting transition temperature $T_c$. In summary, our results suggest the possibility of reaching high-temperature superconductivity by exploiting soft phonon anomalies restricted in momentum space.

Evidence of linear and cubic Rashba effect in non-magnetic heterostructure

Abstract: TheLaAlO3/KTaO3system serves as a prototype to study the electronic properties that emerge as a result of spin-orbit coupling (SOC). In this article, we have used first-principles calculations to systematically study two types of defect-free (0 0 1) interfaces, which are termed as Type-I and Type-II. While the Type-I heterostructure produces a two dimensional (2D) electron gas, the Type-II heterostructure hosts an oxygen-rich 2D hole gas at the interface. Furthermore, in the presence of intrinsic SOC, we have found evidence of both cubic and linear Rashba interactions in the conduction bands of the Type-I heterostructure. On the contrary, there is spin-splitting of both the valence and the conduction bands in the Type-II interface, which are found to be only linear Rashba type. Interestingly, the Type-II interface also harbors a potential photocurrent transition path, making it an excellent platform to study the circularly polarized photogalvanic effect.

Reduced-variance orientational distribution functions from torque sampling

Abstract: Abstract We introduce a method to sample the orientational distribution function in computer simulations. The method is based on the exact torque balance equation for classical many-body systems of interacting anisotropic particles in equilibrium. Instead of the traditional counting of events, we reconstruct the orientational distribution function via an orientational integral of the torque acting on the particles. We test the torque sampling method in two- and three-dimensions, using both Langevin dynamics and overdamped Brownian dynamics, and with two interparticle interaction potentials. In all cases the torque sampling method produces profiles of the orientational distribution function with better accuracy than those obtained with the traditional counting method. The accuracy of the torque sampling method is independent of the bin size, and hence it is possible to resolve the orientational distribution function with arbitrarily small angular resolutions.

Optical absorption measurement of spin Berry curvature and spin Chern marker

Abstract: In two-dimensional time-reversal symmetric topological insulators described by Dirac models, theZ2topological invariant can be described by the spin Chern number. We present a linear response theory for the spin Berry curvature that integrates to the spin Chern number, and introduce its spectral function that can be measured at finite temperature by momentum- and spin-resolved circular dichroism, which may be achieved by pump-probe type of experiments using spin- and time-resolved ARPES. As a result, the sign of the Pfaffian of theZ2invariant can be directly measured. A spin Chern number spectral function is further introduced from the optical spin current response, and is shown to be measurable from the spin-resolved opacity of two-dimensional materials under circularly polarized light, pointing to an optical measurement of theZ2invariant and a frequency sum rule. The spin Chern number expressed in real space is known to yield a spin Chern marker, and we propose that it may be measurable from spin-resolved local heating rate caused by circularly polarized light. A nonlocal spin Chern marker is further proposed to characterize the quantum criticality near topological phase transitions, and is shown to be equivalent to an overlap between spin-selected Wannier states.

World beyond the nearest neighbors

Abstract: Abstract The structure beyond the nearest neighbor atoms in liquid and glass is characterized by the medium-range order (MRO). In the conventional approach, the MRO is considered to result directly from the short-range order (SRO) in the nearest neighbors. To this bottom–up approach starting with the SRO, we propose to add a top–down approach in which global collective forces drive liquid to form density waves. The two approaches are in conflict with each other, and the compromise produces the structure with the MRO. The driving force to produce density waves provides the stability and stiffness to the MRO, and controls various mechanical properties. This dual framework provides a novel perspective for description of the structure and dynamics of liquid and glass.

Effects of alloying elements on diamond/Cu interface properties based on first-principles calculations

Abstract: Diamond/copper composites with high thermal conductivity and a variable thermal expansion coefficient are promising materials for thermal management applications. However, achieving the desired thermal conductivity of the composite material is difficult due to detachment or weak bonding between diamond and Cu. The interfacial properties of diamond/Cu composites can be improved using metal matrix alloying methods. In this study, we investigate the effects of alloying elements (B, Cr, Hf, Mo, Nb, Si, Ti, V, Zr) on the interfacial properties of diamond/Cu using first-principles calculations. Results showed that all alloying components could increase the interfacial bonding of diamond/Cu. Analysis of the electronic structure revealed that increased interfacial bonding strength after doping was the result of the stronger bonding of the alloying element atoms to the C atoms. The C atoms in the first layer of diamond at the interface formed wave peaks near the Fermi energy level after doping with B or Si atoms, facilitating electron-phonon interaction at the interface. The phonon properties of B4C and SiC were similar to those of diamond, which facilitated phonon-phonon coupling. B and Si were shown to be better alloying elements when interfacial bond strength and heat transfer were considered.

Cooperative diffusion in body-centered cubic iron in Earth and super-Earths’ inner core conditions

Abstract: The physical chemistry of iron at the inner-core conditions is key to understanding the evolution and habitability of Earth and super-Earth planets. Based on full first-principles simulations, we report cooperative diffusion along the longitudinally fast ⟨111⟩ directions of body-centered cubic (bcc) iron in temperature ranges of up to 2000–4000 K below melting and pressures of ∼300–4000 GPa. The diffusion is due to the low energy barrier in the corresponding direction and is accompanied by mechanical and dynamical stability, as well as strong elastic anisotropy of bcc iron. These findings provide a possible explanation for seismological signatures of the Earth’s inner core, particularly the positive correlation between P wave velocity and attenuation. The diffusion can also change the detailed mechanism of core convection by increasing the diffusivity and electrical conductivity and lowering the viscosity. The results need to be considered in future geophysical and planetary models and should motivate future studies of materials under extreme conditions.

Monte Carlo study of cuprate superconductors in a four-band <i>d</i>-<i>p</i> model: Role of orbital degrees of freedom

Abstract: Understanding the complex phase diagram of cuprate superconductors is a long-standing challenging problem. Recent studies have shown that orbital degrees of freedom, both Cu $e_g$ orbitals and O $p$ orbitals, are a key ingredient for a unified understanding of cuprate superconductors, including the material dependence. Here we investigate a four-band $d$-$p$ model derived from the first-principles calculations with the variational Monte Carlo method, which allows us to elucidate competing orders on an equal footing. The obtained results can consistently explain the doping dependence of superconductivity, antiferromagnetic and stripe phases, phase separation in the underdoped region, and also novel magnetism in the heavily-overdoped region. Our four-band $d$-$p$ model with neighbouring intersite interactions is a minimal model to describe the phase diagram comprehensively. The presence of $p$ orbitals is critical to the charge-stripe features, which induce two types of stripe phases with $s'$-wave and $d$-wave bond stripe. On the other hand, the presence of $d_{z^2}$ orbital is indispensable to material dependence of the superconducting transition temperature ($T_{\mathrm{c}}$), and enhances local magnetic moment as a source of novel magnetism in the heavily-overdoped region as well. These findings beyond one-band description could provide a major step toward a full explanation of unconventional normal state and high $T_{\mathrm{c}}$ in cuprate supercondutors.

Reduced TiO₂ with prolonged electron lifetime for improving photocatalytic water reduction activity

Abstract: Abstract The reduction of anatase TiO 2 with NaBH 4 under argon atmosphere at a high temperature resulted in a longer electron lifetime and a larger electron population. The reduced gray anatase sample with disorder layer showed a higher evolution rate of H 2 (130.2 μ mol h −1 g −1 ) compared to pristine TiO 2 (24.1 μ mol h −1 g −1 ) in the presence of Pt co-catalyst in an aqueous glucose solution under exposure to ultraviolet light ( λ ⩽ 400 nm). Ti 3+ and oxygen vacancy defects were proposed to exist in the reduced TiO 2 . A continuum tail forms above the valence band edge top as a result of these two defects, which contribute to the lattice disorder. This is presumably also the case with the conduction band, which has a continuum tail composed of mid-gap states as a result of the defects. The Ti 3+ and oxygen vacancy defects operate as shallow traps for photoexcited electrons, thereby preventing recombination. Since the defects are primarily located at the surface, i.e. in the disorder layer, the photoexcited electrons in shallow traps hence become readily available for the reduction of H 3 O + into H 2 . The prolonged electron lifetime increases the photoexcited electron population in the reduced TiO 2 , resulting in enhanced water reduction activity.

Janus-functionalization induced magnetism and improved optoelectronic properties in two-dimension silicene and germanene: insights from first-principles calculations

Abstract: Abstract In this paper, the structural stability, optoelectronic and magnetic properties of silicene and germanene monolayers Janus-functionalized simultaneously with hydrogen and alkali metal atoms (Li and Na) are investigated systematically by using first-principles calculations. The calculated results of the ab initio molecular dynamics simulations and cohesive energies indicate that all functionalized cases have good stability. Meanwhile, the calculated band structures show that all functionalized cases retain the Dirac cone. Particularly, the cases of HSiLi and HGeLi show metallic nature but retain semiconducting characteristics. Besides, the above two cases can present obvious magnetic behavior and their magnetic moments are mainly originated by the p states of Li atom. The metallic property and weak magnetic character can also be found in the case of HGeNa. While the case of HSiNa exhibits the nonmagnetic semiconducting property with a indirect band gap of 0.42 eV calculated by the HSE06 hybrid functional. It is also found that the optical absorption in the visible region of silicene and germanene can be effectively improved by Janus-functionalization. Specifically, a high optical absorption of visible light in an order of 4.5 × 10 5 cm −1 can be observed in the case of HSiNa. Furthermore, in the visible region, the reflection coefficients of all functionalized cases can also be enhanced. These results demonstrate the feasibility of the Janus-functionalization method to modulate the optoelectronic and magnetic properties of silicene and germanene, expanding their potential applications in the fields of spintronics and optoelectronics.

Superconductivity in Mo₄Ga₂₀As with endohedral gallium clusters

Abstract: We report the discovery and detailed investigation of superconductivity in Mo4Ga20As. Mo4Ga20As crystallizes in a space group ofI4/m(No. 87), with the lattice parametersa= 12.86352 Å andc= 5.30031 Å. The resistivity, magnetization, and specific heat data reveal Mo4Ga20As to be a type-II superconductor withTc= 5.6 K. The upper and lower critical fields are estimated to be 2.78 T and 22.0 mT, respectively. In addition, electron-phonon coupling in Mo4Ga20As is possibly stronger than the BCS weak-coupling limit. First-principles calculations suggest the Fermi level being dominated by the Mo-4dand Ga-4porbitals.

The cumulant Green’s functions method for the Hubbard model

Abstract: We use the cumulant Green's functions method (CGFM) to study the single-band Hubbard model. The starting point of the method is to diagonalize a cluster ('seed') containingNcorrelated sites and employ the cumulants calculated from the cluster solution to obtain the full Green's functions for the lattice. All calculations are done directly; no variational or self-consistent process is needed. We benchmark the one-dimensional results for the gap, the double occupancy, and the ground-state energy as functions of the electronic correlation at half-filling and the occupation numbers as functions of the chemical potential obtained from the CGFM against the corresponding results of the thermodynamic Bethe ansatz and the quantum transfer matrix methods. The particle-hole symmetry of the density of states is fulfilled, and the gap, occupation numbers, and ground-state energy tend systematically to the known results as the cluster size increases. We include a straightforward application of the CGFM to simulate the singles occupation of an optical lattice experiment with lithium-6 atoms in an eight-site Fermi-Hubbard chain near half-filling. The method can be applied to any parameter space for one, two, or three-dimensional Hubbard Hamiltonians and extended to other strongly correlated models, like the Anderson Hamiltonian, thet - J, Kondo, and Coqblin-Schrieffer models.

Topological skyrmion phases of matter

Abstract: Abstract We introduce topological phases of matter defined by skyrmions in the ground state spin—or pseudospin—expectation value textures in the Brillouin zone, the chiral and helical topological skyrmion phases of matter. These phases are protected by a symmetry present in centrosymmetric superconductors. We consider a tight-binding model for spin-triplet superconductivity in transition metal oxides and find it realizes each of these topological skyrmion phases. The chiral phase is furthermore realized for a parameter set characterizing Sr 2 RuO 4 with spin-triplet superconductivity. We also find two types of topological phase transitions by which the skyrmion number can change. The second type occurs without the closing of energy gaps in a system described by a quadratic Hamiltonian without breaking the protecting symmetries when atomic spin–orbit coupling is non-negligible and there is a suitable additional degree of freedom. This contradicts the ‘flat band’ limit assumption important in use of entanglement spectrum and Wilson loops, and in construction of the ten-fold way classification scheme of topological phases of matter. We furthermore predict two kinds of bulk-boundary correspondence signatures—one for measurements which execute a partial trace over degrees of freedom other than spin, which yields quantized transport signatures—and a second resulting from skyrmions trapping defects with their own non-trivial topology that is discussed in a second work, which yields generalizations of unpaired Majorana zero-modes.

Effects of spatial quantization and Rabi-shifted resonances in single and double excitation of quantum wells and wires induced by few-photon optical field

Abstract: Abstract We develop a fully quantum theoretical approach which describes the dynamics of Frenkel excitons and bi-excitons induced by few photon quantum light in a quantum well or wire (atomic chain) of finite lateral size. The excitation process is found to consist in the Rabi-like oscillations between the collective symmetric states characterized by discrete energy levels. At the same time, the enhanced excitation of high-lying free exciton states being in resonance with these ‘dressed’ polariton eigenstates is revealed. This found new effect is referred to as the formation of Rabi-shifted resonances and appears to be the most important and new feature established for the excitation of 1D and 2D nanostructures with final lateral size. The found new physics changes dramatically the conventional concepts of exciton formation and play an important role for the development of nanoelectronics and quantum information protocols involving manifold excitations in nanosystems.

Experimental and theoretical thermodynamic studies in Ba₂MgReO₆—the ground state in the context of Jahn-Teller effect

Abstract: We address the degeneracy of the ground state multiplet on the 5$d^1$ Re$^{6+}$ ion in double perovskite Ba$_{2}$MgReO$_{6}$ using a combination of specific heat measurements and density functional calculations. For Ba$_{2}$MgReO$_{6}$, two different ground state multiplets have previously been proposed - a quartet (with degeneracy $N$=4) [1] and a doublet ($N$=2) [2]. Here we employ two independent methods for the estimation of phonon contribution in heat capacity data to obtain the magnetic entropy $S_{mag}$, which reflects the degeneracy of the ground state multiplet $N$ through $S_{mag}=R$ln$N$. In both cases, we obtain a better fit to $S_{mag}=R$ln2 indicating evidence of $N$=2 degeneracy in the range from 2 to 120~K. The detailed nature of the ground state multiplet in Ba$_{2}$MgReO$_{6}$ remains an open question.

A primer on twistronics: a massless Dirac fermion’s journey to moiré patterns and flat bands in twisted bilayer graphene

Abstract: The recent discovery of superconductivity in magic-angle twisted bilayer graphene (TBLG) has sparked a renewed interest in the strongly-correlated physics ofsp2carbons, in stark contrast to preliminary investigations which were dominated by the one-body physics of the massless Dirac fermions. We thus provide a self-contained, theoretical perspective of the journey of graphene from its single-particle physics-dominated regime to the strongly-correlated physics of the flat bands. Beginning from the origin of the Dirac points in condensed matter systems, we discuss the effect of the superlattice on the Fermi velocity and Van Hove singularities in graphene and how it leads naturally to investigations of the moiré pattern in van der Waals heterostructures exemplified by graphene-hexagonal boron-nitride and TBLG. Subsequently, we illuminate the origin of flat bands in TBLG at the magic angles by elaborating on a broad range of prominent theoretical works in a pedagogical way while linking them to available experimental support, where appropriate. We conclude by providing a list of topics in the study of the electronic properties of TBLG not covered by this review but may readily be approached with the help of this primer.

Numerical investigation of localization in two-dimensional quasiperiodic mosaic lattice

Abstract: A one-dimensional lattice model with mosaic quasiperiodic potential is found to exhibit interesting localization properties, e.g. clear mobility edges (Wang et al 2020 Phys. Rev. Lett. 125 196604). We generalize this mosaic quasiperiodic model to a two-dimensional version, and numerically investigate its localization properties: the phase diagram from the fractal dimension of the wavefunction, the statistical and scaling properties of the conductance. Compared with disordered systems, our model shares many common features but also exhibits some different characteristics in the same dimensionality and the same universality class. For example, the sharp peak at g∼0 of the critical distribution and the large g limit of the universal scaling function β resemble those behaviors of three-dimensional disordered systems.

Plane wave implementation of the magnetic force theorem for magnetic exchange constants: application to bulk Fe, Co and Ni

Abstract: Abstract We present a plane wave implementation of the magnetic force theorem, which provides a first principles framework for extracting exchange constants parameterizing a classical Heisenberg model description of magnetic materials. It is shown that the full microscopic exchange tensor may be expressed in terms of the static Kohn–Sham susceptibility tensor and the exchange-correlation magnetic field. This formulation allows one to define arbitrary magnetic sites localized to predefined spatial regions, hence rendering the problem of finding Heisenberg parameters independent of any orbital decomposition of the problem. The susceptibility is calculated in a plane wave basis, which allows for systematic convergence with respect to unoccupied bands and spatial representation. We then apply the method to the well-studied problem of calculating adiabatic spin wave spectra for bulk Fe, Co and Ni, finding good agreement with previous calculations. In particular, we utilize the freedom of defining magnetic sites to show that the calculated Heisenberg parameters are robust towards changes in the definition of magnetic sites. This demonstrates that the magnetic sites can be regarded as well-defined and thus asserts the relevance of the Heisenberg model description despite the itinerant nature of the magnetic state.

Collective excitations in a melt of fast phase change material GeCu₂Te₃

Abstract: Abstract Inelastic x-ray scattering measurements have been carried out to investigate atomic dynamics in a melt of fast phase change material GeCu 2 Te 3 . The dynamic structure factor was analysed using the model function with three damped harmonic oscillator components. By investigating the correlation between the excitation energy and the linewidth, and that between the excitation energy and the intensity on contour maps of a relative approximate probability distribution function proportional to exp ( − χ 2 / N ) , we could judge the reliability of each inelastic excitation in the dynamic structure factor. The results indicate that there are two inelastic excitation modes besides the longitudinal acoustic one in the liquid. The lower energy excitation could be assigned to the transverse acoustic one whereas the higher energy one disperses like fast sound. The latter result may imply that the liquid ternary alloy exhibits a microscopic phase separation tendency.

Effects of metallic electrodes on the thermoelectric properties of zigzag graphene nanoribbons with periodic vacancies

Abstract: Abstract We theoretically analyze the thermoelectric properties of graphene quantum dot arrays (GQDAs) with line- or surface-contacted metal electrodes. Such GQDAs are realized as zigzag graphene nanoribbons (ZGNRs) with periodic vacancies. Gaps and minibands are formed in these GQDAs, which can have metallic and semiconducting phases. The electronic states of the first conduction (valence) miniband with nonlinear dispersion may have long coherent lengths along the zigzag edge direction. With line-contacted metal electrodes, the GQDAs have the characteristics of serially coupled quantum dots (SCQDs) if the armchair edge atoms of the ZGNRs are coupled to the electrodes. By contrast, the GQDAs have the characteristics of parallel quantum dots if the zigzag edge atoms are coupled to the electrodes. The maximum thermoelectric power factors of SCQDs with line-contacted electrodes of Cu, Au, Pt, Pd, or Ti at room temperature were similar or greater than 0.186 nW K −1 ; their figures of merit were greater than three. GQDAs with line-contacted metal electrodes have much better thermoelectric performance than surface contacted metal electrodes.

Superconductivity in Ce-based cage compounds

Abstract: Cerium-based ternary compounds CeNi$_2$Cd$_{20}$ and CePd$_2$Cd$_{20}$ do not exhibit long-range order down to millikelvin temperature range. Given the large separation between cerium ions which significantly reduces the superexchange interactions and vanishingly small RKKY interaction, here we show that nodal superconductivity mediated by the valence fluctuations must be a ground state in these materials. We propose that the critical temperature for the superconducting transition can be significantly increased by applying hydrostatic pressure. We employ an extended periodic Anderson lattice model which includes the long-range Coulomb interactions between the itinerant electrons as well as the local Coulomb interaction between the predominantly localized and itinerant electrons to compute a critical temperature of the superconducting transition. Using the slave-boson approach we show that fluctuations mediated by the repulsive electron-electron interactions lead to the emergence of d-wave superconductivity.

Plasmon-enhanced photoluminescence and Raman spectroscopy of silver nanoparticles grown by solid state dewetting

Abstract: The growth of the metallic nanoparticles (NPs) on the solid substrate with the desired shape and size is a critical issue for application of these NPs in solid-state devices. Solid state dewetting (SSD) technique is simple, low cost and can be used to fabricate the metallic NPs with control on the shape and size on different substrates. In this work, silver NPs (Ag NPs) were grown on corning glass substrate by SSD of silver precursor thin film deposited at different substrate temperatures by RF sputtering. The influence of the substrate temperature on the growth of Ag NPs and their several properties like localized surface plasmon resonance (LSPR), photoluminescence (PL), and Raman spectroscopy is studied. The size of the NPs was found to vary from 25 nm to 70 nm with the variation in substrate temperature from room temperature (RT) to400∘C. For the RT films, the LSPR peak position of Ag NPs is around 474 nm. A red shift in LSPR peak for films deposited at higher temperature is observed due to change in the particle size and interparticle separation. Photoluminescence spectra suggests the presence of two photoluminescence bands at 436 and 474 nm corresponding to Ag NPs radiative interband transition and LSPR band. An intense Raman peak was observed at 1587 cm-1. Enhancement in PL peak intensity and Raman peak intensity is found to be in accordance with the LSPR of Ag NPs.

Cooperative diffusion in body-centered cubic iron in Earth and super-Earths’ inner core conditions

Abstract: Abstract The physical chemistry of iron at the inner-core conditions is key to understanding the evolution and habitability of Earth and super-Earth planets. Based on full first-principles simulations, we report cooperative diffusion along the longitudinally fast ⟨ 111 ⟩ directions of body-centered cubic (bcc) iron in temperature ranges of up to 2000–4000 K below melting and pressures of ∼300–4000 GPa. The diffusion is due to the low energy barrier in the corresponding direction and is accompanied by mechanical and dynamical stability, as well as strong elastic anisotropy of bcc iron. These findings provide a possible explanation for seismological signatures of the Earth’s inner core, particularly the positive correlation between P wave velocity and attenuation. The diffusion can also change the detailed mechanism of core convection by increasing the diffusivity and electrical conductivity and lowering the viscosity. The results need to be considered in future geophysical and planetary models and should motivate future studies of materials under extreme conditions.

Carrier and phonon transport in 2D InSe and its Janus structures

Abstract: Recently, two-dimensional (2D) Indium Selenide (InSe) has been receiving much attention in the scientific community due to its reduced size, extraordinary physical properties, and potential applications in various fields. In this review, we discussed the recent research advancement in the carrier and phonon transport properties of 2D InSe and its related Janus structures. We first introduced the progress in the synthesis of 2D InSe. We summarized the recent experimental and theoretical works on the carrier mobility, thermal conductivity, and thermoelectric characteristics of 2D InSe. Based on the Boltzmann transport equation (BTE), the mechanisms underlying carrier or phonon scattering of 2D InSe were discussed in detail. Moreover, the structural and transport properties of Janus structures based on InSe were also presented, with an emphasis on the theoretical simulations. At last, we discussed the prospects for continued research of 2D InSe.

Valley-polarized and enhanced transmission in graphene with a smooth strain profile

Abstract: Abstract We explore the influence of strain on the valley-polarized transmission of graphene by employing the wave-function matching and the non-equilibrium Green’s function technique. When the transmission is along the armchair direction, we show that the valley polarization and transmission can be improved by increasing the width of the strained region and increasing (decreasing) the extensional strain in the armchair (zigzag) direction. It is noted that the shear strain does not affect transmission and valley polarization. Furthermore, when we consider the smooth strain barrier, the valley-polarized transmission can be enhanced by increasing the smoothness of the strain barrier. We hope that our finding can shed new light on constructing graphene-based valleytronic and quantum computing devices by solely employing strain.

A first-principles study of 1D and 2D C₆₀ nanostructures: strain effects on band alignments and carrier mobility

Abstract: In the breakthrough progress made in the latest experiment Houet al(2022Nature606507), 2DC60polymer was exfoliated from the quasi-hexagonal bulk crystals. BulkC60polymer with quasi-tetragonal phase was found to easily form 1D fullerene structure withC60molecules connected by C=C. Inspired by the experiment, we investigate the strain behaviors of 1D and 2DC60polymers by first-principles calculations. Some physical properties of these low dimensionalC60polymers, including structural stability, elastic behavior, band alignment and carrier mobility, are predicted. Compared with fullereneC60molecule, 1D and 2DC60polymers are metastable. At absolute zero temperature, 1DC60bears a uniaxial tensile strain less than 11.5%, and 2D monolayerC60withstands a biaxial tensile strain less than 7.5%. At 300 K,ab initiomolecular dynamics confirm that they can withstand the strains of 9% and 5%, respectively. Strain engineering can adjust the absolute position of the band edge. In the absence of strain, carrier mobility is predicted to beµe= 398 andµh= 322cm2V-1s-1for 1DC60polymer, andμe,x=74/μe,y= 34cm2V-1s-1andμh,x=646/μh,y= 1487cm2V-1s-1for 2DC60polymer. Compared with other carbon based semiconductors, theseC60polymers exhibit high effective mass, resulting in low mobility.