Intrinsic Ground State Research Articles

The magnetic properties, flat and Dirac bands of two-dimensional room-temperature ferromagnetic Kagome material Mn3Sn3Se2

The Kagome lattice is rich in unique electronic and magnetic properties, such as flat band, superconductivity, charge density waves, and so on. In this paper, the magnetic properties, flat and Dirac bands of monolayer Mn3Sn3Se2 with Kagome lattice are investigated based on first-principles calculations. A total of four magnetic configurations are considered, and the intrinsic ground state of Mn3Sn3Se2 is identified as the ferromagnetic state. Strain has a significant effect on its magnetic ground state, which changes to an in-plane AFM state when the tensile strain exceeds 5 %. Monolayer Mn3Sn3Se2 has an out-of-plane magnetic anisotropy of up to 0.777 meV, and the Curie temperature is 528 K. The band structure of the FM state is shown to be metallic, and spin polarized flat and Dirac bands appear near the Fermi level, which are degenerate. Monolayer Mn3Sn3Se2 changes to half-metallic when a strain of 1%–2% is applied. Strain and correlation effects can significantly alter the flatness of flat band and the relative energy with Dirac bands. These results not only enrich the family of two-dimensional ferromagnets, but also provide a reference for studying the regulation of flat and Dirac bands.

Intrinsic magnetism in superconducting infinite-layer nickelates

The discovery of superconductivity in Nd0.8Sr0.2NiO2 (ref. 1) introduced a new family of layered nickelate superconductors that has now been extended to include a range of strontium doping2,3, praseodymium or lanthanum in place of neodymium4–7, and the five-layer compound Nd6Ni5O12 (ref. 8). A number of studies have indicated that electron correlations are strong in these materials9–15, a feature that often leads to the emergence of magnetism. Here we report muon spin rotation/relaxation studies of a series of superconducting infinite-layer nickelates. Regardless of the rare earth ion or doping, we observe an intrinsic magnetic ground state arising from local moments on the nickel sublattice. The coexistence of magnetism—which is likely to be antiferromagnetic and short-range ordered—with superconductivity is reminiscent of some iron pnictides16 and heavy fermion compounds17, and qualitatively distinct from the doped cuprates18. Measurements of four different infinite-layer nickelates show that magnetic behaviour coexists with superconductivity. This is different from what is seen in cuprates, giving a strong distinction between the two classes of oxide superconductors.

Rotation symmetry breaking in the normal state of a kagome superconductor KV3Sb5

Recently discovered kagome superconductors AV3Sb5 (A=K, Rb, Cs) provide a fresh opportunity to realize and study correlation-driven electronic phenomena on a kagome lattice. The observation of a 2a0 by 2a0 charge density wave (CDW) in the normal state of all members of AV3Sb5 kagome family has generated an enormous amount of interest, in an effort to uncover the nature of this CDW state, and identify any "hidden" broken symmetries. We use spectroscopic-imaging scanning tunneling microscopy to reveal a pronounced intensity anisotropy between different 2a0 CDW directions in KV3Sb5. In particular, by examining the strength of ordering wave vectors as a function of energy in Fourier transforms of differential conductance maps, we find that one of the CDW directions is distinctly different compared to the other two. This observation points towards an intrinsic rotation symmetry broken electronic ground state, where the symmetry is reduced from C6 to C2. Furthermore, in contrast to previous reports, we find that the CDW phase is insensitive to magnetic field direction, regardless of the presence or absence of atomic defects. Our experiments, combined with earlier observations of a stripe 4a0 charge ordering in CsV3Sb5, establish correlation-driven rotation symmetry breaking as a unifying feature of AV3Sb5 kagome superconductors.

Review of the Yb3+:ScBO3 Laser Crystal Growth, Characterization, and Laser Applications

Passive Q-switching is an effective approach for generating pulsed lasers, owing to its compact and additional modulation-free design. However, to compare favorably with active Q-switching and multi-stage amplification, the output energy needs to be enhanced for practical applications. Kramers Ytterbium ion (Yb3+)-doped borate crystals, with their excellent energy storage capacity, have been proven to be high-potential laser gain mediums for achieving pulsed lasers with moderate and high output energy using passive Q-switching technology. In this study, the growth, characterization, and laser generation of one Yb3+-doped borate crystal, the Yb3+:ScBO3 crystal, are systematically reviewed. The continuous-wave and passive Q-switching laser characteristics are presented in detail, and the self-pulsations derived from intrinsic ground-state reabsorption are also demonstrated. The specific characteristics and experiments confirm the potential of the Yb3+:ScBO3 crystal for future pulsed laser applications with moderate or even high energy output.

Effect of external electromagnetic radiation on the anomalous metallic behavior in superconducting Ta thin films

We investigated transport characteristics of superconducting Ta thin films with three configurations in rf radiation filters; no filter, only room-temperature filters, and low-temperature filters in addition to room-temperature filters. The transport properties near the transition temperature are strongly dependent on whether the room-temperature filter is installed or not. The entire transition is shifted to higher temperature with loading layers of the room-temperature filters. Once the zero-resistance state is achieved at B=0, no strong radiation effect is observed even with low-temperature filters installed. When magnetic field is turned on, the nonzero-resistance saturation at low temperatures is revealed without low-temperature filters, which has been considered to be magnetic-field-induced quantum metallic phase. However, the insertion of the additional low-temperature filter weakens the saturation of the resistance, the signature of the metallic behavior. This observation suggests that the previously reported anomalous metallic state in Ta films is mainly induced by the unfiltered radiation and, thus, the intrinsic metallic ground state should be limited to the narrow range of magnetic fields near the critical point, if exists.

Intrinsic phonon-mediated superconductivity in graphene-like BSi lattice

The research of new superconductors is an ongoing field for the fundamental significances and potential applications, and two-dimensional (2D) nanomaterials open a new alluring branch for exploration. Here we predict by first-principles calculations that 2D pristine graphene-like BSi monolayer is a phonon-mediated superconductor above the boiling point of liquid helium. The intrinsic covalent-metallic ground state, large density of states at Fermi energy, proper electronic organization as well as strong coupling of out-of-plane phonons and electrons endow an intermediate electron-phonon coupling of ~1.12, rendering this honeycomb sheet as a conventional superconductor with a relatively high Tc ~ 11 K. As the global minimum structure in the 2D space previously predicted, this superconducting BSi monolayer may be feasible experimentally. Our finding provides a new field of superconducting nanomaterials for study.

Intrinsic Ultracontractivity and Ground State Estimates of Non-local Dirichlet forms on Unbounded Open Sets

In this paper we consider a large class of symmetric Markov processes $${X=(X_t)_{t\ge0}}$$ on $${\mathbb{R}^d}$$ generated by non-local Dirichlet forms, which include jump processes with small jumps of $${\alpha}$$ -stable-like type and with large jumps of super-exponential decay. Let $${D\subset \mathbb{R}^d}$$ be an open (not necessarily bounded and connected) set, and $${X^D=(X_t^D)_{t \ge 0}}$$ be the killed process of X on exiting D. We obtain explicit criterion for the compactness and the intrinsic ultracontractivity of the Dirichlet Markov semigroup $${(P^{D}_t)_{t\ge0}}$$ of XD. When D is a horn-shaped region, we further obtain two-sided estimates of ground state in terms of jumping kernel of X and the reference function of the horn-shaped region D.

Undoped high-Tc superconductivity in T’-La1.8Eu0.2CuO[formula omitted] revealed by 63,65Cu and 139La NMR: Bulk superconductivity and antiferromagnetic fluctuations

We performed 63,65Cu and 139La NMR measurements of T’-La1.8Eu0.2CuO4+δ (T’-LECO) with the Nd2CuO4-type structure (so-called T’-structure). As a result, we detected the 63,65Cu NMR signal under finite magnetic fields and found superconductivity without antiferromagnetic (AF) order only in the reduced T’-LECO, where excess apical oxygen atoms are properly removed. This indicates that the intrinsic ground state of the ideal T’-LECO is a paramagnetic and superconducting (SC) state. Below Tc, the Knight shift was found to rapidly decrease, which indicates the emergence of bulk superconductivity due to spin-singlet Cooper pairs in the reduced T’-LECO. In the SC state of the reduced T’-LECO, moreover, a characteristic temperature dependence of the spin-lattice relaxation rate 1/T1 was observed, which implies the existence of nodal lines in the SC gap. These findings suggest that the superconductivity in the reduced T’-LECO probably has d-wave symmetry. In the normal state of the reduced T’-LECO, on the other hand, AF fluctuations were found to exist from the temperature dependence of 1/T1T, though no clear pseudogap behavior was observed. This suggests that the AF correlation plays a key role in the superconductivity of undoped high-Tc cuprate superconductors with the T’-structure.

Dependence of Ion Transport on the Electronegativity of the Constituting Atoms in Ionic Crystals.

Ion transport in electrode and electrolyte materials is a key process in Li-based batteries. In this work, we study the mechanism and activation energy of ion transport (Ea ) in rock-salt Li-based LiX (X=Cl, Br, and I) materials. It is found that Ea at low external voltages, where Li-X Schottky pairs are the most favorable defect types, is about 0.42 times the Gibbs energy of formation of LiX compound (ΔGf ). The value of 0.42 is the slope of the electronegativity of anions of binary Li-based materials as a function of ΔGf . At high voltages, where the Fermi level is located very close to the valence band maximum (VBM), electrons can be excited from the VB to Li vacancy-induced states close to the Fermi level. Under this condition, the formation of Li vacancies that are compensated by holes is energetically more favorable than that of Li-X Schottky pairs, and therefore, the activation energies are lower in the former case. The wide range of reported experimental values of activation energies lies between calculated values at low and high voltage regimes. This work motivates further studies on the relation between the activation energy for ionic conductivity in solid materials and the intrinsic ground-state properties of their free atoms.

Intrinsic magnetism in penta-hexa-graphene: A first-principles study

Recently, several monolayer carbon allotropes have been proposed. The magnetic properties of these metal-free materials are investigated, and we explore a special type of all carbon system having an intrinsic magnetic ground state. The structure is composed of mixing pentagonal and hexagonal rings of carbon atoms, such that the unit cell consists of eleven atoms, where two C atoms each have an unpaired electron each with a local magnetic moment. The antiferromagnetic (AFM) state has a lower energy than the ferromagnetic (FM) one. However, a strain-driven transition to the FM ground state is possible. The application of strain not only lowers the energy of the FM state but it also induces an energy barrier of about 13 meV/(magnetic atom) to protect the FM state from excitation. Our findings based on first-principles calculations will motivate other works on similar metal-free magnetic monolayer materials and will have an impact on their possible applications in spintronic devices.

Oscillating edge states in one-dimensional MoS2 nanowires.

Reducing the dimensionality of transition metal dichalcogenides to one dimension opens it to structural and electronic modulation related to charge density wave and quantum correlation effects arising from edge states. The greater flexibility of a molecular scale nanowire allows a strain-imposing substrate to exert structural and electronic modulation on it, leading to an interplay between the curvature-induced influences and intrinsic ground-state topology. Herein, the templated growth of MoS2 nanowire arrays consisting of the smallest stoichiometric MoS2 building blocks is investigated using scanning tunnelling microscopy and non-contact atomic force microscopy. Our results show that lattice strain imposed on a nanowire causes the energy of the edge states to oscillate periodically along its length in phase with the period of the substrate topographical modulation. This periodic oscillation vanishes when individual MoS2 nanowires join to form a wider nanoribbon, revealing that the strain-induced modulation depends on in-plane rigidity, which increases with system size.

Enhanced superconductivity by strain and carrier-doping in borophene: A first principles prediction

By first principles calculations, we predict that the recently prepared borophene is a pristine two-dimensional monolayer superconductor in which the superconductivity can be significantly enhanced by strain and charge carrier doping. The intrinsic metallic ground state with high density of states at Fermi energy and strong Fermi surface nesting lead to sizeable electron-phonon coupling, making the freestanding borophene superconduct with Tc close to 19.0 K. The tensile strain can increase the Tc to 27.4 K, while the hole doping can notably increase Tc to 34.8 K. The results indicate that the borophene grown on substrates with large lattice parameters or under photoexcitation can show enhanced superconductivity with Tc far above the liquid hydrogen temperature of 20.3 K, which will largely broaden the applications of such promising material.

Giant exciton oscillator strength and radiatively limited dephasing in two-dimensional platelets

We measured the intrinsic ground-state exciton dephasing and population dynamics in colloidal quasi two-dimensional (2D) CdSe nanoplatelets at low temperature (5-50K) using transient resonant four-wave mixing in heterodyne detection. Our results indicate that below 20K the exciton dephasing is lifetime limited, with the exciton population lifetime being as fast as 1ps. This is consistent with an exciton lifetime given by a fast radiative decay due to the large in-plane coherence area of the exciton center-of-mass motion in these quasi 2D systems compared to spherical nanocrystals.

Translationally Invariant Calculations of Form Factors, Densities and Momentum Distributions for Finite Nuclei with Short–Range Correlations Included: A Fresh Look

The approach proposed in the 70s (Dementiji et al. in Sov J Nucl Phys 22:6–9, 1976), when describing the elastic and inelastic electron scattering off 4He, and elaborated in (Shebeko et al.in Eur Phys J A27:143–155, 2006) for calculations of the one-body, two-body and more complex density matrices of finite bound systems has been applied (Shebeko and Grigorov in Ukr J Phys 52:830–842, 2007; Shebeko et al. in Eur. Phys. J. A48:153–172, 2012) in studying a combined effect of the center-of-mass motion and nucleon–nucleon short-range correlations on the nucleon density and momentum distributions in light nuclei beyond the independent particle model. Unlike a common practice, suitable for infinite bound systems, these distributions are determined as expectation values of appropriate intrinsic operators that depend upon the relative coordinates and momenta (Jacobi variables) and act on the intrinsic ground–state wave functions (WFs). The latter are constructed in the so-called fixed center-of-mass approximation, starting with a mean–field Slater determinant modified by some correlator (e.g., after Jastrow or Villars). Our numerical calculations of the charge form factors (FCH(q)), densities and momentum distributions have been carried out for nuclei 4He and 16O choosing, respectively, the 1s and 1s−1p Slater determinants of the harmonic oscillator model as trial, nontranslationally invariant WFs.

Translationally invariant calculations of form factors, nucleon densities and momentum distributions for finite nuclei with short-range correlations included

Relying upon our previous treatment of the density matrices for nuclei (in general, nonrelativistic self-bound finite systems) we are studying a combined effect of center-of-mass motion and short-range nucleon-nucleon correlations on the nucleon density and momentum distributions in light nuclei (4He and 16O). Their intrinsic ground-state wave functions are constructed in the so-called fixed center-of-mass approximation, starting with mean-field Slater determinants modified by some correlator (e.g., after Jastrow or Villars). We develop the formalism based upon the Cartesian or boson representation, in which the coordinate and momentum operators are linear combinations of the creation and annihilation operators for oscillatory quanta in the three different space directions, and get the own “Tassie-Barker” factors for each distribution and point out other model-independent results. After this separation of the center-of-mass motion effects we propose additional analytic means in order to simplify the subsequent calculations (e.g., within the Jastrow approach or the unitary correlation operator method). The charge form factors, densities and momentum distributions of 4He and 16O evaluated by using the well-known cluster expansions are compared with data, our exact (numerical) results and microscopic calculations.

Semimicroscopic description of backbending phenomena in some deformed even-even nuclei

The mechanism of backbending is semi-phenomenologically investigated based on the hybridization of two rotational bands. These bands are defined by treating a model Hamiltonian describing two interacting subsystems: a set of particles moving in a deformed mean field and interacting among themselves through an effective pairing force and a phenomenological deformed core whose intrinsic ground state is an axially symmetric coherent boson state. The two components interact with each other by a quadrupole-quadrupole and a spin-spin interaction. The total Hamiltonian is considered in the space of states with good angular momentum, projected from a quadrupole deformed product function. The single-particle factor function defines the nature of the rotational bands, one corresponding to the ground band in which all particles are paired and another one built upon a $i_{13/2}$ neutron broken pair. The formalism is applied to six deformed even-even nuclei, known as being good backbenders. Agreement between theory and experiment is fairly good.

Intrinsic Electronic Transitions of the Absorption Spectrum of (OPy)2Ti(TAP)2: Implications Toward Photostructural Modifications

Theoretical calculations based on time-dependent density functional theory are used to characterize the electronic absorption spectrum of a heteroleptic Ti-alkoxide molecule, (OPy)(2)Ti(TAP)(2) [OPy = pyridine carbinoxide, TAP = 2,4,6 tris(dimethylamino)phenoxide] under investigation as a photosensitive precursor for use in optically initiated solution synthesis of the metal oxide. Computational results support the assignment of UV absorption features observed in solid-state precursor films to key intrinsic ground-state transitions that involve ligand-to-metal charge transfer and pi-pi* transitions within the cyclic ligand moieties present. The nature of electron density redistribution associated with these transitions provides early insight into the excitation wavelength dependence of photostructural modification previously observed in this precursor system.

The np interaction effects on the double-beta decay nuclear matrix elements for medium-mass nuclei

The quality of Hartree-Fock-Bogolyubov wave functions is tested by comparing the theoretically calculated results with the available experimental data for a number of spectroscopic properties like yrast spectra, reduced B(E2) transition probabilities, quadrupole moments, and g factors for the nuclei involved in 2νββ decay. It is observed that the np interactions vis-à-vis the deformations of the intrinsic ground states of medium-mass nuclei play a crucial role in the fine tuning of the nuclear matrix elementsM 2ν.

Equal rank embedding and its related construction to superconformal field theories

The lowest lines of Euler multiplets corresponding to massless and massive supersymmetric representations are classified. At the level of representation theory, the Euler multiplets constructed by the GKRS method of equal rank embedding of semisimple complex Lie algebras are found to be the intrinsic ground states of superconformal field theories according to the Kazama–Suzuki construction.

Excited State Effects in the Dielectric Function of a 2D Boson System

We present calculations for the dielectric function and collective modes of a two-dimensional interacting gas of bosons (excitons) in the xy plane which can be polarized by the application of an electric field in the z direction. Previous work has explored the response of the density fluctuations while excitons lie in their intrinsic ground state. We extend the formalism here by taking into account the internal degrees of freedom of the excitons, and their possible interplay with the density-fluctuation modes of the system. In the limit of low temperature, we find collective normal modes related to the various degrees of freedom. Our calculations of the corresponding intrinsic oscillator strength show that optical-like modes associated to the excited states become increasingly damped when temperature is raised, as the occupation factors change the overall response.