Physical Review B
ISSN / EISSN : 2469-9950 / 2469-9969
Published by: American Physical Society (APS) (10.1103)
Total articles ≅ 33,068
Latest articles in this journal
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.184106
We have performed a combined experimental and theoretical study of the system to understand the progressive evolution of the crystal structure and physical properties as a function of Co content. We find that all the arc-melted polycrystalline samples show superstructure ordering similar to CoMnSb. In the CoMnSb superstructure with symmetry, one set of the sites is filled with Co atoms while the other set is vacant. With increasing Co content, although the vacant set of sites gets progressively filled with the Co atoms, some of the Co atoms segregate out of the main phase into the grain boundaries. The maximum Co that enters in the phase is . Thus, we find that the theoretically predicted in phase does not stabilize. All the samples are ferromagnetic above room temperature and the trend in the measured magnetic moments with increasing , agrees reasonably well with the density-functional theory calculations done using the structural and compositional parameters obtained from the Rietveld refinement of the synchrotron x-ray diffraction patterns. However, the electronic structure indicates that in spite of the large magnetic moment, none of the alloys are half metallic. Finally, we find that a minor deviation from stoichiometry in CoMnSb, i.e., excess of Co and Sb as compared to Mn, is accommodated in the set of vacant sites of the superstructure. This explains the increase in the lattice parameter and the saturation magnetization, as compared to the calculated stoichiometric CoMnSb superstructure. Calculations also predict that this minor deviation from stoichiometry destroys the half metallicity in the CoMnSb superstructure.
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.205119
We study the single-orbital Hubbard model on the half-filled decorated honeycomb lattice. In the noninteracting theory at half filling the Fermi energy lies within a flat band where strong correlations are enhanced. The lattice is highly frustrated. We find a correlation driven first-order metal-insulator transition to two different insulating ground states—a dimer valence bond solid Mott insulator when intertriangle correlations dominate, and a broken -symmetry antiferromagnet that arises from frustration when intratriangle correlations dominate. The metal-insulator transitions into these two phases have very different characters. The metal-broken antiferromagnetic transition is driven by spontaneous symmetry breaking that lifts the topologically required degeneracy at the Fermi energy and opens an energy gap in the quasiparticle spectrum. The metal-dimer valence bond solid transition breaks no symmetries of the Hamiltonian. It is caused by strong correlations renormalizing the electronic structure into a phase that is adiabatically connected to both the trivial band insulator and the ground state of the spin-1/2 Heisenberg model in the relevant parameter regime. Therefore, neither of these metal-insulator transitions can be understood in either the Brinkmann-Rice or Slater paradigms.
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.195122
We have carried out soft x-ray photoemission experiments on itinerant ferromagnet to investigate how the electronic state varies with doping concentration. The Ru -derived coherent part of the valence spectra develops significantly with increasing for , which can be explained by the suppression of the ferromagnetic exchange splitting. With further increasing , this development is overwhelmed by the spectral weight transfer from the coherent to the incoherent parts due to the electron correlation. The enhancement of the electron correlation effect with doping is also confirmed by the Ru core-level spectra as the suppression of the well-screened peak. In contrast to the remarkable variation of the Ru spectral intensity as a function of , the valence spectra hardly depend on temperature and do not show any noticeable change across the magnetic transition temperatures, indicating that the temperature dependence of the exchange splitting cannot be explained by a simple Stoner picture. We compare the present photoemission results with those for isostructural ( and Ca) and discuss the origin of the difference in the magnetic property between these doped compounds.
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.174418
Magnetic susceptibility, specific heat, and muon spin relaxation () measurements have been performed on a synthesized three-dimensional sandglass-type lattice , where two inequivalent sets of non-Kramers ions ( and show crystal electrical field effect at different temperature ranges. The existence of an ordered or a glassy state down to 0.1 K in zero field is excluded. The low-energy properties of are dominated by the lowest non-Kramers quasidoublet of , and the energy splitting is regarded as an intrinsic transverse field. Therefore, the low-temperature paramagnetic phenomenon in is explained by a transverse field Ising model, which is supported by the quantitative simulation of specific heat data. In addition, the perturbation from may play an important role in accounting for the low temperature spin dynamics behavior observed by .
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.195416
Graphene with its dispersion relation resembling that of photons offers ample opportunities for applications in electron optics. The spacial variation of carrier density by external gates can be used to create electron waveguides, in analogy to optical fiber, with additional confinement of the carriers in bipolar junctions leading to the formation of few transverse guiding modes. We show that waveguides created by gating graphene with carbon nanotubes (CNTs) allow obtaining sharp conductance plateaus, and propose applications in the Aharonov-Bohm and two-path interferometers, and a pointlike source for injection of carriers in graphene. Other applications can be extended to Bernal-stacked or twisted bilayer graphene or two-dimensional electron gas. Thanks to their versatility, CNT-induced waveguides open various possibilities for electron manipulation in graphene-based devices.
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.205118
Density functional theory is used to calculate the optical absorption of oxygen vacancies in potassium titanyl phosphate (, KTP) crystals. A modified hybrid functional is used for the description of the midgap defect states and the optical excitation energies. Oxygen vacancies in the charge state lead to rather minor modification of the bulk KTP optical response, while the and neutral charge states give rise to characteristic midgap optical absorption covering the whole near-infrared and visible spectrum. Its intensity is strongly polarization dependent and strongest for light polarized parallel to the axis. The modification of the KTP optical absorption by oxygen vacancies predicted here corroborates the picture that the gray-track formation in KTP, i.e., its photochromic damage, is related to a successive charging of oxygen vacancies.
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.174510
The fluctuation conductivity of a moderately clean type II superconductor with strong Pauli paramagnetic pair breaking (PPB) is studied by focusing on the quantum regime at low temperatures and in high magnetic fields. First, it is pointed out that, as the PPB effect becomes stronger, the quantum superconducting fluctuation is generally enhanced so that the renormalized Aslamasov-Larkin (AL) fluctuation conductivity tends to vanish upon cooling above the irreversibility line. Furthermore, by examining other [the DOS and the Maki-Thompson (MT)] terms of the fluctuation conductivity, the field dependence of the resulting total conductivity is found to depend significantly on the type of the vortex lattice (or, glass) ordered state at low temperatures where the strong PPB plays important roles. By comparing the present results on the fluctuation conductivity with insulating and negative magnetoresistance behaviors seen upon entering a PPB-induced novel SC phase of iron selenide (FeSe), it is argued that the vortex matter states of the superconducting order parameter in the second lowest Landau level are realized in FeSe in the parallel field configuration in high fields and at low temperatures.
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.205419
The response of solids to temperature gradients is often described in terms of a gravitational analog: the effect of a space-dependent temperature is modeled using a space-dependent metric. We investigate the validity of this approach in describing the bulk response of quantum Hall states and other gapped chiral topological states. To this end, we consider the prototypical Haldane model in two different cases of (i) a space-dependent electrostatic potential and gravitational potential and (ii) a space-dependent temperature and chemical potential imprinted by a weak coupling to noninteracting electron baths or phonons. We find that the thermal analog applied to theses cases is invalid; while a space-dependent gravitational potential induces transverse energy currents proportional to the third derivative of the gravitational potential, the response to an analogous temperature profile vanishes in limit of weak coupling to the thermal bath. Similarly, the Einstein relation, the analogy between the electrostatic potential and the internal chemical potential, is not valid in such a setup.
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.184417
The interfacial Dzyaloshinskii-Moriya interaction (iDMI) was observed in the bilayer consisting of a heavy metal and a ferromagnetic insulator such as (TIG), but the source and origin are still controversial. Here, we quantitatively investigate the iDMI strength in Pt|TIG by inserting a thin layer and/or a thin Cu layer between Pt and TIG. Our results suggest the iDMI contributed by both the Pt|TIG and the TIG|substrate interfaces. At the Pt|TIG interface, we find that Pt is essential for the strong iDMI. The disentangled iDMIs for Fe-Fe and Tm-Fe pairs are comparable, revealing that the Tm ions provide not only an additional Tm-Fe iDMI, but also the spin-orbit coupling to enhance the iDMI. At the TIG|substrate interface, the iDMI is attributed to the lattice-mismatch-induced deformation of the electron cloud for the ferromagnetic ions.
Physical Review B, Volume 105; https://doi.org/10.1103/physrevb.105.174509
With the aim of including small amplitude quantum nuclear dynamics in solid-state calculations, we derive a set of equations by applying Wick's theorem to the square of the Fröhlich Hamiltonian. These are noninteracting fermionic and bosonic Hamiltonians with terms up to quadratic order in the field operators. They depend on one another's density matrices and are therefore to be solved self-consistently. A Bogoliubov transformation is required to diagonalize both the fermionic and bosonic Hamiltonians since they represent noninteracting quantum field theories with an indefinite number of particles. The Bogoliubov transform for phonons is non-Hermitian in the general case, and the corresponding time evolution is nonunitary. Several sufficient conditions for ensuring that the bosonic eigenvalues are real are provided. The method was implemented in an all-electron code and shown to correctly predict the renormalization of the Kohn-Sham band gap of diamond and silicon due to the electron-phonon interaction. The theory also verifies that niobium and are phonon-mediated superconductors and predicts the existence and magnitude of their superconducting gaps. Lastly, we confirm that copper is not a superconductor even at zero temperature.