M. Höppner

Strong ferromagnetism at the surface of an antiferromagnet caused by buried magnetic moments

Carrying a large, pure spin magnetic moment of 7 μB per atom in the half-filled 4f shell, divalent europium is an outstanding element for assembling novel magnetic devices in which a two-dimensional electron gas may be polarized due to exchange interaction with an underlying magnetically-active Eu layer. Here we show that the Si-Rh-Si surface trilayer of the antiferromagnet EuRh2Si2 bears a surface state, which exhibits an unexpected and large spin splitting controllable by temperature. The splitting sets in below ~32.5 K, well above the ordering temperature of the Eu 4f moments (~24.5 K) in the bulk, indicating a larger ordering temperature in the topmost Eu layers. The driving force for the itinerant ferromagnetism at the surface is the aforementioned exchange interaction. Such a splitting may also be induced into states of functional surface layers deposited onto the surface of EuRh2Si2 or similarly ordered magnetic materials with metallic or semiconducting properties.

Efficient real-frequency solver for dynamical mean-field theory

We here present how a self-consistent solution of the dynamical mean field theory equations can be obtained using exact diagonalization of an Anderson impurity model with accuracies comparable to those found using renormalization group or quantum Monte Carlo methods. We show how one can solve a correlated quantum impurity coupled to several hundred uncorrelated bath sites, using a restricted active basis set. The number of bath sites determines the resolution of the obtained spectral function, which consists of peaks roughly spaced by the band width divided by the number of bath sites. The self-consistency cycles are fully performed on the real frequency axis and expressed as numerical stable matrix operations. The same impurity solver has been used on Ligand Field and finite size cluster calculations and is capable of treating involved Hamiltonians including the full rotational invariant Coulomb interaction, spin-orbit coupling and low symmetry crystal-fields. The proposed method allows for the calculation of a variety of correlation functions at little extra cost.

Combined experimental and computational study of the pressure dependence of the vibrational spectrum of solid picene C22H14

We present high-quality optical data and density functional perturbation theory calculations for the vibrational spectrum of solid picene (C

Interplay of Dirac fermions and heavy quasiparticles in solids

_{22}

Optical anisotropy of the Jeff=1/2 Mott insulator Sr2IrO4

H

Coherent order parameter oscillations in the ground state of the excitonic insulator Ta2NiSe5

_{14}

Spin Orientation of Two-Dimensional Electrons Driven by Temperature-Tunable Competition of Spin–Orbit and Exchange–Magnetic Interactions

) under pressure up to 8 GPa. First-principles calculations reproduce with a remarkable accuracy the pressure effects on both frequency and intensities of the phonon peaks experimentally observed . Through a detailed analysis of the phonon eigenvectors, We use the projection on molecular eigenmodes to unambiguously fit the experimental spectra, resolving complicated spectral structures, in a system with hundreds of phonon modes. With these projections, we can also quantify the loss of molecular character under pressure. Our results indicate that picene, despite a \sim 20 % compression of the unit cell, remains substantially a molecular solid up to 8 GPa, with phonon modes displaying a smooth and uniform hardening with pressure. The Grueneisen parameter of the 1380 cm^{-1} a_1 Raman peak (

Ultrafast dynamics and coherent order parameter oscillations under photo-excitation in the excitonic insulator Ta2NiSe5

\gamma_p=0.1

Tracing the localization of 4f electrons: Angle-resolved photoemission on YbCo2Si2, the stable trivalent counterpart of the heavy-fermion YbRh2Si2

) is much lower than the effective value (

Structural Evolution of Solid Phenanthrene at High Pressures

\gamma_d=0.8