A5066143236- Physics of Superconductivity and Magnetism
- Iron-based superconductors research
- Advanced Condensed Matter Physics
- Quantum and electron transport phenomena
- Magnetic and transport properties of perovskites and related materials
- Particle physics theoretical and experimental studies
- Cold Atom Physics and Bose-Einstein Condensates
- Rare-earth and actinide compounds
- Particle Detector Development and Performance
- High-Energy Particle Collisions Research
- Theoretical and Computational Physics
- Quantum many-body systems
- Computational Physics and Python Applications
- Quantum, superfluid, helium dynamics
- Corporate Taxation and Avoidance
- Superconductivity in MgB2 and Alloys
- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Organic and Molecular Conductors Research
- Quantum Chromodynamics and Particle Interactions
- Surgical Simulation and Training
- Superconducting Materials and Applications
- Atomic and Subatomic Physics Research
- Tactile and Sensory Interactions
- Advanced Chemical Physics Studies
University of Stuttgart
2014-2025
Oak Ridge National Laboratory
2015-2024
University of Vienna
2024
University of San Francisco
2014-2023
Ludwig-Maximilians-Universität München
2012-2020
ETH Zurich
2018-2020
Swiss Federal Institute of Sport Magglingen SFISM
2018
Hudson Institute
2018
Rutherford Appleton Laboratory
2017
SLAC National Accelerator Laboratory
2017
Quantum cluster approaches offer new perspectives to study the complexities of macroscopic correlated fermion systems. These can be understood as generalized mean-field theories. are non-perturbative and always in thermodynamic limit. Their quality systematically improved, they provide complementary information finite size simulations. They have been studied intensively recent years now well established. After a brief historical review, this article comparatively discusses nature advantages...
Weak-coupling approaches to the pairing problem in iron pnictide superconductors have predicted a wide variety of superconducting ground states. We argue here that this is due both inadequacy certain approximations effective low-energy band structure, and natural near degeneracy different channels with many distinct Fermi surface sheets. In particular, we review attempts construct two-orbital models, argument for their fundamental inconsistency symmetry these materials, compare dynamical...
The recent discovery of pressure-induced superconductivity in the bilayer ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ (LNO) has opened a new platform for study unconventional superconductors. In this publication, we investigate theoretically whole family 327-type nickelates ${R}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$ ($R$ = rare-earth elements) under pressure. From La to Lu, lattice constants and volume decrease, leading enhanced in-plane out-of-plane hoppings, resulting an...
Motivated by the recently discovered high-T
The authors investigate here two bilayer nickelates under pressure, establishing substantial qualitative differences between the systems. They find that ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital in La${}_{3}$Ni${}_{2}$O${}_{6}$ and La${}_{3}$Ni${}_{2}$O${}_{7}$ plays a different role: one ``active'' (${d}_{{x}^{2}\ensuremath{-}{y}^{2}})$ vs orbitals (${e}_{g})$, respectively. Fermi surface only has sheets La${}_{3}$Ni${}_{2}$O${}_{6}$, with $\ensuremath{\gamma}$ pocket absent, from...
Atoms can be trapped and guided using nanofabricated wires on surfaces, achieving the scales required by quantum information proposals. These atom chips form basis for robust widespread applications of cold atoms ranging from optics to fundamental questions in mesoscopic physics, possibly systems.
The cluster size dependence of superconductivity in the conventional two-dimensional Hubbard model, commonly believed to describe high-temperature superconductors, is systematically studied using dynamical approximation and quantum Monte Carlo simulations as a solver. Because nonlocality $d$-wave superconducting order parameter, results on small clusters show large geometry effects. In enough clusters, are independent display finite temperature instability superconductivity.
We have designed and experimentally studied a simple beam splitter for atoms guided on an Atom Chip, using current carrying Y-shaped wire bias magnetic field. This other similar designs can be used to build atom optical elements the mesoscopic scale, integrate them in matterwave quantum circuits.
Despite the wealth of experimental data on Fe-pnictide compounds $K{\text{Fe}}_{2}{\text{As}}_{2}$ type, $K=\text{Ba}$, Ca, or Sr, main theoretical work based multiorbital tight-binding models has been restricted so far to study related 1111 compounds. This can be ascribed more three-dimensional electronic structure found by ab initio calculations for 122 materials, making this system less amenable model development. In addition, complicated Brillouin zone (BZ) body-centered tetragonal...
Inelastic neutron scattering provides a probe for studying the spin and momentum structure of superconducting gap. Here, using two-orbital model Fe-pnictide superconductors random-phase approximation--BCS approximation dynamic susceptibility, we explore response various gaps that have been proposed.
Angle-resolved photoemission spectroscopy measurements on the recently discovered superconduc- tors in KFe2Se2 family with critical temperatures up to - 33K suggest that no Fermi pockets of hole character centered {\Gamma} point Brillouin zone are present, contrast all other known ferropnictide and ferrochalcogenide superconductors. Using a fluctuation exchange approximation 5-orbital tight-binding description band structure, we calculate effective pairing interaction. We find state this...
Bulk rutile RuO_{2} has long been considered a Pauli paramagnet. Here we report that exhibits hitherto undetected lattice distortion below approximately 900 K. The is accompanied by antiferromagnetic order up to at least 300 K with small room temperature magnetic moment of 0.05μ_{B} as evidenced polarized neutron diffraction. Density functional theory plus U (DFT+U) calculations indicate antiferromagnetism favored even for values the Hubbard 1 eV. may be traced Fermi surface instability,...
We introduce an effective low-energy pairing model for Fe-based superconductors with $s$- and $d$-wave interaction components a small number of input parameters use it to study the doping evolution symmetry structure superconducting gap. argue that describes entire variety states found so far in allows one understand mechanism attraction ${s}^{\ifmmode\pm\else\textpm\fi{}}$ ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ channels, competition between solutions, origin superconductivity heavily doped...
We discuss the large gap anisotropy found for A1g (s-wave) state in RPA spin-fluctuation and functional renormalization group calculations show how simple arguments leading to isotropic sign-switched s-wave states these systems need be supplemented by a consideration of pair scattering within Fermi surface sheets between individual electron as well. In addition, accounting orbital makeup on is crucial.
In conventional Bardeen-Cooper-Schrieffer (BCS) superconductors, superconductivity occurs when electrons form coherent Cooper pairs below the superconducting transition temperature Tc. Although kinetic energy of paired increases in state relative to normal state, reduction ion lattice is sufficient give condensation energy. For iron pnictide superconductors derived from electron or hole doping their antiferromagnetic (AF) parent compounds, microscopic origin for supercnductivity unclear....
The high-temperature superconducting cuprates are governed by intertwined spin, charge, and orders. While various state-of-the-art numerical methods have demonstrated that these phases also manifest themselves in doped Hubbard models, they differ on which is the actual ground state. Finite-cluster typically indicate stripe order dominates, while embedded quantum-cluster methods, access thermodynamic limit treating long-range correlations with a dynamical mean field, conclude...
Inelastic neutron scattering provides a powerful probe of the magnetic excitations quantum magnets. Altermagnets have recently emerged as new class magnets with vanishing net magnetization characteristic antiferromagnets and spin-split electronic structure typical ferromagnets. Here we introduce minimal Hubbard model two-sublattice orthorhombic anisotropy framework to study altermagnetism. Using unrestricted Hartree-Fock calculations, find an altermagnetic state for this that evolves from...
Motivated by the recently reported signatures of superconductivity in trilayer La_{4}Ni_{3}O_{10} under pressure, we comprehensively study this system using ab initio and random-phase approximation techniques. Without electronic interactions, Ni d_{3z^{2}-r^{2}} orbitals show a bonding-antibonding nonbonding splitting behavior via O p_{z} inducing "trimer" lattice La_{4}Ni_{3}O_{10}, analogous to dimers La_{3}Ni_{2}O_{7}. The Fermi surface consists three electron sheets with mixed e_{g}...
We present the algorithmic details of dynamical cluster approximation (DCA), with a quantum Monte Carlo (QMC) method used to solve effective problem. The DCA is fully-causal approach which systematically restores non-local correlations mean field (DMFA) while preserving lattice symmetries. becomes exact for an infinite size, reducing DMFA size unity. generalization Hirsch-Fye QMC algorithm solution embedded use two-dimensional Hubbard model illustrate performance technique. At half-filling,...
The superconducting instabilities of the doped repulsive 2D Hubbard model are studied in intermediate to strong coupling regime with help dynamical cluster approximation. To solve effective problem we employ an extended noncrossing approximation, which allows for a transition broken symmetry state. At sufficiently low temperatures find stable d-wave solutions off-diagonal long-range order. maximal T(c) approximately 150 K occurs doping delta 20% and dependence agrees well generic high- phase diagram.
The question of whether one should speak a "pairing glue" in the Hubbard and t-J models is basically about dynamics pairing interaction. If interaction arises from virtual states, whose energies correspond to Mott gap, give rise exchange coupling J, instantaneous on relative time scales interest. In this case, while might an "instantaneous glue," differs traditional picture retarded However, as we will show, dominant contribution for both these reflecting spectrum seen dynamic spin...
We show, using a simple model, how ordinary disorder can gap an extended-$s$- $({A}_{1g})$ symmetry superconducting state with nodes. The concomitant crossover of thermodynamic properties, particularly the $T$ dependence superfluid density, from pure power-law behavior to activated one is exhibited. discuss applications this scenario experiments on ferropnictide superconductors.