A5059990598- Rare-earth and actinide compounds
- Physics of Superconductivity and Magnetism
- Iron-based superconductors research
- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Magnetic Properties of Alloys
- Multiferroics and related materials
- Topological Materials and Phenomena
- High-pressure geophysics and materials
- Electronic and Structural Properties of Oxides
- Inorganic Chemistry and Materials
- Theoretical and Computational Physics
- Perovskite Materials and Applications
- Solid-state spectroscopy and crystallography
- Superconductivity in MgB2 and Alloys
- Inorganic Fluorides and Related Compounds
- Organic and Molecular Conductors Research
- Crystal Structures and Properties
- Magnetic properties of thin films
- Advanced Thermodynamics and Statistical Mechanics
- Magnetism in coordination complexes
- Quantum and electron transport phenomena
- Quantum many-body systems
- Corporate Taxation and Avoidance
- Plant and Fungal Species Descriptions
University of Augsburg
2016-2025
Max Planck Institute for Chemical Physics of Solids
2005-2020
Max Planck Society
2004-2020
Augsburg University
2014-2019
University of Göttingen
2008-2017
Max Planck Institute for the Physics of Complex Systems
2016
Rice University
2007
Rutgers, The State University of New Jersey
2007
University of St Andrews
2004-2006
University of Birmingham
2004
Combining thermodynamic measurements with theoretical calculations we demonstrate that the iridates ${A}_{2}{\mathrm{IrO}}_{3}$ ($A=\mathrm{Na}$, Li) are magnetically ordered Mott insulators where magnetism of effective spin-orbital $S=1/2$ moments can be captured by a Heisenberg-Kitaev (HK) model interactions beyond nearest-neighbor exchange. Experimentally, observe an increase Curie-Weiss temperature from $\ensuremath{\theta}\ensuremath{\approx}\ensuremath{-}125\text{ }\text{ }\mathrm{K}$...
We have synthesized single crystals of ${\text{Na}}_{2}{\text{IrO}}_{3}$ and studied their structure, transport, magnetic, thermal properties using powder x-ray diffraction, electrical resistivity, isothermal magnetization $M$ versus magnetic field $H$, susceptibility $\ensuremath{\chi}$ temperature $T$, heat capacity $C$ $T$ measurements. crystallizes in the monoclinic $C2/c$ (No. 15) type structure which is made up Na ${\text{NaIr}}_{2}{\text{O}}_{6}$ layers alternately stacked along $c$...
We report inelastic neutron scattering measurements on Na2IrO3, a candidate for the Kitaev spin model honeycomb lattice. observe spin-wave excitations below 5 meV with dispersion that can be accounted by including substantial further-neighbor exchanges stabilize zigzag magnetic order. The onset of long-range order T(N)=15.3 K is confirmed via observation oscillations in zero-field muon-spin rotation experiments. Combining single-crystal diffraction and density functional calculations we...
The exactly solvable Kitaev model on the honeycomb lattice has recently received enormous attention linked to hope of achieving novel spin-liquid states with fractionalized Majorana-like excitations. In this review, we analyze mechanism proposed by Jackeli and Khaliullin identify materials based spin-orbital dependent bond interactions provide a comprehensive overview its implications in real materials. We set focus experimental results current theoretical understanding planar systems...
We report the first observation of non-Fermi-liquid (NFL) effects in a clean Yb compound at ambient pressure and zero magnetic field. The electrical resistivity specific-heat coefficient high-quality single crystals ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$ present linear logarithmic temperature dependence, respectively, more than decade temperature. ascribe this NFL behavior to presence (presumably) quasi-2D antiferromagnetic spin fluctuations related very weak phase transition...
We report low-temperature calorimetric, magnetic, and resistivity measurements on the antiferromagnetic (AF) heavy-fermion metal YbRh(2)Si(2) ( T(N)=70 mK) as a function of magnetic field B. While for fields exceeding critical value B(c0) at which T(N)-->0 shows an AT2 dependence, 1/(B-B(c0)) divergence A(B) upon reducing B to suggests singular scattering whole Fermi surface heavy quasiparticle mass. The observations are interpreted in terms new type quantum point separating weakly AF...
We report a combined experimental and theoretical investigation of the magnetic structure honeycomb lattice magnet Na$_2$IrO$_3$, strong candidate for realization gapless spin-liquid. Using resonant x-ray scattering at Ir L$_3$-edge, we find 3D long range antiferromagnetic order below T$_N$=13.3 K. From azimuthal dependence Bragg peak, ordered moment is determined to be predominantly along {\it a}-axis. Combining data with first principles calculations, propose that most likely spin novel...
Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some the exciting intriguing phenomena exhibited by oxide systems interfaces. In addition already diverse spectrum properties, nanoscale form oxides provides new dimension hitherto unknown due increased surface-to-volume ratio.
The electronic structure of the honeycomb lattice iridates ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ and ${\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ has been investigated using resonant inelastic x-ray scattering (RIXS). Crystal-field-split $d\mathrm{\text{\ensuremath{-}}}d$ excitations are resolved in high-resolution RIXS spectra. In particular, splitting due to noncubic crystal fields, derived from ${j}_{\mathrm{eff}}=3/2$ states, is much smaller than typical spin-orbit energy scale iridates,...
Muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$) experiments on single crystals of the structurally perfect triangular antiferromagnet ${\mathrm{YbMgGaO}}_{4}$ indicate absence both static long-range magnetic order and freezing down to 0.048 K in a zero field. Below 0.4 K, ${\ensuremath{\mu}}^{+}$ rates, which are proportional dynamic correlation function ${\mathrm{Yb}}^{3+}$ spins, exhibit temperature-independent plateaus. All these $\ensuremath{\mu}\mathrm{SR}$ results unequivocally...
We apply moderate-high-energy inelastic neutron scattering (INS) measurements to investigate ${\mathrm{Yb}}^{3+}$ crystalline electric field (CEF) levels in the triangular spin-liquid candidate ${\mathrm{YbMgGaO}}_{4}$. Three CEF excitations from ground-state Kramers doublet are centered at energies $\ensuremath{\hbar}\ensuremath{\omega}=39$, 61, and 97 meV agreement with effective spin-$1/2$ $g$ factors experimental heat capacity, but reveal sizable broadening. argue that this broadening...
The layered honeycomb magnet $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ has been theoretically proposed as a candidate to display unconventional magnetic behaviour associated with Kitaev interactions between spin-orbit entangled ${j}_{\mathrm{eff}}=1/2$ moments on lattice. Here we report single crystal resonant x-ray diffraction combined powder neutron reveal an incommensurate order in the layers Ir counterrotating nearest-neighbor sites. This unexpected...
We present the structural characterization and low-temperature magnetism of triangular-lattice delafossite NaYbO$_2$. Synchrotron x-ray diffraction neutron scattering exclude both disorder crystal-electric-field randomness, whereas heat-capacity measurements muon spectroscopy reveal absence magnetic order persistent spin dynamics down to at least 70\,mK. Continuous excitations with low-energy spectral weight accumulating $K$-point Brillouin zone indicate formation a novel spin-liquid phase...
Condensed systems of strongly interacting electrons are ideal for the study quantum complexity. It has become possible to promote formation new phases by explicitly tuning toward special low-temperature critical points. So far, clearest examples have been appearances superconductivity near pressure-tuned antiferromagnetic We present experimental evidence a nonsuperconducting phase in vicinity magnetic field–tuned point ultrapure crystals ruthenate metal Sr 3 Ru 2 O 7 , and we discuss...
The superconducting phase transition in heavy fermion CeCoIn5 (T(c)=2.3 K zero field) becomes first order when the magnetic field H parallel [001] is greater than 4.7 T, and temperature below T0 approximately 0.31T(c). change from second at lower fields reflected strong sharpening of both specific heat thermal expansion anomalies associated with transition, a magnetocaloric effect, steplike sample volume. This effect due to Pauli limiting type-II superconductor, was predicted theoretically mid-1960s.
We report thermodynamic measurements in a magnetic-field-driven quantum critical point of heavy fermion metal, YbRh$_2$Si$_2$. The data provide evidence for an energy scale the equilibrium excitation spectrum, that is addition to one expected from slow fluctuations order parameter. Both scales approach zero as reached, thereby providing new class criticality.
We study Na2IrO3 by ARPES, optics, and band structure calculations in the local-density approximation (LDA). The weak dispersion of Ir 5d-t2g manifold highlights importance structural distortions spin-orbit coupling (SO) driving system closer to a Mott transition. detect an insulating gap {\Delta}_gap = 340 meV which, at variance with Slater-type description, is already open 300 K does not show significant temperature dependence even across T_N ~ 15 K. An LDA analysis inclusion SO Coulomb...
We present low-temperature volume thermal expansion, beta, and specific heat, C, measurements on high-quality single crystals of CeNi2Ge2 YbRh2(Si0.95Ge0.05)(2) which are located very near to quantum critical points. For both systems, beta shows a more singular temperature dependence than thus the Grüneisen ratio Gamma proportional beta/C diverges as T-->0. CeNi2Ge2, our results in accordance with spin-density wave (SDW) scenario for three-dimensional spin fluctuations. By contrast, observed...
${\text{EuFe}}_{2}{\text{As}}_{2}$ shows a spin-density wave (SDW) type transition at 190 K and antiferromagnetic (AF) order below 20 K. Here, we have studied the effect of substitution on SDW high temperature AF Eu low temperature. 50% suppresses in turn gives rise to high-temperature superconductivity ${T}_{c}=32\text{ }\text{K}$, as observed electrical resistivity, AC susceptibility, well magnetization. A defined anomaly specific heat provides additional evidence for bulk...
We studied the temperature-pressure phase diagram of ${\text{EuFe}}_{2}{\text{As}}_{2}$ by electrical resistivity measurements. The spin-density-wave transition at ${T}_{0}$ associated with FeAs-layers is continuously suppressed increasing pressure, while antiferromagnetic ordering temperature ${\text{Eu}}^{2+}$ moments seems to be nearly pressure independent up 2.6 GPa. Above 2 GPa a sharp drop resistivity, $\ensuremath{\rho}(T)$, indicates onset superconductivity...
We have grown single crystals of ${\text{EuFe}}_{2}{\text{As}}_{2}$, and investigated its electrical transport thermodynamic properties. Electrical resistivity specific-heat measurements clearly establish the intrinsic nature magnetic phase transitions at 20 195 K. While high-temperature transition is associated with itinerant moment Fe, low-temperature due to order localized Eu moments. Band-structure calculations point out a very close similarity electronic structure...