A5082641408- Rare-earth and actinide compounds
- Iron-based superconductors research
- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Magnetic Properties of Alloys
- Magnetic and transport properties of perovskites and related materials
- High-pressure geophysics and materials
- Magnetic properties of thin films
- Topological Materials and Phenomena
- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Inorganic Chemistry and Materials
- Organic Electronics and Photovoltaics
- Theoretical and Computational Physics
- Corporate Taxation and Avoidance
- Advanced Chemical Physics Studies
- Organic and Molecular Conductors Research
- Quantum and electron transport phenomena
- Advanced Materials Characterization Techniques
- Superconductivity in MgB2 and Alloys
- Semiconductor materials and interfaces
- Thin-Film Transistor Technologies
- Molecular Junctions and Nanostructures
- Conducting polymers and applications
- Advanced Memory and Neural Computing
Goethe University Frankfurt
2016-2025
Czech Academy of Sciences, Institute of Physics
2021
Max Planck Institute for Chemical Physics of Solids
2010-2019
Helmholtz-Zentrum Dresden-Rossendorf
2016
Paul Scherrer Institute
2016
Max Planck Society
2006-2014
University of Cambridge
2012
ETH Zurich
2004-2010
Rice University
2007
Rutgers, The State University of New Jersey
2007
We show that it is possible to reach one of the ultimate goals organic electronics: producing field-effect transistors with trap densities as low in bulk single crystals. studied spectral density localized states band gap [trap (trap DOS)] small-molecule semiconductors derived from electrical characteristics or space-charge-limited current measurements. This was done by comparing data a large number samples including thin-film (TFT's), crystal (SC-FET's) and samples. The compilation all...
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.
Resistivity, specific-heat, and magnetic-susceptibility measurements performed on ${\text{SrFe}}_{2}{\text{As}}_{2}$ samples evidence a behavior very similar to that observed in LaFeAsO ${\text{BaFe}}_{2}{\text{As}}_{2}$, with the difference being formation of spin-density wave lattice deformation occur pronounced first-order transition at ${T}_{0}=205\text{ }\text{K}$. Comparing further data evidences Fe magnetism is stronger ${\text{EuFe}}_{2}{\text{As}}_{2}$ than other layered FeAs...
We report on single crystal high mobility organic field-effect transistors prepared prefabricated substrates using a “flip-crystal” approach. This method minimizes handling and avoids direct processing of the that may degrade transistors' electrical characteristics. A chemical treatment process for substrate ensures reproducible device quality. With limited purification starting materials, hole mobilities 10.7, 1.3, 1.4cm2∕Vs have been measured rubrene, tetracene, pentacene crystals,...
Unconventional superconductivity and other previously unknown phases of matter exist in the vicinity a quantum critical point (QCP): continuous phase change at absolute zero. Intensive theoretical experimental investigations on itinerant systems have shown that metallic ferromagnets tend to develop via either first-order transition or through formation intermediate superconducting inhomogeneous magnetic phases. Here, precision low-temperature measurements, we show Grüneisen ratio heavy...
Quantum criticality arises when a macroscopic phase of matter undergoes continuous transformation at zero temperature. While the collective fluctuations quantum-critical points are being increasingly recognized as playing an important role in wide range quantum materials, nature underlying excitations remains poorly understood. Here we report in-depth measurements Hall effect heavy-fermion metal YbRh2Si2, prototypical system for criticality. We isolate rapid crossover isothermal coefficient...
We report magnetic and calorimetric measurements down to T = 1 mK on the canonical heavy-electron metal YbRh2Si2. The data reveal development of nuclear antiferromagnetic order slightly above 2 mK. latter weakens primary electronic antiferromagnetism, thereby paving way for superconductivity below Tc Our results demonstrate that driven by quantum criticality is a general phenomenon.
The surface conductivity is measured by a four-probe technique for pentacene and rubrene single crystals laminated on polarized nearly unpolarized molecular monolayers with application of perpendicular electric fields. polarization the self-assembled (SAMs) shifts threshold gate voltage, while maintaining very low subthreshold swing single-crystal devices (0.11 V∕decade). results, excluding influences parasitic contacts grain boundaries, demonstrate SAM-induced nanoscale charge injection up...
The density of trap states in the band gap semiconducting organic single crystals has been measured quantitatively and with high energy resolution by means experimental method temperature-dependent space-charge-limited-current spectroscopy. This spectroscopy applied to study bulk rubrene crystals, which are shown this technique be chemical structural quality. A deep as low $\ensuremath{\sim}{10}^{15}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ is purest exponentially varying...
In order to gain further insight into the details of charge transport in organic semiconductor devices it is necessary characterize density trap states at semiconductor∕gate dielectric interface. Here we use technique gate bias stress quantitatively determine interface rubrene single-crystal field-effect transistors with two different types interfaces. A reversible and reproducible shift I-V characteristics observed upon both negative positive stress, whose physical origin identified as...
X-ray and muon spin-relaxation experiments performed on ${\text{SrFe}}_{2}{\text{As}}_{2}$ polycrystals confirm a sharp first-order transition at ${T}_{0}=205\text{ }\text{K}$ corresponding to an orthorhombic phase distortion commensurate antiferromagnetic Fe ordering with larger size of the ordered moment than reported for ${\text{BaFe}}_{2}{\text{As}}_{2}$. The structural magnetic order parameters present remarkable similarity in their temperature dependence from ${T}_{0}$ down low...
We have determined the physical ground state properties of compounds CeRuPO and CeOsPO by means magnetic susceptibility $\ensuremath{\chi}(T)$, specific heat $C(T)$, electrical resistivity $\ensuremath{\rho}(T)$, thermopower $S(T)$ measurements. $\ensuremath{\chi}(T)$ reveals a trivalent $4{f}^{1}$ cerium in both compounds. For pronounced decrease $\ensuremath{\rho}(T)$ below $50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ indicates onset coherent Kondo scattering, which is confirmed enhanced...
We investigate single crystals of the trigonal antiferromagnet ${\mathrm{EuZn}}_{2}{\mathrm{P}}_{2}$ ($P\overline{3}m1$) by means electrical transport, magnetization measurements, x-ray magnetic scattering, optical reflectivity, angle-resolved photoemission spectroscopy (ARPES), and ab initio band structure calculations ($\mathrm{DFT}+U$). find that resistivity increases strongly upon cooling can be suppressed in fields several orders magnitude (colossal magnetoresistance effect). Resonant...
The ground state properties of CeFePO, a homologue the new high temperature superconductors RFePnO1-xFx, were studied by means susceptibility, specific heat, resistivity, and NMR measurements on polycrystals. All results demonstrate that this compound is magnetically nonordered heavy fermion metal with Kondo TK approximately 10 K, Sommerfeld coefficient gamma=700 mJ/mol K2, mass enhancement factor order 50. Analysis susceptibility data spin relaxation time indicates strong electronic...
Electron spin resonance (ESR) measurements of the ferromagnetic (FM) Kondo lattice system CeRuPO show a well defined ESR signal which is related to Ce3+ magnetism. In contrast, no could be observed in antiferromagnetic (AFM) homologue CeOsPO. Additionally, we detect an YbRh while it was absent number Ce or Yb intermetallic compounds with dominant AFM exchange. Thus, observation neither specific nor proximity quantum critical point, but seems connected presence FM fluctuations. These...
Kondo lattices belong to a new class of materials defying standard concepts solid-state physics. Scientists investigate the electronic structure well-known lattice and find that Fermi surface is stable over wide range above below its temperature.
We investigate the magnetic field dependent thermopower, thermal conductivity, resistivity, and Hall effect in heavy fermion metal ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$. In contrast to reports on thermodynamic measurements, we find total three transitions at high fields, rather than a single one 10 T. Using Mott formula together with renormalized band calculations, identify Lifshitz as their origin. The predictions of calculations show that all experimental results rely an interplay smooth...
Abstract The development of materials that are non-magnetic in the bulk but exhibit two-dimensional (2D) magnetism at surface is core spintronics applications. Here, we present valence-fluctuating material EuIr 2 Si , where contrast to its bulk, Si-terminated reveals controllable 2D ferromagnetism. Close Eu ions prefer a magnetic divalent configuration and their large 4 f moments order below 48 K. emerging exchange interaction modifies spin polarization electrons originally induced by strong...
The discovery of a square magnetic-skyrmion lattice in GdRu2Si2, with the smallest so far found skyrmion size and without geometrically frustrated lattice, has attracted significant attention. In this work, we present comprehensive study surface bulk electronic structures GdRu2Si2 by utilizing momentum-resolved photoemission (ARPES) measurements first-principles calculations. We show how structure evolves during antiferromagnetic transition when peculiar helical order 4f magnetic moments...
The mechanism of the peculiar transport properties around magnetic ordering temperature semiconducting antiferromagnetic ${\mathrm{EuCd}}_{2}{\mathrm{P}}_{2}$ is not yet understood. With a huge peak in resistivity observed above N\'eel ${T}_{\mathrm{N}}=10.6\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, it exhibits colossal magnetoresistance effect. Recent reports on observations ferromagnetic contributions ${T}_{\mathrm{N}}$ as well metallic behavior below this have motivated us to perform...
The tetragonal heavy-fermion (HF) metal YbRh2Si2 (Kondo temperature TK≈ 25 K) exhibits a magnetic field-induced quantum critical point related to the suppression of very weak antiferromagnetic (AF) ordering (TN = 70 mK) at field Bc 0.06 T (B⊥ c). To understand influence fields on criticality and Kondo effect, we study evolution various thermodynamic properties upon tuning system by field. At B > Bc, AF component fluctuations becomes suppressed, FM dominate. Their polarization with gives rise...