Faculty Profiles - JESCHKE HARALD OLAF

Papers - JESCHKE HARALD OLAF

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Rashba-like spin splitting along three momentum directions in trigonal layered PtBi<inf>2</inf>

Feng, Y., Jiang, Q., Feng, B., Yang, M., Xu, T., Liu, W., Yang, X., Arita, M., Schwier, E.F., Shimada, K., Jeschke, H.O., Thomale, R., Shi, Y., Wu, X., Xiao, S., Qiao, S., He, S.

Nature Communications 10 ( 1 ) 2019

Two magnetization plateaus in the kagome fluoride Cs2LiTi3 F12

Shirakami, R., Ueda, H., Jeschke, H.O., Nakano, H., Kobayashi, S., Matsuo, A., Sakai, T., Katayama, N., Sawa, H., Kindo, K., Michioka, C., Yoshimura, K.

Physical Review B 100 ( 17 ) 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We synthesized a kagome fluoride Cs2LiTi3F12 with S = 1/2 spins, and studied magnetic properties of the compound. The temperature dependence of the magnetic susceptibility indicates that it has dominant antiferromagnetic interactions and that it has no magnetic order down to 2 K. We found two magnetization plateaus in its magnetization process approximately at 1/3 and 0.8 mu(B) per Ti. The monoclinic crystal structure gives four inequivalent nearest-neighbor exchange interactions. Our density functional theory calculations suggest that three of them are antiferromagnetic and one of them is weakly ferromagnetic, resulting in a magnetic system composed of antiferromagnetically coupled linear chains and Delta chains. This explains the observed suppression of magnetic order. Numerical diagonalization gives a magnetization curve in good agreement with the experimental results.

DOI： 10.1103/PhysRevB.100.174401

An efficient GPU algorithm for tetrahedron-based Brillouin-zone integration Reviewed

Daniel Guterding, Harald O. Jeschke

Computer Physics Communications 231 114 - 121 2018.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier B.V.

We report an efficient algorithm for calculating momentum-space integrals in solid state systems on modern graphics processing units (GPUs). Our algorithm is based on the tetrahedron method, which we demonstrate to be ideally suited for execution in a GPU framework. In order to achieve maximum performance, all floating point operations are executed in single precision. For benchmarking our implementation within the CUDA programming framework we calculate the orbital-resolved density of states in an iron-based superconductor. However, our algorithm is general enough for the achieved improvements to carry over to the calculation of other momentum integrals such as, e.g. susceptibilities. If our program code is integrated into an existing program for the central processing unit (CPU), i.e. when data transfer overheads exist, speedups of up to a factor ∼130 compared to a pure CPU implementation can be achieved, largely depending on the problem size. In case our program code is integrated into an existing GPU program, speedups over a CPU implementation of up to a factor ∼165 are possible, even for moderately sized workloads.

DOI： 10.1016/j.cpc.2018.04.022

Evidence for Electronically Driven Ferroelectricity in a Strongly Correlated Dimerized BEDT-TTF Molecular Conductor Reviewed

Elena Gati, Jonas K. H. Fischer, Peter Lunkenheimer, David Zielke, Sebastian Köhler, Felizitas Kolb, Hans-Albrecht Krug Von Nidda, Stephen M. Winter, Harald Schubert, John A. Schlueter, Harald O. Jeschke, Roser Valentí, Michael Lang

Physical Review Letters 120 ( 24 ) 2018.6

Language：English Publishing type：Research paper (scientific journal) Publisher：American Physical Society

By applying measurements of the dielectric constants and relative length changes to the dimerized molecular conductor κ-(BEDT-TTF)2Hg(SCN)2Cl, we provide evidence for order-disorder type electronic ferroelectricity that is driven by the charge order within the (BEDT-TTF)2 dimers and stabilized by a coupling to the anions. According to our density functional theory calculations, this material is characterized by a moderate strength of dimerization. This system thus bridges the gap between strongly dimerized materials, often approximated as dimer-Mott systems at 1/2 filling, and nondimerized or weakly dimerized systems at 1/4 filling, exhibiting a charge order. Our results indicate that intradimer charge degrees of freedom are of particular importance in correlated κ-(BEDT-TTF)2X salts and can create novel states, such as electronically driven multiferroicity or charge-order-induced quasi-one-dimensional spin liquids.

DOI： 10.1103/PhysRevLett.120.247601

Role of the Open-Shell Character on the Pressure-Induced Conductivity of an Organic Donor–Acceptor Radical Dyad Reviewed

Manuel Souto, Maria Chiara Gullo, HengBo Cui, Nicola Casati, Fabio Montisci, Harald O. Jeschke, Roser Valentí, Imma Ratera, Concepció Rovira, Jaume Veciana

Chemistry - A European Journal 24 ( 21 ) 5500 - 5505 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Wiley-VCH Verlag

Single-component conductors based on neutral organic radicals have received a lot of attention due to the possibility that the unpaired electron can serve as a charge carrier without the need of a previous doping process. Although most of these systems are based on delocalized planar radicals, we present here a nonplanar and spin localized radical based on a tetrathiafulvalene (TTF) moiety, linked to a perchlorotriphenylmethyl (PTM) radical by a conjugated bridge, which exhibits a semiconducting behavior upon application of high pressure. The synthesis, electronic properties, and crystal structure of this neutral radical TTF-Ph-PTM derivative (1) are reported and implications of its crystalline structure on its electrical properties are discussed. On the other hand, the non-radical derivative (2), which is isostructural with the radical 1, shows an insulating behavior at all measured pressures. The different electronic structures of these two isostructural systems have a direct influence on the conducting properties, as demonstrated by band structure DFT calculations.

DOI： 10.1002/chem.201800881

Origin of the pressure-dependent T-c valley in superconducting simple cubic phosphorus Reviewed

Wu Xianxin, Jeschke Harald O, Di Sante Domenico, von Rohr Fabian O, Cava Robert J, Thomale Ronny

PHYSICAL REVIEW MATERIALS 2 ( 3 ) 2018.3

Enhanced superconducting transition temperatures in the rocksalt-type superconductors In1-xSnxTe (x≤0.5) ENHANCED SUPERCONDUCTING TRANSITION ... KOBAYASHI, AI, JESCHKE, and AKIMITSU Reviewed

Kaya Kobayashi, Yukio Ai, Harald O. Jeschke, Jun Akimitsu

Physical Review B 97 ( 10 ) 2018.3

Language：English Publishing type：Research paper (scientific journal) Publisher：American Physical Society

We investigate superconductivity in In1-xSnxTe (x≤0.5) synthesized at high pressures of up to 2 GPa and observe an enhancement of the superconducting transition temperature Tc for increasing tin concentration x. These compounds have not been accessible in rocksalt structure via conventional ambient pressure synthesis. While the lattice constant smoothly increases with x, Tc saturates around x=0.4. Electronic structure calculations indicate that the Tc modulation is brought on by the change of the density of states in the vicinity of the Fermi energy [N(EF)]. However, differences between the calculated N(EF) and the observed electronic specific-heat coefficient indicate that the phonon dispersion plays an important role in the system and that the mechanism of superconductivity may not be the same in the entire doping range.

DOI： 10.1103/PhysRevB.97.104511

Dynamics and fragmentation mechanism of (C5H4CH3)Pt(CH3)3 on SiO2 surfaces Reviewed

Kaliappan Muthukumar, Harald O. Jeschke, Roser Valentí

Beilstein Journal of Nanotechnology 9 ( 1 ) 711 - 720 2018

Language：English Publishing type：Research paper (scientific journal) Publisher：Beilstein-Institut Zur Forderung der Chemischen Wissenschaften

The interaction of trimethyl(methylcyclopentadienyl)platinum(IV) ((C5H4CH3)Pt(CH3)3) molecules on fully and partially hydroxylated SiO2 surfaces, as well as the dynamics of this interaction were investigated using density functional theory (DFT) and finite temperature DFT-based molecular dynamics simulations. Fully and partially hydroxylated surfaces represent substrates before and after electron beam treatment and this study examines the role of electron beam pretreatment on the substrates in the initial stages of precursor dissociation and formation of Pt deposits. Our simulations show that on fully hydroxylated surfaces or untreated surfaces, the precursor molecules remain inactivated while we observe fragmentation of (C5H4CH3)Pt(CH3)3 on partially hydroxylated surfaces. The behavior of precursor molecules on the partially hydroxylated surfaces has been found to depend on the initial orientation of the molecule and the distribution of surface active sites. Based on the observations from the simulations and available experiments, we discuss possible dissociation channels of the precursor.

DOI： 10.3762/bjnano.9.66

Two-Dome Superconductivity in FeS Induced by a Lifshitz Transition Reviewed

Shimizu Makoto, Takemori Nayuta, Guterding Daniel, Jeschke Harald O

Physical Review Letters 121 ( 13 ) 2018

Stability of the spiral spin liquid in MnSc2S4 Reviewed

Iqbal Yasir, Mueller Tobias, Jeschke Harald O, Thomale Ronny, Reuther Johannes

Physical Review B 98 ( 6 ) 2018

Signatures of a gearwheel quantum spin liquid in a spin-1/2 pyrochlore molybdate Heisenberg antiferromagnet Reviewed

Yasir Iqbal, Tobias Mueller, Kira Riedl, Johannes Reuther, Stephan Rachel, Roser Valenti, Michel J. P. Gingras, Ronny Thomale, Harald O. Jeschke

PHYSICAL REVIEW MATERIALS 1 ( 7 ) 2017.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We theoretically investigate the low-temperature phase of the recently synthesized Lu2Mo2O5N2 material, an extraordinarily rare realization of a S = 1/2 three-dimensional pyrochlore Heisenberg antiferromagnet in which Mo5+ are the S = 1/2 magnetic species. Despite a Curie-Weiss temperature (Theta(CW)) of -121( 1) K, experiments have found no signature of magnetic ordering or spin freezing down to T* approximate to 0.5 K. Using density functional theory, we find that the compound is well described by a Heisenberg model with exchange parameters up to third nearest neighbors. The analysis of this model via the pseudofermion functional renormalization group method reveals paramagnetic behavior down to a temperature of at least T = |Theta(CW)|/100, in agreement with the experimental findings hinting at a possible three-dimensional quantum spin liquid. The spin susceptibility profile in reciprocal space shows momentum-dependent features forming a "gearwheel" pattern, characterizing what may be viewed as a molten version of a chiral noncoplanar incommensurate spiral order under the action of quantum fluctuations. Our calculated reciprocal space susceptibility maps provide benchmarks for future neutron scattering experiments on single crystals of Lu2Mo2O5N2.

DOI： 10.1103/PhysRevMaterials.1.071201

Microscopic origin of the mobility enhancement at a spinel/perovskite oxide heterointerface revealed by photoemission spectroscopy Reviewed

P. Schuetz, D. V. Christensen, V. Borisov, F. Pfaff, P. Scheiderer, L. Dudy, M. Zapf, J. Gabel, Y. Z. Chen, N. Pryds, V. A. Rogalev, V. N. Strocov, C. Schlueter, T. -L. Lee, H. O. Jeschke, R. Valenti, M. Sing, R. Claessen

PHYSICAL REVIEW B 96 ( 16 ) 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

The spinel/perovskite heterointerface gamma-Al2O3/SrTiO3 hosts a two-dimensional electron system (2DES) with electron mobilities exceeding those in its all-perovskite counterpart LaAlO3/SrTiO3 by more than an order of magnitude, despite the abundance of oxygen vacancies which act as electron donors as well as scattering sites. By means of resonant soft x-ray photoemission spectroscopy and ab initio calculations, we reveal the presence of a sharply localized type of oxygen vacancies at the very interface due to the local breaking of the perovskite symmetry. We explain the extraordinarily high mobilities by reduced scattering resulting from the preferential formation of interfacial oxygen vacancies and spatial separation of the resulting 2DES in deeper SrTiO3 layers. Our findings comply with transport studies and pave the way towards defect engineering at interfaces of oxides with different crystal structures.

DOI： 10.1103/PhysRevB.96.161409

Basic electronic properties of iron selenide under variation of structural parameters Reviewed

Daniel Guterding, Harald O. Jeschke, Roser Valenti

PHYSICAL REVIEW B 96 ( 12 ) 2017.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Since the discovery of high-temperature superconductivity in the thin-film FeSe/SrTiO3 system, iron selenide and its derivates have been intensively scrutinized. Using ab initio density functional theory calculations we review the electronic structures that could be realized in iron selenide if the structural parameters could be tuned at liberty. We calculate the momentum dependence of the susceptibility and investigate the symmetry of electron pairing within the random phase approximation. Both the susceptibility and the symmetry of electron pairing depend on the structural parameters in a nontrivial way. These results are consistent with the known experimental behavior of binary iron chalcogenides and, at the same time, reveal two promising ways of tuning superconducting transition temperatures in these materials: on one hand by expanding the iron lattice of FeSe at constant iron-selenium distance and, on the other hand, by increasing the iron- selenium distance with unchanged iron lattice.

DOI： 10.1103/PhysRevB.96.125107

From magnetic order to spin-liquid ground states on the S=3/2 triangular lattice Reviewed

J. Tapp, C. R. dela Cruz, M. Bratsch, N. E. Amuneke, L. Postulka, B. Wolf, M. Lang, H. O. Jeschke, R. Valenti, P. Lemmens, A. Moeller

PHYSICAL REVIEW B 96 ( 6 ) 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

The series of compounds AAg(2)Cr[VO4](2), with A = Ag, K, or Rb, is layered S = 3/2 triangular-lattice (TL) systems in which the magnetic exchange interactions between Cr3+ (3d(3)) ions are mediated by nonmagnetic [VO4](3-) entities. Here, the relative orientation of the vanadate is altered with respect to the TL as a function of the A site, which corresponds to an induced symmetry change of the [CrO6] complex. All members of this series of compounds belong to the class of frustrated TL antiferromagnets. We find that the distorted TL (A = Ag) exhibits collinear antiferromagnetic long-range order (LRO) at T-N approximate to 10 K, whereas the high-symmetry cases (A = K, Rb) evade LRO in zero field down to 0.03 K, the lowest temperature of our experiments. The latter members of the series belong to the undistorted TL and are candidates for spin-liquid ground states presumably not related to Ising anisotropy or dimerization.

DOI： 10.1103/PhysRevB.96.064404

Influence of oxygen vacancies on two-dimensional electron systems at SrTiO3-based interfaces and surfaces Reviewed

Michael Sing, Harald O. Jeschke, Frank Lechermann, Roser Valenti, Ralph Claessen

EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS 226 ( 11 ) 2457 - 2475 2017.7

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER HEIDELBERG

The insulator SrTiO3 can host high-mobility two-dimensional electron systems on its surfaces and at interfaces with other oxides. While for the bare surface a two-dimensional electron system can only be induced by oxygen vacancies, it is believed that the metallicity of heterostructure interfaces as in LaAlO3/SrTiO3 is caused by other mechanisms related to the polar discontinuity at the interface. Based on calculations using density functional and dynamical mean-field theory as well as on experimental results using photoemission spectroscopy we elucidate the role of oxygen vacancies, thereby highlighting their importance for the electronic and magnetic properties of the systems under study.

DOI： 10.1140/epjst/e2017-70059-7

J Freezing and Hund's Rules in Spin-Orbit-Coupled Multiorbital Hubbard Models Reviewed

Aaram J. Kim, Harald O. Jeschke, Philipp Werner, Roser Valenti

PHYSICAL REVIEW LETTERS 118 ( 8 ) 2017.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We investigate the phase diagram of the spin-orbit-coupled three orbital Hubbard model at arbitrary filling by means of dynamical mean-field theory combined with the continuous-time quantum Monte Carlo method. We find that the spin-freezing crossover occurring in the metallic phase of the nonrelativistic multiorbital Hubbard model can be generalized to a J-freezing crossover, with J = L + S, in the spin-orbit-coupled case. In the J-frozen regime the correlated electrons exhibit a nontrivial flavor selectivity and energy dependence. Furthermore, in the regions near n = 2 and n = 4 the metallic states are qualitatively different from each other, which reflects the atomic Hund's third rule. Finally, we explore the appearance of magnetic order from exciton condensation at n = 4 and discuss the relevance of our results for real materials.

DOI： 10.1103/PhysRevLett.118.086401

Combined experimental and theoretical studies of pressure effects in La2Sb Reviewed

Stephan Knoener, Elena Gati, Bernd Wolf, Mariano de Souza, Amir Haghighirad, Markus Kuhnt, Wolf Assmus, Harald O. Jeschke, Milan Tomic, Roser Valenti, Michael Lang

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 254 ( 1 ) 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

The 5K superconductor La2Sb shares some structural similarities with the iron-pnictides and -chalgogenides, especially the so-called 122-compounds, despite lacking a 3d-metal component. In order to look for similarities and dissimilarities of this layered metal pnictide with the higher-T-c Fe-based superconductors, we have performed a combined experimental and theoretical investigation of the effects of hydrostatic pressure. Magnetic measurements reveal a linear increase of T-c with pressure at a rate dTc/dP=(0.71 +/- 0.01)K GPa(-1). Band structure calculations show that (i) the states at the Fermi level have predominantly La 5d character and (ii) that the density of states increases linearly with increasing pressure. By using these theoretical results and a BCS formalism, a quantitative description of the experimentally revealed pressure dependence of T-c is possible within a reasonable range of parameters. Our results indicate that La2Sb, despite its structural similarities to the 122 Fe-based superconductors, exhibits a BCS-type of superconductivity. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.201600168

Electronic excitations in gamma-Li2IrO3 Reviewed

Ying Li, Stephen M. Winter, Harald O. Jeschke, Roser Valenti

PHYSICAL REVIEW B 95 ( 4 ) 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We investigate the electronic properties of the three-dimensional stripyhoneycomb gamma-Li2IrO3 via relativistic density functional theory calculations as well as exact diagonalization of finite clusters and explore the details of the optical conductivity. Our analysis of this quantity reveals the microscopic origin of the experimentally observed (i) optical transitions and (ii) anisotropic behavior along the various polarization directions. In particular, we find that the optical excitations are overall dominated by transitions between j(eff) = 1/2 and 3/2 states and the weight of transitions between jeff = 1/2 states at low frequencies can be correlated to deviations from a pure Kitaev description. We furthermore reanalyze within this approach the electronic excitations in the known two-dimensional honeycomb systems alpha-Li2IrO3 and Na2IrO3 and discuss the results in comparison to gamma-Li2IrO3.

DOI： 10.1103/PhysRevB.95.045129

Nontrivial Role of Interlayer Cation States in Iron-Based Superconductors Reviewed

Daniel Guterding, Harald O. Jeschke, I. I. Mazin, J. K. Glasbrenner, E. Bascones, Roser Valenti

PHYSICAL REVIEW LETTERS 118 ( 1 ) 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Unconventional superconductivity in iron pnictides and chalcogenides has been suggested to be controlled by the interplay of low-energy antiferromagnetic spin fluctuations and the particular topology of the Fermi surface in these materials. Based on this premise, one would also expect the large class of isostructural and isoelectronic iron germanide compounds to be good superconductors. As a matter of fact, they, however, superconduct at very low temperatures or not at all. In this work we establish that superconductivity in iron germanides is suppressed by strong ferromagnetic tendencies, which surprisingly do not originate from changes in bond angles or bond distances with respect to iron pnictides and chalcogenides, but are due to changes in the electronic structure in a wide range of energies happening upon substitution of atom species (As by Ge and the corresponding spacer cations). Our results indicate that superconductivity in iron-based materials may not always be fully understood based on d or d-p model Hamiltonians only.

DOI： 10.1103/PhysRevLett.118.017204

Ab initio perspective on structural and electronic properties of iron-based superconductors Reviewed

Daniel Guterding, Steffen Backes, Milan Tomic, Harald O. Jeschke, Roser Valenti

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 254 ( 1 ) 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

The discovery of iron pnictides and iron chalcogenides as a new class of unconventional superconductors in 2008 has generated an enormous amount of experimental and theoretical work that identifies these materials as correlated metals with multi-orbital physics, where magnetism, nematicity, and superconductivity are competing phases that appear as a function of pressure and doping. A microscopic understanding of the appearance of these phases is crucial in order to determine the nature of superconductivity in these systems. Here, we review our recent theoretical efforts to describe and understand from first principles the properties of iron pnictides and chalcogenides with special focus on (i) pressure dependence, (ii) effects of electronic correlation, and (iii) origin of magnetism and superconductivity. (C) 2016 WILEY- VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.201600164

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