المؤلفون: Christian Thurn, Paul Eibisch, Arif Ata, Maximilian Winkler, Peter Lunkenheimer, István Kézsmárki, Ulrich Tutsch, Yohei Saito, Steffi Hartmann, Jan Zimmermann, Abanoub R. N. Hanna, A. T. M. Nazmul Islam, Shravani Chillal, Bella Lake, Bernd Wolf, Michael Lang

المصدر: npj Quantum Materials, Vol 6, Iss 1, Pp 1-7 (2021)

مصطلحات موضوعية: Materials of engineering and construction. Mechanics of materials, TA401-492, Atomic physics. Constitution and properties of matter, QC170-197

الوصف: Abstract Geometrical frustration among interacting spins combined with strong quantum fluctuations destabilize long-range magnetic order in favor of more exotic states such as spin liquids. By following this guiding principle, a number of spin liquid candidate systems were identified in quasi-two-dimensional (quasi-2D) systems. For 3D, however, the situation is less favorable as quantum fluctuations are reduced and competing states become more relevant. Here we report a comprehensive study of thermodynamic, magnetic and dielectric properties on single crystalline and pressed-powder samples of PbCuTe2O6, a candidate material for a 3D frustrated quantum spin liquid featuring a hyperkagome lattice. Whereas the low-temperature properties of the powder samples are consistent with the recently proposed quantum spin liquid state, an even more exotic behavior is revealed for the single crystals. These crystals show ferroelectric order at T FE ≈ 1 K, accompanied by strong lattice distortions, and a modified magnetic response—still consistent with a quantum spin liquid—but with clear indications for quantum critical behavior.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/2397-4648Test

الوصول الحر: https://doaj.org/article/75b46d2188c14aacb487bb3ebc1d7d23Test

المؤلفون: Elena Gati, Ulrich Tutsch, Ammar Naji, Markus Garst, Sebastian Köhler, Harald Schubert, Takahiko Sasaki, Michael Lang

المصدر: Crystals, Vol 8, Iss 1, p 38 (2018)

مصطلحات موضوعية: organic conductor, Mott transition, pressure, disorder, X-ray irradiation, Crystallography, QD901-999

الوصف: We present a study of the influence of disorder on the Mott metal-insulator transition for the organic charge-transfer salt κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl. To this end, disorder was introduced into the system in a controlled way by exposing the single crystals to X-ray irradiation. The crystals were then fine-tuned across the Mott transition by the application of continuously controllable He-gas pressure at low temperatures. Measurements of the thermal expansion and resistance show that the first-order character of the Mott transition prevails for low irradiation doses achieved by irradiation times up to 100 h. For these crystals with a moderate degree of disorder, we find a first-order transition line which ends in a second-order critical endpoint, akin to the pristine crystals. Compared to the latter, however, we observe a significant reduction of both, the critical pressure p c and the critical temperature T c . This result is consistent with the theoretically-predicted formation of a soft Coulomb gap in the presence of strong correlations and small disorder. Furthermore, we demonstrate, similar to the observation for the pristine sample, that the Mott transition after 50 h of irradiation is accompanied by sizable lattice effects, the critical behavior of which can be well described by mean-field theory. Our results demonstrate that the character of the Mott transition remains essentially unchanged at a low disorder level. However, after an irradiation time of 150 h, no clear signatures of a discontinuous metal-insulator transition could be revealed anymore. These results suggest that, above a certain disorder level, the metal-insulator transition becomes a smeared first-order transition with some residual hysteresis.

وصف الملف: electronic resource

العلاقة: http://www.mdpi.com/2073-4352/8/1/38Test; https://doaj.org/toc/2073-4352Test

الوصول الحر: https://doaj.org/article/12a10c9d2ea0423cb3b14bab9955af59Test

المؤلفون: Franz Ritter, Bernd Wolf, L. Postulka, Ch. Thurn, S. K. Thallapaka, Cornelius Krellner, Michael Lang, Ulrich Tutsch

المصدر: Journal of Magnetism and Magnetic Materials. 480:108-111

مصطلحات موضوعية: 010302 applied physics, Materials science, Condensed matter physics, Hydrostatic pressure, 02 engineering and technology, 021001 nanoscience & nanotechnology, Condensed Matter Physics, 01 natural sciences, Inductive coupling, Magnetic susceptibility, Electronic, Optical and Magnetic Materials, Octahedron, Ferromagnetism, Magnet, 0103 physical sciences, Condensed Matter::Strongly Correlated Electrons, 0210 nano-technology, Anisotropy, Solid solution

الوصف: In single crystals of the solid solution Cs2 CuCl 4 - x Br x ( 0 ⩽ x ⩽ 4 ), depending on the growth conditions, two structural modifications with a tetrahedral or an octahedral Cu environment can be realized. The border compounds (x = 0 and 4) with a tetrahedral Cu coordination have been recognized as model systems for quasi-2D frustrated anisotropic triangular quantum antiferromagnets. This holds true also for the newly discovered stoichiometric compounds with x = 1 and 2. In contrast, the systems exhibiting an octahedral Cu environment can be classified as quasi-2D ferromagnets characterized by ferromagnetic layers with a weak inter-layer coupling. Here we study the magnetic and magneto-elastic couplings for the low-dimensional Heisenberg quantum magnet Cs2CuCl2Br2 with octahedral Cu coordination. By applying magnetic susceptibility measurements under varying hydrostatic (He-gas) pressure, χ ( T , p ) , we determine the pressure dependence of the magnetic coupling constant ∂ J / ∂ p and estimate the magneto-elastic couplings ∂ J / ∂ ∊ v . These values are enhanced by almost one order of magnitude compared to Cs2CuCl2Br2 with tetrahedral Cu coordination.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_________::d49e955c89e6c28fa3d0fb7abf31b55eTest
https://doi.org/10.1016/j.jmmm.2019.02.070Test

المؤلفون: Ulrich Tutsch, Raquel A. Ribeiro, Paul C. Canfield, Michael Lang, Arif Ata, Li Xiang, Sergey L. Bud'ko, Elena Gati

المصدر: The Review of scientific instruments. 91(9)

مصطلحات موضوعية: 010302 applied physics, Materials science, Piston cylinder, Analytical chemistry, 01 natural sciences, Pressure coefficient, 010305 fluids & plasmas, law.invention, Pressure range, Pressure measurement, Temperature and pressure, law, 0103 physical sciences, Practical algorithm, Instrumentation, Manganin, Ambient pressure

الوصف: We report measurements of the temperature- and pressure-dependent resistance, R(T, p), of a manganin manometer in a 4He-gas pressure setup from room temperature down to the solidification temperature of 4He (Tsolid ∼ 50 K at 0.8 GPa) for pressures, p, between 0 GPa and ∼0.8 GPa. The same manganin wire manometer was also measured in a piston-cylinder cell (PCC) from 300 K down to 1.8 K and for pressures between 0 GPa and ∼2 GPa. From these data, we infer the temperature and pressure dependence of the pressure coefficient of manganin, α(T, p), defined by the equation Rp = (1 + αp)R0, where R0 and Rp are the resistances of manganin at ambient pressure and finite pressure, respectively. Our results indicate that upon cooling, α first decreases, then goes through a broad minimum at ∼120 K, and increases again toward lower temperatures. In addition, we find that α is almost pressure-independent at T ≳ 60 K up to p ∼ 2 GPa, but shows a pronounced p dependence at T ≲ 60 K. Using this manganin manometer, we demonstrate that p overall decreases with decreasing temperature in the PCC for the full pressure range and that the size of the pressure difference between room temperature and low temperatures (T = 1.8 K), Δp, decreases with increasing pressure. We also compare the pressure values inferred from the manganin manometer with the low-temperature pressure, determined from the superconducting transition temperature of elemental lead (Pb). As a result of these data and analysis, we propose a practical algorithm to infer the evolution of pressure with temperature in a PCC.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::a54957228a1f3f9a23f74c99eb302fefTest
https://pubmed.ncbi.nlm.nih.gov/33003820Test

المؤلفون: Christian Balz, Jonas Sonnenschein, Bella Lake, Jose A. Rodriguez-Rivera, Michael Lang, Hanjo Ryll, Johannes Reuther, A. T. M. Nazmul Islam, Ulrich Tutsch

المصدر: Physical Review B. 100

مصطلحات موضوعية: Physics, Condensed matter physics, Heisenberg model, Fermi surface, 02 engineering and technology, Neutron scattering, 021001 nanoscience & nanotechnology, 01 natural sciences, Heat capacity, Spinon, Mean field theory, 0103 physical sciences, Condensed Matter::Strongly Correlated Electrons, Quantum spin liquid, 010306 general physics, 0210 nano-technology, Energy (signal processing)

الوصف: We present new experimental low-temperature heat capacity and detailed dynamical spin-structure factor data for the quantum spin-liquid candidate material ${\mathrm{Ca}}_{10}{\mathrm{Cr}}_{7}{\mathrm{O}}_{28}$. The measured heat capacity shows an almost-perfect linear temperature dependence in the range $0.1\phantom{\rule{0.28em}{0ex}}\mathrm{K}\phantom{\rule{4pt}{0ex}}\ensuremath{\lesssim}T\ensuremath{\lesssim}0.5\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, reminiscent of fermionic spinon degrees of freedom. The spin-structure factor exhibits two energy regimes of strong signal which display rather different but solely diffuse scattering features. We theoretically describe these findings by an effective spinon-hopping model which crucially relies on the existence of strong ferromagnetically coupled triangles in the system. Our spinon theory is shown to naturally reproduce the overall weight distribution of the measured spin-structure factor. Particularly, we argue that various different observed characteristic properties of the spin-structure factor and the heat capacity consistently indicate the existence of a spinon Fermi surface. A closer analysis of the heat capacity at the lowest accessible temperatures hints toward the presence of weak $f$-wave spinon-pairing terms inducing a small partial gap along the Fermi surface (except for discrete nodal Dirac points) and suggesting an overall ${\mathbb{Z}}_{2}$ quantum spin-liquid scenario for ${\mathrm{Ca}}_{10}{\mathrm{Cr}}_{7}{\mathrm{O}}_{28}$.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_________::7cbf963a3cea532ceb8ff498469c9595Test
https://doi.org/10.1103/physrevb.100.174428Test

المؤلفون: Oleksandr Tsyplyatyev, Bernd Wolf, P. T. Cong, W. Aßmus, Franz Ritter, Michael Lang, Peter Thalmeier, Cornelius Krellner, L. Postulka, Ulrich Tutsch, Peter Kopietz, M. Kuhnt, Bernd Schmidt

المصدر: Physical Review Letters. 123

مصطلحات موضوعية: Physics, Quantum phase transition, Specific heat, Condensed matter physics, 0103 physical sciences, General Physics and Astronomy, Condensed Matter::Strongly Correlated Electrons, 010306 general physics, Anisotropy, 01 natural sciences, Quantum, Magnetic susceptibility, Spinon

الوصف: We report an experimental and theoretical study of the low-temperature specific heat $C$ and magnetic susceptibility $\ensuremath{\chi}$ of the layered anisotropic triangular-lattice spin-$1/2$ Heisenberg antiferromagnets ${\mathrm{Cs}}_{2}{\mathrm{CuCl}}_{4\ensuremath{-}x}{\mathrm{Br}}_{x}$ with $x=0$, 1, 2, and 4. We find that the ratio ${J}^{\ensuremath{'}}/J$ of the exchange couplings ranges from 0.32 to $\ensuremath{\approx}0.78$, implying a change (crossover or quantum phase transition) in the materials' magnetic properties from one-dimensional (1D) behavior for ${J}^{\ensuremath{'}}/Jl0.6$ to two-dimensional (2D) behavior for ${J}^{\ensuremath{'}}/J\ensuremath{\approx}0.78$. For ${J}^{\ensuremath{'}}/Jl0.6$, realized for $x=0$, 1, and 4, we find a magnetic contribution to the low-temperature specific heat, ${C}_{m}\ensuremath{\propto}T$, consistent with spinon excitations in 1D spin-$1/2$ Heisenberg antiferromagnets. Remarkably, for $x=2$, where ${J}^{\ensuremath{'}}/J\ensuremath{\approx}0.78$ implies a 2D magnetic character, we also observe ${C}_{m}\ensuremath{\propto}T$. This finding, which contrasts the prediction of ${C}_{m}\ensuremath{\propto}{T}^{2}$ made by standard spin-wave theories, shows that Fermi-like statistics also plays a significant role for the magnetic excitations in spin-$1/2$ frustrated 2D antiferromagnets.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_________::6bcf6de0c990c3b4fdc80d268cd48308Test
https://doi.org/10.1103/physrevlett.123.147202Test

المؤلفون: Lang, Elena Gati, Ulrich Tutsch, Ammar Naji, Markus Garst, Sebastian Köhler, Harald Schubert, Takahiko Sasaki, Michael

المصدر: Crystals; Volume 8; Issue 1; Pages: 38

مصطلحات موضوعية: organic conductor, Mott transition, pressure, disorder, X-ray irradiation, Condensed Matter::Strongly Correlated Electrons

الوصف: We present a study of the influence of disorder on the Mott metal-insulator transition for the organic charge-transfer salt κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl. To this end, disorder was introduced into the system in a controlled way by exposing the single crystals to X-ray irradiation. The crystals were then fine-tuned across the Mott transition by the application of continuously controllable He-gas pressure at low temperatures. Measurements of the thermal expansion and resistance show that the first-order character of the Mott transition prevails for low irradiation doses achieved by irradiation times up to 100 h. For these crystals with a moderate degree of disorder, we find a first-order transition line which ends in a second-order critical endpoint, akin to the pristine crystals. Compared to the latter, however, we observe a significant reduction of both, the critical pressure p c and the critical temperature T c . This result is consistent with the theoretically-predicted formation of a soft Coulomb gap in the presence of strong correlations and small disorder. Furthermore, we demonstrate, similar to the observation for the pristine sample, that the Mott transition after 50 h of irradiation is accompanied by sizable lattice effects, the critical behavior of which can be well described by mean-field theory. Our results demonstrate that the character of the Mott transition remains essentially unchanged at a low disorder level. However, after an irradiation time of 150 h, no clear signatures of a discontinuous metal-insulator transition could be revealed anymore. These results suggest that, above a certain disorder level, the metal-insulator transition becomes a smeared first-order transition with some residual hysteresis.

وصف الملف: application/pdf

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=multidiscipl::c56998790501ff259c895bff647c0606Test

المؤلفون: P. T. Cong, Ulrich Tutsch, Michael Lang, Yulia Borozdina, Martin Baumgarten, Volker Enkelmann, Evgeny A. Mostovich, Bernd Wolf

المصدر: Journal of Materials Chemistry C

مصطلحات موضوعية: Coupling constant, Nitroxide mediated radical polymerization, Materials science, General Chemistry, Crystal structure, law.invention, Coupling (physics), law, Computational chemistry, Chemical physics, Materials Chemistry, Antiferromagnetism, Electron paramagnetic resonance, Spin (physics), Quantum

الوصف: In the present study we report the synthesis of some novel nitronyl nitroxide biradical systems 1–4c with various π-bridges between the radical centres. UV-Vis, IR, EPR and X-ray diffraction studies, along with MS and NMR data where appropriate, are described. Magnetic measurements revealed that the biradicals 1c, 3c and 4c exhibit a moderately strong antiferromagnetic intra-molecular exchange, whereas nitroxide 2c shows a significantly higher exchange coupling, which can only be explained by the presence of strong inter-molecular interactions. From DFT calculations performed on the basis of the X-ray crystal structure of compound 4c, a theoretical value of the intra-dimer coupling constant Jintra = −8.6 K is obtained. Direct proof also for inter-molecular arrangement with Jinter ∼ −2 K was provided by the low temperature AC studies of biradical 4c. According to the magnetic characterization, the nitronyl biradical 4c is a promising candidate for a purely organic-based low-dimensional quantum magnet.

وصف الملف: application/pdf

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::d491acb321820eb1bac69d2ea0eee202Test
https://doi.org/10.1039/c4tc00399cTest

المؤلفون: Elena Gati, Harald Schubert, Takahiko Sasaki, Bernd Wolf, Ulrich Tutsch, Markus Garst, John A. Schlueter, Lorenz Bartosch, Michael Lang, Rudra Sekhar Manna

المصدر: Science Advances

مصطلحات موضوعية: High Energy Physics::Lattice, Critical phenomena, 02 engineering and technology, Electron, thermodynamic studies, 01 natural sciences, Mott metal-insulator-transiton, Moduli, symbols.namesake, Lattice (order), Quantum mechanics, 0103 physical sciences, ddc:530, 010306 general physics, Research Articles, thermal expansion, Condensed Matter::Quantum Gases, Physics, Multidisciplinary, Condensed matter physics, Condensed Matter::Other, effects of hydrostatic pressure, Hooke's law, SciAdv r-articles, Strongly correlated electron systems, critical phenomena, organic charge-transfer salts, Condensed Matter Physics, 021001 nanoscience & nanotechnology, Mott transition, Compressibility, symbols, Condensed Matter::Strongly Correlated Electrons, Strongly correlated material, coupling of electrons to lattice degrees of freedom, 0210 nano-technology, Research Article

الوصف: The coupling of the critical electronic system to a compressible lattice is found to drastically alter the Mott criticality.
The Mott metal-insulator transition, a paradigm of strong electron-electron correlations, has been considered as a source of intriguing phenomena. Despite its importance for a wide range of materials, fundamental aspects of the transition, such as its universal properties, are still under debate. We report detailed measurements of relative length changes ΔL/L as a function of continuously controlled helium-gas pressure P for the organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl across the pressure-induced Mott transition. We observe strongly nonlinear variations of ΔL/L with pressure around the Mott critical endpoint, highlighting a breakdown of Hooke’s law of elasticity. We assign these nonlinear strain-stress relations to an intimate, nonperturbative coupling of the critical electronic system to the lattice degrees of freedom. Our results are fully consistent with mean-field criticality, predicted for electrons in a compressible lattice with finite shear moduli. We argue that the Mott transition for all systems that are amenable to pressure tuning shows the universal properties of an isostructural solid-solid transition.

وصف الملف: application/pdf

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::e43329fc685fc3a93b29d304b9fbcd5dTest
https://doi.org/10.1126/sciadv.1601646Test

المؤلفون: Elena Gati, Yuan Li, Cornelius Krellner, Franz Ritter, Peter Thalmeier, Roser Valentí, Bernd Wolf, L. Postulka, S. K. Thallapaka, Vladislav Borisov, Ulrich Tutsch, Burkhard Schmidt, Michael Lang

المصدر: physica status solidi (b). 256:1900044

مصطلحات موضوعية: 010302 applied physics, Physics, Coupling constant, Degree (graph theory), Condensed matter physics, media_common.quotation_subject, Hydrostatic pressure, Frustration, 02 engineering and technology, 021001 nanoscience & nanotechnology, Condensed Matter Physics, 01 natural sciences, Magnetic susceptibility, Electronic, Optical and Magnetic Materials, 0103 physical sciences, Antiferromagnetism, Hexagonal lattice, 0210 nano-technology, Energy (signal processing), media_common

الوصف: We present a study of the magnetic susceptibility $\chi_{mol}$ under variable hydrostatic pressure on single crystals of Cs$_2$CuCl$_{4-x}$Br$_x$. This includes the border compounds \textit{x} = 0 and 4, known as good realizations of the distorted triangular-lattice spin-1/2 Heisenberg antiferromagnet, as well as the isostructural stoichiometric systems Cs$_2$CuCl$_{3}$Br$_1$ and Cs$_2$CuCl$_{2}$Br$_2$. For the determination of the exchange coupling constants $J$ and $J^{\prime}$, $\chi_{mol}$ data were fitted by a $J-J^{\prime}$ model \cite{Schmidt2015}. Its application, validated for the border compounds, yields a degree of frustration $J^{\prime}$/$J$ = 0.47 for Cs$_2$CuCl$_3$Br$_1$ and $J^{\prime}$/$J$ $\simeq$ 0.63 - 0.78 for Cs$_2$CuCl$_2$Br$_2$, making these systems particular interesting representatives of this family. From the evolution of the magnetic susceptibility under pressure up to about 0.4\,GPa, the maximum pressure applied, two observations were made for all the compounds investigated here. First, we find that the overall energy scale, given by $J_c = (J^2$ + $J^{\prime 2}$)$^{1/2}$, increases under pressure, whereas the ratio $J^{\prime}$/$J$ remains unchanged in this pressure range. These experimental observations are in accordance with the results of DFT calculations performed for these materials. Secondly, for the magnetoelastic coupling constants, extraordinarily small values are obtained. We assign these observations to a structural peculiarity of this class of materials.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_________::6ea57801fb7ae2da7be489c627d04ea5Test
https://doi.org/10.1002/pssb.201900044Test