Bulletin of the American Physical Society, Mar 5, 2019
Transitions between topologically distinct electronic states have been predicted in different cla... more Transitions between topologically distinct electronic states have been predicted in different classes of materials and observed in some. A major goal is the identification of measurable properties that directly expose the topological nature of such transitions. Here we focus on the giant-Rashba material bismuth tellurium iodine (BiTeI) which exhibits a pressure-driven phase transition between topological and trivial insulators in threedimensions. We demonstrate that this transition, which proceeds through an intermediate Weyl semi-metallic state, is accompanied by a giant enhancement of the Berry curvature dipole which can be probed in transport and optoelectronic experiments. From first-principles calculations, we show that the Berrry-dipole -a vector along the polar axis of this material-has opposite orientations in the trivial and topological insulating phases and peaks at the insulator-to-Weyl critical points, at which the nonlinear Hall conductivity can increase by over two orders of magnitude.
We analyze the nature of Mott metal-insulator transition in multiorbital systems using dynamical ... more We analyze the nature of Mott metal-insulator transition in multiorbital systems using dynamical mean-field theory (DMFT). The auxiliary multiorbital quantum impurity problem is solved using continuous time quantum Monte Carlo (CTQMC) and the rotationally invariant slave-boson (RISB) mean field approximation. We focus our analysis on the Kanamori Hamiltonian and find that there are two markedly different regimes determined by the nature of the lowest energy excitations of the atomic Hamiltonian. The RISB results at T→0 suggest the following rule of thumb for the order of the transition at zero temperature: a second order transition is to be expected if the lowest lying excitations of the atomic Hamiltonian are charge excitations, while the transition tends to be first order if the lowest lying excitations are in the same charge sector as the atomic ground state. At finite temperatures the transition is first order and its strength, as measured e.g. by the jump in the quasiparticle w...
Even if Weyl semimetals are characterized by quasiparticles with well-defined chirality, exploiti... more Even if Weyl semimetals are characterized by quasiparticles with well-defined chirality, exploiting this experimentally is severely hampered by Weyl lattice-fermions coming in pairs with opposite chirality, typically causing the net chirality picked up by experimental probes to vanish. Here we show this issue can be circumvented in a controlled manner when both time-reversal- and inversion- symmetry are broken. To this end, we investigate chirality-disbalance in the carbide family RMC_2 (R a rare-earth and M a transition metal), showing several members to be Weyl semimetals. Using the noncentrosymmetric ferromagnet NdRhC_2 as an illustrating example, we show that an odd number of Weyl nodes can be stabilized at its Fermi surface by properly tilting its magnetization. The tilt direction determines the sign of the resulting net chirality, opening up a simple route to control it.
Even if Weyl semimetals are characterized by quasiparticles with well-defined chirality, exploiti... more Even if Weyl semimetals are characterized by quasiparticles with well-defined chirality, exploiting this experimentally is severely hampered by Weyl lattice fermions coming in pairs with opposite chirality, typically causing the net chirality picked up by experimental probes to vanish. Here, we show this issue can be circumvented in a controlled manner when both time-reversal- and inversion symmetry are broken. To this end, we investigate chirality disbalance in the carbide family RMC2 (R a rare-earth and M a transition metal), showing several members to be Weyl semimetals. Using the noncentrosymmetric ferromagnet NdRhC2 as an illustrating example, we show that an odd number of Weyl nodes can be stabilized at its Fermi surface by properly tilting its magnetization. The chiral configuration endows a topological phase transition as the Weyl node transitions across the Fermi sheets, which triggers interesting chiral electromagnetic responses. Further, the tilt direction determines the ...
This article presents an analytical framework for understanding and studying the value structures... more This article presents an analytical framework for understanding and studying the value structures that govern participation in sport. We combine insights from a Norwegian Monitor survey with existential philosophical reasoning to present an empirically based value structure and discern three fundamental ways of engaging in sport: being, having and belonging. We argue that distinguishing between these modes of engagement can contribute to describing, analysing and navigating in the variety of ways that participants engage in sport. Using friluftsliv and football as illustrative cases, we analyse how these existential dimensions can be prevalent in different forms of participation. Towards the end of the article, we discuss the strengths and weaknesses of our approach, and how the existential dimensions may relate and intertwine in practice.
Marius Scholten, Jorge I. Facio, Rajyavardhan Ray, 2 Ilya M. Eremin, Jeroen van den Brink, 4 and ... more Marius Scholten, Jorge I. Facio, Rajyavardhan Ray, 2 Ilya M. Eremin, Jeroen van den Brink, 4 and Flavio S. Nogueira Institute for Theoretical Solid State Physics, IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany Dresden Center for Computational Materials Science (DCMS), TU Dresden, 01062 Dresden, Germany Institut für Theoretische Physik III, Ruhr-Universität Bochum, D-44780 Bochum, Germany Institute for Theoretical Physics and Würzburg-Dresden Cluster of Excellence ct.qmat, TU Dresden, 01069 Dresden, Germany (Dated: July 14, 2021)
Jorge I. Facio,1 Sanjib Kumar Das,1 Yang Zhang,1, 2 Klaus Koepernik,1 Jeroen van den Brink,1, 3, ... more Jorge I. Facio,1 Sanjib Kumar Das,1 Yang Zhang,1, 2 Klaus Koepernik,1 Jeroen van den Brink,1, 3, 4 and Ion Cosma Fulga1 1IFW Dresden and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtzstr. 20, 01069 Dresden, Germany 2Max Planck Institute for the Physics of Complex Systems, Nöthnitzerstr. 38, 01187 Dresden, Germany 3Department of Physics, Technical University Dresden and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtzstr. 10, 01062 Dresden, Germany 4Department of Physics, Washington University, St. Louis, MO 63130, USA
Transitions between topologically distinct electronic states have been predicted in different cla... more Transitions between topologically distinct electronic states have been predicted in different classes of materials and observed in some. A major goal is the identification of measurable properties that directly expose the topological nature of such transitions. Here we focus on the giant-Rashba material bismuth tellurium iodine (BiTeI) which exhibits a pressure-driven phase transition between topological and trivial insulators in three-dimensions. We demonstrate that this transition, which proceeds through an intermediate Weyl semi-metallic state, is accompanied by a giant enhancement of the Berry curvature dipole which can be probed in transport and optoelectronic experiments. From first-principles calculations, we show that the Berrry-dipole-a vector along the polar axis of this material-has opposite orientations in the trivial and topological insulating phases and peaks at the insulator-to-Weyl critical points. Consequently, near the topological phase transitions, in a low electronic density regime the nonlinear Hall conductivity increases by two orders of magnitude.
We analyze theoretically a common experimental process used to obtain the magnetic contribution t... more We analyze theoretically a common experimental process used to obtain the magnetic contribution to the specific heat of a given magnetic material. In the procedure, the specific heat of a non-magnetic analog is measured and used to subtract the non-magnetic contributions, which are generally dominated by the lattice degrees of freedom in a wide range of temperatures. We calculate the lattice contribution to the specific heat for the magnetic compounds GdMIn5 (M1⁄4Co, Rh) and for the non-magnetic YMIn5 and LaMIn5 (M1⁄4Co, Rh), using density functional theory based methods. We find that the best non-magnetic analog for the subtraction depends on the magnetic material and on the range of temperatures. While the phonon specific heat contribution of YRhIn5 is an excellent approximation to the one of GdCoIn5 in the full temperature range, for GdRhIn5 we find a better agreement with LaCoIn5, in both cases, as a result of an optimum compensation effect between masses and volumes. We present...
We study the Hall conductivity of a two-dimensional electron gas under an inhomogeneous magnetic ... more We study the Hall conductivity of a two-dimensional electron gas under an inhomogeneous magnetic field B(x). First, we prove using the quantum kinetic theory that an odd magnetic field can lead to a purely nonlinear Hall response. Second, considering a real-space magnetic dipole consisting of a sign-changing magnetic field and based on numerical semiclassical dynamics, we unveil a parametric resonance involving the cyclotron ratio and a characteristic width of B(x), which can greatly enhance the Hall response. Different from previous mechanisms that rely on the bulk Berry curvature dipole, the effect largely stems from boundary states associated with the real-space magnetic dipole. Our findings pave a new way to engineer current rectification and higher harmonic generation in two-dimensional materials having or not crystal inversion symmetry.
Symmetry breaking in topological matter became, in the last decade, a key concept in condensed ma... more Symmetry breaking in topological matter became, in the last decade, a key concept in condensed matter physics to unveil novel electronic states. In this work, we reveal that broken inversion symmetry and strong spin-orbit coupling in trigonal PtBi2 lead to a Weyl semimetal band structure, with unusually robust two-dimensional superconductivity in thin fims. Transport measurements show that high-quality PtBi2 crystals are three-dimensional superconductors (Tc≈600 mK) with an isotropic critical field (Bc≈50 mT). Remarkably, we evidence in a rather thick flake (60 nm), exfoliated from a macroscopic crystal, the two-dimensional nature of the superconducting state, with a critical temperature Tc≈370 mK and highly-anisotropic critical fields. Our results reveal a Berezinskii-Kosterlitz-Thouless transition with TBKT≈310 mK and with a broadening of Tc due to inhomogenities in the sample. Due to the very long superconducting coherence length ξ in PtBi2, the vortex-antivortex pairing mechanis...
We show that Weyl Fermi arcs are generically accompanied by a divergence of the surface Berry cur... more We show that Weyl Fermi arcs are generically accompanied by a divergence of the surface Berry curvature scaling as 1/k 2 , where k is the distance to a hot-line in the surface Brillouin zone that connects the projection of Weyl nodes with opposite chirality but which is distinct from the Fermi arc itself. Such surface Berry curvature appears whenever the bulk Weyl dispersion has a velocity tilt toward the surface of interest. This divergence is reflected in a variety of Berry curvature mediated effects that are readily accessible experimentally, and in particular leads to a surface Berry curvature dipole that grows linearly with the thickness of a slab of a Weyl semimetal material in the limit of long lifetime of surface states. This implies the emergence of a gigantic contribution to the non-linear Hall effect in such devices.
Abstract A new intermetallic ternary compound La6Pd2.28Sb15 was synthesized from the reaction of ... more Abstract A new intermetallic ternary compound La6Pd2.28Sb15 was synthesized from the reaction of lanthanum and palladium metals in a molten antimony flux. The compound crystallizes in the orthorhombic space group Immm with a = 4.3082(9) A, b = 15.399(3) A and c = 19.689(4) A. The crystal structure contains a three-dimensional framework of Sb squares and ribbons that extend along the a axis, including complex Sb–Sb bonding. La6Pd2.28Sb15 is diamagnetic, with a magnetic susceptibility weakly dependent on temperature (T). The resistivity (ρ) decreases when lowering the temperature, indicating metallic behavior, and at low temperatures ρ depends quadratically on T. Interestingly, both the Hall resistivity and magnetoresistance present a nonlinear dependence on the applied magnetic field, suggesting a multiband behavior. This is supported by density-functional electronic structure calculations which show a complex Fermi surface originated in the antimonide substructures and containing both electron and hole pockets as well as open sheets.
Weyl semimetals exhibit interesting electronic properties due to their topological band structure... more Weyl semimetals exhibit interesting electronic properties due to their topological band structure. In particular, large anomalous Hall and anomalous Nernst signals are often reported, which allow for a detailed and quantitative study of subtle features. We pattern single crystals of the magnetic Weyl semimetal Co3Sn2S2 into nanoribbon devices using focused ion beam cutting and optical lithography. This approach enables a very precise study of the galvano- and thermomagnetic transport properties. Indeed, we found interesting features in the temperature dependency of the anomalous Hall and Nernst effects. We present an analysis of the data based on the Mott relation and identify in the Nernst response signatures of magnetic fluctuations enhancing the anomalous Nernst conductivity at the magnetic phase transition.
We report detailed thermal expansion and magnetostriction experiments on GdCoIn5 and GdRhIn5 sing... more We report detailed thermal expansion and magnetostriction experiments on GdCoIn5 and GdRhIn5 single crystal samples that show a sudden change in the dilation at a field B for temperatures below the Néel transition temperature TN. We present a first-principles model including crystal-field effects, dipolar and exchange interactions, and the dependence of the exchange couplings with lattice distortions in order to fully account for the magnetostriction and magnetic susceptibility data. The mean-field solution of the model shows that a transition between metastable states occurs at the field B. It also indicates that two degenerate phases coexist in the sample at temperatures below TN. This allows to explain the lack of observation, in high resolution x-ray experiments, of an orthorhombic distortion at the Néel transition even though the magnetic structure breaks the tetragonal symmetry and the magnetoelastic coupling is significant. These conclusions could be extended to other tetragonal Gd-based compounds that present the same phenomenology.
The kagome lattice based on 3d transition metals is a versatile platform for novel topological ph... more The kagome lattice based on 3d transition metals is a versatile platform for novel topological phases hosting symmetry-protected electronic excitations and exotic magnetic ground states. However, the paradigmatic states of the idealized two-dimensional (2D) kagome lattice -Dirac fermions and topological flat bands -have not been simultaneously observed, partly owing to the complex stacking structure of the kagome compounds studied to date. Here, we take the approach of examining FeSn, an antiferromagnetic single-layer kagome metal with spatially-decoupled kagome planes. Using polarization-and termination-dependent angleresolved photoemission spectroscopy (ARPES), we detect the momentum-space signatures of coexisting flat bands and Dirac fermions in the vicinity of the Fermi energy. Intriguingly, when complemented with bulk-sensitive de Haas-van Alphen (dHvA) measurements, our data reveal an even richer electronic structure that exhibits robust surface Dirac fermions on specific crystalline terminations. Through band structure calculations and matrix element simulations, we demonstrate that the bulk Dirac bands arise from in-plane localized Fe-3d orbitals under kagome symmetry, while the surface state realizes a rare example of fully spin-polarized 2D Dirac fermions when combined with spin-layer locking in FeSn. These results highlight FeSn as a prototypical host for the emergent excitations of the kagome lattice. The prospect to harness these excitations for novel topological phases and spintronic devices is a frontier of great promise at the confluence of topology, magnetism, and strongly-correlated electron physics.
Bulletin of the American Physical Society, Mar 5, 2019
Transitions between topologically distinct electronic states have been predicted in different cla... more Transitions between topologically distinct electronic states have been predicted in different classes of materials and observed in some. A major goal is the identification of measurable properties that directly expose the topological nature of such transitions. Here we focus on the giant-Rashba material bismuth tellurium iodine (BiTeI) which exhibits a pressure-driven phase transition between topological and trivial insulators in threedimensions. We demonstrate that this transition, which proceeds through an intermediate Weyl semi-metallic state, is accompanied by a giant enhancement of the Berry curvature dipole which can be probed in transport and optoelectronic experiments. From first-principles calculations, we show that the Berrry-dipole -a vector along the polar axis of this material-has opposite orientations in the trivial and topological insulating phases and peaks at the insulator-to-Weyl critical points, at which the nonlinear Hall conductivity can increase by over two orders of magnitude.
We analyze the nature of Mott metal-insulator transition in multiorbital systems using dynamical ... more We analyze the nature of Mott metal-insulator transition in multiorbital systems using dynamical mean-field theory (DMFT). The auxiliary multiorbital quantum impurity problem is solved using continuous time quantum Monte Carlo (CTQMC) and the rotationally invariant slave-boson (RISB) mean field approximation. We focus our analysis on the Kanamori Hamiltonian and find that there are two markedly different regimes determined by the nature of the lowest energy excitations of the atomic Hamiltonian. The RISB results at T→0 suggest the following rule of thumb for the order of the transition at zero temperature: a second order transition is to be expected if the lowest lying excitations of the atomic Hamiltonian are charge excitations, while the transition tends to be first order if the lowest lying excitations are in the same charge sector as the atomic ground state. At finite temperatures the transition is first order and its strength, as measured e.g. by the jump in the quasiparticle w...
Even if Weyl semimetals are characterized by quasiparticles with well-defined chirality, exploiti... more Even if Weyl semimetals are characterized by quasiparticles with well-defined chirality, exploiting this experimentally is severely hampered by Weyl lattice-fermions coming in pairs with opposite chirality, typically causing the net chirality picked up by experimental probes to vanish. Here we show this issue can be circumvented in a controlled manner when both time-reversal- and inversion- symmetry are broken. To this end, we investigate chirality-disbalance in the carbide family RMC_2 (R a rare-earth and M a transition metal), showing several members to be Weyl semimetals. Using the noncentrosymmetric ferromagnet NdRhC_2 as an illustrating example, we show that an odd number of Weyl nodes can be stabilized at its Fermi surface by properly tilting its magnetization. The tilt direction determines the sign of the resulting net chirality, opening up a simple route to control it.
Even if Weyl semimetals are characterized by quasiparticles with well-defined chirality, exploiti... more Even if Weyl semimetals are characterized by quasiparticles with well-defined chirality, exploiting this experimentally is severely hampered by Weyl lattice fermions coming in pairs with opposite chirality, typically causing the net chirality picked up by experimental probes to vanish. Here, we show this issue can be circumvented in a controlled manner when both time-reversal- and inversion symmetry are broken. To this end, we investigate chirality disbalance in the carbide family RMC2 (R a rare-earth and M a transition metal), showing several members to be Weyl semimetals. Using the noncentrosymmetric ferromagnet NdRhC2 as an illustrating example, we show that an odd number of Weyl nodes can be stabilized at its Fermi surface by properly tilting its magnetization. The chiral configuration endows a topological phase transition as the Weyl node transitions across the Fermi sheets, which triggers interesting chiral electromagnetic responses. Further, the tilt direction determines the ...
This article presents an analytical framework for understanding and studying the value structures... more This article presents an analytical framework for understanding and studying the value structures that govern participation in sport. We combine insights from a Norwegian Monitor survey with existential philosophical reasoning to present an empirically based value structure and discern three fundamental ways of engaging in sport: being, having and belonging. We argue that distinguishing between these modes of engagement can contribute to describing, analysing and navigating in the variety of ways that participants engage in sport. Using friluftsliv and football as illustrative cases, we analyse how these existential dimensions can be prevalent in different forms of participation. Towards the end of the article, we discuss the strengths and weaknesses of our approach, and how the existential dimensions may relate and intertwine in practice.
Marius Scholten, Jorge I. Facio, Rajyavardhan Ray, 2 Ilya M. Eremin, Jeroen van den Brink, 4 and ... more Marius Scholten, Jorge I. Facio, Rajyavardhan Ray, 2 Ilya M. Eremin, Jeroen van den Brink, 4 and Flavio S. Nogueira Institute for Theoretical Solid State Physics, IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany Dresden Center for Computational Materials Science (DCMS), TU Dresden, 01062 Dresden, Germany Institut für Theoretische Physik III, Ruhr-Universität Bochum, D-44780 Bochum, Germany Institute for Theoretical Physics and Würzburg-Dresden Cluster of Excellence ct.qmat, TU Dresden, 01069 Dresden, Germany (Dated: July 14, 2021)
Jorge I. Facio,1 Sanjib Kumar Das,1 Yang Zhang,1, 2 Klaus Koepernik,1 Jeroen van den Brink,1, 3, ... more Jorge I. Facio,1 Sanjib Kumar Das,1 Yang Zhang,1, 2 Klaus Koepernik,1 Jeroen van den Brink,1, 3, 4 and Ion Cosma Fulga1 1IFW Dresden and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtzstr. 20, 01069 Dresden, Germany 2Max Planck Institute for the Physics of Complex Systems, Nöthnitzerstr. 38, 01187 Dresden, Germany 3Department of Physics, Technical University Dresden and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtzstr. 10, 01062 Dresden, Germany 4Department of Physics, Washington University, St. Louis, MO 63130, USA
Transitions between topologically distinct electronic states have been predicted in different cla... more Transitions between topologically distinct electronic states have been predicted in different classes of materials and observed in some. A major goal is the identification of measurable properties that directly expose the topological nature of such transitions. Here we focus on the giant-Rashba material bismuth tellurium iodine (BiTeI) which exhibits a pressure-driven phase transition between topological and trivial insulators in three-dimensions. We demonstrate that this transition, which proceeds through an intermediate Weyl semi-metallic state, is accompanied by a giant enhancement of the Berry curvature dipole which can be probed in transport and optoelectronic experiments. From first-principles calculations, we show that the Berrry-dipole-a vector along the polar axis of this material-has opposite orientations in the trivial and topological insulating phases and peaks at the insulator-to-Weyl critical points. Consequently, near the topological phase transitions, in a low electronic density regime the nonlinear Hall conductivity increases by two orders of magnitude.
We analyze theoretically a common experimental process used to obtain the magnetic contribution t... more We analyze theoretically a common experimental process used to obtain the magnetic contribution to the specific heat of a given magnetic material. In the procedure, the specific heat of a non-magnetic analog is measured and used to subtract the non-magnetic contributions, which are generally dominated by the lattice degrees of freedom in a wide range of temperatures. We calculate the lattice contribution to the specific heat for the magnetic compounds GdMIn5 (M1⁄4Co, Rh) and for the non-magnetic YMIn5 and LaMIn5 (M1⁄4Co, Rh), using density functional theory based methods. We find that the best non-magnetic analog for the subtraction depends on the magnetic material and on the range of temperatures. While the phonon specific heat contribution of YRhIn5 is an excellent approximation to the one of GdCoIn5 in the full temperature range, for GdRhIn5 we find a better agreement with LaCoIn5, in both cases, as a result of an optimum compensation effect between masses and volumes. We present...
We study the Hall conductivity of a two-dimensional electron gas under an inhomogeneous magnetic ... more We study the Hall conductivity of a two-dimensional electron gas under an inhomogeneous magnetic field B(x). First, we prove using the quantum kinetic theory that an odd magnetic field can lead to a purely nonlinear Hall response. Second, considering a real-space magnetic dipole consisting of a sign-changing magnetic field and based on numerical semiclassical dynamics, we unveil a parametric resonance involving the cyclotron ratio and a characteristic width of B(x), which can greatly enhance the Hall response. Different from previous mechanisms that rely on the bulk Berry curvature dipole, the effect largely stems from boundary states associated with the real-space magnetic dipole. Our findings pave a new way to engineer current rectification and higher harmonic generation in two-dimensional materials having or not crystal inversion symmetry.
Symmetry breaking in topological matter became, in the last decade, a key concept in condensed ma... more Symmetry breaking in topological matter became, in the last decade, a key concept in condensed matter physics to unveil novel electronic states. In this work, we reveal that broken inversion symmetry and strong spin-orbit coupling in trigonal PtBi2 lead to a Weyl semimetal band structure, with unusually robust two-dimensional superconductivity in thin fims. Transport measurements show that high-quality PtBi2 crystals are three-dimensional superconductors (Tc≈600 mK) with an isotropic critical field (Bc≈50 mT). Remarkably, we evidence in a rather thick flake (60 nm), exfoliated from a macroscopic crystal, the two-dimensional nature of the superconducting state, with a critical temperature Tc≈370 mK and highly-anisotropic critical fields. Our results reveal a Berezinskii-Kosterlitz-Thouless transition with TBKT≈310 mK and with a broadening of Tc due to inhomogenities in the sample. Due to the very long superconducting coherence length ξ in PtBi2, the vortex-antivortex pairing mechanis...
We show that Weyl Fermi arcs are generically accompanied by a divergence of the surface Berry cur... more We show that Weyl Fermi arcs are generically accompanied by a divergence of the surface Berry curvature scaling as 1/k 2 , where k is the distance to a hot-line in the surface Brillouin zone that connects the projection of Weyl nodes with opposite chirality but which is distinct from the Fermi arc itself. Such surface Berry curvature appears whenever the bulk Weyl dispersion has a velocity tilt toward the surface of interest. This divergence is reflected in a variety of Berry curvature mediated effects that are readily accessible experimentally, and in particular leads to a surface Berry curvature dipole that grows linearly with the thickness of a slab of a Weyl semimetal material in the limit of long lifetime of surface states. This implies the emergence of a gigantic contribution to the non-linear Hall effect in such devices.
Abstract A new intermetallic ternary compound La6Pd2.28Sb15 was synthesized from the reaction of ... more Abstract A new intermetallic ternary compound La6Pd2.28Sb15 was synthesized from the reaction of lanthanum and palladium metals in a molten antimony flux. The compound crystallizes in the orthorhombic space group Immm with a = 4.3082(9) A, b = 15.399(3) A and c = 19.689(4) A. The crystal structure contains a three-dimensional framework of Sb squares and ribbons that extend along the a axis, including complex Sb–Sb bonding. La6Pd2.28Sb15 is diamagnetic, with a magnetic susceptibility weakly dependent on temperature (T). The resistivity (ρ) decreases when lowering the temperature, indicating metallic behavior, and at low temperatures ρ depends quadratically on T. Interestingly, both the Hall resistivity and magnetoresistance present a nonlinear dependence on the applied magnetic field, suggesting a multiband behavior. This is supported by density-functional electronic structure calculations which show a complex Fermi surface originated in the antimonide substructures and containing both electron and hole pockets as well as open sheets.
Weyl semimetals exhibit interesting electronic properties due to their topological band structure... more Weyl semimetals exhibit interesting electronic properties due to their topological band structure. In particular, large anomalous Hall and anomalous Nernst signals are often reported, which allow for a detailed and quantitative study of subtle features. We pattern single crystals of the magnetic Weyl semimetal Co3Sn2S2 into nanoribbon devices using focused ion beam cutting and optical lithography. This approach enables a very precise study of the galvano- and thermomagnetic transport properties. Indeed, we found interesting features in the temperature dependency of the anomalous Hall and Nernst effects. We present an analysis of the data based on the Mott relation and identify in the Nernst response signatures of magnetic fluctuations enhancing the anomalous Nernst conductivity at the magnetic phase transition.
We report detailed thermal expansion and magnetostriction experiments on GdCoIn5 and GdRhIn5 sing... more We report detailed thermal expansion and magnetostriction experiments on GdCoIn5 and GdRhIn5 single crystal samples that show a sudden change in the dilation at a field B for temperatures below the Néel transition temperature TN. We present a first-principles model including crystal-field effects, dipolar and exchange interactions, and the dependence of the exchange couplings with lattice distortions in order to fully account for the magnetostriction and magnetic susceptibility data. The mean-field solution of the model shows that a transition between metastable states occurs at the field B. It also indicates that two degenerate phases coexist in the sample at temperatures below TN. This allows to explain the lack of observation, in high resolution x-ray experiments, of an orthorhombic distortion at the Néel transition even though the magnetic structure breaks the tetragonal symmetry and the magnetoelastic coupling is significant. These conclusions could be extended to other tetragonal Gd-based compounds that present the same phenomenology.
The kagome lattice based on 3d transition metals is a versatile platform for novel topological ph... more The kagome lattice based on 3d transition metals is a versatile platform for novel topological phases hosting symmetry-protected electronic excitations and exotic magnetic ground states. However, the paradigmatic states of the idealized two-dimensional (2D) kagome lattice -Dirac fermions and topological flat bands -have not been simultaneously observed, partly owing to the complex stacking structure of the kagome compounds studied to date. Here, we take the approach of examining FeSn, an antiferromagnetic single-layer kagome metal with spatially-decoupled kagome planes. Using polarization-and termination-dependent angleresolved photoemission spectroscopy (ARPES), we detect the momentum-space signatures of coexisting flat bands and Dirac fermions in the vicinity of the Fermi energy. Intriguingly, when complemented with bulk-sensitive de Haas-van Alphen (dHvA) measurements, our data reveal an even richer electronic structure that exhibits robust surface Dirac fermions on specific crystalline terminations. Through band structure calculations and matrix element simulations, we demonstrate that the bulk Dirac bands arise from in-plane localized Fe-3d orbitals under kagome symmetry, while the surface state realizes a rare example of fully spin-polarized 2D Dirac fermions when combined with spin-layer locking in FeSn. These results highlight FeSn as a prototypical host for the emergent excitations of the kagome lattice. The prospect to harness these excitations for novel topological phases and spintronic devices is a frontier of great promise at the confluence of topology, magnetism, and strongly-correlated electron physics.
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