2024
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Huber, N.; Mishra, S.; Sheikin, I.; Alpin, K.; Schnyder, A. P.; Benka, G.; Bauer, A.; Pfleiderer, C.; Wilde, M. A. Fermi surface of the chiral topological semimetal CoSi Journal Article Phys. Rev. B 109, 205115, 2024. @article{huber_fermi_2024,
title = {Fermi surface of the chiral topological semimetal CoSi},
author = {N. Huber and S. Mishra and I. Sheikin and K. Alpin and A. P. Schnyder and G. Benka and A. Bauer and C. Pfleiderer and M. A. Wilde},
doi = {10.1103/PhysRevB.109.205115},
year = {2024},
date = {2024-05-06},
urldate = {2024-05-01},
journal = {Phys. Rev. B},
volume = {109},
number = {20},
pages = {205115},
abstract = {We report a study of the Fermi surface of the chiral semimetal CoSi and its relationship to a network of multifold topological crossing points, Weyl points, and topological nodal planes in the electronic band structure. Combining quantum oscillations in the Hall resistivity, magnetization, and torque magnetization with ab initio electronic structure calculations, we identify two groups of Fermi-surface sheets, one centered at the 𝑅 point and the other centered at the Γ point. The presence of topological nodal planes at the Brillouin zone boundary enforces topological protectorates on the Fermi-surface sheets centered at the 𝑅 point. In addition, Weyl points exist close to the Fermi-surface sheets centered at the 𝑅 and the Γ points. In contrast, topological crossing points at the 𝑅 point and the Γ point, which have been advertised to feature exceptionally large Chern numbers, are located at a larger distance to the Fermi level. Representing a unique example in which the multitude of topological band crossings has been shown to form a complex network, our observations in CoSi highlight the need for detailed numerical calculations of the Berry curvature at the Fermi level, regardless of the putative existence and the possible character of topological band crossings in the band structure.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report a study of the Fermi surface of the chiral semimetal CoSi and its relationship to a network of multifold topological crossing points, Weyl points, and topological nodal planes in the electronic band structure. Combining quantum oscillations in the Hall resistivity, magnetization, and torque magnetization with ab initio electronic structure calculations, we identify two groups of Fermi-surface sheets, one centered at the 𝑅 point and the other centered at the Γ point. The presence of topological nodal planes at the Brillouin zone boundary enforces topological protectorates on the Fermi-surface sheets centered at the 𝑅 point. In addition, Weyl points exist close to the Fermi-surface sheets centered at the 𝑅 and the Γ points. In contrast, topological crossing points at the 𝑅 point and the Γ point, which have been advertised to feature exceptionally large Chern numbers, are located at a larger distance to the Fermi level. Representing a unique example in which the multitude of topological band crossings has been shown to form a complex network, our observations in CoSi highlight the need for detailed numerical calculations of the Berry curvature at the Fermi level, regardless of the putative existence and the possible character of topological band crossings in the band structure. |  |
Wu, X.; Chakraborty, D.; Schnyder, A. P.; Greco, A. Crossover between electron-electron and electron-phonon mediated pairing on the Kagome lattice Journal Article Phys. Rev. B 109, 014517, 2024. @article{wu_crossover_2024,
title = {Crossover between electron-electron and electron-phonon mediated pairing on the Kagome lattice},
author = {X. Wu and D. Chakraborty and A. P. Schnyder and A. Greco},
doi = {10.1103/physrevb.109.014517},
year = {2024},
date = {2024-01-01},
urldate = {2024-01-01},
journal = {Phys. Rev. B},
volume = {109},
number = {1},
pages = {014517},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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Hu, Y.; Ma, J.; Li, Y.; Jiang, Y.; Gawryluk, D. J.; Hu, T.; Teyssier, J.; Multian, V.; Yin, Z.; Xu, S.; others, Phonon promoted charge density wave in topological kagome metal ScV6Sn6 Journal Article Nat. Commun. 15, 1658, 2024. @article{hu_phonon_2024,
title = {Phonon promoted charge density wave in topological kagome metal ScV_{6}Sn_{6}},
author = {Y. Hu and J. Ma and Y. Li and Y. Jiang and D. J. Gawryluk and T. Hu and J. Teyssier and V. Multian and Z. Yin and S. Xu and others},
doi = {10.1038/s41467-024-45859-y},
year = {2024},
date = {2024-01-01},
urldate = {2024-01-01},
journal = {Nat. Commun.},
volume = {15},
number = {1},
pages = {1658},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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Alpin, K. Perturbative description of high-Tc superconductivity in the Hubbard model via unitary transformation and classical spins Unpublished 2024, arXiv.2403.09765. @unpublished{alpin_perturbative_2024,
title = {Perturbative description of high-T_{c} superconductivity in the Hubbard model via unitary transformation and classical spins},
author = {K. Alpin},
doi = {10.48550/arXiv.2403.09765},
year = {2024},
date = {2024-03-14},
urldate = {2024-03-01},
abstract = {A unitary transformation is applied to the Hubbard model, which maps the Hubbard interaction to a single particle term. The resulting Hamiltonian consists of unconstrained fermions, which is then mapped to a Hamiltonian of spinless fermions coupled to pseudospins. The fermions are integrated out using second order perturbation theory in $1/U$, resulting in an effective spin Hamiltonian. An order parameter is identified, stabilizing d-wave superconductivity. The groundstate energy of classical spin configurations is minimized at a finite value of this order parameter after a critical chemical potential, resulting in d-wave superconductivity at non-zero doping. This suggests, that the onset of high-$T_c$ superconductivity is governed by the groundstate of a classical spin system.},
note = {arXiv.2403.09765},
keywords = {},
pubstate = {published},
tppubtype = {unpublished}
}
A unitary transformation is applied to the Hubbard model, which maps the Hubbard interaction to a single particle term. The resulting Hamiltonian consists of unconstrained fermions, which is then mapped to a Hamiltonian of spinless fermions coupled to pseudospins. The fermions are integrated out using second order perturbation theory in $1/U$, resulting in an effective spin Hamiltonian. An order parameter is identified, stabilizing d-wave superconductivity. The groundstate energy of classical spin configurations is minimized at a finite value of this order parameter after a critical chemical potential, resulting in d-wave superconductivity at non-zero doping. This suggests, that the onset of high-$T_c$ superconductivity is governed by the groundstate of a classical spin system. | |
Parshukov, K.; Wiedmann, R.; Schnyder, A. P. Topological responses from gapped Weyl points in 2D altermagnets Unpublished 2024, arXiv.2403.09520. @unpublished{parshukov_topological_2024,
title = {Topological responses from gapped Weyl points in 2D altermagnets},
author = {K. Parshukov and R. Wiedmann and A. P. Schnyder},
doi = {10.48550/arXiv.2403.09520},
year = {2024},
date = {2024-03-01},
urldate = {2024-04-12},
abstract = {Altermagnetism combines aspects of both ferromagnetism and antiferromagnetism, breaking spin degeneracy while possessing no net magnetization. In this work, we study the symmetry requirements for topologically protected Weyl points in 2D altermagnets, involving bands with the same spin quantum number. We classify all spin-wallpaper groups whose symmetries protect 2D Weyl points and show that their nontrivial topology is charactrized by a quantized $textbackslashpi$-Berry phase. Representative electronic tight-binding and magnonic linear spin-wave models are constructed to investigate the unusual transport characteristics of these 2D Weyl points. Different mass terms, induced for example through strain or via coupling to light or a substrate, gap out the Weyl points leading to emerging gapped topological phases. Depending on the mass terms, these phases carry finite Chern and/or spin Chern numbers and exhibit protected edge states as well as anomalous electronic and thermal Hall responses. We calculate these Hall currents for the different topological phases.},
note = {arXiv.2403.09520},
keywords = {},
pubstate = {published},
tppubtype = {unpublished}
}
Altermagnetism combines aspects of both ferromagnetism and antiferromagnetism, breaking spin degeneracy while possessing no net magnetization. In this work, we study the symmetry requirements for topologically protected Weyl points in 2D altermagnets, involving bands with the same spin quantum number. We classify all spin-wallpaper groups whose symmetries protect 2D Weyl points and show that their nontrivial topology is charactrized by a quantized $textbackslashpi$-Berry phase. Representative electronic tight-binding and magnonic linear spin-wave models are constructed to investigate the unusual transport characteristics of these 2D Weyl points. Different mass terms, induced for example through strain or via coupling to light or a substrate, gap out the Weyl points leading to emerging gapped topological phases. Depending on the mass terms, these phases carry finite Chern and/or spin Chern numbers and exhibit protected edge states as well as anomalous electronic and thermal Hall responses. We calculate these Hall currents for the different topological phases. | |
2023
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Alpin, K.; Hirschmann, M. M.; Heinsdorf, N.; Leonhardt, A.; Yau, W. Y.; Wu, X.; Schnyder, A. P. Fundamental laws of chiral band crossings: Local constraints, global constraints, and topological phase diagrams Journal Article Phys. Rev. Research 5, 043165, 2023. @article{alpin_fundamental_2023,
title = {Fundamental laws of chiral band crossings: Local constraints, global constraints, and topological phase diagrams},
author = {K. Alpin and M. M. Hirschmann and N. Heinsdorf and A. Leonhardt and W. Y. Yau and X. Wu and A. P. Schnyder},
doi = {10.1103/PhysRevResearch.5.043165},
year = {2023},
date = {2023-11-01},
urldate = {2023-11-01},
journal = {Phys. Rev. Research},
volume = {5},
number = {4},
pages = {043165},
abstract = {We derive two fundamental laws of chiral band crossings: (i) a local constraint relating the Chern number to phase jumps of rotation eigenvalues and (ii) a global constraint determining the number of chiral crossings on rotation axes. Together with the fermion doubling theorem, these laws describe all conditions that a network of chiral band crossing must satisfy. We apply the fundamental laws to prove the existence of enforced double Weyl points, nodal planes, and generic Weyl points, among others. In addition, we show that chiral space group symmetries can not stabilize nodal lines with finite Chern numbers. Combining the local constraint with explicit low-energy models, we determine the generic topological phase diagrams of all multifold crossings. Remarkably, we find a fourfold crossing with Chern number 5, which exceeds the previously conceived maximum Chern number of 4. We identify materials crystallizing in space group 198, such as B20 materials and BaAsPt, as suitable compounds with this Chern number 5 crossing.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We derive two fundamental laws of chiral band crossings: (i) a local constraint relating the Chern number to phase jumps of rotation eigenvalues and (ii) a global constraint determining the number of chiral crossings on rotation axes. Together with the fermion doubling theorem, these laws describe all conditions that a network of chiral band crossing must satisfy. We apply the fundamental laws to prove the existence of enforced double Weyl points, nodal planes, and generic Weyl points, among others. In addition, we show that chiral space group symmetries can not stabilize nodal lines with finite Chern numbers. Combining the local constraint with explicit low-energy models, we determine the generic topological phase diagrams of all multifold crossings. Remarkably, we find a fourfold crossing with Chern number 5, which exceeds the previously conceived maximum Chern number of 4. We identify materials crystallizing in space group 198, such as B20 materials and BaAsPt, as suitable compounds with this Chern number 5 crossing. | |
Huber, N.; Leeb, V.; Bauer, A.; Benka, G.; Knolle, J.; Pfleiderer, C.; Wilde, M. A. Quantum oscillations of the quasiparticle lifetime in a metal Journal Article Nature 621, 276, 2023. @article{huber_quantum_2023,
title = {Quantum oscillations of the quasiparticle lifetime in a metal},
author = {N. Huber and V. Leeb and A. Bauer and G. Benka and J. Knolle and C. Pfleiderer and M. A. Wilde},
doi = {10.1038/s41586-023-06330-y},
issn = {0028-0836},
year = {2023},
date = {2023-08-01},
urldate = {2023-08-01},
journal = {Nature},
volume = {621},
pages = {276},
abstract = {Following nearly a century of research, it remains a puzzle that the low-lying excitations of metals are remarkably well explained by effective single-particle theories of non-interacting bands(1-4). The abundance of interactions in real materials raises the question of direct spectroscopic signatures of phenomena beyond effective single-particle, single-band behaviour. Here we report the identification of quantum oscillations (QOs) in the three-dimensional topological semimetal CoSi, which defy the standard description in two fundamental aspects. First, the oscillation frequency corresponds to the difference of semiclassical quasiparticle (QP) orbits of two bands, which are forbidden as half of the trajectory would oppose the Lorentz force. Second, the oscillations exist up to above 50 K, in strong contrast to all other oscillatory components, which vanish below a few kelvin. Our findings are in excellent agreement with generic model calculations of QOs of the QP lifetime (QPL). Because the only precondition for their existence is a nonlinear coupling of at least two electronic orbits, for example, owing to QP scattering on defects or collective excitations, such QOs of the QPL are generic for any metal featuring Landau quantization with several orbits. They are consistent with certain frequencies in topological semimetals(5-9), unconventional superconductors(10,11), rare-earth compounds(12-14) and Rashba systems(15), and permit to identify and gauge correlation phenomena, for example, in two-dimensional materials(16,17) and multiband metals(18).},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Following nearly a century of research, it remains a puzzle that the low-lying excitations of metals are remarkably well explained by effective single-particle theories of non-interacting bands(1-4). The abundance of interactions in real materials raises the question of direct spectroscopic signatures of phenomena beyond effective single-particle, single-band behaviour. Here we report the identification of quantum oscillations (QOs) in the three-dimensional topological semimetal CoSi, which defy the standard description in two fundamental aspects. First, the oscillation frequency corresponds to the difference of semiclassical quasiparticle (QP) orbits of two bands, which are forbidden as half of the trajectory would oppose the Lorentz force. Second, the oscillations exist up to above 50 K, in strong contrast to all other oscillatory components, which vanish below a few kelvin. Our findings are in excellent agreement with generic model calculations of QOs of the QP lifetime (QPL). Because the only precondition for their existence is a nonlinear coupling of at least two electronic orbits, for example, owing to QP scattering on defects or collective excitations, such QOs of the QPL are generic for any metal featuring Landau quantization with several orbits. They are consistent with certain frequencies in topological semimetals(5-9), unconventional superconductors(10,11), rare-earth compounds(12-14) and Rashba systems(15), and permit to identify and gauge correlation phenomena, for example, in two-dimensional materials(16,17) and multiband metals(18). | |
Deyerling, A.; Wilde, M. A.; Pfleiderer, C. Electronic structure of CeAuAl3 using density functional theory Journal Article SciPost Phys. Proc. 008, 2023. @article{deyerling_electronic_2023,
title = {Electronic structure of CeAuAl_{3} using density functional theory},
author = {A. Deyerling and M. A. Wilde and C. Pfleiderer},
doi = {10.21468/SciPostPhysProc.11.008},
year = {2023},
date = {2023-06-05},
urldate = {2023-06-05},
journal = {SciPost Phys. Proc.},
pages = {008},
abstract = {We studied the magnetic properties and electronic structure of CeAuAl3 using density functional theory. This compound shows a large Sommerfeld coefficient, a Kondo temperature, TK=4K and antiferromagnetic order below TN=1.1K. We calculated the magnetic groundstate of CeAuAl3 and the magnetic anisotropy energies. Treating the 4f-electrons as localized with DFT+U we obtain a good match with the magnetic properties observed experimentally. We also report salient features of the electronic structure of CeAuAl3, including features of the Fermi surface and associated quantum oscillatory spectra, when the 4f-electrons are treated either as localized or itinerant.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We studied the magnetic properties and electronic structure of CeAuAl3 using density functional theory. This compound shows a large Sommerfeld coefficient, a Kondo temperature, TK=4K and antiferromagnetic order below TN=1.1K. We calculated the magnetic groundstate of CeAuAl3 and the magnetic anisotropy energies. Treating the 4f-electrons as localized with DFT+U we obtain a good match with the magnetic properties observed experimentally. We also report salient features of the electronic structure of CeAuAl3, including features of the Fermi surface and associated quantum oscillatory spectra, when the 4f-electrons are treated either as localized or itinerant. | |
Kumar, V.; Bauer, A.; Franz, C.; Spallek, J.; Schönmann, R.; Stekiel, M.; Schneidewind, A.; Wilde, M. A.; Pfleiderer, C. Low-temperature antiferromagnetic order in orthorhombic CePdAl3 Journal Article Phys. Rev. Research 5, 023157, 2023. @article{kumar_low-temperature_2023,
title = {Low-temperature antiferromagnetic order in orthorhombic CePdAl_{3}},
author = {V. Kumar and A. Bauer and C. Franz and J. Spallek and R. Schönmann and M. Stekiel and A. Schneidewind and M. A. Wilde and C. Pfleiderer},
doi = {10.1103/PhysRevResearch.5.023157},
year = {2023},
date = {2023-06-01},
urldate = {2023-06-01},
journal = {Phys. Rev. Research},
volume = {5},
number = {2},
pages = {023157},
abstract = {We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of CePdAl3. In comparison to the properties of polycrystalline CePdAl3 reported in the literature, which displays a tetragonal crystal structure and no long-range magnetic order, our single crystals exhibit an orthorhombic structure (𝐶𝑚𝑐𝑚) and antiferromagnetic order below a Néel temperature 𝑇1=5.6 K. The specific heat at zero field shows two anomalies, namely, a broad transition at 𝑇1=5.6 K followed by a 𝜆-anomaly at 𝑇2=5.4 K. A conservative estimate of the Sommerfeld coefficient of the electronic specific heat, 𝛾=121mJK−2mol−1, indicates a moderately enhanced heavy-fermion ground state. A twin microstructure evolves in the family of planes spanned by the basal plane lattice vectors 𝐚o and 𝐜o , with the magnetic hard axis 𝐛o common to all twins. The antiferromagnetic state is characterized by a strong ao, co easy-plane magnetic anisotropy where the ao direction is the easy axis in the easy plane. A spin-flop transition induced under magnetic field along the easy directions, results in complex magnetic phase diagrams. Taken together, our results reveal a high sensitivity of the magnetic and electronic properties of CePdAl3 to its structural modifications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of CePdAl3. In comparison to the properties of polycrystalline CePdAl3 reported in the literature, which displays a tetragonal crystal structure and no long-range magnetic order, our single crystals exhibit an orthorhombic structure (𝐶𝑚𝑐𝑚) and antiferromagnetic order below a Néel temperature 𝑇1=5.6 K. The specific heat at zero field shows two anomalies, namely, a broad transition at 𝑇1=5.6 K followed by a 𝜆-anomaly at 𝑇2=5.4 K. A conservative estimate of the Sommerfeld coefficient of the electronic specific heat, 𝛾=121mJK−2mol−1, indicates a moderately enhanced heavy-fermion ground state. A twin microstructure evolves in the family of planes spanned by the basal plane lattice vectors 𝐚o and 𝐜o , with the magnetic hard axis 𝐛o common to all twins. The antiferromagnetic state is characterized by a strong ao, co easy-plane magnetic anisotropy where the ao direction is the easy axis in the easy plane. A spin-flop transition induced under magnetic field along the easy directions, results in complex magnetic phase diagrams. Taken together, our results reveal a high sensitivity of the magnetic and electronic properties of CePdAl3 to its structural modifications. | |
Heinsdorf, N.; Joshi, D. G.; Katsura, H.; Schnyder, A. P. Stable Bosonic Topological Edge Modes in the Presence of Many-Body Interactions Unpublished 2023, arXiv:2309.15113. @unpublished{heinsdorf_stable_2023,
title = {Stable Bosonic Topological Edge Modes in the Presence of Many-Body Interactions},
author = {N. Heinsdorf and D. G. Joshi and H. Katsura and A. P. Schnyder},
doi = {10.48550/arXiv.2309.15113},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
note = {arXiv:2309.15113},
keywords = {},
pubstate = {published},
tppubtype = {unpublished}
}
| |
