arXiv subjects

Claudia Felser

Publications and source records attributed to Claudia Felser.

At least 91 records · Page 5Linked to original sources

arXiv2024

Recognizing molecular chirality via twisted 2D materials

Chirality pervades natural processes from the atomic to the cosmic scales, crucially impacting molecular chemistry and pharmaceutics. Traditional chirality sensing methods face challenges in sensitivity and efficiency, prompting the quest of novel chiral recognition solutions based on nanophotonics. In this work we theoretically investigate the possibility to carry out enantiomeric discrimination by measuring the spontaneous emission rate of chiral molecules on twisted two-dimensional materials. We first present a general theoretical framework based on dyadic Green's functions to calculate the chiral contribution to the decay rate in the presence of a generic chiral bilayer interface. We then combine this theory with density functional theory to obtain numerical estimates of the decay rate of helical bilayer nanographene molecules placed on top of twisted bilayer graphene.

cond-mat.mes-hall↗

arXiv2024

Twisted bilayer graphene for enantiomeric sensing of chiral molecules

Selective sensing of chiral molecules is a key aspect in fields spanning biology, chemistry, and pharmacology. However, conventional optical methods, such as circular dichroism (CD), encounter limitations owing to weak chiral light-matter interactions. Several strategies have been investigated to enhance CD or circularly polarised luminescence (CPL), including superchiral light, plasmonic nanoresonators and dielectric nanostructures. However, a compromise between spatial uniformity and high sensitivity, without requiring specific molecular functionalization, remains a challenge. In this work, we propose a novel approach using twisted bilayer graphene (TBG), a chiral 2D material with a strong CD peak which energy is tunable through the twist angle. By matching the CD resonance of TBG with the optical transition energy of the molecule, we achieve a decay rate enhancement mediated by resonant energy transfer that depends on the electric-magnetic interaction, that is, on the chirality of both the molecules and TBG. This leads to an enantioselective quenching of the molecule fluorescence, allowing to retrieve the molecule chirality from time-resolved photoluminescence measurements. This method demonstrates high sensitivity down to single layer of molecules, with the potential to achieve the ultimate goal of single-molecule chirality sensing, while preserving the spatial uniformity and integrability of 2D heterostructures.

cond-mat.mes-hall↗

arXiv2024

Topological Quantum Materials with Kagome Lattice

In this account, we will give an overview of our research progress on novel quantum properties in topological quantum materials with kagome lattice. Here, there are mainly two categories of kagome materials: magnetic kagome materials and nonmagnetic ones. On one hand, magnetic kagome materials mainly focus on the 3d transition-metal-based kagome systems, including Fe$_3$Sn$_2$, Co$_3$Sn$_2$S$_2$, YMn6Sn6, FeSn, and CoSn. The interplay between magnetism and topological bands manifests vital influence on the electronic response. For example, the existence of massive Dirac or Weyl fermions near the Fermi level signicantly enhances the magnitude of Berry curvature in momentum space, leading to a large intrinsic anomalous Hall effect. In addition, the peculiar frustrated structure of kagome materials enables them to host a topologically protected skyrmion lattice or noncoplaner spin texture, yielding a topological Hall effect that arises from the realspace Berry phase. On the other hand, nonmagnetic kagome materials in the absence of longrange magnetic order include CsV3Sb5 with the coexistence of superconductivity, charge density wave state, and band topology and van der Waals semiconductor Pd$_3$P$_2$S$_8$. For these two kagome materials, the tunability of electric response in terms of high pressure or carrier doping helps to reveal the interplay between electronic correlation effects and band topology and discover the novel emergent quantum phenomena in kagome materials.

cond-mat.supr-con↗

arXiv2024

Striped magnetization plateau and chirality-reversible anomalous Hall effect in a magnetic kagome metal

Kagome materials with magnetic frustration in two-dimensional networks are known for their exotic properties, such as the anomalous Hall effect (AHE) with non-collinear spin textures. However, the effects of one-dimensional (1D) spin chains within these networks are less understood. Here, we report a distinctive AHE in the bilayer-distorted kagome material GdTi$_3$Bi$_4$, featuring 1D Gd zigzag spin chains, a one-third magnetization plateau, and two successive metamagnetic transitions. At these metamagnetic transitions, Hall resistivity shows abrupt jumps linked to the formation of stripe domain walls, while within the plateau, the absence of detectable domain walls suggests possible presence of skyrmion phase. Reducing the sample size to a few microns reveals additional Hall resistivity spikes, indicating domain wall skew scattering contributions. Magnetic atomistic spin dynamics simulations reveal that the magnetic textures at these transitions have reverse chirality, explaining the evolution of AHE and domain walls with fields. These results underscore the potential of magnetic and crystal symmetry interplay, and magnetic field-engineered spin chirality, for controlling domain walls and tuning transverse properties, advancing spintronic applications.

cond-mat.str-el↗

arXiv2024

New magnetic topological materials from high-throughput search

We conducted a high-throughput search for topological magnetic materials on 522 new, experimentally reported commensurate magnetic structures from MAGNDATA, doubling the number of available materials on the Topological Magnetic Materials database. This brings up to date the previous studies which had become incomplete due to the discovery of new materials. For each material, we performed first-principle electronic calculations and diagnosed the topology as a function of the Hubbard U parameter. Our high-throughput calculation led us to the prediction of 250 experimentally relevant topologically non-trivial materials, which represent 47.89% of the newly analyzed materials. We present five remarkable examples of these materials, each showcasing a different topological phase: Mn${}_2$AlB${}_2$ (BCSID 1.508), which exhibits a nodal line semimetal to topological insulator transition as a function of SOC, CaMnSi (BCSID 0.599), a narrow gap axion insulator, UAsS (BCSID 0.594) a 5f-orbital Weyl semimetal, CsMnF${}_4$ (BCSID 0.327), a material presenting a new type of quasi-symmetry protected closed nodal surface and FeCr${}_2$S${}_4$ (BCSID 0.613), a symmetry-enforced semimetal with double Weyls and spin-polarised surface states.

cond-mat.mtrl-sci↗

arXiv2024

Transfer learning relaxation, electronic structure and continuum model for twisted bilayer MoTe$_2$

Large-scale moiré systems are extraordinarily sensitive, with even minute atomic shifts leading to significant changes in electronic structures. Here, we investigate the lattice relaxation effect on moiré band structures in twisted bilayer MoTe$_2$ with two approaches: (a) large-scale plane-wave basis first principle calculation down to $2.88^{\circ}$, (b) transfer learning structure relaxation + local-basis first principles calculation down to $1.1^{\circ}$. We use two types of van der Waals corrections: the D2 method of Grimme and the density-dependent energy correction, and find that the density-dependent energy correction yields a continuous evolution of bandwidth with twist angles. Based on the above results. we develop a more complete continuum model with a single set of parameters for a wide range of twist angles, and perform many-body simulations at $ν=-1,-2/3, -1/3$.

cond-mat.str-el↗

arXiv2024

Observation of surface Fermi arcs in altermagnetic Weyl semimetal CrSb

As a special type of collinear antiferromagnetism (AFM), altermagnetism has garnered significant research interest recently. Altermagnets exhibit broken parity-time symmetry and zero net magnetization in real space, leading to substantial band splitting in momentum space even in the absence of spin-orbit coupling. Meanwhile, parity-time symmetry breaking always induce nontrivial band topology such as Weyl nodes. While Weyl semimetal states and nodal lines have been theoretically proposed in altermagnets, rare reports of experimental observation have been made up to this point. Using ARPES and first-principles calculations, we systematically studied the electronic structure of the room-temperature altermagnet candidate CrSb. At generic locations in momentum space, we clearly observed band spin splitting. Furthermore, we identified discrete surface Fermi arcs on the (100) cleaved side surface close to the Fermi level originating from bulk band topology. Our results imply that CrSb contains interesting nontrivial topological Weyl physics, in addition to being an excellent room temperature altermagnet.

cond-mat.mtrl-sci↗

arXiv2024

2024 roadmap on 2D topological insulators

2D topological insulators promise novel approaches towards electronic, spintronic, and quantum device applications. This is owing to unique features of their electronic band structure, in which bulk-boundary correspondences enforces the existence of 1D spin-momentum locked metallic edge states - both helical and chiral - surrounding an electrically insulating bulk. Forty years since the first discoveries of topological phases in condensed matter, the abstract concept of band topology has sprung into realization with several materials now available in which sizable bulk energy gaps - up to a few hundred meV - promise to enable topology for applications even at room-temperature. Further, the possibility of combining 2D TIs in heterostructures with functional materials such as multiferroics, ferromagnets, and superconductors, vastly extends the range of applicability beyond their intrinsic properties. While 2D TIs remain a unique testbed for questions of fundamental condensed matter physics, proposals seek to control the topologically protected bulk or boundary states electrically, or even induce topological phase transitions to engender switching functionality. Induction of superconducting pairing in 2D TIs strives to realize non-Abelian quasiparticles, promising avenues towards fault-tolerant topological quantum computing. This roadmap aims to present a status update of the field, reviewing recent advances and remaining challenges in theoretical understanding, materials synthesis, physical characterization and, ultimately, device perspectives.

cond-mat.mes-hall↗

arXiv2024

Revealing the hidden Dirac gap in a topological antiferromagnet using Floquet-Bloch manipulation

Manipulating solids using the time-periodic drive of a laser pulse is a promising route to generate new phases of matter. Whether such `Floquet-Bloch' manipulation can be achieved in topological magnetic systems with disorder has so far been unclear. In this work, we realize Floquet-Bloch manipulation of the Dirac surface-state mass of the topological antiferromagnet (AFM) MnBi$_2$Te$_4$. Using time- and angle-resolved photoemission spectroscopy (tr-ARPES), we show that opposite helicities of mid-infrared circularly polarized light result in substantially different Dirac mass gaps in the AFM phase, despite the equilibrium Dirac cone being massless. We explain our findings in terms of a Dirac fermion with a random mass. Our results underscore Floquet-Bloch manipulation as a powerful tool for controlling topology even in the presence of disorder, and for uncovering properties of materials that may elude conventional probes.

cond-mat.mes-hall↗

arXiv2024

Orbital selective commensurate modulations of the local density of states in ScV6Sn6 probed by nuclear spins

The Kagome network is a unique platform in solid state physics that harbors a diversity of special electronic states due to its inherent band structure features comprising Dirac cones, van-Hove singularities, and flat bands. Some Kagome-based non-magnetic metals have recently been found to exhibit favorable properties, including unconventional superconductivity, charge density waves (CDW), switchable chiral transport, and signatures of an anomalous Hall effect (AHE). The Kagome metal ScV6Sn6 is another promising candidate for studying the emergence of an unconventional CDW and accompanying effects. We use 51V nuclear magnetic resonance (NMR) to study the local properties of the CDW phase in single crystalline ScV6Sn6, aided by density functional theory (DFT). We trace the dynamics of the local magnetic field during the CDW phase transition and determine a loss in the density of states (DOS) by a factor of $\sqrt{2}$, in excellent agreement with DFT. The local charge symmetry of the V surrounding in the CDW phase reflects the commensurate modulation of the charge density with wave vector q=(1/3,1/3,1/3). An unusual orientation dependent change in the NMR shift splitting symmetry, however, reveals orbital selective modulations of the local DOS.

cond-mat.mtrl-sci↗

arXiv2024

Multifold topological semimetals

The discovery of topological semimetals with multifold band crossings has opened up a new and exciting frontier in the field of topological physics. These materials exhibit large Chern numbers, leading to long double Fermi arcs on their surfaces, which are protected by either crystal symmetries or topological order. The impact of these multifold crossings extends beyond surface science, as they are not constrained by the Poincaré classification of quasiparticles and only need to respect the crystal symmetry of one of the 1651 magnetic space groups. Consequently, we observe the emergence of free fermionic excitations in solid-state systems that have no high-energy counterparts, protected by non-symmorphic symmetries. In this work, we review the recent theoretical and experimental progress made in the field of multifold topological semimetals. We begin with the theoretical prediction of the so-called multifold fermions and discuss the subsequent discoveries of chiral and magnetic topological semimetals. Several experiments that have realized chiral semimetals in spectroscopic measurements are described, and we discuss the future prospects of this field. These exciting developments have the potential to deepen our understanding of the fundamental properties of quantum matter and inspire new technological applications in the future.

cond-mat.mtrl-sci↗

arXiv2024

Sublinear transport in Kagome metals: Interplay of Dirac cones and Van Hove singularities

Kagome metals are known to host Dirac fermions and saddle point Van Hove singularities near Fermi level. With the minimal two-pocket model (Dirac cone + Van Hove singularity), we propose a semiclassical theory to explain the experimentally observed sublinear resistivity in Ni$_3$In and other Kagome metals. We derive the full semiclassical description of kinetic phenomena using Boltzmann equation, and demonstrate that internode electron-electron interaction leads to sublinear in $T$ scaling for both electrical and thermal transport at low temperatures. At higher temperatures above the Dirac node chemical potential, thermal and electric current dissipate through distinct scattering channels, making a ground for Wiedemann-Franz law violation.

cond-mat.str-el↗

arXiv2024

Observation of Chiral Surface State in Superconducting NbGe$_2$

The interplay between topology and superconductivity in quantum materials harbors rich physics ripe for discovery. In this study, we investigate the topological properties and superconductivity of the nonsymmorphic chiral superconductor NbGe$_2$ using high-resolution angle-resolved pho-toemission spectroscopy (ARPES), transport measurements, and ab initio calculations. The ARPES data revealed exotic chiral surface states on the (100) surface originating from the inherent chiral crystal structure. Supporting calculations indicate that NbGe$_2$ likely hosts elusive Weyl fermions in its bulk electronic structure. Furthermore, we uncovered the signatures of van Hove singularities that can enhance many-body interactions. Additionally, transport measurements demonstrated that NbGe$_2$ exhibits superconductivity below 2K. Overall, our comprehensive results provide the first concrete evidence that NbGe$_2$ is a promising platform for investigating the interplay between non-trivial band topology, possible Weyl fermions, van Hove singularities, and superconductivity in chiral quantum materials.

cond-mat.mes-hall↗

arXiv2024

Photon condensation, Van Vleck paramagnetism, and chiral cavities

We introduce a gauge-invariant model of planar, square molecules coupled to a quantized spatially-varying cavity electromagnetic vector potential A(r). Specifically, we choose a temporally chiral cavity hosting a uniform magnetic field B, as this is the simplest instance in which a transverse spatially-varying A(r) is at play. We show that when the molecules are in the Van Vleck paramagnetic regime, an equilibrium quantum phase transition to a photon condensate state occurs.

cond-mat.mes-hall↗

arXiv2024

Tuning charge density wave of kagome metal ScV6Sn6

Compounds with a kagome lattice exhibit intriguing properties and the charge density wave (CDW) adds an additional layer of interest to research on them. In this study, we investigate the temperature and magnetic field dependent electrical properties under a chemical substitution and hydrostatic pressure of ScV6Sn6, a non-magnetic charge density wave (CDW) compound. Substituting 5 % Cr at the V site or applying 1.5 GPa of pressure shifts the CDW to 50 K from 92 K. This shift is attributed to the movement of the imaginary phonon band, as revealed by the phonon dispersion relation. The longitudinal and Hall resistivities respond differently under these stimuli. The magnetoresistance (MR) maintains its quasilinear behavior under pressure, but it becomes quadratic after Cr substitution. The anomalous Hall-like behavior of the parent compound persists up to the respective CDW transition under pressure, after which it sharply declines. In contrast, the longitudinal and Hall resistivities of Cr substituted compounds follow a two-band model and originates from the multi carrier effect. These results clearly highlight the role of phonon contributions in the CDW transition and call for further investigation into the origin of the anomalous Hall-like behavior in the parent compound.

cond-mat.mtrl-sci↗

arXiv2024

Observation of Giant Spin Splitting and d-wave Spin Texture in Room Temperature Altermagnet RuO2

Recently, a novel magnetic phase called altermagnetism has been proposed, ushering in a third distinct magnetic phase beyond ferromagnetism and antiferromagnetism. It is expected that this groundbreaking phase exhibits unique physical properties such as C-paired spin-valley locking, anomalous Hall effect, nontrivial Berry phase, and giant magnetoresistance, etc. Among all the predicted candidates, several room temperature altermagnets are suggested to host significant potential applications in the near future. Nevertheless, direct evidence about the spin pattern of the room temperature altermagnet is still unrevealed. Previous studies found that RuO2 is identified as the most promising candidate for room temperature d-wave altermagnetism, exhibiting a substantial spin splitting of up to 1.4 eV. In this study, utilizing angle-resolved photoemission spectroscopy (ARPES), we report experimental observation of the spin splitting in RuO2. Furthermore, employing spin-ARPES, we directly observed the d-wave spin pattern. Our results unequivocally show that RuO2 is a perfect d-wave altermagnet with great potential for upcoming spintronic applications.

cond-mat.mtrl-sci↗

arXiv2024

Untangle charge-order dependent bulk states from surface effects in a topological kagome metal ScV$_6$Sn$_6$

Kagome metals with charge density wave (CDW) order exhibit a broad spectrum of intriguing quantum phenomena. The recent discovery of the novel kagome CDW compound ScV$_6$Sn$_6$ has spurred significant interest. However, understanding the interplay between CDW and the bulk electronic structure has been obscured by a profusion of surface states and terminations in this quantum material. Here, we employ photoemission spectroscopy and potassium dosing to elucidate the complete bulk band structure of ScV$_6$Sn$_6$, revealing multiple van Hove singularities near the Fermi level. We surprisingly discover a robust spin-polarized topological Dirac surface resonance state at the M point within the two-fold van Hove singularities. Assisted by the first-principle calculations, the temperature dependence of the $k_z$- resolved ARPES spectrum provides unequivocal evidence for the proposed $\sqrt{3}$$\times$$\sqrt{3}$$\times3$ charge order over other candidates. Our work not only enhances the understanding of the CDW-dependent bulk and surface states in ScV$_6$Sn$_6$ but also establishes an essential foundation for potential manipulation of the CDW order in kagome materials.

cond-mat.str-el↗

arXiv2024

Discovery of a Topological Charge Density Wave

Charge density waves (CDWs) appear in numerous condensed matter platforms, ranging from high-Tc superconductors to quantum Hall systems. Despite such ubiquity, there has been a lack of direct experimental study on boundary states that can uniquely stem from the charge order. Here, using scanning tunneling microscopy, we directly visualize the bulk and boundary phenomenology of CDW in a topological material, Ta2Se8I. Below the transition temperature (TCDW = 260 K), tunneling spectra on an atomically resolved lattice reveal a large insulating gap in the bulk and on the surface, exceeding 500 meV, surpassing predictions from standard weakly-coupled mean-field theory. Spectroscopic imaging confirms the presence of CDW, with LDOS maxima at the conduction band corresponding to the LDOS minima at the valence band, thus revealing a π phase difference in the respective CDW order. Concomitantly, at a monolayer step edge, we detect an in-gap boundary mode with modulations along the edge that match the CDW wavevector along the edge. Intriguingly, the phase of the edge state modulation shifts by π within the charge order gap, connecting the fully gapped bulk (and surface) conduction and valence bands via a smooth energy-phase relation. This bears similarity to the topological spectral flow of edge modes, where the boundary modes bridge the gapped bulk modes in energy and momentum magnitude but in Ta2Se8I, the connectivity distinctly occurs in energy and momentum phase. Notably, our temperature-dependent measurements indicate a vanishing of the insulating gap and the in-gap edge state above TCDW, suggesting their direct relation to CDW. The theoretical analysis also indicates that the observed boundary mode is topological and linked to CDW.

cond-mat.str-el↗