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Results for “chiral topological matter”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Topological quantum computation on a chiral Kondo chain

We describe the chiral Kondo chain model based on the symplectic Kondo effect and demonstrate that it has a quantum critical ground state populated by non-Abelian anyons. We show that the fusion channel of two arbitrary anyons can be detected by locally coupling the two anyons to an extra single channel of chiral current and measuring the corresponding conductance at a finite frequency. Based on such measurements, we propose that the chiral Kondo chain model with symplectic symmetry can be used for the implementation of measurement-only topological quantum computations, and it possesses several distinct features favorable for such applications. Furthermore, the sources and effects of errors in the proposed system are analyzed and possible material realizations are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Electromagnetic signatures of a chiral quantum spin liquid

Quantum spin liquids (QSL) have emerged as a captivating subject within interacting spin systems that exhibit no magnetic ordering even at the lowest temperature accessible experimentally. However, definitive experimental evidence remains elusive. In light of the recent surge in theoretical and experimental interest in the half-filled Hubbard model on a triangular lattice, which offers the potential for stabilizing a chiral QSL, we investigate the electromagnetic signatures of this phase to facilitate experimental detection. Utilizing a combination of parton mean-field theory and unbiased density-matrix renormalization group calculations, we systematically examine the electrical charge and orbital electrical current associated with a spinon excitation in the chiral QSL. Additionally, we calculate the longitudinal and transverse optical conductivities below the Mott gap. Furthermore, employing quantum field theory analysis, we unravel the connection between spinon excitations and emergent as well as physical gauge fields. Our results demonstrate that the chiral QSL phase exhibits a distinct electromagnetic response, even within a Mott insulator regime. This finding holds great potential for enabling the experimental detection of this long-sought-after phase.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Discretized evolution of solitons in the achiral stripe phase of a Fe/Gd thin film

Understanding magnetic phase transitions from stripe to skyrmion textures provide fundamental scientific insights into the details of the intermediate topologies through which the system evolves. The solitonic nature of spin texture in both stripe and skyrmion phases has been observed in materials with Dzyaloshinskii-Moriya interaction. In this study we show that the field evolution in a dipolar interaction mediated Fe/Gd multilayer that exhibits achiral stripe textures behaves similar to a finite-sized chiral soliton lattice. As a function of magnetic field, the stripes exhibit discrete jumps in periodicity indicative of intermediate topologies as the stripes get wound into skyrmions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Kondo enabled transmutation between spinons and superconducting vortices: Origin of magnetic memory in 4 H b − TaS 2

Recent experiments [Persky , ] demonstrate a magnetic memory effect in 4 H b − TaS 2 above its superconducting transition temperature, where Abriokosov vortices are spontaneously generated by lowering the temperature at zero magnetic field after field training the normal state. Motivated by the experiment, we propose the chiral quantum spin liquid (QSL) stabilized in the constituent layers of 4 H b − TaS 2 as a mechanism. We model 4 H b − TaS 2 as coupled layers of the chiral QSL and the superconductor. Through the Kondo coupling between the localized moments and conduction electrons, there is mutual transmutation between spinons and vortices during the thermal-cycling process, which yields the magnetic memory effect observed in experiments. We also propose a mechanism to stabilize chiral and nematic superconductivity in 4 H b − TaS 2 through the Kondo coupling of conduction electrons to the chiral QSL. Our picture suggests 4 H b − TaS 2 as an exciting platform to explore the interplay between QSL and superconductivity through the Kondo effect. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Chern Fermi pocket, topological pair density wave, and charge-4e and charge-6e superconductivity in kagomé superconductors

Abstract The recent discovery of novel charge density wave (CDW) and pair density wave (PDW) in kagomé lattice superconductors A V 3 Sb 5 ( A = K, Rb, Cs) hints at unexpected time-reversal symmetry breaking correlated and topological states whose physical origin and broader implications are not understood. Here, we make conceptual advances toward a mechanism behind the striking observations and new predictions for novel macroscopic phase coherent quantum states. We show that the metallic CDW state with circulating loop currents is a doped orbital Chern insulator near van Hove filling. The emergent Chern Fermi pockets (CFPs) carry concentrated Berry curvature and orbital magnetic moment. We find that the pairing of electrons on the CFPs leads to a superconducting state with an emergent vortex-antivortex lattice and the formation of a complex triple- Q PDW. A plethora of correlated and topological states emerge, including a never-before-encountered chiral topological PDW superconductor, a loop-current pseudogap phase, and vestigial charge-4 e and charge-6 e superconductivity in staged melting of the vortex-antivortex lattice and hexatic liquid crystal. Our findings reveal previously unknown nature of the superconducting state of a current-carrying Chern metal, with broad implications for correlated and topological materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Quantum spin liquids bootstrapped from Ising criticality in Rydberg arrays

Arrays of Rydberg atoms constitute a highly tunable, strongly interacting venue for the pursuit of exotic states of matter. We develop a strategy for accessing a family of fractionalized phases known as quantum spin liquids in two-dimensional Rydberg arrays. We specifically use effective field theory methods to study arrays assembled from Rydberg chains tuned to an Ising phase transition that famously hosts emergent fermions propagating within each chain. This highly entangled starting point allows us to naturally access spin liquids familiar from Kitaev's honeycomb model—albeit from an entirely different framework. In particular, we argue that finite-range repulsive Rydberg interactions, which frustrate nearby symmetry-breaking orders, can enable coherent propagation of emergent fermions between the chains in which they were born. Delocalization of emergent fermions across the full two-dimensional Rydberg array yields a gapless Z 2 spin liquid with a single massless Dirac cone. Here, the Rydberg occupation numbers exhibit universal power-law correlations that provide a straightforward experimental diagnostic of this phase. We further show that explicitly breaking symmetries perturbs the gapless spin liquid into gapped, topologically ordered descendants: Breaking lattice symmetries generates toric-code topological order, whereas introducing Floquet-mediated chirality generates non-Abelian Ising topological order. In the toric-code phase, we analytically construct microscopic incarnations of non-Abelian defects, which can be created and transported by dynamically controlling the atom positions in the array. Our work suggests that appropriately tuned Rydberg arrays provide a cold-atoms counterpart of solid-state “Kitaev materials” and, more generally, it spotlights a different angle for pursuing experimental platforms for Abelian and non-Abelian fractionalization.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Unconventional self-similar Hofstadter superconductivity from repulsive interactions

Abstract Fractal Hofstadter bands have become widely accessible with the advent of moiré superlattices, opening the door to studies of the effect of interactions in these systems. In this work we employ a renormalization group (RG) analysis to demonstrate that the combination of repulsive interactions with the presence of a tunable manifold of Van Hove singularities provides a new mechanism for driving unconventional superconductivity in Hofstadter bands. Specifically, the number of Van Hove singularities at the Fermi energy can be controlled by varying the flux per unit cell and the electronic filling, leading to instabilities toward nodal superconductivity and chiral topological superconductivity with Chern number $${{{{{{{\mathcal{C}}}}}}}}=\pm 6$$ C = ± 6 . The latter is characterized by a self-similar fixed trajectory of the RG flow and an emerging self-similarity symmetry of the order parameter. Our results establish Hofstadter quantum materials such as moiré heterostructures as promising platforms for realizing novel reentrant Hofstadter superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Topological Magneto-optics in the Noncoplanar Antiferromagnet Co 1/3 ⁢NbS 2 : Imaging and Writing Chiral Magnetic Domains

Despite its tiny net magnetization, the antiferromagnetic (AFM) van der Waals material Co 1/3 ⁢NbS 2 exhibits a large transverse Hall conductivity 𝜎 𝑥⁢𝑦 even at zero applied magnetic field, which arises, as recently shown, from the topological nature of its noncoplanar “tetrahedral” AFM order. Here, this triple-𝐪 magnetic order can be regarded as the short-length-scale limit of a magnetic skyrmion lattice and has an intrinsic spin chirality. Here, we show, using optical wavelengths spanning the ultraviolet to infrared (400–1000 nm), that magnetic circular dichroism provides an incisive optical probe of the topological AFM order in Co 1/3 ⁢NbS 2 . Measurements as a continuous function of photon energy are directly compared with first-principles calculations, revealing the influence of the underlying quantum geometry on optical conductivity. Leveraging the power and flexibility of optical methods, we use scanning magnetic circular dichroism microscopy to directly image chiral AFM domains and demonstrate writing of chiral AFM domains.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Transferring orbital angular momentum to an electron beam reveals toroidal and chiral order

Orbital angular momentum (OAM) and torque transfer play central roles in a wide range of magnetic textures and devices including skyrmions and spin-torque electronics. Analogous topological structures are now also being explored in ferroelectrics, including polarization vortex arrays in ferroelectric/dielectric superlattices. Unlike magnetic toroidal order, electric toroidal order does not couple directly to linear external fields. Instead, we find that the presence of an electric toroidal moment in a ferrorotational phase transfers measurable torque and OAM to a localized electron beam in the ballistic limit. We record these torque transfers from a high-energy electron beam using a momentum-resolved detector. This approach provides a high-sensitivity method to detect polarization fields and their more complex order parameters and topologies. In addition to toroidal order, we also demonstrate high-precision measurements of vorticity and chirality for polar vortexlike phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Quantum Hall effect in a Weyl-Hubbard model: Interplay between topology and correlation

The interplay between topology and electronic correlations offer a rich avenue for discovering emergent quantum phenomena in condensed matter systems. Here, in this work, starting from the Weyl-Hubbard model, we investigate the quantum Hall effect to explore the consequence of onsite Hubbard repulsion on nontrivial Weyl band topology in the presence of an external magnetic field. Within the Gutzwiller projected wavefunction method, we find the system to undergo multiple topological phase transitions by tuning on-site Coulomb interaction, including two distinct Weyl phases with different numbers of Weyl node pairs and a trivial narrow band insulator. Crucially, these two Weyl phases may be identified by the sign of their chiral Landau levels. The possible experimental signature of these topological phases and correlation effects is provided by the magnetic-field dependent quantum Hall conductivity within the Kubo response theory.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Nanoparticle localization within chiral liquid crystal defect lines and nanoparticle interactions

Self-assembly of colloidal particles into predefined structures is a promising way to design inexpensive manmade materials with advanced macroscopic properties. Doping of nematic liquid crystals (LCs) with nanoparticles has a series of advantages in addressing these grand scientific and engineering challenges. It also provides a very rich soft matter platform for the discovery of unique condensed matter phases. The LC host naturally allows the realization of diverse anisotropic interparticle interactions, enriched by the spontaneous alignment of anisotropic particles due to the boundary conditions of the LC director. Here we demonstrate theoretically and experimentally that the ability of LC media to host topological defect lines can be used as a tool to probe the behavior of individual nanoparticles as well as effective interactions between them. LC defect lines irreversibly trap nanoparticles enabling controlled particle movement along the defect line with the use of a laser tweezer. Minimization of Landau–de Gennes free energy reveals a sensitivity of the ensuing effective nanoparticle interaction to the shape of the particle, surface anchoring strength, and temperature, which determine not only the strength of the interaction but also its repulsive or attractive character. Theoretical results are supported qualitatively by experimental observations. Furthermore, this work may pave the way toward designing controlled linear assemblies as well as one-dimensional crystals of nanoparticles such as gold nanorods or quantum dots with tunable interparticle spacing.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Classification of (2 + 1) D invertible fermionic topological phases with symmetry

Here we provide a classification of invertible topological phases of interacting fermions with symmetry in two spatial dimensions for general fermionic symmetry groups G f and general values of the chiral central charge c - . Here G f is a central extension of a bosonic symmetry group G b by fermion parity, (-1) F , specified by a second cohomology class [ω 2 ]∈ $\mathscr{H}^2$(Gb,$\mathbb{Z}_2$). Our approach proceeds by gauging fermion parity and classifying the resulting G b symmetry-enriched topological orders while keeping track of certain additional data and constraints. We perform this analysis through two perspectives, using G-crossed braided tensor categories and Spin(2c - ) 1 Chern-Simons theory coupled to a background G gauge field. These results give a way to characterize and classify invertible fermionic topological phases in terms of a concrete set of data and consistency equations, which is more physically transparent and computationally simpler than the more abstract methods using cobordism theory and spectral sequences. Our results also generalize and provide a different approach to the recent classification of fermionic symmetry-protected topological phases by Wang and Gu, which have chiral central charge c - = 0. We show how the tenfold way classification of topological insulators and superconductors fits into our scheme, along with general nonperturbative constraints due to certain choices of c - and G f . Mathematically, our results also suggest an explicit general parametrization of deformation classes of (2 + 1)D invertible topological quantum field theories with G f symmetry.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Observing photo-induced chiral edge states of graphene nanoribbons in pump-probe spectroscopies

Photo-induced edge states in low-dimensional materials have attracted considerable attention due to the tunability of topological properties and dispersion. Specifically, graphene nanoribbons have been predicted to host chiral edge modes upon irradiation with circularly polarized light. Here, we present numerical calculations of time-resolved angle resolved photoemission spectroscopy and trRIXS of a graphene nanoribbon. We characterize pump-probe spectroscopic signatures of photo-induced edge states, illustrate the origin of distinct spectral features that arise from Floquet topological edge modes, and investigate the roles of incoming photon energies and finite core–hole lifetime in RIXS. With momentum, energy, and time resolution, pump-probe spectroscopies can play an important role in understanding the behavior of photo-induced topological states of matter.

36 MATERIALS SCIENCE↗
DOE OSTI2024

New insight into tuning magnetic phases of RMn6Sn6 kagome metals

Abstract Predicting magnetic ordering in kagome compounds offers the possibility of harnessing topological or flat-band physical properties through tuning of the magnetism. Here, we examine the magnetic interactions and phases of ErMn 6 Sn 6 which belongs to a family of R Mn 6 Sn 6 , R = Sc, Y, Gd–Lu, compounds with magnetic kagome Mn layers, triangular R layers, and signatures of topological properties. Using results from single-crystal neutron diffraction and mean-field analysis, we find that ErMn 6 Sn 6 sits close to the critical boundary separating the spiral-magnetic and ferrimagnetic ordered states typical for non-magnetic versus magnetic R layers, respectively. Finding interlayer magnetic interactions and easy-plane Mn magnetic anisotropy consistent with other members of the family, we predict the existence of a number of temperature and field dependent collinear, noncollinear, and noncoplanar magnetic phases. We show that thermal fluctuations of the Er magnetic moment, which act to weaken the Mn-Er interlayer magnetic interaction and quench the Er magnetic anisotropy, dictate magnetic phase stability. Our results provide a starting point and outline a multitude of possibilities for studying the behavior of Dirac fermions in R Mn 6 Sn 6 compounds with control of the Mn spin orientation and real-space spin chirality.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Intrinsic anharmonicity and thermal properties of ultralow thermal conductivity Ba 6 Sn 6 Se 13

Ultralow thermal conductivity materials continue to be of great interest for technologically important applications such as thermal insulators and thermoelectrics. Often, such materials possess constituents with extensive dynamic disorder, or “rattlers,” or structural disorder such as metallic glasses. Nevertheless, targeted crystalline bonding order and anharmonicity can provide effective means for the scattering of the phonons in certain materials. Our combined experimental and theoretical investigation of Ba 6 Sn 6 Se 13 reveals such a material, with ultralow thermal conductivity measured over a large temperature range. Optic phonon modes hybridize with acoustic modes at relatively low energies resulting in strong acoustic-optic scattering and limited phonon lifetimes. Moreover, our investigations reveal various avoided crossings at low energies that contribute to phonon scattering. These are derived from chiral phase symmetries and may result in nontrivial topological behaviors for phonon band crossings in this chiral material. This work contributes to the ongoing research on low thermal conductivity materials and the underlying mechanisms that affect their thermal behaviors. Manipulation of these effects may provide pathways for enhancement of material properties for targeted thermal applications using similar materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Unhinging the Surfaces of Higher-Order Topological Insulators and Superconductors

Here, we show that the chiral Dirac and Majorana hinge modes in three-dimensional higher-order topological insulators (HOTIs) and superconductors (HOTSCs) can be gapped while preserving the protecting C$_{2n}\mathcal{T}$ symmetry upon the introduction of non-Abelian surface topological order. In both cases, the topological order on a single side surface breaks time-reversal symmetry, but appears with its time-reversal conjugate on alternating sides in a C$_{2n}\mathcal{T}$ preserving pattern. In the absence of the HOTI/HOTSC bulk, such a pattern necessarily involves gapless chiral modes on hinges between C$_{2n}\mathcal{T}$-conjugate domains. However, using a combination of K -matrix and anyon condensation arguments, we show that on the boundary of a 3D HOTI/HOTSC these topological orders are fully gapped and hence “anomalous.” Our results suggest that new patterns of surface and hinge states can be engineered by selectively introducing topological order only on specific surfaces.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Charge density waves in the 2.5-dimensional quantum heterostructure

Charge density wave (CDW) and their interplay with correlated and topological quantum states are at the forefront of condensed matter research. The 4H b -TaS 2 is a CDW ordered quantum heterostructure that is formed by alternative stacking of Mott insulating 1T-TaS 2 and Ising superconducting 1H-TaS 2 . While the $\sqrt{13}$ ×$\sqrt{13}$ and 3 × 3 CDWs have been respectively observed in the bulk 1T-TaS 2 and 2H-TaS 2 , the CDWs and their pivotal role for unconventional superconductivity in the 4⁢Hb-TaS 2 remain unsolved. In this Letter, we reveal the two-dimensional (2D) $\sqrt{13}$ ×$\sqrt{13}$ chiral CDW in the 1T layers and intraunit cell coupled 2D 2 × 2 CDW in the 1H and 1H' layers of 4⁢H b -TaS 2 . Here, our results establish 4⁢H b -TaS 2 a 2.5D quantum heterostructure, where 2D quantum states emerge from 3D crystalline structure.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Proximity-induced equilibrium supercurrent and perfect superconducting diode effect due to band asymmetry

Herein we theoretically investigate the consequences of proximity-induced conventional superconductivity in metals that break time-reversal and inversion symmetries through their energy dispersion. We discover behaviors impossible in an isolated superconductor such as an equilibrium supercurrent that apparently violates a no-go theorem and, at suitable topological defects, nonconservation of electric charge reminiscent of the chiral anomaly. The equilibrium supercurrent is expected to be trainable by a helical electromagnetic field in the normal state. Remarkably, if the band asymmetry exceeds the critical current of the parent superconductor in appropriate units, we predict a perfect superconducting diode effect with diode coefficient unity. We propose toroidal metals such as UNi 4 ⁢B and metals with directional scalar spin chiral order as potential platforms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗