254 research outputs found

    Disorder effects in spiral spin liquids: Long-range spin textures, Friedel-like oscillations, and spiral spin glasses

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    Spiral spin liquids are correlated states of matter in which a frustrated magnetic system evades order by fluctuating between a set of (nearly) degenerate spin spirals. Here, we investigate the response of spiral spin liquids to quenched disorder in a J1J_1-J2J_2 honeycomb-lattice Heisenberg model. At the single-impurity level, we identify different order-by-quenched-disorder phenomena and analyze the ensuing spin textures. In particular, we show that the latter generally display Friedel-like oscillations, which encode direct information about the spiral contour, i.e., the classical ground-state manifold. At finite defect concentrations, we perform extensive numerical simulations and characterize the resulting phases at zero temperature. As a result, we find that the competition between incompatible order-by-quenched-disorder mechanisms can lead to spiral spin glass states already at low to moderate disorder. Finally, we discuss extensions of our conclusions to nonzero temperatures and higher-dimensional systems, as well as their applications to experiments.Comment: 15+11 pages, 12+6 figure

    Interplay of charge density waves, disorder, and superconductivity in 2H-TaSe2 elucidated by NMR

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    Single crystals of pristine and 6% Pd-intercalated 2H‐TaSe2 have been studied by means of 77Se nuclear magnetic resonance. The temperature dependence of the 77Se spectrum, with an unexpected line narrowing upon Pd intercalation, unravels the presence of correlated local lattice distortions far above the transition temperature of the charge density wave (CDW) order, thereby supporting a strong-coupling CDW mechanism in 2H‐TaSe2. While, the Knight shift data suggest that the incommensurate CDW transition involves a partial Fermi surface gap opening. As for spin dynamics, the 77Se spin-lattice relaxation rate T1-1 as a function of temperature shows that a pseudogap behavior dominates the low-energy spin excitations even within the CDW phase, and gets stronger along with superconductivity in the Pd-6% sample. We discuss that CDW fluctuations may be responsible for the pseudogap as well as superconductivity, although the two phenomena are unlikely to be directly linked each other

    SU(2)-symmetric spin-boson model: Quantum criticality, fixed-point annihilation, and duality

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    Dissipative quantum impurity models represent conceptually simple yet non-trivial settings for quantum criticality. Here we present results from high-accuracy quantum Monte Carlo calculations for the SU(2)-symmetric spin-boson (or Bose-Kondo) model, relevant to diverse problems such as cavity quantum electrodynamics, magnetic moments in quantum critical magnets, and Kondo-breakdown transitions in heavy-fermion metals. We study the model with a power-law bath spectrum ωs\propto \omega^s where, in addition to a critical phase predicted by perturbative renormalization group (RG), a stable strong-coupling phase is present for all values of 0<s<10<s<1. The critical phase ceases to exist for s<s=0.6540(2)s<s^\ast = 0.6540(2), rendering the perturbative prediction invalid. We provide direct numerical evidence for the collision and annihilation of two intermediate-coupling RG fixed points at ss^\ast responsible for that. We uncover a surprising duality between the two fixed points, corresponding to a reflection symmetry of the RG beta function. We then utilize this duality to make analytical predictions for critical properties at strong coupling which are in excellent agreement with the numerical results. We comment on the consequences for impurity moments in critical magnets.Comment: 6 pages, 6 figures (plus supplemental material: 7 pages, 6 figures, 2 tables

    Marginal Fermi liquid at magnetic quantum criticality from dimensional confinement

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    Metallic quantum criticality is frequently discussed as a source for non-Fermi liquid behavior, but controlled theoretical treatments are scarce. Here we identify and study a novel magnetic quantum critical point in a two-dimensional antiferromagnet coupled to a three-dimensional environment of conduction electrons. Using sign-problem-free quantum Monte Carlo simulations and an effective field-theory analysis, we demonstrate that the quantum critical point is characterized by marginal Fermi liquid behavior. In particular, we compute the electrical resistivity for transport across the magnetic layer, which is shown to display a linear temperature dependence at criticality. Experimental realizations in Kondo heterostructures are discussed.Comment: 6 pages, 4 figure; Supplement: 12 pages, 12 figure

    Magnetic quantum phase transition in a metallic Kondo heterostructure

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    We consider a two-dimensional quantum spin system described by a Heisenberg model that is embedded in a three-dimensional metal. The two systems couple via an antiferromagnetic Kondo interaction. In such a setup, the ground state generically remains metallic down to the lowest temperatures and allows us to study magnetic quantum phase transitions in metallic environments. From the symmetry point of view, translation symmetry is present in two out of three lattice directions such that crystal momentum is only partially conserved. Importantly, the construction provides a route to study, with negative-sign-free auxiliary-field quantum Monte Carlo methods, the physics of local moments in metallic environments. Our large-scale numerical simulations show that as a function of the Kondo coupling, the system has two metallic phases. In the limit of strong Kondo coupling, a paramagnetic heavy-fermion phase emerges. Here, the spin degree of freedom is screened by means of the formation of a composite quasiparticle that participates in the Luttinger count. At weak Kondo coupling, magnetic order is present. This phase is characterized by Landau-damped Goldstone modes. Furthermore, the aforementioned composite quasiparticle remains intact across the quantum phase transition.Comment: 19 pages, 15 figure

    Flux crystals, Majorana metals, and flat bands in exactly solvable spin-orbital liquids

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    International audienceSpin-orbital liquids are quantum disordered states in systems with entangled spin and orbital degrees of freedom. We study exactly solvable spin-orbital models in two dimensions with selected Heisenberg-, Kitaev-, and Γ-type interactions, as well as external magnetic fields. These models realize a variety of spin-orbital-liquid phases featuring dispersing Majorana fermions with Fermi surfaces, nodal Dirac or quadratic band touching points, or full gaps. In particular, we show that Zeeman magnetic fields can stabilize nontrivial flux patterns and induce metamagnetic transitions between states with different topological character. Solvable nearest-neighbor biquadratic spin-orbital perturbations can be tuned to stabilize zero-energy flat bands. We discuss in detail the examples of SO(2)- and SO(3)-symmetric spin-orbital models on the square and honeycomb lattices, and use group-theoretical arguments to generalize to SO(ν)-symmetric models with arbitrary integer ν>1. These results extend the list of exactly solvable models with spin-orbital-liquid ground states and highlight the intriguing general features of such exotic phases. Our models are thus excellent starting points for more realistic modelling of candidate materials