17 research outputs found

    Coexistence of ΘII\Theta_{II}-loop-current order with checkerboard d-wave CDW/PDW order in a hot-spot model for cuprate superconductors

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    We investigate the strong influence of the ΘII\Theta_{II}-loop-current order on both unidirectional and bidirectional d-wave charge-density-wave/pair-density-wave (CDW/PDW) composite orders along axial momenta (±Q0,0)(\pm Q_0,0) and (0,±Q0)(0,\pm Q_0) that emerge in an effective hot spot model departing from the three-band Emery model relevant to the phenomenology of the cuprate superconductors. This study is motivated by the compelling evidence that the ΘII\Theta_{II}-loop-current order described by this model may explain groundbreaking experiments such as spin-polarized neutron scattering performed in these materials. Here, we demonstrate, within a saddle-point approximation, that the ΘII\Theta_{II}-loop-current order clearly coexists with bidirectional (i.e. checkerboard) d-wave CDW and PDW orders along axial momenta, but is visibly detrimental to the unidirectional (i.e. stripe) case. This result has potentially far-reaching implications for the physics of the cuprates and agrees well with very recent x-ray experiments on YBCO that indicate that at higher dopings the CDW order has indeed a tendency to be bidirectional.Comment: Published in Physical Review

    Complete renormalization group calculation up to two-loop order of an effective two-band model for iron-based superconductors

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    We perform a renormalization group (RG) study up to two-loop order of an effective low-energy two-band model to describe some of the recently discovered iron-based superconductors. Our starting point is the itinerant electronic model proposed by Chubukov \emph{et al.} [Phys. Rev. B \textbf{78}, 134512 (2008)], which displays two small, almost nested Fermi pockets with one hole pocket centered at (0,0)(0,0) and one electron pocket centered at Q=(π,π)\mathbf{Q} = (\pi,\pi) in the folded Brillouin zone. We then proceed to implement a complete two-loop RG calculation for this model of four-point vertex corrections, quasiparticle weight and several order-parameter susceptibilities in order to evaluate the robustness of one-loop RG results available in the literature with respect to including self-energy effects and higher-order quantum fluctuations.Comment: 6 pages, 6 figures; accepted for publication in Europhysics Letter

    DC resistivity near a nematic quantum critical point: Effects of weak disorder and acoustic phonons

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    We calculate the resistivity associated with an Ising-nematic quantum critical point in the presence of disorder and acoustic phonons in the lattice model. We use the memory-matrix transport theory, which has a crucial advantage compared to other methods of not relying on the existence of well-defined quasiparticles in the low-energy effective theory. As a result, we obtain that by including an inevitable interaction between the nematic fluctuations and the elastic degrees of freedom of the lattice (parametrized by the nemato-elastic coupling κlatt\kappa_{\text{latt}}), the resistivity ρ(T)\rho(T) of the system as a function of temperature obeys a universal scaling form described by ρ(T)Tln(1/T)\rho(T)\sim T\ln (1/T) at high temperatures, reminiscent of the paradigmatic strange metal regime observed in many strongly correlated compounds. For a window of temperatures comparable with κlatt3/2εF\kappa^{3/2}_{\text{latt}}\varepsilon_F (where εF\varepsilon_F is the Fermi energy of the microscopic model), the system displays another regime in which the resistivity is consistent with a description in terms of ρ(T)Tα\rho(T)\sim T^{\alpha}, where the effective exponent roughly satisfies the inequality 1α21\lesssim\alpha\lesssim 2. However, in the low-temperature limit (i.e., Tκlatt3/2εFT\ll\kappa^{3/2}_{\text{latt}}\varepsilon_F), the properties of the quantum critical state change in an important way depending on the types of disorder present in the system: It can either recover a conventional Fermi liquid described by ρ(T)T2\rho(T)\sim T^2 or it could exhibit yet another non-Fermi liquid regime characterized by the scaling form ρ(T)ρ0T2lnT\rho(T)-\rho_0\sim T^2\ln T. Our results emphasize the key role played by both phonon and disorder effects in the scenario of nematic quantum criticality and might be fundamental for addressing recent transport experiments in some iron-based superconductors.Comment: 18 pages, 9 figure

    Multipolar spin liquid in an exactly solvable model for jeff=32j_\mathrm{eff} = \frac{3}{2} moments

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    We study an exactly solvable model with bond-directional quadrupolar and octupolar interactions between spin-orbital entangled jeff=32j_{\mathrm{eff}} = \frac{3}{2} moments on the honeycomb lattice. We show that this model features a multipolar spin liquid phase with gapless fermionic excitations. In the presence of perturbations that break time-reversal and rotation symmetries, we find Abelian and non-Abelian topological phases in which the Chern number evaluates to 00, ±1\pm 1, and ±2\pm 2. We also investigate quantum phase transitions out of the multipolar spin liquid using a parton mean-field approach and orbital wave theory. In the regime of strong integrability-breaking interactions, the multipolar spin liquid gives way to ferroquadrupolar-vortex and antiferro-octupolar ordered phases that harbor a hidden spin-12\frac{1}{2} Kitaev spin liquid. Our work unveils mechanisms for unusual multipolar orders and quantum spin liquids in Mott insulators with strong spin-orbit coupling.Comment: 14 pages, 9 figure

    Strong competition between ΘII\Theta_{II}-loop-current order and dd-wave charge order along the diagonal direction in a two-dimensional hot spot model

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    We study the fate of the so-called ΘII\Theta_{II}-loop-current order that breaks both time-reversal and parity symmetries in a two-dimensional hot spot model with antiferromagnetically mediated interactions, using Fermi surfaces relevant to the phenomenology of the cuprate superconductors. We start from a three-band Emery model describing the hopping of holes in the CuO2_{2} plane that includes two hopping parameters tppt_{pp} and tpdt_{pd}, local on-site Coulomb interactions UdU_{d} and UpU_{p} and nearest-neighbor VpdV_{pd} couplings between the fermions in the copper [Cu(3dx2y2)(3d_{x^{2}-y^{2}})] and oxygen [O(2px)(2p_{x}) and O(2py)(2p_{y})] orbitals. By focusing on the lowest-energy band, we proceed to decouple the local interaction UdU_{d} of the Cu orbital in the spin channel using a Hubbard-Stratonovich transformation to arrive at the interacting part of the so-called spin-fermion model. We also decouple the nearest-neighbor interaction VpdV_{pd} to introduce the order parameter of the ΘII\Theta_{II}-loop-current order. In this way, we are able to construct a consistent mean-field theory that describes the strong competition between the composite order parameter made of a quadrupole-density-wave and dd-wave pairing fluctuations proposed in Efetov \emph{et al.} [Nat. Phys. \textbf{9}, 442 (2013)] with the ΘII\Theta_{II}-loop-current order parameter that is argued to be relevant for explaining important aspects of the physics of the pseudogap phase displayed in the underdoped cuprates.Comment: 16 pages, 5 figures. v2: minor revisions, references added. The magnetic moment per unit-cell associated with the ΘII\Theta_{II}-loop-current-phase is calculated and compared with experimental results. Accepted for publication in Physical Review

    Topological transition from nodal to nodeless Zeeman splitting in altermagnets

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    In an altermagnet, the symmetry that relates configurations with flipped magnetic moments is a rotation. This makes it qualitatively different from a ferromagnet, where no such symmetry exists, or a collinear antiferromagnet, where this symmetry is a lattice translation. In this paper, we investigate the impact of the crystalline environment on the magnetic and electronic properties of an altermagnet. We find that, because each component of the magnetization acquires its own angular dependence, the Zeeman splitting of the bands has symmetry-protected nodal lines residing on mirror planes of the crystal. Upon crossing the Fermi surface, these nodal lines give rise to pinch points that behave as single or double type-II Weyl nodes. We show that an external magnetic field perpendicular to these mirror planes can only move the nodal lines, such that a critical field value is necessary to collapse the nodes and make the Weyl pinch points annihilate. This unveils the topological nature of the transition from a nodal to a nodeless Zeeman splitting of the bands. We also classify the altermagnetic states of common crystallographic point groups in the presence of spin-orbit coupling, revealing that a broad family of magnetic orthorhombic perovskites can realize altermagnetism.Comment: manuscript + supplementary materia

    Superconductivity Mediated by Nematic Fluctuations in Tetragonal FeSe1xSx\textrm{Fe}\textrm{Se}_{1-x}\textrm{S}_{x}

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    Nematic phases, where electrons in a solid spontaneously break rotational symmetry while preserving the translational symmetry, exist in several families of unconventional superconductors [1, 2]. Although superconductivity mediated by nematic fluctuations is well established theoretically [3-7], it has yet to be unambiguously identified experimentally [8, 9]. A major challenge is that nematicity is often intertwined with other degrees of freedom, such as magnetism and charge order. The FeSe1x_{1-x}Sx_x family of iron based superconductors provides a unique opportunity to explore this concept, as it features an isolated nematic phase that can be suppressed by sulfur substitution at a quantum critical point (QCP) near xc=0.17x_c = 0.17, where nematic fluctuations are the largest [10-12]. Here, we performed scanning tunneling spectroscopy measurements to visualize Boguliubov quasiparticle interference patterns, from which we determined the momentum structure of the superconducting gap near the Brillouin zone Γ\Gamma point of FeSe0.81_{0.81}S0.19_{0.19}. The results reveal an anisotropic, near nodal gap with minima that are 4545^\circ rotated with respect to the Fe-Fe direction, characteristic of a nematic pairing interaction, contrary to the usual isotropic gaps due to spin mediated pairing in other tetragonal Fe-based superconductors. The results are also in contrast with pristine FeSe, where the pairing is mediated by spin fluctuations and the gap minima are aligned with the Fe-Fe direction. Therefore, the measured gap structure demonstrates not only a fundamental change of the pairing mechanism across the phase diagram of FeSe1x_{1-x}Sx_x, but it also indicates the existence of superconductivity mediated by nematic fluctuations in FeSe0.81_{0.81}S0.19_{0.19}
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