Carrier-Concentration Dependence of the Pseudogap Ground State of Superconducting Bi2Sr2-xLaxCuO6+delta Revealed by 63,65Cu-Nuclear Magnetic Resonance in Very High Magnetic Fields

We report the results of the Knight shift by 63,65Cu-nuclear-magnetic resonance (NMR) measurements on single-layered copper-oxide Bi2Sr2-xLaxCuO6+delta conducted under very high magnetic fields up to 44 T. The magnetic field suppresses superconductivity completely and the pseudogap ground state is revealed. The 63Cu-NMR Knight shift shows that there remains a finite density of states (DOS) at the Fermi level in the zero-temperature limit, which indicates that the pseudogap ground state is a metallic state with a finite volume of Fermi surface. The residual DOS in the pseudogap ground state decreases with decreasing doping (increasing x) but remains quite large even at the vicinity of the magnetically ordered phase of x > 0.8, which suggests that the DOS plunges to zero upon approaching the Mott insulating phase.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let

Charge Density Wave Order in the Topological Insulator Bi2Se3Bi_2Se_3

Hexagonally deformed Fermi surfaces and strong nesting, found in topological insulators (TIs) such as $Bi_2Se_3$ and $Bi_2Te_3$ over the past decade, have led to several predictions of possible Density Wave order in these systems. Recent evidence for strong Fermi nesting in superconducting $Cu-Bi_2Se_3$ and $Nb-Bi_2Se_3$ has led to further speculation about the importance of charge order in the context of unconventional superconductivity. Here, we report what we believe is the first direct observation of Charge Density Wave (CDW) order in $Bi_2Se_3$. Our results include the observation of a 140K metal-insulator-metal transition in resistivity as a function of temperature. We corroborate this with nuclear magnetic resonance (NMR) studies of the spin-lattice relaxation $\frac{1}{T_1}$ rate of the $^{209}Bi$ nucleus, which also displays a transition at 140K. Additionally, we use electron diffraction to reveal a periodic lattice distortion (PLD) in $Bi_2Se_3$, together with diffuse charge order between $\vec{k}$ and $\vec{k} \pm \Delta\vec{k}$. This diffuse scattering points toward the presence of an incommensurate charge density wave (I-CDW) above room temperature, which locks into a CDW upon cooling below $\sim140K$. We also observe two additional transitions in $\frac{1}{T_1}$ near 200K and 15K. The transition at 200K appears to display some anisotropy with the direction of applied magnetic field. In this report, we focus on the CDW transition at 140K. We include some speculation of the two other transitions observed at 15K and 200K by NMR, also revealed here for the first time.Comment: 16 pages, 5 figure

Effects of charge doping on Mott insulator with strong spin-orbit coupling, Ba2Na1−xCaxOsO6

The effects of doping on the electronic evolution of the Mott insulating state have been extensively studied in efforts to understand mechanisms of emergent quantum phases of materials. The study of these effects becomes ever more intriguing in the presence of entanglement between spin and orbital degrees of freedom. Here, we present a comprehensive investigation of charge doping in the double perovskite Ba2NaOsO6, a complex Mott insulator where such entanglement plays an important role. We establish that the insulating magnetic ground state evolves from canted antiferromagnet (cAFM) [Lu et al., Nat. Commun. 8, 14407 (2017)] to Neel order for dopant levels exceeding approximate to 10%. Furthermore, we determine that a broken local point symmetry (BLPS) phase, precursor to the magnetically ordered state, occupies an extended portion of the (H-T) phase diagram with increased doping. This finding reveals that the breaking of the local cubic symmetry is driven by a multipolar order, most likely of the antiferro-quadrupolar type [Khaliullin et al., Phys. Rev. Res. 3, 033163 (2021); Churchill and Kee, Phys. Rev. B 105, 014438 (2022)]. Future dynamical measurements will be instrumental in determination of the precise nature of the identified multipolar order

Antiferromagnetic Switching Driven by the Collective Dynamics of a Coexisting Spin Glass

The theory behind the electrical switching of antiferromagnets is premised on the existence of a well defined broken symmetry state that can be rotated to encode information. A spin glass is in many ways the antithesis of this state, characterized by an ergodic landscape of nearly degenerate magnetic configurations, choosing to freeze into a distribution of these in a manner that is seemingly bereft of information. In this study, we show that the coexistence of spin glass and antiferromagnetic order allows a novel mechanism to facilitate the switching of the antiferromagnet Fe$_{1/3+\delta}$NbS$_2$, which is rooted in the electrically-stimulated collective winding of the spin glass. The local texture of the spin glass opens an anisotropic channel of interaction that can be used to rotate the equilibrium orientation of the antiferromagnetic state. The use of a spin glass' collective dynamics to electrically manipulate antiferromagnetic spin textures has never been applied before, opening the field of antiferromagnetic spintronics to many more material platforms with complex magnetic textures.Comment: 7 pages, 4 Figures, supplement available on reasonable reques

Hidden magnetism at the pseudogap critical point of a high temperature superconductor

The mysterious pseudogap phase of cuprate superconductors ends at a critical hole doping level p* but the nature of the ground state below p* is still debated. Here, we show that the genuine nature of the magnetic ground state in La2-xSrxCuO4 is hidden by competing effects from superconductivity: applying intense magnetic fields to quench superconductivity, we uncover the presence of glassy antiferromagnetic order up to the pseudogap boundary p* ~ 0.19, and not above. There is thus a quantum phase transition at p*, which is likely to underlie highfield observations of a fundamental change in electronic properties across p*. Furthermore, the continuous presence of quasi-static moments from the insulator up to p* suggests that the physics of the doped Mott insulator is relevant through the entire pseudogap regime and might be more fundamentally driving the transition at p* than just spin or charge ordering.Comment: 26 pages, supplementary info include

\u3csup\u3e27\u3c/sup\u3eAl field-swept and frequency-stepped NMR for sites with large quadrupole coupling constants

Spectra of nonspinning samples with large quadrupole coupling constants, 16-32 MHz, are acquired by frequency-stepping. A series of spin-echoes are acquired at arbitrary frequency increments, frequency-shifted in the time domain, and co-added as magnitude spectra. This procedure is derived from a method in use for field-swept NMR. The two methods are compared. © 2000 Elsevier Science B.V. All rights reserved

1H and 195Pt NMR Study of the Parallel Two-Chain Compound Per2[Pt(mnt)2]

1H and 195Pt NMR are used to probe the spin ½ anion chain in the quasi-one-dimensional conductor Per2[Pt(mnt)2], which exhibits nearly simultaneous charge density wave (CDW) and spin-Peierls (SP) transitions at low temperatures (Tc ~ 8 K). Below Tc the [Pt(mnt)2] chain forms a spin-singlet state that is evident in 1H NMR spectra and spin relaxation (1/T1) rates; however minority unpaired Pt spins may remain in the SP ground state. With increasing magnetic field, the SP and CDW order parameters decrease in unison, indicating they are coupled up to a critical field Bc ~ 20 T. Above Bc, the spin singlet evolves into a spin-polarized configuration. The 195Pt NMR signals vanish as either Tc or Bc are approached from within the SP ground state, suggesting the hyperfine field of the Pt nucleus is significantly stronger than at the proton sites. Simulations yield a consistent picture of the angular, temperature, and magnetic field-dependent spectral features

Two coupled chains are simpler than one: field-induced chirality in a frustrated spin ladder

Although the frustrated (zigzag) spin chain is the Drosophila of frustrated magnetism, our understanding of a pair of coupled zigzag chains (frustrated spin ladder) in a magnetic field is still lacking. We address this problem through nuclear magnetic resonance (NMR) experiments on BiCu2PO6 in magnetic fields up to 45 T, revealing a field-induced spiral magnetic structure. Conjointly, we present advanced numerical calculations showing that even a moderate rung coupling dramatically simplifies the phase diagram below half-saturation magnetization by stabilizing a field-induced chiral phase. Surprisingly for a one-dimensional model, this phase and its response to Dzyaloshinskii-Moriya (DM) interactions adhere to classical expectations. While explaining the behavior at the highest accessible magnetic fields, our results imply a different origin for the solitonic phases occurring at lower fields in BiCu2PO6. An exciting possibility is that the known, DM-mediated coupling between chirality and crystal lattice may give rise to a new kind of spin-Peierls instability.ISSN:2045-232