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The infinite-layer nickelates, isostructural to the high-Tc superconductor cuprates, have risen as a promising platform to host unconventional superconductivity and stimulated growing interests in the condensed matter community. Despite numerous researches, the superconducting pairing symmetry of the nickelate superconductors, the fundamental characteristic of a superconducting state, is still under debate. Moreover, the strong electronic correlation in the nickelates may give rise to a rich phase diagram, where the underlying interplay between the superconductivity and other emerging quantum states with broken symmetry is awaiting exploration. Here, we study the angular dependence of the transport properties on the infinite-layer nickelate Nd0.8Sr0.2NiO2 superconducting films with Corbino-disk configuration. The azimuthal angular dependence of the magnetoresistance (R({\phi})) manifests the rotational symmetry breaking from isotropy to four-fold (C4) anisotropy with increasing magnetic field, revealing a symmetry breaking phase transition. Approaching the low temperature and large magnetic field regime, an additional two-fold (C2) symmetric component in the R({\phi}) curves and an anomalous upturn of the temperature-dependent critical field are observed simultaneously, suggesting the emergence of an exotic electronic phase. Our work uncovers the evolution of the quantum states with different rotational symmetries and provides deep insight into the global phase diagram of the nickelate superconductors.

Exotic correlated insulating phases emerge in the ABC-stacked trilayer graphene-boron nitride Moire super-lattice at both quarter and half-filling. A single-band minimal model with valley contrasting staggered-flux is proposed to capture the relevant band structure, where the conspiracy of perfect Fermi-surface nesting and van Hove singularity strongly enhance the valley fluctuation, leading to inter-valley spiral (IVS) order at half filling. In this paper, we consider a strong coupling U(1)$_{v}\times $SU(2)$_{s}$ symmetric spin-valley model to obtain the correlated insulating state and the pairing instability near quarter filling. A significant ingredient in the strong coupling model is the Dzyaloshinsky-Moriya like interaction inherited from the flux, which breaks not only the valley SU(2)$_{v}$ symmetry but also the sub-valley spatial reflection symmetry. We discuss all the possible long-range orders stabilized by the effective spin-valley-exchange interactions, and it turns out that the flux remarkably enhance the ferro-spin inter-valley 120$^{\circ}$ order, which shares the same valley feature as the IVS order. Upon doping, the leading pairing instability lies in the inter-valley channel with a trigonally warped $p\pm ip$-wave form factor in the presence of the sub-valley reflection symmetry breaking. Depending on the sign of Hund's coupling, the total pairing state could be either spin singlet or triplet. While the spin singlet chiral topological pairing state $(p\pm ip)_{\uparrow\downarrow }-(p\pm ip)_{\downarrow \uparrow }$ is necessarily chiral, the spin triplet topological pairing state could be chiral $(p\pm ip)_{\uparrow\uparrow }+(p\pm ip)_{\downarrow \downarrow }$, or helical $(p\pm ip)_{\uparrow \uparrow }+(p\mp ip)_{\downarrow \downarrow }$., Comment: 11 pages, 6 figures, revised version

The critical theories for the topological phase transitions of integer quantum Hall states to a trivial insulating state with the same symmetry can be obtained by calculating the ground state entanglement spectrum under a symmetric checkerboard bipartition. In contrast to the gapless edge excitations under the left-right bipartition, a quantum network with bulk gapless excitations naturally emerges at the Brillouin zone center without fine tuning. On a large finite lattice, the resulting critical theory for the $\nu =1$ state is the (2+1) dimensional relativistic quantum field theory characterized by a \textit{single} Dirac cone spectrum and a pair of \textit{fractionalized} zero-energy states, while for the $\nu =2$ state the critical theory exhibits a parabolic spectrum and no sign of fractionalization in the zero-energy states. A triangular correspondence is established among the bulk topological theory, gapless edge theory, and the critical theory via the ground state entanglement spectrum., Comment: 5 pages, 4 figures, published version

A correct general formula for the spin current through an interacting quantum dot coupled to ferromagnetic leads with magnetization at an arbitrary angle $\theta$ is derived within the framework of the Keldysh formalism. Under asymmetric conditions, the spin current component J_{z} may change sign for $0<\theta<\pi$. It is shown that the spin current and spin tunneling magnetoresistance exhibit different angle dependence in the free and Coulomb blockade regimes. In the latter case, the competition of spin precession and the spin-valve effect could lead to an anomaly in the angle dependence of the spin current., Comment: 7 pages, 4 figures; some parts of the text has been revised in this version accepted by J. Phys.: Condens. Matter

An important characteristic of topological band insulators is the necessary presence of in-gap edge states on the sample boundary. We utilize this fact to show that when the boundary is reconnected with a twist, there are always zero-energy defect states. This provides a natural connection between novel defects in the two-dimensional $p_{x}+ip_{y}$ superconductor, the Kitaev model, the fractional quantum Hall effect, and the one-dimensional domain wall of polyacetylene., Comment: 4 pages, 4 figures. The figures have been revised. accepted for publication by Physical Review Letters

We investigate the spectral and transport properties of parallel double-quantum-dot (DQD) system with interdot tunneling coupling in both the equilibrium and nonequilibrium cases. The special geometry of DQD system is considered, in which each dot is connected to two leads by the tunneling barriers. With the help of Keldysh nonequilibrium Green function technique and the equation-of-motion approach, the spectral function and the conductance spectra of DQD system are calculated in two cases with and without the intradot Coulomb interaction, respectively. The exact calculation is performed in the absence of intradot Coulomb interaction. For the case with intradot Coulomb interaction, the Hartree-Fock approximation is applied to truncate the equation of motion for the high-order Green functions at high temperatures. The phenomenon of correlated electron transport is clearly shown in the linear conductance of each dot in the presence of interdot tunneling when setting one dot level and tuning another. The interplay between the intradot Coulomb interaction and the interdot tunneling coupling is displayed., Comment: 11 pages, 10 figures

In the strong coupling limit, an effective resonant level model is derived for the spin-1 underscreened Kondo impurity model. A local quantum critical behavior is induced by the formation of a bound state with partially screened magnetic moment, displaying a residual $Z_2$ symmetry, leading to a $\delta $-resonance at the Fermi level in the impurity spectral function. As a consequence, a logarithmic singularity appears in the real part of the impurity dynamic spin susceptibility as a function of $\max (\omega, T)$, with $\omega $ as frequency, $T$ temperature. A small magnetic field breaks this $Z_2$ symmetry and suppresses the singularity. We also discuss the possible manifestation of such a quantum critical behavior in the spin-1/2 two Kondo impurity model and the single quantum dot system with even electron occupation., Comment: 8 pages, no figures; revised version

We consider an effective mass model for an electron-hole pair in a simplified confinement potential, which is applicable to both a nanoscopic self-assembled semiconducting InAs ring and a quantum dot. The linear optical susceptibility, proportional to the absorption intensity of near-infrared transmission, is calculated as a function of the ring radius $% R_0$. Compared with the properties of the quantum dot corresponding to the model with a very small radius $R_0$, our results are in qualitative agreement with the recent experimental measurements by Pettersson {\it et al}., Comment: 4 pages, 4 figures, revised and accepted by Phys. Rev. B