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Register a new userDensity of States and Magnetic Correlations at a Metal-Mott Insulator Interface
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The possibility of novel behavior at interfaces between strongly and weakly correlated materials has come under increased study recently. In this paper, we use determinant Quantum Monte Carlo to determine the inter-penetration of metallic and Mott insulator physics across an interface in the two dimensional Hubbard Hamiltonian. We quantify the behavior of the density of states at the Fermi level and the short and long range antiferromagnetism as functions of the distance from the interface and with different interaction strength, temperature and hopping across the interface. Induced metallic behavior into the insulator is evident over several lattice spacings, whereas antiferromagnetic correlations remain small on the metallic side. At large interface hopping, singlets form between the two boundary layers, shielding the two systems from each other.
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We compute the spin-active scattering matrix and the local spectrum at the interface between a metal and a three-dimensional topological band insulator. We show that there exists a critical incident angle at which complete (100%) spin flip reflection occurs and the spin rotation angle jumps by $pi$. We discuss the origin of this phenomena, and systematically study the dependence of spin-flip and spin-conserving scattering amplitudes on the interface transparency and metal Fermi surface parameters. The interface spectrum contains a well-defined Dirac cone in the tunneling limit, and smoothly evolves into a continuum of metal induced gap states for good contacts. We also investigate the complex band structure of Bi$_2$Se$_3$.
We present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca$_3$Ru$_2$O$_7$. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.
We present a computationally efficient method to obtain the spectral function of bulk systems in the framework of steady-state density functional theory (i-DFT) using an idealized Scanning Tunneling Microscope (STM) setup. We calculate the current through the STM tip and then extract the spectral function from the finite-bias differential conductance. The fictitious non-interacting system of i-DFT features an exchange-correlation (xc) contribution to the bias which guarantees the same current as in the true interacting system. Exact properties of the xc bias are established using Fermi-liquid theory and subsequently implemented to construct approximations for the Hubbard model. We show for two different lattice structures that the metal-insulator transition is captured by i-DFT.
The correlation-driven Mott transition is commonly characterized by a drop in resistivity across the insulator-metal phase boundary; yet, the complex permittivity provides a deeper insight into the microscopic nature. We investigate the frequency- and temperature-dependent dielectric response of the Mott insulator $kappa$-(BEDT-TTF)$_{2}$-Cu$_2$(CN)$_3$ when tuning from a quantum spin liquid into the Fermi-liquid state by applying external pressure and chemical substitution of the donor molecules. At low temperatures the coexistence region at the first-order transition leads to a strong enhancement of the quasi-static dielectric constant $epsilon_1$ when the effective correlations are tuned through the critical value. Several dynamical regimes are identified around the Mott point and vividly mapped through pronounced permittivity crossovers. All experimental trends are captured by dynamical mean-field theory of the single-band Hubbard model supplemented by percolation theory.
Recent experiments demonstrating large spin-transfer torques in topological insulator (TI)-ferromagnetic metal (FM) bilayers have generated a great deal of excitement due to their potential applications in spintronics. The source of the observed spin-transfer torque, however, remains unclear. This is because the large charge transfer from the FM to TI layer would prevent the Dirac cone at the interface from being anywhere near the Fermi level to contribute to the observed spin-transfer torque. Moreover, there is yet little understanding of the impact on the Dirac cone at the interface from the metallic bands overlapping in energy and momentum, where strong hybridization could take place. Here, we build a simple microscopic model and perform first-principles-based simulations for such a TI-FM heterostructure, considering the strong hybridization and charge transfer effects. We find that the original Dirac cone is destroyed by the hybridization as expected. Instead, we find a new interface state which we dub descendent state to form near the Fermi level due to the strong hybridization with the FM states at the same momentum. Such a `descendent state carries a sizable weight of the original Dirac interface state, and thus inherits the localization at the interface and the same Rashba-type spin-momentum locking. We propose that the `descendent state may be an important source of the experimentally observed large spin-transfer torque in the TI-FM heterostructure.
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