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Interplay between antiferromagnetism and superconductivity is studied by using the 3-dimensional nearly half-filled Hubbard model with anisotropic transfer matrices $t_{\rm z}$ and $t_{\perp}$. The phase diagrams are calculated for varying…
We study the frequency dependence of the electron self energy and the optical conductivity in a recently developed field theory of the spin density wave quantum phase transition in two dimensional metals. We focus on the interplay between…
A family of titanium oxypnictide materials BaTi2Pn2O (Pn = pnictogen) becomes superconducting when a charge and/or spin density wave is suppressed. With hole doping, isovalent doping and pressure, a whole range of tuning parameters is…
A systematic investigation has been performed by synthesis and comprehensive characterization of a series of SmFe1-xCuxAsO0.8F0.2 bulks (x = 0 to 0.2). These samples are well characterized by structural, Raman spectroscopy, microstructural,…
We have measured the reflectivity spectra of the iron based superconductor LiFeAs (Tc = 17.6 K) in the temperature range from 4 to 300 K. In the superconducting state (T < Tc), the clear opening of the optical absorption gap was observed…
One of the central issues in the recent study of cuprate superconductors is the interplay of charge order with superconductivity. Here the interplay of charge order with superconductivity in cuprate superconductors is studied based on the…
The critical temperature of an underdoped cuprate superconductor is limited by its phase stiffness $\rho$. In this Letter we argue that the dependence of $\rho$ on doping $x$ should be understood as a consequence of deleterious competition…
Sr3Ir4Sn13 is an interesting compound showing a coexistence of structural phase transition and superconductivity. The structural phase transition at 147 K leads to the formation of a superlattice. We performed optical spectroscopy…
Recent results in electric-field control of magnetism have paved the way for the design of alternative magnetic and spintronic devices with enhanced functionalities and low power consumption. Among the diversity of reported magnetoelectric…
The critical theory of the onset of antiferromagnetism in metals, with concomitant Fermi surface reconstruction, has recently been shown to be strongly coupled in two spatial dimensions. The onset of unconventional superconductivity near…
With infrared spectroscopy we investigated the spin-reorientation transition from an orthorhombic antiferromagnetic (o-AF) to a tetragonal AF (t-AF) phase and the reentrance of the o-AF phase in the superconducting state of underdoped Ba$…
Subsequent to our recent report of SDW type transition at 190 K and antiferromagnetic order below 20 K in EuFe2As2, we have studied the effect of K-doping on the SDW transition at high temperature and AF order at low temperature. 50% K…
We report transport and magnetization measurements on graphitic materials that have been hydrogenated after being treated with octane. The temperature-dependent electrical resistivity shows anomalies manifested as re-entrant insulator-metal…
The observations of quantum oscillations in overdoped cuprate superconductors were in agreement with a charge density contained in a cylindrical Fermi surface but the frequencies of lightly doped compounds were much smaller than expected.…
We report measurements of the in-plane magnetic penetration depth $\Delta \lambda $(T) in single crystals of ErNi$_{2}$B$_{2}$C down to $\sim$0.1 K using a tunnel-diode based, self-inductive technique at 21 MHz. We observe four features:…
We have performed a temperature-dependent angle-integrated photoemission study of lightly-doped to heavily-overdoped La$_{2-x}$Sr$_{x}$CuO$_4$ and oxygen-doped La$_2$CuO$_{4.10}$. We found that both the magnitude $\Delta$* of the (small)…
Neutron diffraction studies of Ba(Fe[1-x]Co[x])2As2 reveal that commensurate antiferromagnetic order gives way to incommensurate magnetic order for Co compositions between 0.056 < x < 0.06. The incommensurability has the form of a small…
The pairing temperature of superconducting thin films is expected to display, within the Bardeen-Cooper-Schrieffer theory, oscillations as a function of the film thickness. We show that the pattern of these oscillations switches between two…
We present fermi liquid expressions for the low temperature behavior of the superfluid stiffness, explain why they differ from those suggested recently by Lee and Wen, and discuss their applicability to data on high-$T_c$ superconductors.…
Understanding the origin of electron incoherence is the first step toward a theoretical description of the non-Fermi liquid behavior of the high-T$_{c}$ cuprate superconductors. Such electron incoherence manifests itself most evidently in…