We study two mechanisms for enhancing the superconducting mean-field transition temperature ${T}_{c}$ by nonmagnetic disorder in both conventional (sign-preserving gaps) and unconventional (sign-changing superconductors (SCs). In first scenario, relevant to multiband systems of SCs, we demonstrate how favorable density-of-states enhancements driven resonant states off-Fermi-level bands lead significant condensate formed near-Fermi-level bands. The second scenario focuses on close...

We perform a microscopic theoretical study of the generic properties competing magnetic phases in iron pnictides. As function electron filling and temperature, stripe (single-Q) order forms dome, but non-collinear non-uniform double-Q exist at foot dome agreement with recent experiments. compute compare electronic different phases, investigate role superconductivity, show how disorder may stabilize order. Superconductivity is shown to compete more strongly which can lead re-entrance C2...

We consider the role of potential scatterers in nematic phase Fe-based superconductors above transition temperature to (π, 0) magnetic state but below orthorhombic structural transition. The anisotropic spin fluctuations this region can be frozen by disorder, create elongated droplets whose anisotropy grows as is approached. Such states act strong defect potentials that scatter with much higher probability perpendicular their length than parallel, although actual crystal symmetry breaking...

Recent experimental studies have revealed several unexpected properties of Mn-doped BaFe(2)As(2). These include extension the stripelike magnetic (π,0) phase to high temperatures above a critical Mn concentration only, presence diffusive and weakly temperature dependent (π,π) checkerboard scattering, an apparent absent structural distortion from tetragonal orthorhombic symmetry. Here, we study effects impurities both below Néel transition within real-space five-band model appropriate iron...

We study the effects of disorder on unconventional superconductors in presence correlations, and explore a novel correlated paradigm dominated by strong deviations from standard Abrikosov-Gor'kov theory due to generation local bound states cooperative impurity behavior driven Coulomb interactions. Specifically we explain under which circumstances magnetic acts as poison destroying high-T_{c} superconductivity at sub-1% level, when nonmagnetic disorder, counterintuitively, hardly affects...

Motivated by the experimental observation that superconductivity in bulk doped ${\mathrm{SrTiO}}_{3}$ is enhanced as a putative ferroelectric quantum critical point (FE-QCP) approached, we study pairing instability of cubic system which electrons exchange low-energy fluctuations. Instead gradient coupling to lattice distortion associated with ferroelectricity, consider direct between and bosonic field appears presence spin-orbit coupling. Working weak-coupling regime, find interaction...

Experimental evidence suggests that superconductivity in ${\mathrm{SrTiO}}_{3}$ is mediated by a soft transverse ferroelectric mode which, according to conventional theories, has negligible coupling with electrons. A phenomenological Rashba-type been proposed on symmetry arguments but microscopic derivation lacking. Here, we fill this gap and obtain linear directly from minimal model of the electronic structure. We find effective electron-electron pairing interaction strong momentum...

The nature of superconductivity and its interplay with strong spin-orbit coupling at the KTaO3(111) interfaces remain a subject debate. To address this problem, we grew epitaxial LaMnO3/KTaO3(111) heterostructures. We show that is robust against in-plane magnetic field, critical field reaching ∼25 T in optimally doped superconducting order parameter highly sensitive to carrier density. argue drives formation anomalous quasiparticles vanishing moment, providing significant condensate immunity...

Metallic strontium titanate (SrTiO3) is known to have both normal-state and superconducting properties that strongly vary over a wide range of charge carrier densities, but the complex interplay between lattice electronic degrees freedom has hindered development clear qualitative description observed behavior. A major challenge understand how carriers themselves evolve with doping temperature, possible polaronic effects evidence an effective mass increases temperature. Here we use 47,49Ti...

The superconducting order parameter at the KTaO3 interfaces and its dependence on interface orientation remains a subject of debate. superconductivity these exhibits strong resilience against in-plane magnetic field violates Pauli limit. critical violation limit, however, have not been investigated. To address this problem, we grew epitaxial LaMnO3/KTaO3 heterostructures using molecular beam epitaxy. We show that is extremely robust field. Our results indicate orientation, despite impacting...

We study impurity bound states and impurity-induced order in the superconducting state of LiFeAs within a realistic five-band model based on band structure potentials obtained from density functional theory. In agreement with recent experiments, we find that Co impurities are too weak to produce subgap states, whereas stronger like Cu do. also obtain bound-state spectrum for magnetic impurities, such as Mn, show how spin-resolved tunneling may determine nature various defect sites iron...

Motivated by the observation of superconductivity in ${\mathrm{SrTiO}}_{3}$ and Bi, we analyze phonon-mediated three-dimensional systems at low carrier density, when chemical potential $\ensuremath{\mu}$ is comparable to or even smaller than characteristic phonon frequency ${\ensuremath{\omega}}_{L}$. We consider attractive part Bardeen-Pines pairing interaction, which frequency-dependent electron-phonon interaction dressed Coulomb potential. This dressing endows with momentum dependence....

${\mathrm{SrTiO}}_{3}$ is known for its proximity to a ferroelectric phase and showing an ``optimal'' doping superconductivity with characteristic domelike behavior resembling systems close quantum critical point. Several mechanisms have been proposed link these phenomena, but the abundance of undetermined parameters prevents definite assessment. Here, we use ab initio computations supplemented microscopic model study linear coupling between conduction electrons soft transverse modes allowed...

This is the first microscopic theory of impurity-induced local spin nematic order in iron-based superconductors that explains experimentally observed transport anisotropy their spin-density-wave phase.

We report wide-doping-range ($8 \times 10^{17}$ to $4 10^{20}$ cm$^{-3}$ Hall electron density) low temperature specific heat measurements on single crystal SrTiO$_3$:Nb, correlated with electronic transport data and tight-binding modeling. Lattice dynamic contributions are shown be well understood, albeit unusual sensitivity doping, likely related the behavior of soft modes. Electronic provide effective masses that increase substantially, from $1.8$ $4.8 m_e$, across two SrTiO$_3$ Lifshitz...

The unusual temperature dependence of the resistivity and its in-plane anisotropy observed in Fe-based superconducting materials, particularly Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, has been a longstanding puzzle. Here we consider effect impurity scattering on average within simple two-band model dirty spin density wave metal. sharp drop below N\'eel $T_N$ parent compound can only be understood terms Lifshitz transition following Fermi surface reconstruction upon magnetic ordering. We show that...

We present a general study of the magnetic excitations within weak-coupling five-orbital model relevant to itinerant iron pnictides. As function enhanced electronic correlations, spin in symmetry-broken spin-density wave phase evolve from broad low-energy modes limit weak interactions sharply dispersing waves prevailing higher energies at larger interaction strengths. show how resulting response high depends qualitatively on magnitude interactions. also calculate nematic by including an...

The study of subtle effects on transport in semiconductors requires high-quality epitaxial structures with low defect density. Using hybrid molecular beam epitaxy (MBE), SrTiO3 films a low-temperature mobility exceeding 42,000 cm2 V-1 s-1 at carrier density 3 × 1017 cm-3 were achieved. A sudden and sharp decrease residual resistivity accompanied by an enhancement the superconducting transition temperature observed across second Lifshitz where third band becomes occupied, revealing dominant...

We investigate the properties of coexistence phase itinerant antiferromagnetism and nodal $d$-wave superconductivity (Q-phase) discovered in heavy fermion CeCoIn5 under applied magnetic field. solve minimal model that includes underlying correlations real space to elucidate structure $Q$-phase presence an externally further focus on role impurities, show they nucleate Q-phase at lower fields. Our most crucial finding is that, even zero field, dilute impurities cooperate via RKKY-like...

The understanding of the microscopic origin electron pairing in strongly correlated systems remains an ultimate goal field unconventional superconductivity. Detailed tunneling spectroscopy vortex core states can provide important insight to momentum structure superconducting order parameter, which is closely related nature pairing. authors performed a fully self-consistent real-space BdG study five-orbital models relevant Fe-based superconductors. was stabilized by spin fluctuation-derived...

Abstract Motivated by the discovery of superconductivity in KTaO 3 -based heterostructures, we study a pairing mechanism based on spin-orbit assisted coupling between conduction electrons and ferroelectric (FE) modes present material. We use ab initio frozen-phonon computations to show linear-in-momentum Rashba-like with strong angular dependence momentum for lower <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>j</mml:mi> <mml:mo>=</mml:mo>...

$^{75}\mathrm{As}$ nuclear magnetic (NMR) and quadrupolar (NQR) resonance were used, together with M\"ossbauer spectroscopy, to investigate the state induced by Mn for Fe substitutions in F-doped ${\mathrm{LaFe}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{AsO}$ superconductors. The results show that 0.5% of doping is enough suppress superconducting transition temperature ${T}_{c}$ from 27 K zero recover structure observed parent undoped LaFeAsO. Also tetragonal orthorhombic compound...

Flat monolayers of silver(II) fluoride, which could be obtained by epitaxial deposition on an appropriate substrate, have been recently predicted to exhibit very strong antiferro-magnetic superexchange and large potential for ambient pressure superconductivity if doped optimal level. It was shown that AgF2 become a magnetic glue-based superconductor with critical superconducting temperature approaching 200 K at optimum doping. In the current work we calculate doping correspond 14% holes per...