The Drude-Smith model has been used extensively in fitting the THz conductivities of nanomaterials with carrier confinement on mesoscopic scale. Here, we show that conventional 'backscattering' explanation for suppression low-frequency is not consistent a confined Drude gas classical non-interacting electrons and derive modified conductivity formula based diffusive restoring current. We perform Monte Carlo simulations system reproduces extracted without free parameters. This alternate route...

The electron Green's function in the superconducting state can be solved either at discrete Matsubara frequencies along imaginary axis, or as a of continuous variable real frequency axis. former is considerably more convenient to calculate than latter. We derive formally exact analytic continuation imaginary-axis solutions procedure applicable general problems involving functions. apply our method calculating tunneling density states for lead.

We study within BCS theory the properties of an effective Hamiltonian to describe conduction by holes through oxygen anion network. The contains on-site repulsive interaction ${U}_{p}$ and a modulated hopping $\ensuremath{\Delta}t$ that yields larger amplitude between sites when other are present on those sites. superconducting state is found be $s$ wave with energy-dependent gap. Superconductivity restricted low hole densities critical temperature increases amplitude. particular form allows...

We discuss predictions of the hole-pairing mechanism superconductivity for various experimentally measurable properties high-${\mathit{T}}_{\mathit{c}}$ oxides. The model considered describes conduction by holes through oxygen anion network in oxides, and pairing originates a term Hamiltonian describing an enhanced hopping amplitude hole presence other holes. includes on-site nearest-neighbor Coulomb repulsions different amplitudes within between planes. use information from experiments to...

Over the past six years, superconductivity at high temperatures has been reported in a variety of hydrogen-rich compounds under pressure. That temperature should exist these materials is expected according to conventional theory superconductivity, as shown by detailed calculations. However, here we argue that experimental observations rule out materials. Our results indicate either are unconventional superconductors novel kind, which term ``nonstandard superconductors,'' or alternatively,...

We have calculated simple approximate expressions for the normalized specific-heat difference between superconducting (S) and normal (N) states at below ${T}_{c}$ ratio \ensuremath{\gamma}${T}_{c}^{2}$/${H}_{c}^{2}$(0), using a square-well model gap. While our approach is very different, formulas obtained same general form as those that already appeared in literature. Each contains two parameters, which we determine through phenomenological fit to exact numerical results from Eliashberg...

We critique a Pad\'e analytic continuation method whereby rational polynomial function is fit to set of input points by means single matrix inversion. This procedure accomplished an extremely high accuracy using symbolic computation algorithm. As example this in action, it applied the problem determining spectral single-particle thermal Green's known only at finite number Matsubara frequencies with two self energies drawn from T-matrix theory Hubbard model. present systematic analysis...

In this Letter we show how, for small values of the Fermi energy compared to spin-orbit splitting Rashba type, a topological change surface leads an effective reduction dimensionality in electronic density states low charge regime. We investigate its consequences on onset superconducting instability. that critical temperature is significantly tuned regime by coupling. suggest materials with strong coupling are good candidates enhanced superconductivity.

The combination of spin-orbit coupling with interactions results in many exotic phases matter. In this Letter, we investigate the superconducting pairing instability two-dimensional extended Hubbard model both Rashba and Dresselhaus within mean-field level at zero finite temperature. We find that first- second-order time-reversal symmetry breaking topological gapped can be achieved under appropriate parameters temperature regimes due to presence a favored even-parity $s+id$-wave even absence...

The spectral function of a single hole moving in two-dimensional antiferromagnetic background is calculated, using the self-consistent Born approximation for self-energy. For small systems, good agreement found with results exact diagonalization studies. In thermodynamic limit, quasiparticle residue, effective mass, and incoherent multiple spin-wave are determined as functions ratio Heisenberg exchange J hopping amplitude t. relevance single-hole to physical problem finite concentration...

We study the two-dimensional Holstein model at half-filling for small systems using quantum Monte Carlo methods and through diagrammatic perturbation techniques in Migdal-Eliashberg approximation. It is found that latter approximation very accurate as long phonon self-energy taken into account a self-consistent way. Vertex corrections are not required.

It was recently pointed out that so-called "superhydrides", hydrogen-rich materials appear to become superconducting at high temperatures and pressures, exhibit physical properties are different from both conventional unconventional standard type I II superconductors [1,2]. Here we consider magnetic field expulsion in the first material this class discovered 2015, sulfur hydride [3]. A nuclear resonant scattering experiment has been interpreted as demonstration Meissner effect takes place...

It has been claimed that measurements of trapped magnetic flux in hydrides under pressure provide evidence for superconductivity these materials (Minkov et al., 2022; Minkov 2023). In recent work we have questioned claim (Hirsch and Marsiglio, 2022). Here point out experiments (Bud'ko 2023) further supporting our questioning claim. We also present calculations a thin disk compare with those previously calculated long cylinder. The results are qualitatively similar, therefore reinforce...

The role of the Cu ${\mathit{d}}_{\mathit{x}}^{2}$-${\mathit{y}}^{2}$ orbitals in theory hole superconductivity oxides is considered. We use a two-band model type introduced by Suhl et al., describing purely oxygen band coupled to copper-oxygen band. pure O nearly full, and Cu-O half-filled parameter range interest. It found that many features single-band hole-pairing description survive generalization model. new feature present existence second, smaller, superconducting gap associated with...

Structural phase transitions and superconducting properties in three phases ($9R$, fcc, $cI16$) of solid Li are investigated using a pseudopotential plane-wave method based on density functional perturbation theory. In particular, it is shown that phonon softening responsible for pressure-induced $\text{fcc}\ensuremath{\rightarrow}cI16$ transition as well significant enhancement electron-phonon coupling temperature ${T}_{c}$ preceding this structural transformation. The nature...

The double-well potential is arguably one of the most important potentials in quantum mechanics, because solution contains notion a state as linear superposition 'classical' states, concept which has become very information theory. It therefore desirable to have solutions simple that are accessible undergraduate student. We describe method for obtaining numerically exact eigenenergies and eigenstates such model, along with energies obtained through Wentzel–Kramers–Brillouin (WKB)...

In a recent experiment [M. Feld et al., Nature (London) 480, 75 (2011); B. Fr\"ohlich Phys. Rev. Lett. 109, 130403 (2012)], pairing gap was detected in two-dimensional (2D) Fermi gas with attractive interaction at temperatures where superfluidity does not occur. The question remains open as to whether this is pseudogap phenomenon or due molecular state. paper, by using $t\ensuremath{-}\text{matrix}$ approach, we reproduce quite well the experimental data for 2D gas, and set boundary between...