Transport properties of zinc-doped YBa2Cu3O7- delta thin films

Pseudogap formation due to charge-transfer transition and Kondo effect

We investigate the doping evolution of the electronic state of the three-bandt-J-Umodel considering the normal state of the hole-doped high-Tcsuperconducting cuprate. In our model, when some number of holes are doped into the undoped state, thedelectron exhibits the charge-transfer (CT)-type Mott-Hubbard transition along with a chemical potential jump. A reduced CT gap is formed from thepband and the coherent component of thedband, and it shrinks due to charge fluctuations as more holes are doped as in the pseudogap (PG) phenomenon. This trend is reinforced as thed-pband hybridization is increased, and a Fermi liquid state is retrieved as in the Kondo effect. These suggest that the PG in the hole-doped cuprate emerges due to the CT transition and the Kondo effect.

Mooij Law Violation from Nanoscale Disorder

Nanoscale inhomogeneity can profoundly impact properties of two-dimensional van der Waals materials. Here, we reveal how sulfur substitution on the selenium atomic sites in Fe_1-ySe_1-xS_x (0 ≤ x ≤ 1, y ≤ 0.1) causes Fe-Ch (Ch = Se, S) bond length differences and strong disorder for 0.4 ≤ x ≤ 0.8. There, the superconducting transition temperature T_c is suppressed and disorder-related scattering is enhanced. The high-temperature metallic resistivity in the presence of strong disorder exceeds the Mott limit and provides an example of the violation of Matthiessen's rule and the Mooij law, a dominant effect when adding moderate disorder past the Drude/Matthiessen's regime in all materials. The scattering mechanism responsible for the resistivity above the Mott limit is unrelated to phonons and arises for strong Se/S atom disorder in the tetrahedral surrounding of Fe. Our findings shed light on the intricate connection between the nanostructural details and the unconventional scattering mechanism, which is possibly related to charge-nematic or magnetic spin fluctuations.

Review of pseudogaps in strongly interacting Fermi gases

A central challenge in modern condensed matter physics is developing the tools for understanding nontrivial yet unordered states of matter. One important idea to emerge in this context is that of a 'pseudogap': the fact that under appropriate circumstances the normal state displays a suppression of the single particle spectral density near the Fermi level, reminiscent of the gaps seen in ordered states of matter. While these concepts arose in a solid state context, they are now being explored in cold gases. This article reviews the current experimental and theoretical understanding of the normal state of strongly interacting Fermi gases, with particular focus on the phenomonology which is traditionally associated with the pseudogap.

Charge order and resistivity transition of Zn-doped cuprate superconductors

Impurity doping using Zn atoms was largely studied in cuprates because this process substantially reduces the superconducting critical temperature T(c) without any effect on the pseudogap onset T*. Earlier theories missed the recently established ubiquitous presence of incommensurate charge modulations in these materials. The charge order is a consequence of a phase separation transition which we describe by a continuity equation of the local free energy density. The Zn atoms generate a local magnetic moment, freezing their neighbors' spins, slowing down the electronic segregation process. Then the Zn-doped properties are that of a granular superconductor whose size of the charge order modulations are dictated by the degree of phase separation.

In-plane magnetoresistance obeys Kohler's rule in the pseudogap phase of cuprate superconductors

We report in-plane resistivity (ρ) and transverse magnetoresistance (MR) measurements for underdoped HgBa(2)CuO(4+δ) (Hg1201). Contrary to the long-standing view that Kohler's rule is strongly violated in underdoped cuprates, we find that it is in fact satisfied in the pseudogap phase of Hg1201. The transverse MR shows a quadratic field dependence, δρ/ρ(0)=aH(2), with a(T)∝T(-4). In combination with the observed ρ∝T(2) dependence, this is consistent with a single Fermi-liquid quasiparticle scattering rate. We show that this behavior is typically masked in cuprates with lower structural symmetry or strong disorder effects.

Effect of irradiation-induced disorder on the conductivity and critical temperature of the organic superconductor kappa-(BEDT-TTF)2Cu(SCN)2

We have introduced defects into clean samples of the organic superconductor kappa-(BEDT-TTF)(2)Cu(SCN)(2) in order to determine their effect on the temperature dependence of the interlayer conductivity and the critical temperature T(c). We find a violation of Matthiessen's rule that can be explained by a model of involving a defect-assisted interlayer channel which acts in parallel with the bandlike conductivity. We observe an unusual dependence of T(c) on residual resistivity, inconsistent with the generalized Abrikosov-Gor'kov theory for an order parameter with a single component, providing an important constraint on models of the superconductivity in this material.

Nickel impurity-induced enhancement of the pseudogap of cuprate high-T(c) superconductors

The influence of magnetic Ni and nonmagnetic Zn impurities on the normal-state pseudogap (PG) in the c-axis optical conductivity of (Sm,Nd)Ba(2){Cu(1-y)(Ni,Zn)(y)}(3)O(7-delta) crystals was studied by spectral ellipsometry. We find that these impurities, which strongly suppress superconductivity, have a profoundly different impact on the PG. Zn gives rise to a gradual and inhomogeneous PG suppression while Ni strongly enhances the PG. Our results challenge theories that relate the PG either to precursor superconductivity or to other phases with exotic order parameters, such as flux phase or d-density wave states, that should be suppressed by potential scattering. The apparent difference between magnetic and nonmagnetic impurities instead points towards an important role of magnetic correlations in the PG state.