Spin paramagnetism in d-wave superconductors

The Ginzburg-Landau equations are derived from the microscopic theory for clean layered superconductors with $d_{x^2-y^2}$ pairing symmetry, including the Pauli paramagnetism effect. The upper critical field $H_{c2}$ parallel to the $c$ axis is calculated. A comparison with the experimental data for YBCO suggests that, relative to the orbital effect, the Pauli paramagnetism contribution to $H_{c2}$ is significant. The reversible magnetization $M$ in high magnetic fields is also calculated, showing strong temperature dependence of the slope $dM/dH$, as a consequence of the spin paramagnetism. A simple expression for the high temperature spin susceptibility is derived, in a good agreement with the Knight shift measurements on YBCO.Comment: 8 pages, 3 figures; minor changes are included; reference 35 is added; shorter version will be published in Phys. Rev. B, scheduled issue 01 July 200

Quantum Critical Transport Near the Mott Transition

We perform a systematic study of incoherent transport in the high temperature crossover region of the half-filled one-band Hubbard model. We demonstrate that the family of resistivity curves displays characteristic quantum critical scaling of the form $\rho(\delta U,T)=\rho_{c}(T)f(T/T_{o}(\delta U))$, with $T_{o}(\delta U)\sim\delta U^{z\nu}$, and $\rho_{c}(T)\sim T$. The corresponding $\beta$-function displays a "strong coupling" form $\beta\sim\ln(\rho_{c}/\rho)$, reflecting the peculiar mirror symmetry of the scaling curves. This behavior, which is surprisingly similar to some experimental findings, indicates that Mott quantum criticality may be acting as the fundamental mechanism behind the unusual transport phenomena in many systems near the metal-insulator transition.Comment: Published version; 4+epsilon pages, 4 figure

Phase diagram, energy scales and nonlocal correlations in the Anderson lattice model

We study the Anderson lattice model with one f-orbital per lattice site as the simplest model which describes generic features of heavy fermion materials. The resistivity and magnetic susceptibility results obtained within dynamical mean field theory (DMFT) for a nearly half-filled conduction band show the existence of a single energy scale $T^*$ which is similar to the single ion Kondo temperature $T_K^o$. To determine the importance of inter-site correlations, we have also solved the model within cellular DMFT (CDMFT) with two sites in a unit cell. The antiferromagnetic region on the phase diagram is much narrower than in the single-site solution, having a smaller critical hybridization $V_c$ and N\'eel temperature $T_N$. At temperatures above $T_N$ the nonlocal correlations are small, and the DMFT paramagnetic solution is in this case practically exact, which justifies the ab initio LDA+DMFT approach in theoretical studies of heavy fermions. Strong inter-site correlations in the CDMFT solution for $T<T_N$, however, indicate that they have to be properly treated in order to unravel the physical properties near the quantum critical point.Comment: 10 page

Wigner-Mott scaling of transport near the two-dimensional metal-insulator transition

Electron-electron scattering usually dominates the transport in strongly correlated materials. It typically leads to pronounced resistivity maxima in the incoherent regime around the coherence temperature $T^{*}$, reflecting the tendency of carriers to undergo Mott localization following the demise of the Fermi liquid. This behavior is best pronounced in the vicinity of interaction-driven (Mott-like) metal-insulator transitions, where the $T^{*}$ decreases, while the resistivity maximum $\rho_{max}$ increases. Here we show that, in this regime, the entire family of resistivity curves displays a characteristic scaling behavior $\rho(T)/\rho_{max}\approx F(T/T_{max}),$ while the $\rho_{max}$ and $T_{max}\sim T^{*}$ assume a powerlaw dependence on the quasi-particle effective mass $m^{*}$. Remarkably, precisely such trends are found from an appropriate scaling analysis of experimental data obtained from diluted two-dimensional electron gases in zero magnetic fields. Our analysis provides strong evidence that inelastic electron-electron scattering -- and not disorder effects -- dominates finite temperature transport in these systems, validating the Wigner-Mott picture of the two-dimensional metal-insulator transition.Comment: 7 page

Experimental research of the tube absorbers of kinetic energy during collision

Razvoj elemenata za apsorbciju energije sudara je sastavni deo pasivne zaštite putničkih vagona. Pasivna zaštita ima zadatak da posledice sudara svede na minimum. Apsorber prikazan u radu napravljen je od standardne bešavne cevi u kvalitetu P235T1 i konusnog prstena kvaliteta C45E. Predstavljeno rešenje se zasniva na korišćenju specijalnih elemenata koji apsorbuju određenu količinu kinetičke energije sudara putem kontrolisane plastične deformacije, čime se značajno smanjuje deo energije koji se prenosi na noseću strukturu vozila. Pri sudaru dolazi do sabijanja-provlačenja cevi kroz konusni prsten. Težište rada je na eksperimentalnim istraživanjima radi određivanja stvarnih karakteristika apsorbera ovog tipa. Na osnovu analize dobijenih rezultata ispitivanja, predloženo je konačno konstruktivno rešenje apsorbera, kao elementa buduće konstrukcije čeonog dela postolja vagona.Development of collision energy absorbing elements is a constituent part of passive protection of passenger coaches. The target of passive protection is to minimize the collision consequences. The absorber, described in this paper, is constructed from a standard seamless tube of the quality P235T1 and conical ring of the quality C45E. The solution presented is based on the application of special elements that absorb a certain amount of collision kinetic energy by means of controlled plastic deformation, significantly decreasing the part of the energy which is transferred to the vehicle bearing structure. The tube is compressed - pushed through the conical ring in collision. The paper focuses on the quasi-static and dynamics experimental research. Based on the analysis of the results obtained in the research, a final design of the absorber is suggested as a part of the future front part of vehicle bearing structure

Effective model of the electronic Griffiths phase

We present simple analytical arguments explaining the universal emergence of electronic Griffiths phases as precursors of disorder-driven metal-insulator transitions in correlated electronic systems. A simple effective model is constructed and solved within Dynamical Mean Field Theory. It is shown to capture all the qualitative and even quantitative aspects of such Griffiths phases.Comment: 9 pages, 7 figures, one reference corrected; minor corrections include

Experimental research of the tube absorbers of kinetic energy during collision

Razvoj elemenata za apsorbciju energije sudara je sastavni deo pasivne zaštite putničkih vagona. Pasivna zaštita ima zadatak da posledice sudara svede na minimum. Apsorber prikazan u radu napravljen je od standardne bešavne cevi u kvalitetu P235T1 i konusnog prstena kvaliteta C45E. Predstavljeno rešenje se zasniva na korišćenju specijalnih elemenata koji apsorbuju određenu količinu kinetičke energije sudara putem kontrolisane plastične deformacije, čime se značajno smanjuje deo energije koji se prenosi na noseću strukturu vozila. Pri sudaru dolazi do sabijanja-provlačenja cevi kroz konusni prsten. Težište rada je na eksperimentalnim istraživanjima radi određivanja stvarnih karakteristika apsorbera ovog tipa. Na osnovu analize dobijenih rezultata ispitivanja, predloženo je konačno konstruktivno rešenje apsorbera, kao elementa buduće konstrukcije čeonog dela postolja vagona.Development of collision energy absorbing elements is a constituent part of passive protection of passenger coaches. The target of passive protection is to minimize the collision consequences. The absorber, described in this paper, is constructed from a standard seamless tube of the quality P235T1 and conical ring of the quality C45E. The solution presented is based on the application of special elements that absorb a certain amount of collision kinetic energy by means of controlled plastic deformation, significantly decreasing the part of the energy which is transferred to the vehicle bearing structure. The tube is compressed - pushed through the conical ring in collision. The paper focuses on the quasi-static and dynamics experimental research. Based on the analysis of the results obtained in the research, a final design of the absorber is suggested as a part of the future front part of vehicle bearing structure