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EXCHANGE INTERACTION BETWEEN CONDUCTION ELECTRONS AND MAGNETIC SHELL ELECTRONS IN RARE-EARTH METALS

Description: The interaction Hamiltonian for the Coulomb exchange effect between conduction electrons and magnetic-shell electrons in rare-earth metals was derived from first principles. The approximations under which the interaction can be represented by the product of electron and ion spin vectors are exhibited. (auth)
Date: January 15, 1961
Creator: Liu, S.H.
Partner: UNT Libraries Government Documents Department

Simple model of the anisotropic penetration depth in high T{sub c} superconductors

Description: We present a simple model of some high {Tc} cuprates based upon superconducting (S) and normal (N) layers, which quantitatively fits the data of Bonn et al. for the low-temperature T dependence of the penetration depths {lambda}{sub a,b,c} in untwinned YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}, assuming s-wave intralyer pairing. This SN model also leads to anisotropic surface states, which complicate analysis of photoemission and tunneling measurements.
Date: April 1, 1996
Creator: Klemm, R.A. & Liu, S.H.
Partner: UNT Libraries Government Documents Department

Energy gap structure and tunneling characteristics of layered superconductors

Description: The authors have analyzed the energy gaps and density-of-states (DOS) of layered superconductors with two inequivalent layers in a unit cell along the c-axis. In the physically interesting parameter range where the interlayer hopping strengths of the quasiparticles are comparable to the critical temperature, the peaks in the DOS curve do not correspond to the order parameters (OP`s) of each layer, but depend on the OP`s and the interlayer hopping strengths in a complex manner. In contrast to a BCS superconductor, the DOS of layered systems have logarithmic singularities. The simulated tunneling characteristics bear close resemblance to experimental results.
Date: June 1, 1993
Creator: Liu, S.H. & Klemm, R.A.
Partner: UNT Libraries Government Documents Department

Spin and charge dynamics of chromium alloys

Description: Both the spin- and charge-density waves of Cr alloys are produced by the Coulomb attraction between electrons and holes on nearly nested Fermi surfaces. Driven by quasi-particle transitions, transverse spin- wave and longitudinal phason modes are associated with rotational and translational symmetries of pure Cr and its dilute alloys. At low frequencies, both spin and charge phasons have a nearly linear dispersion with a mode velocity which approaches the spin-wave velocity as T approaches T{sub N} or as the mismatch between the Fermi surfaces increases.
Date: July 1, 1996
Creator: Fishman, R.S.; Viswanath, V.S. & Liu, S.H.
Partner: UNT Libraries Government Documents Department

Surface state and normal layer effects

Description: In addition to the conducting CuO{sub 2} (S) layers, most high-T{sub c} superconductors also contain other conducting (N) layers, which are only superconducting due to the proximity effect. The combination of S and N layers can give rise to complicated electronic densities of states, leading to quasilinear penetration depth and NMR relaxation rate behavior at low temperatures. Surface states can also complicate the analysis of tunneling and, photoemission measurements. Moreover, geometrical considerations and in homogeneously trapped flux axe possible explanations of the paramagnetic Meissner effect and of corner and ring SQUID experiments. Hence, all of the above experiments could be consistent with isotropic s-wave superconductivity within the S layers.
Date: August 1, 1995
Creator: Klemm, R.A.; Ledvij, M. & Liu, S.H.
Partner: UNT Libraries Government Documents Department

Comment on {open_quotes}superfluid anisotropy in YBCO: Evidence for pair tunneling superconductivity{close_quotes}

Description: Recently, Xiang and Wheatley extended our proximity coupling SN model of the (S) CuO{sub 2} plane and (N) CuO chain layers in YBCO compounds, using the single particle bands {epsilon}{sup 0}{sub 1k} = -t(cos k{sub a} + cos k{sub b}) - {mu}{sub 1} and {epsilon}{sup 0}{sub 2k} = -t{sub 2y}cos k{sub b} - {mu}{sub 2}, respectively. Although we showed that it was possible to fit the penetration depth {lambda}{sub ab}(T) in twinned YBCO with either s- or d-wave pairing and both bands free-particle-like, they claimed that: (1) It is impossible to fit the quasi-linear {lambda}{sub a}(T) in untwinned YBCO without order parameter line nodes, such as for d{sub x2-y2} pairing. (2) Even d-wave SN fits to the {lambda}{sub a,b,c} data are inferior to those obtained from a model of d-wave interlayer pair tunneling (DIPT). We remark that their claim is false, and ignores other data favoring proximity coupling.
Date: January 17, 1996
Creator: Klemm, R.A.; Ledvij, M. & Liu, S.H.
Partner: UNT Libraries Government Documents Department