arXiv subjects

A. J. Schofield

Publications and source records attributed to A. J. Schofield.

46 records · Page 3Linked to original sources

arXiv2000

Measuring anisotropic scattering in the cuprates

A simple model of anisotropic scattering in a quasi two-dimensional metal is studied. Its simplicity allows an analytic calculation of transport properties using the Boltzmann equation and relaxation time approximation. We argue that the c-axis magnetoresistance provides the key test of this model of transport. We compare this model with experiments on overdoped Tl-2201 and find reasonable agreement using only weak scattering anisotropy. We argue that optimally doped Tl-2201 should show strong angular-dependent magnetoresistance within this model and would provide a robust way of determining the in-plane scattering anisotropy in the cuprates.

cond-mat.str-el↗

arXiv1999

Magnetotunneling as a Probe of Luttinger-Liquid Behavior

A novel method for detecting Luttinger-liquid behavior is proposed. The idea is to measure the tunneling conductance between a quantum wire and a parallel two-dimensional electron system as a function of both the potential difference between them, $V$, and an in-plane magnetic field, $B$. We show that the two-parameter dependence on $B$ and $V$ allows for a determination of the characteristic dependence on wave vector $q$ and frequency $ω$ of the {\it spectral function}, $A_{\rm LL}(q,ω)$, of the quantum wire. In particular, the separation of spin and charge in the Luttinger liquid should manifest itself as singularities in the $I$-$V$-characteristic. The experimental feasibility of the proposal is discussed.

cond-mat.str-el↗

arXiv1997

High field study of normal state magneto-transport in the thallium cuprate Tl-2201

We present a study of in-plane normal state magneto-transport in single crystal Tl-2201 in 60T pulsed magnetic fields. In optimally doped samples (Tc ~ 80K) the weak-magnetic-field regime extends to fields as high as 60T, but in overdoped samples (Tc ~ 30K) we are able to leave the weak field regime, as shown by the behavior of both the magnetoresistance and the Hall resistance. Data from samples of both dopings provide constraints on the class of model necessary to describe normal state transport in the cuprates.

cond-mat.str-el↗

arXiv1997

Two lifetimes in the thermopower of the cuprate metals

We study the temperature-dependence of thermoelectric transport in proton-irradiated thin films of the high Tc cuprate Tl2212. All the anomalous transport conductivities are affected by the irradiation but maintain their non-Fermi liquid forms. We note however that the anomalous temperature dependence of the thermopower scales precisely with the temperature dependent Hall coefficient. This provides strong evidence that the two relaxation rates observed to control magnetotransport are also responsible for the anomalous temperature dependence of the thermopower.

cond-mat.str-el↗

arXiv1996

How should we interpret the two transport relaxation times in the cuprates ?

We observe that the appearance of two transport relaxation times in the various transport coefficients of cuprate metals may be understood in terms of scattering processes that discriminate between currents that are even, or odd under the charge conjugation operator. We develop a transport equation that illustrates these ideas and discuss its experimental and theoretical consequences.

cond-mat↗

arXiv1996

Bosonization in the two-channel Kondo model

The bosonization of the $S=1/2$ anisotropic two-channel Kondo model is shown to yield two equivalent representations of the original problem. In a straight forward extension of the Emery-Kivelson approach, the interacting resonant level model previously derived by the Anderson-Yuval technique is obtained. In addition, however, a ``($σ$,$τ$)'' description is also found. The strong coupling fixed point of the ($σ$,$τ$) model was originally postulated to be related to the intermediate coupling fixed point of the two-channel Kondo model. The equivalence of the $σ$,$τ$ model to the two-channel Kondo model is formally established. A summary of what one may learn from a simple study of these different representations is also given.

cond-mat↗

arXiv1996

Phenomenological Transport Equation for the Cuprate Metals

cond-mat↗

arXiv1995

Simple description of the anisotropic two-channel Kondo problem

We adapt strong-coupling methods first used in the one-channel Kondo model to develop a simple description of the spin-$1\over 2$ two-channel Kondo model with channel anisotropy. Our method exploits spin-charge decoupling to develop a compactified Hamiltonian that describes the spin excitations. The structure of the fixed-point Hamiltonian and quasiparticle impurity S-matrix are incompatible with a Fermi liquid description.

cond-mat↗

arXiv1994

Upper critical field in the gauge model

An analysis of the upper critical field in the gauge model is presented. It is shown that a `strange metallic' normal state has implications for the pairing transition even if the resulting superconducting state is essentially conventional. The gauge model is considered as one example of an unconventional normal state and the optimally doped and overdoped cases are examined. In the optimally doped regime $B_{c2}$ rises linearly with decreasing temperature to an enhanced value at $T=0$ relative to BCS. In the overdoped regime the gauge model predicts Fermi-liquid behavior but there is a weakly temperature dependent interaction. This can give rise to some upward curvature of the upper critical field and an enhanced zero temperature value.

cond-mat↗

arXiv1992

Combination Rules, Charge Symmetry, and Hall Effect in Cuprates

The rule relating the observed Hall coefficient to the spin and charge responses of the uniform doped Mott insulator is derived. It is essential to include the contribution of holon and spinon three-current correlations to the effective action of the gauge field. In the vicinity of the Mott insulating point the Hall coefficient is holon dominated and weakly temperature dependent. In the vicinity of a point of charge conjugation symmetry the holon contribution to the observed Hall coefficient is small: the Hall coefficient follows the temperature dependence of the diamagnetic susceptibility with a sign determined by the Fermi surface shape. NOTE: document prepared using REVTEX. (3 Figs, not included, available on request from: ajs16@phx.cam.ac.uk)

cond-mat↗