arXiv subjects

Iddo Ussishkin

Publications and source records attributed to Iddo Ussishkin.

14 recordsLinked to original sources

arXiv2004

Signatures of spin-charge separation in scanning probe microscopy

We analyze the effect of an auxiliary scatterer, such as the potential of a scanning tip, on the conductance of an interacting one-dimensional electron system. We find that the differential conductance for tunneling into the end of a semi-infinite quantum wire reflects the separation of the elementary excitations into spin and charge modes. The separation is revealed as a specific pattern in the dependence of the conductance on bias and on the position of the scatterer.

cond-mat.mes-hall↗

arXiv2004

Critical scaling of thermal transport in model A dynamics for a superconductor

We consider the scaling of thermal transport in the presence of electric and magnetic fields near the finite temperature transition from the metallic normal state to the superconductor. We do so with fully relaxational, model A, dynamics for the order parameter and particle-hole symmetry. This enables us to determine the exact scaling dimension of the heat current operator and hence critical exponents for all transport coefficients in terms of the (approximately) known values of the correlation length exponent and the dynamic scaling exponent. In particular, we determine the critical behavior for the Nernst coefficient.

cond-mat.supr-con↗

arXiv2004

Nernst effect, quasiparticles, and d-density waves in cuprates

We examine the possibility that the large Nernst signal observed in the pseudogap regime of hole-doped cuprates originates from quasiparticle transport in a state with d-density wave (DDW) order, proposed by S. Chakravarty et al. [Phys. Rev. B 63, 094503 (2001)]. We find that the Nernst coefficient can be moderately enhanced in magnitude by DDW order, and is generally of negative sign. Thus, the quasiparticles of the DDW state cannot account for the large and positive Nernst signal observed in the pseudogap phase of the cuprates. However, the general considerations outlined in this paper may be of broader relevance, in particular to the recent measurements of Bel et al. in NbSe_2 and CeCoIn_5 [Phys. Rev. Lett. 91, 066602 (2003); ibid. 92, 217002 (2004)].

cond-mat.str-el↗

arXiv2004

On the interpretation of the Nernst effect measurements in the cuprates

We consider the large Nernst signal discovered by Ong and collaborators in hole-doped cuprates, in particular in the pseudogap regime. Based on our previous quantitative calculations together with Huse [Phys. Rev. Lett. 89, 287001 (2002)], we discuss the interpretation of the experimental observations as arising from superconducting fluctuations and its relation to the vortex scenario proposed by Ong. We also comment on the implications of the Nernst analysis for understanding the full range of pseudogap phenomena.

cond-mat.supr-con↗

arXiv2003

Gaussian superconducting fluctuations, thermal transport, and the Nernst effect

We calculate the contribution of superconducting fluctuations to thermal transport in the normal state, for low magnetic fields. We do so in the Gaussian approximation to their critical dynamics which is also the Aslamazov-Larkin approximation in the microscopics. Our results for the thermal conductivity tensor and the transverse thermoelectric response are new. The latter compare favorably with the data of Ong and collaborators on the Nernst effect in the cuprates.

cond-mat.supr-con↗

arXiv2002

Superconducting fluctuations and the Nernst effect: A diagrammatic approach

We calculate the contribution of superconducting fluctuations above the critical temperature $T_c$ to the transverse thermoelectric response $α_{xy}$, the quantity central to the analysis of the Nernst effect. The calculation is carried out within the microscopic picture of BCS, and to linear order in magnetic field. We find that as $T \to T_c$, the dominant contribution to $α_{xy}$ arises from the Aslamazov-Larkin diagrams, and is equal to the result previously obtained from a stochastic time-dependent Ginzburg-Landau equation [Ussishkin, Sondhi, and Huse, arXiv:cond-mat/0204484]. We present an argument which establishes this correspondence for the heat current. Other microscopic contributions, which generalize the Maki-Thompson and density of states terms for the conductivity, are less divergent as $T \to T_c$.

cond-mat.supr-con↗

arXiv2001

Two band transport and the question of a metal-insulator transition in GaAs/GaAlAs two dimensional holes

The magnetotransport of two dimensional holes in a GaAs/AlGaAs heterostructure is studied experimentally and theoretically. Spin-orbit splitting of the heavy hole band is manifested at high carrier densities in two Shubnikov-de Haas frequencies, classical positive magnetoresistance, and weak antilocalization. The latter effect combined with inelastic scattering between the spin-orbit split bands lead to metallic characteristics, namely resistance increase with temperature. At lower densities, when splitting is smaller than the inverse elastic scattering time, the two bands effectively merge to yield the expected insulating characteristics and negative magnetoresistance due to weak localization and interaction corrections to the conductivity. The "metal to insulator" transition at intermediate densities is found to be a smooth crossover between the two regimes rather than a quantum phase transition. Two band calculations of conventional interference and interaction effects account well for the data in the whole parameter range.

cond-mat.mes-hall↗

arXiv1998

Coulomb drag at ν= 1/2: Composite fermion pairing fluctuations

We consider the Coulomb drag between two two-dimensional electron layers at filling factor ν= 1/2 each, using a strong coupling approach within the composite fermion picture. Due to an attractive interlayer interaction, composite fermions are expected to form a paired state below a critical temperature T_c. We find that above T_c pairing fluctuations make the longitudinal transresistivity ρ_D increase with decreasing temperature. The pairing mechanism we study is very sensitive to density variations in the two layers, and to an applied current. We discuss possible relation to an experiment by Lilly et al. [Phys. Rev. Lett. 80, 1714 (1998)].

cond-mat.mes-hall↗

arXiv1997

Coulomb drag in the quantum Hall $ν= 1/2$ state: Role of disorder

We consider Coulomb drag between two layers of two-dimensional electron gases subject to a strong magnetic field, with the Landau level filling factor in each layer being 1/2. We find $ρ_D$ to be very large, as compared to the zero magnetic field case. We attribute this enhancement to the slow decay of density fluctuations in a strong magnetic field. For a clean system, the linear $q$-dependence of the longitudinal conductivity, characteristic of the $ν=1/2$ state, leads a unique temperature dependence---$\rd \propto T^{4/3}$. Within a semiclassical approximation, disorder leads to a decrease of the transresistivity as compared with the clean case, and a temperature dependence of $T^2\log T$ at low temperatures.

cond-mat.mes-hall↗

arXiv1997

Coulomb drag in compressible quantum Hall states

We consider the Coulomb drag between two layers of two-dimensional electronic gases subject to a strong magnetic field. We first focus on the case in which the electronic density is such that the Landau level filling fraction $ν$ in each layer is at, or close to, $ν=1/2$. Discussing the coupling between the layers in purely electronic terms, we show that the unique dependence of the longitudinal conductivity on wave-vector, observed in surface acoustic waves experiments, leads to a very slow decay of density fluctuations. Consequently, it has a crucial effect on the Coulomb drag, as manifested in the transresistivity $ρ_D$. We find that the transresistivity is very large compared to its typical values at zero magnetic field, and that its temperature dependence is unique -- $ρ_D \propto T^{4/3}$. For filling factors at or close to $1/4$ and $3/4$ the transresistivity has the same $T$-dependence, and is larger than at $ν= 1/2$. We calculate $ρ_D$ for the $ν=3/2$ case and propose that it might shed light on the spin polarization of electrons at $ν=3/2$. We compare our results to recent calculations of $ρ_D$ at $ν=1/2$ where a composite fermion approach was used and a $T^{4/3}$-dependence was obtained. We conclude that what appears in the composite fermion language to be drag induced by Chern-Simons interaction is, physically, electronic Coulomb drag.

cond-mat.mes-hall↗

arXiv1996

Penumbra diffraction in the quantization of concave billiards

The semiclassical description of billiard spectra is extended to include the diffractive contributions from orbits which are nearly tangent to a concave part of the boundary. The leading correction for an unstable isolated orbit is of the same order as the standard Gutzwiller expression itself. The importance of the diffraction corrections is further emphasized by an estimate which shows that for any large fixed k almost all contributing periodic orbits are affected. The theory is tested numerically using the annulus and the Sinai billiard. For the Sinai billiard the investigation of the spectral density is complemented by an analysis which is based on the scattering approach to quantization. The merits of this approach as a tool to investigate refined semiclassical theories are discussed and demonstrated.

chao-dyn↗

arXiv1995

The Role of Diffraction in the Quantization of Dispersing Billiards

We study diffraction corrections to the semiclassical spectral density of dispersing (Sinai) billiards. They modify the contributions of periodic orbits (PO's), with at least one segment which is almost tangent to the concave part of the boundary. Given a wavenumber $k$, all the PO's with length up to the Heisenberg length $O(k)$ are required for quantization. We show that most of the contributions of PO's which are longer than a limit $O(k^{2/3})$ must be corrected for diffraction effects. For orbits which just miss tangency, the corrections are of the same magnitude as the semiclassical contributions themselves. Orbits which bounce at extreme forward angles give very small terms in the standard semiclassical theory. The diffraction corrections increase their amplitude substantially.

chao-dyn↗

arXiv1995

Semiclassical Quantization of Billiards with Mixed Boundary Conditions

The semiclassical theory for billiards with mixed boundary conditions is developed and explicit expressions for the smooth and the oscillatory parts of the spectral density are derived. The parametric dependence of the spectrum on the boundary condition is shown to be a very useful diagnostic tool in the semiclassical analysis of the spectrum of billiards. It is also used to check in detail some recently proposed parametric spectral statistics. The methods are illustrated in the analysis of the spectrum of the Sinai billiard and its parametric dependence on the boundary condition on the dispersing arc.

chao-dyn↗

arXiv1995

Inside-Outside Duality for Planar Billiards -- A Numerical Study

This paper reports the results of extensive numerical studies related to spectral properties of the Laplacian and the scattering matrix for planar domains (called billiards). There is a close connection between eigenvalues of the billiard Laplacian and the scattering phases, basically that every energy at which a scattering phase is $2π$ corresponds to an eigenenergy of the Laplacian. Interesting phenomena appear when the shape of the domain does not allow an extension of the eigenfunction to the exterior. In this paper these phenomena are studied and illustrated from several points of view.

chao-dyn↗