Tineke Thio

Bio: Tineke Thio is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Electrical resistivity and conductivity & Conductivity. The author has an hindex of 10, co-authored 12 publications receiving 888 citations.

Antisymmetric exchange and its influence on the magnetic structure and conductivity of La 2 Cu O 4

Abstract: Measurements of the magnetic moment of antiferromagnetic ${\mathrm{La}}_{2}$Cu${\mathrm{O}}_{4}$ at high fields reveal a new phase boundary originating from a previously undetected canting of the ${\mathrm{Cu}}^{2+}$ spins out of the Cu${\mathrm{O}}_{2}$ planes. This canting, together with the exponential temperature dependence of the two-dimensional correlation length, accounts quantitatively for the susceptibility peak at the N\'eel temperature. Enhancement of the conductivity in the ferromagnetic phase demonstrates a strong connection between the magnetism and charge transport.

Soft-phonon behavior and transport in single-crystal La 2 CuO 4

Abstract: Using a flux technique we have grown sizable single crystals of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_{4}$. With x rays and neutrons we have studied both the static and dynamic aspects of the tetragonal to orthorhombic structural phase transition; classic soft-phonon behavior is observed at the ((1/2, 1) / 2 , 0) zone boundary involving rotations of ${\mathrm{CuO}}_{6}$ octahedra. The pure and lightly-doped single crystals show hopping conductivity, ln\ensuremath{\rho}\ensuremath{\sim}(${T}_{0}$/T${)}^{1/4}$, indicating that the electronic states at the Fermi energy are localized.

Resistivity of nonmetallic La2-ySryCu1-xLixO4- delta single crystals and ceramics.

Abstract: The resistivity of nonmetallic La/sub 2-//sub y/Sr/sub y/Cu/sub 1-//sub x/Li/sub x/O/sub 4-//sub delta/ single crystals and ceramics accurately follows the functional form exp((T/sub 0//T)/sup 1/4/), characteristic of variable-range hopping. For each of the crystals grown from Li-containing flux and CuO flux, pure reduced ceramics, and ceramics containing 0.025 to 0.2 mol % Li, the values of T/sub 0/ are in the range 0.3--7 x 10/sup 6/ K. The hopping conductivity shows that the crystals, which also manifest the two-dimensional quantum spin fluid state, antiferromagnetism, and the tetragonal-to-orthorhombic transition, are nonmetallic because the electronic states at the Fermi energy are localized. No evidence of a large gap is observed, and all samples, including the reduced ceramic, are p type, leading to the suggestion that in the nonmetallic state as well as the superconductor, the Fermi energy lies near the top of the band of singly occupied states (lower Hubbard band). The suppression of superconductivity by Li impurities is discussed.

Frequency and magnetic-field dependence of the dielectric constant and conductivity of La 2 CuO 4 + y

Abstract: Detailed measurements are reported of the conductivity and dielectric constant at frequencies up to 20 MHz for single crystals of ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4+\mathit{y}}$, with y varied in the range 0.001--0.01. The hole concentration is determined for each y by Hall measurements. The conductivity shows a power-law dependence on frequency (${\mathrm{\ensuremath{\omega}}}^{\mathit{s}}$), which is typical of thermally assisted tunneling between localized states. The exponent s1 decreases with increasing temperature and increasing oxygen content. The dielectric constant decreases with increasing frequency at low frequency with the power law ${\mathrm{\ensuremath{\omega}}}^{\mathit{s}\mathrm{\ensuremath{-}}1}$, showing that it is dominated by the same hopping mechanism. At high frequency the dielectric constant saturates and, for the electric field parallel to the ${\mathrm{CuO}}_{2}$ layers, the saturation value increases with oxygen content. From the polarizability at low acceptor concentration the radius of the bound hole is found to be \ensuremath{\sim}8 \AA{}, a value that is consistent with a simple hydrogenic model of the impurity state. The small binding energy of the hole to the impurity, 35 meV as determined from Hall measurements, together with this radius of 8 \AA{}, requires that the mass of the hole be fairly small, \ensuremath{\sim}2${\mathit{m}}_{\mathit{e}}$. The growth of the localization length with hole density is almost purely two dimensional, implying that there is no true insulator-to-metal transition, but rather a crossover from strong to weak localization. From studies of the magnetic-field dependence of the frequency-dependent conductivity and dielectric constant one finds new evidence for the strong coupling of the excess holes to the antiferromagnetically ordered Cu spins.

Magnetoresistance and the spin-flop transition in single-crystal La 2 CuO 4 + y

Abstract: Measurements are reported of the magnetoresistance (MR) for fields up to 23 T in ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ single crystals, which order antiferromagnetically at ${T}_{N}$\ensuremath{\sim}240 K, and in which the conductivity at low temperature is characterized by hopping in localized states. Using the MR, the phase diagram of the spin-flop transition, observed when the magnetic field is applied parallel to the zero-field staggered magnetization, is mapped out. Two transitions of the background ${\mathrm{Cu}}^{2+}$ spins are observed, which are governed by the symmetric and antisymmetric anisotropic components of the superexchange tensor. The antiferromagnetic propagation vector changes from \ensuremath{\tau}\ensuremath{\parallel}a at zero field to \ensuremath{\tau}\ensuremath{\parallel}c at the highest fields. This subtle change in the ordering of the ${\mathrm{Cu}}^{2+}$ spins is accompanied by a large enhancement of the interlayer hopping conductivity up to a factor 2. We show that the magnetoconductance is proportional to the three-dimensional staggered moment with \ensuremath{\tau}\ensuremath{\parallel}c direction. In an appendix we discuss the possible relevance of these results to the behavior of superconducting ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$(Sr,Ba${)}_{\mathrm{x}}$${\mathrm{CuO}}_{4}$.

Localization: theory and experiment

Abstract: The transport properties of disordered solids have been the subject of much work since at least the 1950s, but with a new burst of activity during the 1980s which has survived up to the present day. There have been numerous reviews of a more or less specialized nature. The present review aims to fill the niche for a non-specialized review of this very active area of research. The basic concepts behind the theory are introduced with more detailed sections covering experimental results, one-dimensional localization, scaling theory, weak localization, magnetic field effects and fluctuations.

Electronic structure of the high-temperature oxide superconductors

Abstract: Since the discovery of superconductivity above 30 K by Bednorz and M\"uller in the La copper oxide system, the critical temperature has been raised to 90 K in Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and to 110 and 125 K in Bi-based and Tl-based copper oxides, respectively. In the two years since this Nobel-prize-winning discovery, a large number of electronic structure calculations have been carried out as a first step in understanding the electronic properties of these materials. In this paper these calculations (mostly of the density-functional type) are gathered and reviewed, and their results are compared with the relevant experimental data. The picture that emerges is one in which the important electronic states are dominated by the copper $d$ and oxygen $p$ orbitals, with strong hybridization between them. Photon, electron, and positron spectroscopies provide important information about the electronic states, and comparison with electronic structure calculations indicates that, while many features can be interpreted in terms of existing calculations, self-energy corrections ("correlations") are important for a more detailed understanding. The antiferromagnetism that occurs in some regions of the phase diagram poses a particularly challenging problem for any detailed theory. The study of structural stability, lattice dynamics, and electron-phonon coupling in the copper oxides is also discussed. Finally, a brief review is given of the attempts so far to identify interaction constants appropriate for a model Hamiltonian treatment of many-body interactions in these materials.

Chemistry of High-Temperature Superconductors

Abstract: Spectacular advances in superconductors have taken place in the past two years. The upper temperature for superconductivity has risen from 23 K to 122 K, and there is reason to believe that the ascent is still ongoing. The materials causing this excitement are oxides. Those oxides that superconduct at the highest temperatures contain copper-oxygen sheets; however, other elements such as bismuth and thallium play a key role in this new class of superconductors. These superconductors are attracting attention because of the possibility of a wide range of applications and because the science is fascinating. A material that passes an electrical current with virtually no loss is more remarkable when this occurs at 120 K instead of 20 K.

High-temperature interface superconductivity between metallic and insulating copper oxides

Abstract: The realization of high-transition-temperature (high-T(c)) superconductivity confined to nanometre-sized interfaces has been a long-standing goal because of potential applications and the opportunity to study quantum phenomena in reduced dimensions. This has been, however, a challenging target: in conventional metals, the high electron density restricts interface effects (such as carrier depletion or accumulation) to a region much narrower than the coherence length, which is the scale necessary for superconductivity to occur. By contrast, in copper oxides the carrier density is low whereas T(c) is high and the coherence length very short, which provides an opportunity-but at a price: the interface must be atomically perfect. Here we report superconductivity in bilayers consisting of an insulator (La(2)CuO(4)) and a metal (La(1.55)Sr(0.45)CuO(4)), neither of which is superconducting in isolation. In these bilayers, T(c) is either approximately 15 K or approximately 30 K, depending on the layering sequence. This highly robust phenomenon is confined within 2-3 nm of the interface. If such a bilayer is exposed to ozone, T(c) exceeds 50 K, and this enhanced superconductivity is also shown to originate from an interface layer about 1-2 unit cells thick. Enhancement of T(c) in bilayer systems was observed previously but the essential role of the interface was not recognized at the time.

Lattice symmetry breaking in cuprate superconductors: stripes, nematics, and superconductivity

Abstract: This article gives an overview of both theoretical and experimental developments concerning states with lattice symmetry breaking in the cuprate high-temperature superconductors. Recent experiments have provided evidence for states with broken rotation as well as translation symmetry, and will be discussed in terms of nematic and stripe physics. Of particular importance here are results obtained using the techniques of neutron and X-ray scattering and scanning tunnelling spectroscopy. Ideas on the origin of lattice-symmetry-broken states will be reviewed, and effective models accounting for various experimentally observed phenomena will be summarized. These include both weak-coupling and strong-coupling approaches, with a discussion of their distinctions and connections. The collected experimental data indicate that the tendency toward uni-directional stripe-like ordering is common to underdoped cuprates, but becomes weaker with increasing number of adjacent CuO2 layers.