ABSTRACT
Charge density waves (CDWs) in the second and third Landau levels (LLs) are investigated by both nonlinear electronic transport and noise. The use of a Corbino geometry ensures that only bulk properties are probed, with no contribution from edge states. Sliding transport of CDWs is revealed by narrow band noise in reentrant quantum Hall states R2a and R2c of the second LL, as well as in pinned CDWs of the third LL. Competition between various phases-stripe, pinned CDW, or fractional quantum Hall liquid-in both LLs are clearly revealed by combining noise data with maps of conductivity versus magnetic field and bias voltage.
ABSTRACT
Removing electrons from the CuO2 plane of cuprates alters the electronic correlations sufficiently to produce high-temperature superconductivity. Associated with these changes are spectral-weight transfers from the high-energy states of the insulator to low energies. In theory, these should be detectable as an imbalance between the tunneling rate for electron injection and extraction-a tunneling asymmetry. We introduce atomic-resolution tunneling-asymmetry imaging, finding virtually identical phenomena in two lightly hole-doped cuprates: Ca(1.88)Na(0.12)CuO(2)Cl2 and Bi2Sr2Dy(0.2)Ca(0.8)Cu2O(8+delta). Intense spatial variations in tunneling asymmetry occur primarily at the planar oxygen sites; their spatial arrangement forms a Cu-O-Cu bond-centered electronic pattern without long-range order but with 4a(0)-wide unidirectional electronic domains dispersed throughout (a(0): the Cu-O-Cu distance). The emerging picture is then of a partial hole localization within an intrinsic electronic glass evolving, at higher hole densities, into complete delocalization and highest-temperature superconductivity.
ABSTRACT
The phase diagram of hole-doped copper oxides shows four different electronic phases existing at zero temperature. Familiar among these are the Mott insulator, high-transition-temperature superconductor and metallic phases. A fourth phase, of unknown identity, occurs at light doping along the zero-temperature bound of the 'pseudogap' regime. This regime is rich in peculiar electronic phenomena, prompting numerous proposals that it contains some form of hidden electronic order. Here we present low-temperature electronic structure imaging studies of a lightly hole-doped copper oxide: Ca2-xNaxCuO2Cl2. Tunnelling spectroscopy (at energies |E| > 100 meV) reveals electron extraction probabilities greatly exceeding those for injection, as anticipated for a doped Mott insulator. However, for |E| < 100 meV, the spectrum exhibits a V-shaped energy gap centred on E = 0. States within this gap undergo intense spatial modulations, with the spatial correlations of a four CuO2-unit-cell square 'checkerboard', independent of energy. Intricate atomic-scale electronic structure variations also exist within the checkerboard. These data are consistent with an unanticipated crystalline electronic state, possibly the hidden electronic order, existing in the zero-temperature pseudogap regime of Ca2-xNaxCuO2Cl2.
ABSTRACT
The transport of heat and charge in cuprates was measured in single crystals of La(2-x)Sr(x)CuO(4+delta) (LSCO) across the doping phase diagram at low temperatures. In underdoped LSCO, the thermal conductivity is found to decrease with increasing magnetic field in the T-->0 limit, in striking contrast to the increase observed in all superconductors, including cuprates at higher doping. In heavily underdoped LSCO, where superconductivity can be entirely suppressed with an applied magnetic field, we show that a novel thermal metal-to-insulator transition takes place upon going from the superconducting state to the field-induced normal state.
ABSTRACT
The thermal conductivity of borocarbide superconductor LuNi(2)B(2)C was measured down to 70 mK (T(c)/200) in a magnetic field perpendicular to the heat current from H = 0 to above H(c2) = 7 T. As soon as vortices enter the sample, the conduction at T-->0 grows rapidly, showing unambiguously that delocalized quasiparticles are present at the lowest energies. The field dependence is very similar to that of UPt(3), a heavy-fermion superconductor with a line of nodes in the gap, and very different from the exponential dependence characteristic of s-wave superconductors. This is strong evidence for a highly anisotropic gap function in LuNi(2)B(2)C, possibly with nodes.
ABSTRACT
We present a study of the electronic ultrasound attenuation alpha in the unconventional superconductor Sr(2)RuO(4). The power law behavior of alpha at temperatures down to T(c)/30 clearly indicates the presence of nodes in the gap. In the normal state, we find an enormous anisotropy of alpha in the basal plane of the tetragonal structure. In the superconducting state, the temperature dependence of alpha also exhibits significant anisotropy. We discuss these results in relation to possible gap functions.
ABSTRACT
In 16 patients with abdominal trauma, ultrasonic abnormalities of the spleen were demonstrated shortly after trauma (mean 3.7 days). Initial sonographic abnormalities included: splenic laceration in 3 cases, intrasplenic fluid (hematoma) in 4, splenic inhomogeneity (contusion) in 8, perisplenic fluid (subcapsular hematoma) in 11, intraperitoneal fluid in 10, and a left pleural effusion in 7. Follow-up sonograms showed that pleural effusions and intraperitoneal fluid collections disappeared quickly (2 and 4 weeks, respectively). However, intrasplenic hematomas and contusions usually resorbed over a period of months (up to a year). When followed to complete resolution, the spleen may become normal sonographically or there may be small linear foci of echogenic material, which probably represent scar tissue.
Subject(s)
Spleen/injuries , Ultrasonography , Adolescent , Adult , Aged , Child , Female , Humans , Male , Middle Aged , Wound HealingABSTRACT
The important role of serum beta-human chorionic gonadotropin (beta-HCG) in detecting spread of trophoblastic disease following evacuation of a hydatidiform mole is well established (1,2). Although sonography is accepted as the primary imaging technique in the diagnosis of hydatidiform mole (3), only a few authors have described the post-evacuation appearances of the pelvis, in particular the regression of theca lutein cysts (4,5). We here report a patient in whom there was delayed regression of huge theca lutein cysts compared to the regression of the serum beta-HCG levels after evacuation of a benign non-recurring hydatidiform mole.