M. A. Kastner

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

Are you M. A. Kastner?

Claim your profile

Publications (255)887.31 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The discovery of the spin density wave (SDW) state defined as stripe in the doped Cu oxides becomes a central issue in the elucidation of the high-temperature superconducting mechanism. We present the coexistence of the stripe order and superconductivity, and the change of the stripe structure associated with the insultor–metal transition. Both static and dynamical SDW are robust of the high-temperature superconducting Cu oxides.
    Physica B Condensed Matter 05/2000; 280(1-4-280):201-204. DOI:10.1016/S0921-4526(99)01573-2 · 1.28 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present results for dark current measurements on large close-packed arrays of CdSe nanocrystals. The nanocrystals are chemically synthesized in solution and then deposited between gold electrodes onto a silicon substrate. In response to an applied voltage step, we observe a power-law decay of the current over five orders of magnitude in time and four orders of magnitude in current; we do not observe steady-state dark current for fields up to 10^6 V/cm and times out to 5 × 10^4 seconds. We see clear evidence for injection of electrons into the array, but do not observe hole injection. The number of electrons in the array can be increased by cooling the sample with a positive gate voltage. However, as the number of electrons is increased, the magnitude of the current transient decreases substantially. Preliminary results suggest that the array is much more conductive at very short times ( < 1ms after the voltage step). We believe our results can be understood in the context of the Coulomb glass model, where transport is dominated by the long-range electrostatic interactions between electrons at different sites.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The optical absorption spectrum from 0.1 to 1.5 eV photon energy ispresented for extremely lightly oxygen doped crystals of La2CuO4. Crystals grown by two different methods have different low temperaturespectra and different temperature dependencies. However, at roomtemperature the spectra are nearly identical, suggesting that theyresult from the optical absorption of free isolated holes in thetwo dimensional antiferromagnetic CuO2 square lattice.
    Journal of the Physical Society of Japan 03/2000; 69(3):749-753. DOI:10.1143/JPSJ.69.749 · 1.48 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present an experimental study of the uctuations of Coulomb blockade peak positions of a quantum dot. The dot is deÿned by patterning the two-dimensional electron gas of a silicon MOSFET structure using stacked gates. The ratio of charging energy to single-particle energy is considerably larger than in comparable GaAs=AlGaAs quantum dots. The statistical distribution of the conductance peak spacings in the Coulomb blockade regime was found to be unimodal and does not follow the Wigner surmise. The uctuations of the spacings are much larger than the typical single-particle level spacing and thus clearly contradict the expectation of random matrix theory. Measurements of the natural line width of a set of several adjacent conductance peaks suggest that all of the peaks in the set are dominated by electrons being transported through a single-broad energy level. ? 2000 Elsevier Science B.V. All rights reserved.
    Physica E Low-dimensional Systems and Nanostructures 02/2000; 6(1-4):382-387. DOI:10.1016/S1386-9477(99)00186-1 · 1.86 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the results of an extensive elastic neutron-scattering study of the incommensurate (IC) static spin correlations in La1.95Sr0.05CuO4, which is an insulating spin glass at low temperatures. Recent work by Wakimoto et al. has revealed the presence of new two-dimensional satellite peaks in La1.95Sr0.05CuO4 at positions rotated by ∼45° in reciprocal space from those found in superconducting samples. The present neutron-scattering experiments on the same x=0.05 crystal employ a narrower instrumental Q resolution and thereby have revealed that the crystal has only two, rather than four, orthorhombic twins at low temperatures with relative populations of 2:1. This has made possible the precise characterization of the IC elastic peaks around (1,0,0) and (0,1,0) (orthorhombic notation) in each domain separately. We find that, in a single twin, only two satellites are observed at (1,±0.064,L)ortho and (0,1±0.064,L)ortho, that is, the modulation vector is only along the orthorhombic b* axis. This demonstrates unambiguously that La1.95Sr0.05CuO4 has a one-dimensional rather than two-dimensional static diagonal spin modulation at low temperatures, consistent with certain stripe models. From the L dependence we conclude that the spin correlations are predominantly two dimensional. We have also reexamined the x=0.04 crystal that previously was reported to show a single commensurate peak. By mounting the sample in the (H,K,0) zone, we have discovered that the x=0.04 sample in fact has the same IC structure as the x=0.05 sample. The incommensurability parameter δ for x=0.04 and 0.05, where δ is the distance from (1/2,1/2) in tetragonal reciprocal lattice units, follows the linear relation δ≃x. These results demonstrate that the insulator to superconductor transition in the underdoped regime (0.05<~x<~0.06) in La2-xSrxCuO4 is coincident with a transition from diagonal to collinear static stripes at low temperatures thereby evincing the intimate coupling between the one-dimensional spin density modulation and the superconductivity.
    Physical Review B 02/2000; 61(5):3699-3706. DOI:10.1103/PhysRevB.61.3699 · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A spin-glass compound, La1.98Sr0.02CuO4, shows quasi-three-dimensional magnetic ordering below ~40 K. A remarkable feature is that the magnetic correlation length along the orthorhombic aortho axis is much longer than that along the bortho axis, suggesting that the spin structure is closely related to the diagonal stripe structure. The spin-glass state can be expressed as a random freezing of quasi-three-dimensional spin clusters with anisotropic spin correlations (ξ'a~160 Å , ξ'b~25 Å , and ξ'c~4.7 Å at 1.6 K). The new magnetic state is important as an intermediate phase between the three-dimensional antiferromagnetic ordered phase in La2CuO4 and the incommensurate phase in La1.95Sr0.05CuO4 in which the positions of the incommensurate peaks are rotated by 45° in reciprocal space about (π,π) from those observed in the superconducting La2CuO4 compounds.
    Physical Review B 02/2000; 61(6):4326-4333. DOI:10.1103/PhysRevB.61.4326 · 3.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: ARPES studies on Sr2CuO2Cl2 and Ca2CuO2Cl2 are presented. The integrated spectral weight of the low energy feature shows a drop across the AF zone boundary, suggesting a remnant Fermi surface. Along the remnant Fermi surface the dispersion fits the functional from of |cos(kxa) - cos(kya)| remarkably well. However, additional experiments with improved angular resolution demonstrate that the dispersion near (π/2, π/2) does not contain a cusp as would be expected from a simple d-wave theory predicting the above functional form. The rounded node region and the total dispersion of approximately 350meV is shown to be independent of photon energy.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The energy spectrum of incommensurate spinfluctuations in superconducting Sr-doped La2CuO4 has beenstudied by inelastic neutron scattering experiments. An energy gap inthe spin excitation spectrum is observed in the superconducting stateof optimally doped (x=0.15) and slightly overdoped (x=0.18)samples. At temperatures well below T c, the incommensurate peaksdiminish rapidly in intensity with decreasing energy below ˜8 meV andmerge into the background below ˜3.5 meV for x=0.15 and ˜4.5 meVfor x=0.18. Forboth samples, the energy spectrum of the q-integrated spin susceptibility,chi''(omega), exhibits an enhancement around 7 meV, which is caused by abroadeningin the momentum width of the incommensurate peaks. The gap-like structure inthe energy spectrum and the enhancement of chi''(omega)survive at T c. On the other hand, for both underdoped(x=0.10) and heavily overdoped(x=0.25) samples there is neither a clear energy gap nor anenhancement of chi'' (omega) below T c.
    Journal of the Physical Society of Japan 01/2000; 69(4):1170-1176. DOI:10.1143/JPSJ.69.1170 · 1.48 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have observed asymmetric Fano resonances in the conductance of a single electron transistor resulting from interference between a resonant and a nonresonant path through the system. The resonant component shows all the features typical of quantum dots, but the origin of the non-resonant path is unclear. A unique feature of this experimental system, compared to others that show Fano line shapes, is that changing the voltages on various gates allows one to alter the interference between the two paths. Comment: 8 pages, 6 figures. Submitted to PRB
    Physical review. B, Condensed matter 12/1999; DOI:10.1103/PhysRevB.62.2188 · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent neutron-scattering experiments on La2−xSrxCuO4 single crystals by Wakimoto et al. (unpublished) have revealed that elastic magnetic peaks appear at low temperatures in both insulating (x=0.02–0.05) and superconducting (x=0.06) samples. We have carried out further investigations particularly on the elastic incommensurate peaks for x=0.06, and found that the integrated intensity drastically changes across the low temperature insulator–superconductor boundary; the intensity of x=0.06 is four times smaller than that of x=0.05, whereas the intensity in the insulating region stays constant.
    Journal of Physics and Chemistry of Solids 09/1999; 60(8-9):1079-1081. DOI:10.1016/S0022-3697(99)00052-9 · 1.59 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Elastic magnetic peaks around (π,π) have been studied in La2−xSrxCuO4 (LSCO) by neutron scattering. Recently in superconducting LSCO of x=0.12, we found that the incommensurate elastic peak (ICpeak) appears around 31K which is very close to Tc. The line width reaches almost resolution limit, which indicates that the static magnetic correlation length exceeds 200Å−1 isotropically in the CuO2 planes. Furthermore recently in the course of studying the ICpeak, we found the new experimental condition where the signals can be observed more clearly. The signal-to-noise ratio (S/N) is much more improved (∼1.4) than that at the previous experiment (∼0.6).
    Journal of Physics and Chemistry of Solids 09/1999; 60(8):1067-1070. DOI:10.1016/S0022-3697(99)00049-9 · 1.59 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report neutron-scattering measurements of spin-density wave order within the superconducting state of a single crystal of predominately stage-4 La{sub 2}CuO{sub 4+y} with a T{sub c} (onset) of 42 K. The low-temperature elastic magnetic scattering is incommensurate with the lattice and is characterized by long-range order in the copper-oxide plane with the spin direction identical to that in the insulator. Between neighboring planes, the spins exhibit short-range correlations with a stacking arrangement reminiscent of that in the undoped antiferromagnetic insulator. The elastic magnetic peak intensity appears at the same temperature within the errors as the superconductivity, suggesting that the two phenomena are strongly correlated. These observations directly reveal the persistent influence of the antiferromagnetic order as the doping level increases from the insulator to the superconductor. In addition, our results confirm that spin-density wave order for incommensurabilities near 1/8 is a robust feature of the La{sub 2}CuO{sub 4}-based superconductors. {copyright} {ital 1999} {ital The American Physical Society}
    Physical review. B, Condensed matter 08/1999; 60(5). DOI:10.1103/PhysRevB.60.3643 · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Neutron-scattering experiments have been performed on lightly doped La{sub 2-x}SrâCuOâ single crystals in both the insulating (x=0.03,0.04,0.05) and superconducting (x=0.06) regions. Elastic magnetic peaks are observed at low temperatures in all samples with the maximum peak linewidth occurring at the critical concentration x{sub c}=0.05. Incommensurate peaks are observed only at x=0.05, the positions of which are rotated by 45° in reciprocal space about (Ï,Ï) from those observed for xâ¥0.06 in the superconducting phase. {copyright} {ital 1999} {ital The American Physical Society}
    Physical review. B, Condensed matter 07/1999; 60(2). DOI:10.1103/PhysRevB.60.R769 · 3.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Sr2Cu3O4Cl2 has CuI and CuII subsystems, forming interpenetrating S = 1/2 square lattice Heisenberg antiferromagnets. The classical ground state is degenerate, due to frustration of the intersubsystem interactions. Magnetic neutron scattering experiments show that quantum fluctuations cause a two dimensional Ising ordering of the CuII's, lifting the degeneracy, and a dramatic increase of the CuI out-of-plane spin-wave gap, unique for order out of disorder. The spin-wave energies are quantitatively predicted by calculations which include quantum fluctuations.
    Physical Review Letters 07/1999; 83(4):852-855. DOI:10.1103/PhysRevLett.83.852 · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have carried out a neutron-scattering study of the instantaneous spin-spin correlations in La2CuO4 (TN=325 K) over the temperature range 337-824 K. Incident neutron energies varying from 14.7-115 meV have been employed in order to guarantee that the energy integration is carried out properly. The results so obtained for the spin-correlation length as a function of temperature when expressed in reduced units agree quantitatively both with previous results for the two-dimensional (2D) tetragonal material Sr2CuO2Cl2 and with quantum Monte Carlo results for the nearest-neighbor square lattice S=12 Heisenberg model. All of the experimental and numerical results for the correlation length are well described without any adjustable parameters by the behavior predicted for the quantum nonlinear sigma model in the low-temperature renormalized classical regime. The amplitude, on the other hand, deviates subtly from the predicted low-temperature behavior. These results are discussed in the context of recent theory for the 2D quantum Heisenberg model.
    Physical Review B 06/1999; 59(21):1276043-13794. DOI:10.1103/PhysRevB.59.13788 · 3.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Cu3O4 layer in Sr2Cu3O4Cl2 is a variant of the square CuO2 lattice of the high-temperature superconductors, in which the center of every second plaquette contains an extra Cu2+ ion. The ions that make up the conventional CuO2 network, called CuI, have CuI-CuI exchange energy ~130 meV, and order antiferromagnetically at about 380 K; the CuII-CuII exchange is only ~10 meV, and the CuII's order at ~40 K. A study is reported here of the dependence of the magnetization on field, temperature, and crystallographic orientation for this interesting system. We show that the small permanent ferromagnetic moment, that appears when the CuI spins order, and the unusual spin rotation transitions seen most clearly for one particular direction of the magnetic field, are the result of several small bond-dependent anisotropic terms in the spin Hamiltonian that are revealed because of the frustration of the isotropic Heisenberg interaction between CuI and CuII spins. These include a term which favors collinearity of the CuI and CuII spins, which originates from quantum fluctuations, and also the pseudodipolar interaction. Some of these small interactions also come into play in other lamellar cuprates, connected with the high-Tc superconductivity materials, and in many spin-chain and spin-ladder compounds.
    Physical review. B, Condensed matter 06/1999; 59(22):14702-14711. DOI:10.1103/PhysRevB.59.14702 · 3.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Cu3O4 layer in Sr2Cu3O4Cl2 is a variant of the square CuO2 lattice of the high-temperature superconductors, in which the center of every second plaquette contains an extra Cu2+ ion. The ions that make up the conventional CuO2 network, called CuI, have CuI-CuI exchange energy ≈130meV, and order antiferromagnetically at about 380 K; the CuII-CuII exchange is only ≈10meV, and the CuII’s order at ≈40K. A study is reported here of the dependence of the magnetization on field, temperature, and crystallographic orientation for this interesting system. We show that the small permanent ferromagnetic moment, that appears when the CuI spins order, and the unusual spin rotation transitions seen most clearly for one particular direction of the magnetic field, are the result of several small bond-dependent anisotropic terms in the spin Hamiltonian that are revealed because of the frustration of the isotropic Heisenberg interaction between CuI and CuII spins. These include a term which favors collinearity of the CuI and CuII spins, which originates from quantum fluctuations, and also the pseudodipolar interaction. Some of these small interactions also come into play in other lamellar cuprates, connected with the high-Tc superconductivity materials, and in many spin-chain and spin-ladder compounds.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a synchrotron x-ray-scattering study of the magnetoresistive manganite La0.875Sr0.125MnO3. At low temperatures, this material undergoes an x-ray-induced structural transition at which charge ordering of Mn3+ and Mn4+ ions characteristic to the low-temperature state of this compound is destroyed. The transition is persistent but the charge-ordered state can be restored by heating above the charge-ordering transition temperature and subsequently cooling. The charge-ordering diffraction peaks, which are broadened at all temperatures, broaden more upon x-ray irradiation, indicating the finite correlation length of the charge-ordered state. Together with the recent reports on x-ray-induced transitions in Pr1-xCaxMnO3, our results demonstrate that the photoinduced structural change is a common property of the charge-ordered perovskite manganites.
    Physical review. B, Condensed matter 03/1999; 59(10). DOI:10.1103/PhysRevB.59.R6581 · 3.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Neutron-scattering measurements have been performed to search for possible elastic incommensurate magnetic peaks in superconducting La{sub 2-x}SrâCuOâ with x=0.10, 0.12, and 0.15. The most dramatic effects are found for x=0.12; in this case, the peak intensity first appears at the onset of superconductivity T{sub c}(=31 K). The resolution-limited peak width indicates that the static magnetic correlation length exceeds 200 â« isotropically in the CuOâ planes. Weak elastic peaks are also observed at low temperatures for x=0.10 while for x=0.15 any incommensurate elastic scattering is below the limit of detectability. Elastic peaks are observed in Zn-substituted nonsuperconducting La{sub 1.88}Sr{sub 0.12}Cu{sub 0.97}Zn{sub 0.03}0â. However, in this case, the Zn substitution degrades the magnetic order; the peak appears at lower temperature (17 K) and the correlation length is shorter (80 â«) than that in the Zn-free x=0.12 sample. {copyright} {ital 1999} {ital The American Physical Society}
    Physical review. B, Condensed matter 03/1999; 59(9):6517-6523. DOI:10.1103/PhysRevB.59.6517 · 3.66 Impact Factor

Publication Stats

15k Citations
887.31 Total Impact Points

Institutions

  • 1981–2012
    • Massachusetts Institute of Technology
      • • Department of Physics
      • • Department of Materials Science and Engineering
      • • Research Laboratory of Electronics
      Cambridge, Massachusetts, United States
  • 1989–2001
    • Tel Aviv University
      • Department of Physics and Astronomy
      Tell Afif, Tel Aviv, Israel
  • 1988
    • Nippon Telegraph and Telephone
      Edo, Tōkyō, Japan