Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (21 results)

  • Article
  • Peer Reviewed
UC Irvine Previously Published Works (2010)
Pressure-dependent electrical resistivity and ac-calorimetry measurements on single crystals of the heavy-fermion antiferromagnet U(2)Zn(17) at pressures to 5.5 GPa reveal that the low temperature magnetic order changes above ∼3 GPa. The Neél temperature (T(N) = 9.7 K at ambient pressure) decreases slowly for pressures below 3 GPa, but above this pressure a new magnetic state develops at T(M)≈8.7 K. This magnetic phase becomes more stable with pressure increase (dT(M)/dP = 1 K GPa(-1), T(M) = 10.5 K at 5.3 GPa). The heavy-electron state in U(2)Zn(17) is robust against pressure--the electronic specific heat coefficient γ≈0.4 J mol(-1) K(-2) is nearly pressure independent for both magnetic phases. Magnetic ac-susceptibility measurements show that the pressure-induced state is not ferromagnetic.
    Cover page: Magnetic transitions in a heavy-fermion antiferromagnet U2Zn17 at high pressureCreative Commons 'BY' version 4.0 license
    • Article
    LBL Publications (2002)

    Sub-Angstrom TEM of materials at intermediate voltages requires a sub-Angstrom information limit for the microscope. With a Scherzer resolution of 1.7 Angstrom, but a sub-Angstrom information limit, the one-Angstrom microscope (OAM) project at the NCEM is able to generate resolution below 0.8 Angstrom. Microscope information limit comes from damping of transfer by the temporal coherence. A major term contributing to temporal coherence is energy spread in the electron beam. We derive a new expression for the energy spread, and show how it can be measured from the result that is obtained using a standard electron spectrometer.

      Cover page: Measurement of the energy-spread contribution to information transfer limits in HR-TEM
      • Article
      LBL Publications (2002)

      Sub-Angstrom TEM of materials requires focal-series reconstruction (FSR) or electron holography to retrieve the electron wave at the specimen exit-surface to very high resolution. As a consequence, we need to measure the microscope information limit. With a sub-Angstrom information limit, the one-Angstrom microscope (OAM) project at the NCEM has achieved sub-Angstrom resolution by FSR. We present a new method of estimating the information limit of the microscope, based on energy-spread measurements with an image filter.

        Cover page: Estimation of the electron beam energy spread for TEM information limit
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2005)
        The Kondo lattice system Ce Zn0.66 Sb2 is studied by electrical resistivity and ac magnetic susceptibility measurements at several pressures. At P=0 kbar, ferromagnetic and antiferromagnetic transitions appear at 3.6 and 0.8 K, respectively. The electrical resistivity at TN dramatically changes from the Fisher-Langer type (ferromagneticlike) to the Suezaki-Mori (SM) type near 17 kbar, i.e., from a positive divergence to a negative divergence in the temperature derivative of the resistivity. The pressure-induced SM-type anomaly, which shows thermal hysteresis, is easily suppressed by a small magnetic field (1.9 kOe for 19.8 kbar), indicating a weakly first-order nature of the transition. By subtracting a low-pressure data set, we directly compare the resistivity anomaly with the SM theory without any assumption on backgrounds, where the negative divergence in dρ dT is ascribed to enhanced critical fluctuations in the presence of superzone gaps. © 2005 The American Physical Society.
          Cover page: Pressure-tuned first-order phase transition and accompanying resistivity anomaly in CeZn1−δSb2Creative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC Irvine Previously Published Works (2005)
          Measurements of electrical resistivity at applied pressures up to 55 kbar have been carried out on single crystals of the ferromagnet CeNiSb 3 revealing a complex magnetic phase diagram. The ferromagnetism at ambient pressure at T c=6 K first increases with pressure up to 25 kbar, then decreases slightly for P > 25 kbar. In the pressure range 35 kbar≤P≤55 kbar, a second anomaly in the resistivity is found at T M2, below another higher temperature magnetic phase that is conjectured to be different than the ferromagnetism present at lower pressure. Changes in the physical properties such as the residual resistivity, and low temperature maximum in ρ mag(T) suggest a modification of the electronic structure where the two magnetic phases coexist with one another above 35 kbar. The critical pressure for the suppression of the lower temperature phase is estimated to be P cmag2≃55 kbar, while the increase of both the T 2 coefficient of the electrical resistivity A and residual resistivity ρ 0 is suggestive of a quantum critical point associated with the higher temperature magnetic phase at P cmag1∼60 kbar. ©2005 The American Physical Society.
            Cover page: Complex magnetic phase diagram of ferromagnetic CeNiSb3Creative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Irvine Previously Published Works (2012)
            The f-electron compound CeAuSb 2, which crystallizes in the ZrCuSi 2-type tetragonal structure, orders antiferromagnetically between 5 and 6.8 K, where the antiferromagnetic transition temperature T N depends on the occupancy of the Au site. Here we report the electrical resistivity and heat capacity of a high-quality crystal CeAuSb 2 with T N of 6.8 K, the highest for this compound. The magnetic transition temperature is initially suppressed with pressure, but is intercepted by a new magnetic state above 2.1 GPa. The new phase shows a dome shape with pressure and coexists with another phase at pressures higher than 4.7 GPa. The electrical resistivity shows a T2 Fermi-liquid behavior in the complex magnetic state, and the residual resistivity and the T2 resistivity coefficient increases with pressure, suggesting the possibility of a magnetic quantum critical point at a higher pressure. © 2012 American Physical Society.
              Cover page: Pressure effects on the heavy-fermion antiferromagnet CeAuSb2Creative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2017)
              [This corrects the article DOI: 10.1186/s11689-017-9195-8.].
                Cover page: Erratum to: Delta rhythmicity is a reliable EEG biomarker in Angelman syndrome: a parallel mouse and human analysis
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2017)

                Background

                Clinicians have qualitatively described rhythmic delta activity as a prominent EEG abnormality in individuals with Angelman syndrome, but this phenotype has yet to be rigorously quantified in the clinical population or validated in a preclinical model. Here, we sought to quantitatively measure delta rhythmicity and evaluate its fidelity as a biomarker.

                Methods

                We quantified delta oscillations in mouse and human using parallel spectral analysis methods and measured regional, state-specific, and developmental changes in delta rhythms in a patient population.

                Results

                Delta power was broadly increased and more dynamic in both the Angelman syndrome mouse model, relative to wild-type littermates, and in children with Angelman syndrome, relative to age-matched neurotypical controls. Enhanced delta oscillations in children with Angelman syndrome were present during wakefulness and sleep, were generalized across the neocortex, and were more pronounced at earlier ages.

                Conclusions

                Delta rhythmicity phenotypes can serve as reliable biomarkers for Angelman syndrome in both preclinical and clinical settings.
                  Cover page: Delta rhythmicity is a reliable EEG biomarker in Angelman syndrome: a parallel mouse and human analysis
                  • Article
                  • Peer Reviewed
                  UC Irvine Previously Published Works (2011)
                  β-UB2C exhibits itinerant ferromagnetism below T c 75 K; whereas, UNiSi2 exhibits ferromagnetism of localized uranium moments below Tc 95 K and Kondo lattice behaviour at higher temperatures. We have found that ferromagnetism in both compounds is quenched at high pressure. In β-UB2C the Curie temperature continuously approaches zero at 2.95 GPa, where resistivity and specific heat reveal the behaviour similar to that observed in Ce-based antiferromagnets near quantum critical points. In UNiSi2 the Curie temperature decreases gradually to 25 K at 5.34 GPa. Above this pressure hysteretic phenomena appear in the temperature dependences of resistivity between 5 and 17 K, signalling a change in the magnetic order. No signature of magnetism was found above 5.5 GPa down to 1.15 K. Kondo lattice behaviour of resistivity with the enhanced residual resistivity is observed in UNiSi2 above 5.5 GPa. © Published under licence by IOP Publishing Ltd.
                    Cover page: Quenching of ferromagnetism in β-UB2C and UNiSi2 at high pressureCreative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    UC Irvine Previously Published Works (2003)
                    Electrical resistivity and ac-calorimetric measurements reveal a complex magnetic phase diagram for single crystals of the ferromagnetic Kondo-lattice compound CeAgSb2 at high pressures up to 80 kbar. The ferromagnetic order at TC = 9.6 K at ambient pressure is completely suppressed at a critical pressure PC = 35 kbar. Another magnetic transition, possibly antiferromagnetic, found above 27 kbar, attains a maximum value TN 6 K at 44 kbar and then appears to be completely suppressed by 50 kbar. Thermodynamic and transport measurements in the ferromagnetic state indicate an energy gap Δ 30 K in the spin-wave excitation spectrum at ambient pressure which decreases to Δ 10 K at P = 30 kbar. No superconductivity is observed at ambient pressure above T 0.1 K, under applied pressure in the ferromagnetic state (P = 28.5 kbar), nor in the antiferromagnetic state (P = 33 − 46 kbar) above 0.3 K. © 2003 The American Physical Society.
                      Cover page: Magnetic phase diagram of the ferromagnetic Kondo-lattice compound CeAgSb2 up to 80 kbarCreative Commons 'BY' version 4.0 license
                      Top