arXiv subjects

N. D. Mathur

Publications and source records attributed to N. D. Mathur.

24 records · Page 2Linked to original sources

arXiv2005

Strain control of superlattice implies weak charge-lattice coupling in La$_{0.5}$Ca$_{0.5}$MnO$_3$

We have recently argued that manganites do not possess stripes of charge order, implying that the electron-lattice coupling is weak [Phys Rev Lett \textbf{94} (2005) 097202]. Here we independently argue the same conclusion based on transmission electron microscopy measurements of a nanopatterned epitaxial film of La$_{0.5}$Ca$_{0.5}$MnO$_3$. In strain relaxed regions, the superlattice period is modified by 2-3% with respect to the parent lattice, suggesting that the two are not strongly tied.

cond-mat.mes-hall↗

arXiv2005

Weak charge-lattice coupling requires reinterpretation of stripes of charge order in La1-xCaxMnO3

Modulations in manganites attributed to stripes of charge/orbital/spin order are thought to result from strong electron-lattice interactions that lock the superlattice and parent lattice periodicities. Surprisingly in La1-xCaxMnO3(x>0.5, 90 K), convergent beam (3.6 nm spot) electron diffraction patterns rule out charge stacking faults and indicate a superlattice with uniform periodicity. Moreover, large area electron diffraction peaks are sharper than simulations with stacking faults. Since the electron-lattice coupling does not lock the two periodicities (to yield stripes) it may be too weak to strongly localise charge.

cond-mat.str-el↗

arXiv2004

The structure of intercalated water in superconducting Na$_{0.35}$CoO$_{2}\cdot$1.37D$_{2}$O: Implications for the superconducting phase diagram

We have used electron and neutron powder diffraction to elucidate the structural properties of superconducting \NaD. Our measurements show that our superconducting sample exhbits a number of supercells ranging from ${1/3}a^{*}$ to ${1/15}a^{*}$, but the most predominant one, observed also in the neutron data, is a double hexagonal cell with dimensions \dhx. Rietveld analysis reveals that \deut\space is inserted between CoO$_{2}$ sheets as to form a layered network of NaO$_{6}$ triangular prisms. Our model removes the need to invoke a 5K superconducting point compound and suggests that a solid solution of Na is possible within a constant amount of water $y$.

cond-mat.supr-con↗

arXiv2000

Superconductivity on the threshold of magnetism in CePd2Si2 and CeIn3

The magnetic ordering temperature of some rare earth based heavy fermion compounds is strongly pressure-dependent and can be completely suppressed at a critical pressure, p$_c$, making way for novel correlated electron states close to this quantum critical point. We have studied the clean heavy fermion antiferromagnets CePd$_2$Si$_2$ and CeIn$_3$ in a series of resistivity measurements at high pressures up to 3.2 GPa and down to temperatures in the mK region. In both materials, superconductivity appears in a small window of a few tenths of a GPa on either side of p$_c$. We present detailed measurements of the superconducting and magnetic temperature-pressure phase diagram, which indicate that superconductivity in these materials is enhanced, rather than suppressed, by the closeness to magnetic order.

cond-mat.str-el↗

arXiv2000

Mesoscale magnetism at the grain boundaries in colossal magnetoresistive films

We report the discovery of mesoscale regions with distinctive magnetic properties in epitaxial La$_{1-x}$Sr$_{x}$MnO$_{3}$ films which exhibit tunneling-like magnetoresistance across grain boundaries. By using temperature-dependent magnetic force microscopy we observe that the mesoscale regions are formed near the grain boundaries and have a different Curie temperature (up to 20 K {\it higher}) than the grain interiors. Our images provide direct evidence for previous speculations that the grain boundaries in thin films are not magnetically and electronically sharp interfaces. The size of the mesoscale regions varies with temperature and nature of the underlying defect.

cond-mat.str-el↗

arXiv1998

Anomalous Low Temperature States in CeNi2Ge2

Ambient pressure studies on high purity single crystals of the stoichiometric 4f-electron metal CeNi2Ge2 reveal anomalous low temperature forms of the resistivity which challenge our understanding of the metallic state. Comparisons are made with the isostructural and isoelectronic compound CePd2Si2 near the border of magnetism at high pressure, and possible reasons for this novel non-Fermi liquid form of the resistivity are discussed. Phase diagrams of further anomalies are presented, which involve a loss of resistance at low temperature in some samples of CeNi2Ge2 and unexpected high pressure phases.

cond-mat.str-el↗