E. Elhami
University of Kentucky
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Featured researches published by E. Elhami.
Physical Review B | 2004
G. Cao; X.N. Lin; S. Chikara; V. Durairaj; E. Elhami
The 5d-electron based BaIrO3 is a nonmetallic weak ferromagnet with a Curie temperature at Tc=175 K. Its largely extended orbitals generate strong electron-lattice coupling, and magnetism and electronic structure are thus critically linked to the lattice degree of freedom. Here we report results of our transport and magnetic study on slightly Sr doped BaIrO3. It is found that dilute Sr-doping drastically suppresses Tc, and instantaneously leads to a nonmetal-metal transition at high temperatures. All results highlight the instability of the ground state and the subtle relation between magnetic ordering and electron mobility. It is clear that BaIrO3 along with very few other systems represents a class of materials where the magnetic and transport properties can effectively be tuned by slight alterations in lattice parameters.
Physical Review B | 2004
G. Cao; L. Balicas; X.N. Lin; S. Chikara; E. Elhami; V. Duairaj; J. W. Brill; R. C. Rai; J. E. Crow
Ca3Ru2O7 with a Mott-like transition at 48 K and a Neel temperature at 56 K features different in-plane anisotropies of the magnetization and magnetoresistance. Applying a magnetic field along the magnetic easy- axis precipitates a spin-polarized state via a first-order metamagnetic transition, but does not lead to a full suppression of the Mott state, whereas applying a magnetic field along the magnetic hard axis does, causing a resistivity reduction of three orders of magnitude. The colossal magnetoresistivity is attributed to the collapse of an orbitally ordered and spin-polarized state. This phenomenon is striking in that the spin polarization, which is a fundamental driving force for all other magnetoresistive systems, is detrimental to the colossal magnetoresistence in this 4 d-based electron system. Evidence of a density wave is also presented. DOI: 10.1103/PhysRevB.69.014404 PACS number~s!: 75.47.Gk, 71.70.Ej The physics of magnetoresistance has generated enor- mous interest in recent years. While this quantum mechani- cal phenomenon is in general associated with the spin scat- tering process of conduction electrons, the origins of various kinds of magnetoresistance are vastly different. The giant magnetoresistance observed in magnetic metallic multiplayer structures can be qualitatively explained using the two cur- rent model, corresponding to up-spin and down-spin electrons. 1 Tunneling magnetoresistance, often seen in mag- netic tunnel junctions separated by an insulating spacer layer, is a consequence of spin-polarization. On the other hand, colossal magnetoresistance ~CMR!, seen only in the mixed- valence manganites so far, originates from a metal-insulator transition in the vicinity of the Curie temperature driven pri- marily by double exchange due to the hopping of eg elec- trons of Mn 31 ions and the Jahn-Teller effect. 2 The novelty of the bilayered Ca3Ru2O7 , as presented in this paper, is that the colossal magnetoresistivity is a result of the collapse of the orbitally ordered state that is realized by demolishing the spin-polarized state . This phenomenon is striking in that the spin polarization, which is a fundamental driving force for all other magnetoresistive systems, is detri- mental to the colossal magnetoresistence in this 4 d-based electron system. Indeed, the electron kinetic energy hinges on the spin-orbital-lattice coupling in such a way that apply- ing magnetic field, B, along the magnetic easy axis ~a axis! precipitates a spin-polarized state via a first-order metamag- netic transition, but does not lead to a full suppression of the Mott state, whereas applying B along the magnetic hard axis ~b axis! does, giving rise to a resistivity reduction of three orders of magnitude. Our previous work indicated the puz- zling anisotropic behavior observed in the field dependence
Physical Review C | 2008
J. N. Orce; S. N. Choudry; B. P. Crider; E. Elhami; S. Mukhopadhyay; M. Scheck; M. T. McEllistrem; S. W. Yates
In our previous work [1], we presented a new lifetime measurement for the 21 state in 112Sn, as determined through the Doppler-shift attenuation method following the (n, n′γ ) reaction [2]. Here, the theoretical F (τ ) value with which one compares the measured F (τ )exp should be modified by an additional term to correct for the recoil velocity distribution when scattering at a neutron energy, En, well above the energy threshold, Elevel [2]. For an angular distribution approximately isotropic in the center of mass, the total F (τ ) is given by
Physical Review C | 2011
A. Chakraborty; J. N. Orce; S. F. Ashley; B. P. Crider; E. Elhami; M. T. McEllistrem; S. Mukhopadhyay; E. E. Peters; B. Singh
Measurements consisting of γ-ray excitation functions and angular distributions were performed using the (n,n ′ γ) reaction on Ni62. The excitation function data allowed us to check the consistency of the placement of transitions in the level scheme. From γ-ray angular distributions, the lifetimes of levels up to ~3.8 MeV in excitation energy were extracted with the Doppler-shift attenuation method. The experimentally deduced values of reduced transition probabilities were compared with the predictions of the quadrupole vibrator model and with large-scale shell model calculations in the fp shell configuration space. Two-phonon states were found to exist with some notable deviation from the predictions of the quadrupole vibrator model, but no evidence for the existence of three-phonon states could be established. Z=28 proton core excitations played a major role in understanding the observed structure.
CAPTURE GAMMA‐RAY SPECTROSCOPY AND RELATED TOPICS: Proceedings of the 13th#N#International Symposium on Capture Gamma‐Ray Spectroscopy and Related Topics | 2009
M. Scheck; S. Mukhopadhyay; B. P. Crider; S. N. Choudry; E. Elhami; E. E. Peters; M. T. McEllistrem; J. N. Orce; S. W. Yates
Low‐lying collective states in 136Ba were investigated with (n,n′γ) techniques, including Doppler‐shift attenuation lifetime measurements. The level spins, lifetimes, branching ratios, multipole‐mixing ratios and transition strengths reveal candidates for symmetric‐phonon states up to third order. The 2ms+ mixed‐symmetry state was confirmed as unfragmented and a candidate for a [21+⊗2ms+]3+ two‐phonon mixed‐symmetry state is proposed.
Physical Review C | 2008
S. Mukhopadhyay; M. Scheck; B. P. Crider; S. N. Choudry; E. Elhami; M. T. McEllistrem; J. N. Orce; E. E. Peters
Low-lying multiphonon states in {sup 136}Ba have been populated with the inelastic neutron scattering reaction. Excitation functions were performed at neutron energies from 2.2 to 3.9 MeV, and {gamma}-ray angular distributions were measured at 2.5, 3.0, and 3.5 MeV. Lifetimes have been determined using the Doppler-shift attenuation method, and electromagnetic transition rates have been deduced. The previously assigned 2{sub 1,ms}{sup +} mixed-symmetry state at 2128.9 keV has been confirmed and is not greatly fragmented. For the first time in the N=80 isotones, a 3{sub 2,ms}{sup +} two-phonon mixed-symmetry state is proposed. In addition, the 2{sub 5}{sup +} and the 4{sub 3}{sup +} levels at 2222.7 and 2356.4 keV, respectively, decay with large B(M1) values to the two-phonon 2{sub 2}{sup +} and 4{sub 1}{sup +} states, respectively, which suggests two-phonon mixed-symmetric character. Their excitation energies, however, are not consistent with this interpretation.Low-lying multiphonon states in 136 Ba have been populated with the inelastic neutron scattering reaction. Excitation functions were performed at neutron energies from 2.2 to 3.9 MeV, and γ-ray angular distributions were measured at 2.5, 3.0, and 3.5 MeV. Lifetimes have been determined using the Doppler-shift attenuation method, and electromagnetic transition rates have been deduced. The previously assigned 2 + 1,ms mixed-symmetry state at 2128.9 keV has been confirmed and is not greatly fragmented. For the first time in the N = 80 isotones, a 3 + 2,ms two-phonon mixed-symmetry state is proposed. In addition, the 2 + 5 and the 4 + 3 levels at 2222.7 and 2356.4 keV, respectively, decay with large B(Ml) values to the two-phonon 2 + 2 and 4 + 1 states, respectively, which suggests two-phonon mixed-symmetric character. Their excitation energies, however, are not consistent with this interpretation.
Physical Review B | 2005
G. Cao; S. Chikara; X.N. Lin; E. Elhami; V. Durairaj; P. Schlottmann
Physical Review C | 2007
E. Elhami; J. N. Orce; S. Mukhopadhyay; S. N. Choudry; M. Scheck; M. T. McEllistrem; S. W. Yates
Physical Review C | 2011
A. Chakraborty; J. N. Orce; S. F. Ashley; B. A. Brown; B. P. Crider; E. Elhami; M. T. McEllistrem; S. Mukhopadhyay; E. E. Peters; B. Singh; S. W. Yates
Physical Review C | 2007
J. N. Orce; S. N. Choudry; B. P. Crider; E. Elhami; S. Mukhopadhyay; M. Scheck; M. T. McEllistrem; S. W. Yates