11 research outputs found
Reconciling Semiclassical and Bohmian Mechanics: III. Scattering states for continuous potentials
In a previous paper [J. Chem. Phys. 121 4501 (2004)] a unique bipolar
decomposition, Psi = Psi1 + Psi2 was presented for stationary bound states Psi
of the one-dimensional Schroedinger equation, such that the components Psi1 and
Psi2 approach their semiclassical WKB analogs in the large action limit. The
corresponding bipolar quantum trajectories, as defined in the usual Bohmian
mechanical formulation, are classical-like and well-behaved, even when Psi has
many nodes, or is wildly oscillatory. A modification for discontinuous
potential stationary stattering states was presented in a second paper [J.
Chem. Phys. 124 034115 (2006)], whose generalization for continuous potentials
is given here. The result is an exact quantum scattering methodology using
classical trajectories. For additional convenience in handling the tunneling
case, a constant velocity trajectory version is also developed.Comment: 16 pages and 14 figure
Muon Spin Relaxation Studies of Magnetic-Field-Induced Effects in High- Superconductors
Muon spin relaxation (SR) measurements in high transverse magnetic
fields () revealed strong field-induced quasi-static
magnetism in the underdoped and Eu doped (La,Sr)CuO and
LaBaCuO, existing well above and . The
susceptibility-counterpart of Cu spin polarization, derived from the muon spin
relaxation rate, exhibits a divergent behavior towards K. No
field-induced magnetism was detected in overdoped
LaSrCuO, optimally doped Bi2212, and Zn-doped
YBaCuO.Comment: 4 pages, 4 color figure
Phase separation and suppression of critical dynamics at quantum transitions of itinerant magnets: MnSi and (SrCa)RuO
Quantum phase transitions (QPTs) have been studied extensively in correlated
electron systems. Characterization of magnetism at QPTs has, however, been
limited by the volume-integrated feature of neutron and magnetization
measurements and by pressure uncertainties in NMR studies using powderized
specimens. Overcoming these limitations, we performed muon spin relaxation
(SR) measurements which have a unique sensitivity to volume fractions of
magnetically ordered and paramagnetic regions, and studied QPTs from itinerant
heli/ferro magnet to paramagnet in MnSi (single-crystal; varying pressure) and
(SrCa)RuO (ceramic specimens; varying ). Our results
provide the first clear evidence that both cases are associated with
spontaneous phase separation and suppression of dynamic critical behavior,
revealed a slow but dynamic character of the ``partial order'' diffuse spin
correlations in MnSi above the critical pressure, and, combined with other
known results in heavy-fermion and cuprate systems, suggest a possibility that
a majority of QPTs involve first-order transitions and/or phase separation.Comment: 11 pages, 4 figures, 21 authors, to appear in Nature Physic
Frustration-driven spin freezing in the S=1/2 fcc perovskite Sr2MgReO6
The ordered perovskite Sr2MgReO6 of tetragonal symmetry [I4/m, a=5.5670(1)\uc5, c=7.9318(2)\uc5 at T=295K] has been synthesized and characterized by x-ray and neutron diffraction, thermal gravimetric analysis dc susceptibility, heat capacity, and muon spin relaxation (\u3bcSR) experiments. The B site cations Re6+ and Mg2+ appear to be ordered due the large difference in formal charge. The Re6+ magnetic ions form a distorted fcc lattice of S=1/2 spins providing a frustrated topology of edge-shared tetrahedra. The material exhibits a weak magnetic glassiness shown by a cusp at 3c50 K in the dc susceptibility, a weak but broad heat capacity anomaly, and a low-temperature \u3bcSR line shape characteristic of a spin-glass state. A broad and strongly field- dependent maximum in the dc susceptibility suggests that magnetic correlations persist to 3c175 K, accompanied by a divergence in the field-cooled and zero-field-cooled susceptibility. The anisotropic nature of the superexchange pathways due to the tetragonal distortion is thought to disrupt the ideal frustrated environment and lead to weaker glassiness than Sr2CaReO6, which has TG 3c14K, and a large specific heat anomaly. In contrast, Sr2MgReO6 has a small anomaly, and only about 3% of the entropy is released at TG 3c50K, which is comparable to other unconventional spin glasses such as the jarosite (H3O)Fe3(SO4)2(OH)6( 3c6%). TG 3c50K is unusually high for this class of materials.NRC publication: N
New magnetic phase diagram of (Sr,Ca)\u2082RuO\u2084
High- Tc cuprates, iron pnictides, organic BEDT and TMTSF, alkali-doped C60, and heavy-fermion systems have superconducting states adjacent to competing states exhibiting static antiferromagnetic or spin density wave order. This feature has promoted pictures for their superconducting pairing mediated by spin fluctuations. Sr2RuO4 is another unconventional superconductor which almost certainly has a p-wave pairing. The absence of known signatures of static magnetism in the Sr-rich side of the (Ca, Sr) substitution space, however, has led to a prevailing view that the superconducting state in Sr2RuO4 emerges from a surrounding Fermi-liquid metallic state. Using muon spin relaxation and magnetic susceptibility measurements, we demonstrate here that (Sr,Ca)2RuO4 has a ground state with static magnetic order over nearly the entire range of (Ca, Sr) substitution, with spin-glass behaviour in Sr1.5Ca0.5RuO4 and Ca1.5Sr0.5RuO4. The resulting new magnetic phase diagram establishes the proximity of superconductivity in Sr2RuO4 to competing static magnetic order.Peer reviewed: YesNRC publication: Ye