171 research outputs found
Orbitally-driven Behavior: Mott Transition, Quantum Oscillations and Colossal Magnetoresistance in Bilayered Ca3Ru2O7
We report recent transport and thermodynamic experiments over a wide range of
temperatures for the Mott-like system Ca3Ru2O7 at high magnetic fields, B, up
to 30 T. This work reveals a rich and highly anisotropic phase diagram, where
applying B along the a-, b-, and c-axis leads to vastly different behavior. A
fully spin-polarized state via a first order metamagnetic transition is
obtained for B||a, and colossal magnetoresistance is seen for B||b, and quantum
oscillations in the resistivity are observed for B||c, respectively. The
interplay of the lattice, orbital and spin degrees of freedom are believed to
give rise to this strongly anisotropic behavior.Comment: 26 pages and 8 figure
Non-Fermi-liquid behavior in nearly ferromagnetic metallic SrIrO3 single crystals
We report transport and thermodynamic properties of single-crystal SrIrO3 as
a function of temperature T and applied magnetic field H. We find that SrIrO3
is a non-Fermi-liquid metal near a ferromagnetic instability, as characterized
by the following properties: (1) small ordered moment but no evidence for
long-range order down to 1.7 K; (2) strongly enhanced magnetic susceptibility
that diverges as T or T1/2 at low temperatures, depending on the applied field;
(3) heat capacity C(T,H) ~ -Tlog T that is readily amplified by low applied
fields; (4) a strikingly large Wilson ratio at T< 4K; and (5) a T3/2-dependence
of electrical resistivity over the range 1.7 < T < 120 K. A phase diagram based
on the data implies SrIrO3 is a rare example of a stoichiometric oxide compound
that exhibits non-Fermi-liquid behavior near a quantum critical point (T = 0
and H = 0.23 T)
Pressure-Induced Insulating State in Ba1-xRExIrO3 (RE = Gd, Eu) Single Crystals
BaIrO3 is a novel insulator with coexistent weak ferromagnetism, charge and
spin density wave. Dilute RE doping for Ba induces a metallic state, whereas
application of modest pressure readily restores an insulating state
characterized by a three-order-of-magnitude increase of resistivity. Since
pressure generally increases orbital overlap and broadens energy bands, a
pressure-induced insulating state is not commonplace. The profoundly dissimilar
responses of the ground state to light doping and low hydrostatic pressures
signal an unusual, delicate interplay between structural and electronic degrees
of freedom in BaIrO3
Decoupling of the Antiferromagnetic and Insulating States in Tb doped Sr2IrO4
Sr2IrO4 is a spin-orbit coupled insulator with an antiferromagnetic (AFM)
transition at TN=240 K. We report results of a comprehensive study of
single-crystal Sr2Ir1-xTbxO4. This study found that mere 3% (x=0.03)
tetravalent Tb4+(4f7) substituting for Ir4+ (rather than Sr2+) completely
suppresses the long-range collinear AFM transition but retains the insulating
state, leading to a phase diagram featuring a decoupling of magnetic
interactions and charge gap. The insulating state at x=0.03 is characterized by
an unusually large specific heat at low temperatures and an incommensurate
magnetic state having magnetic peaks at (0.95, 0, 0) and (0, 0.95, 0) in the
neutron diffraction, suggesting a spiral or spin density wave order. It is
apparent that Tb doping effectively changes the relative strength of the SOI
and the tetragonal CEF and enhances the Hund's rule coupling that competes with
the SOI, and destabilizes the AFM state. However, the disappearance of the AFM
accompanies no metallic state chiefly because an energy level mismatch for the
Ir and Tb sites weakens charge carrier hopping and renders a persistent
insulating state. This work highlights an unconventional correlation between
the AFM and insulating states in which the magnetic transition plays no
critical role in the formation of the charge gap in the iridate.Comment: 8 figure
High-temperature weak ferromagnetism on the verge of a metallic state: Impact of dilute Sr-doping on BaIrO3
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
Anomalous itinerant magnetism in single crystal Sr4Ru3O10: A thermodynamic and transport investigation
A thermodynamic and transport study of Sr4Ru3O10 as a function of temperature
and magnetic field is presented. The central results include a growing specific
heat C with increasing field B, a magnetic contribution to C/T at low
temperatures proportional to -log(T), an abrupt jump and a peak in C/T at 2.90
T and 7 T for B||ab-plane and B||c-axis, respectively, and corresponding
changes in the low T power laws of the resistivity. The novelty of this work
lies in the fact that this system is strongly anisotropic displaying
spontaneous ferromagnetism along the c-axis and an intralayer metamagnetic
transition with a possibility of a nearby quantum critical point. The exotic
behavior reflects new physics that is yet to be understood
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