619 research outputs found
Giant Carrier Mobility in Single Crystals of FeSb2
We report the giant carrier mobility in single crystals of FeSb2. Nonlinear
field dependence of Hall resistivity is well described with the two-carrier
model. Maximum mobility values in high mobility band reach ~10^5 cm^2/Vs at 8
K, and are ~10^2 cm^2/Vs at the room temperature. Our results point to a class
of materials with promising potential for applications in solid state
electronics.Comment: 5 pages, 3 figures. Applied Physics Letters (in press
Probing many-body localization in a disordered quantum magnet
Quantum states cohere and interfere. Quantum systems composed of many atoms
arranged imperfectly rarely display these properties. Here we demonstrate an
exception in a disordered quantum magnet that divides itself into nearly
isolated subsystems. We probe these coherent clusters of spins by driving the
system beyond its linear response regime at a single frequency and measuring
the resulting "hole" in the overall linear spectral response. The Fano shape of
the hole encodes the incoherent lifetime as well as coherent mixing of the
localized excitations. For the disordered Ising magnet,
, the quality factor for spectral holes
can be as high as 100,000. We tune the dynamics of the quantum degrees of
freedom by sweeping the Fano mixing parameter through zero via the
amplitude of the ac pump as well as a static external transverse field. The
zero-crossing of is associated with a dissipationless response at the drive
frequency, implying that the off-diagonal matrix element for the two-level
system also undergoes a zero-crossing. The identification of localized
two-level systems in a dense and disordered dipolar-coupled spin system
represents a solid state implementation of many-body localization, pushing the
search forward for qubits emerging from strongly-interacting, disordered,
many-body systems.Comment: 22 pages, 6 figure
Anisotropy in magnetic and transport properties of Fe1-xCoxSb2
Anisotropic magnetic and electronic transport measurements were carried out
on large single crystals of Fe1-xCoxSb2 (0<= x <=1). The semiconducting state
of FeSb2 evolves into metallic and weakly ferromagnetic by substitution of Fe
with Co for x<0.5. Further doping induces structural transformation from
orthorhombic Pnnm structure of FeSb2 to monoclinic P21/c structure of CoSb2
where semiconducting and diamagnetic ground state is restored again. Large
magnetoresistance and anisotropy in electronic transport were observed.Comment: 7 pages, 6 figure
Quantum and Classical Glass Transitions in
When performed in the proper low field, low frequency limits, measurements of
the dynamics and the nonlinear susceptibility in the model Ising magnet in
transverse field, , prove the existence
of a spin glass transition for = 0.167 and 0.198. The classical behavior
tracks for the two concentrations, but the behavior in the quantum regime at
large transverse fields differs because of the competing effects of quantum
entanglement and random fields.Comment: 5 pages, 5 figures. Updated figure 3 with corrected calibration
information for thermometr
Anomalous low temperature state of CeOs4Sb12: Magnetic field and La-impurity study
Specific heat for single crystalline samples of Ce1-xLaxOs4Sb12 at zero-field
and magnetic fields to 14 T is reported. Our results confirm enhanced value of
the electronic specific heat coefficient in the paramagnetic state. They
provide arguments for the intrinsic origin of the 1.1 K anomaly. This
transition leads to opening of the gap at the Fermi surface. This low
temperature state of CeOs4Sb12 is extremely sensitive to chemical impurities.
2% of La substituted for Ce suppresses the transition and reduces the
electronic specific heat coefficient. The magnetic field response of the
specific heat is also anomalous.Comment: 4 pages, 3 figure
Competing topological and Kondo insulator phases on a honeycomb lattice
We investigate the competition between the spin-orbit interaction of
itinerant electrons and their Kondo coupling with local moments densely
distributed on the honeycomb lattice. We find that the model at half-filling
displays a quantum phase transition between topological and Kondo insulators at
a nonzero Kondo coupling. In the Kondo-screened case, tuning the electron
concentration can lead to a new topological insulator phase. The results
suggest that the heavy-fermion phase diagram contains a new regime with a
competition among topological, Kondo-coherent and magnetic states, and that the
regime may be especially relevant to Kondo lattice systems with -conduction
electrons. Finally, we discuss the implications of our results in the context
of the recent experiments on SmB implicating the surface states of a
topological insulator, as well as the existing experiments on the phase
transitions in SmB under pressure and in CeNiSn under chemical pressure.Comment: (v3) Published version including the main text (5 pages + 4 figures)
and a supplementary material discussing the effects of quantum fluctuations
of the slave bosons and antiferromagnetic ordering of the local moments on
the transitions among the Kondo, magnetic and topological state
Scaling of magnetic fluctuations near a quantum phase transition
We use inelastic neutron scattering to measure the magnetic fluctuations in a
single crystal of the heavy fermion alloy CeCu_5.9Au_0.1 close to the
antiferromagnetic quantum critical point. The energy and temperature-dependent
spectra obey (E/T) scaling at Q near (1,0,0). The neutron data and earlier bulk
susceptibility are consistent with the form 1/X ~ f(Q)+(-iE+bT)^a, with an
anomalous exponent a=0.8. We confirm the earlier observation of quasi-low
dimensionality and show how both the magnetic fluctuations and the
thermodynamics can be understood in terms of a quantum Lifshitz point.Comment: Latex file with two postscript figure
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