96 research outputs found
The structure of a single sharp quantum Hall edge probed by momentum-resolved tunneling
Momentum resolved magneto-tunnelling spectroscopy is performed at a single
sharp quantum Hall edge. We directly probe the structure of individual integer
quantum Hall (QH) edge modes, and find that an epitaxially overgrown cleaved
edge realizes the sharp edge limit, where the Chklovskii picture relevant for
soft etched or gated edges is no longer valid. The Fermi wavevector in the
probe quantum well probes the real-space position of the QH edge modes, and
reveals inter-channel distances smaller than both the magnetic length and the
Bohr radius. We quantitatively describe the lineshape of principal conductance
peaks and deduce an edge filling factor from their position consistent with the
bulk value. We observe features in the dispersion which are attributed to
fluctuations in the ground energy of the quantum Hall system.Comment: 4 pages, 3 figure
Direct evidence for superconductivity in the organic charge density-wave compound alpha-(BEDT-TTF)_2KHg(SCN)_4 under hydrostatic pressure
We present direct evidence of a superconducting state existing in the title
compound below 300 mK under quasi-hydrostatic pressure. The superconducing
transition is observed in the whole pressure range studied, 0 < P < 4 kbar.
However, the character of the transition drastically changes with suppressing
the charge-density wave state.Comment: 2 pages, 2 figure
Low temperature vortex liquid states induced by quantum fluctuations in the quasi two dimensional organic superconductor kappa-(BEDT-TTF)_{2} Cu(NCS)_{2}
We report the transport properties in the vortex liquid states induced by
quantum fluctuations at low temperature in the layered organic superconductor
kappa-(BEDT-TTF)_{2} Cu(NCS)_{2}. A steep drop of the resistivity observed
below about 1 K separates the liquid state into two regions. In the low
resistance state at lower temperature, a finite resistivity with weak
temperature dependence persists down to 100 mK at least. The finite resistivity
in the vortex state at T ~= 0 K indicates the realization of quantum vortex
liquid assisted by the strong quantum fluctuations instead of the thermal one.
A possible origin for separating these liquid states is a remnant vortex
melting line at the original position, which is obscured and suppressed by the
quantum fluctuations. A non-linear behavior of the in-plane resistivity appears
at large current density in only the low resistance state, but not in another
vortex liquid state at higher temperature, where the thermal fluctuations are
dominant. The transport properties in the low resistance state are well
understood in the vortex slush concept with a short-range order of vortices.
Thus the low resistance state below 1 K is considered to be a novel quantum
vortex slush state.Comment: 7 pages, 5 figure
Magnetic Field Induced Coherence-Incoherence Crossover in the Interlayer Conductivity of a Layered Organic Metal
The angle-dependent interlayer magnetoresistance of the layered organic metal
-(BEDT-TTF)KHg(SCN) is found to undergo a dramatic change from
the classical conventional behavior at low magnetic fields to an anomalous one
at high fields. This field-induced crossover and its dependence on the sample
purity and temperature imply the existence of two parallel channels in the
interlayer transport: a classical Boltzmann conductivity and an
incoherent channel . We propose a simple model for
explaining its metallic temperature dependence and low sensitivity to the
inplane field component.Comment: 5 page
Probing the Electrostatics of Integer Quantum Hall Edges with Momentum-Resolved Tunnel Spectroscopy
We present measurements of momentum-resolved magneto-tunneling from a
perpendicular two-dimensional (2D) contact into integer quantum Hall (QH) edges
at a sharp edge potential created by cleaved edge overgrowth. Resonances in the
tunnel conductance correspond to coincidences of electronic states of the QH
edge and the 2D contact in energy-momentum space. With this dispersion relation
reflecting the potential distribution at the edge we can directly measure the
band bending at our cleaved edge under the influence of an external voltage
bias. At finite bias we observe significant deviations from the flat-band
condition in agreement with self-consistent calculations of the edge potential
Magnetic Transformations in the Organic Conductor kappa-(BETS)2Mn[N(CN)2]3 at the Metal-Insulator Transition
A complex study of magnetic properties including dc magnetization, 1H NMR and
magnetic torque measurements has been performed for the organic conductor
kappa-(BETS)2Mn[N(CN)2]3 which undergoes a metal-insulator transition at
T_MI~25K. NMR and the magnetization data indicate a transition in the manganese
subsystem from paramagnetic to a frozen state at T_MI, which is, however, not a
simple Neel type order. Further, a magnetic field induced transition resembling
a spin flop has been detected in the torque measurements at temperatures below
T_MI. This transition is most likely related to the spins of pi-electrons
localized on the organic molecules BETS and coupled with the manganese 3d spins
via exchange interaction.Comment: 6 pages, 5 Figures, 1 Table; Submitted to Phys.Rev.B (Nov.2010
Magnetic Breakdown in the electron-doped cuprate superconductor NdCeCuO: the reconstructed Fermi surface survives in the strongly overdoped regime
We report on semiclassical angle-dependent magnetoresistance oscillations
(AMRO) and the Shubnikov-de Haas effect in the electron-overdoped cuprate
superconductor NdCeCuO. Our data provide convincing evidence
for magnetic breakdown in the system. This shows that a reconstructed
multiply-connected Fermi surface persists, at least at strong magnetic fields,
up to the highest doping level of the superconducting regime. Our results
suggest an intimate relation between translational symmetry breaking and the
superconducting pairing in the electron-doped cuprate superconductors.Comment: 5 pages, 4 figures, submitted to PR
Field-induced charge-density-wave transitions in the organic metal α-(BEDT-TTF)₂KHg(SCN)₄ under pressure
Successive magnetic-field-induced charge-density-wave transitions in the layered molecular conductor α-(BEDT-TTF)₂KHg(SCN)₄ are studied in the hydrostatic pressure regime, in which the zero field chargedensity-wave (CDW) state is completely suppressed. The orbital effect of the magnetic field is demonstrated to restore the density wave, while the orbital quantization induces transitions between different CDW states at changing the field strength. The latter appear as distinct anomalies in the magnetoresistance as a function of field. The interplay between the orbital and Pauli paramagnetic effects acting, respectively, to enhance and to suppress the CDW instability is particularly manifest in the angular dependence of the field-induced anomalies
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