1,207 research outputs found
On the destruction of the hidden order in URuSi by a strong magnetic field
We present a study of transport properties of the heavy fermion URuSi
in pulsed magnetic field. The large Nernst response of the hidden order state
is found to be suppressed when the magnetic field exceeds 35 T. The combination
of resistivity, Hall and Nernst data outlines the reconstruction of the Fermi
surface in the temperature-field phase diagram. The zero-field ground state is
a compensated heavy-electron semi-metal, which is destroyed by magnetic field
through a cascade of field-induced transitions. Above 40 T, URuSi
appears to be a polarized heavy fermions metal with a large density of carriers
whose effective mass rapidly decreases with increasing magnetic polarization.Comment: published versio
Berry Phase in Cuprate Superconductors
Geometrical Berry phase is recognized as having profound implications for the
properties of electronic systems. Over the last decade, Berry phase has been
essential to our understanding of new materials, including graphene and
topological insulators. The Berry phase can be accessed via its contribution to
the phase mismatch in quantum oscillation experiments, where electrons
accumulate a phase as they traverse closed cyclotron orbits in momentum space.
The high-temperature cuprate superconductors are a class of materials where the
Berry phase is thus far unknown despite the large body of existing quantum
oscillations data. In this report we present a systematic Berry phase analysis
of Shubnikov - de Haas measurements on the hole-doped cuprates
YBaCuO, YBaCuO, HgBaCuO, and the
electron-doped cuprate NdCeCuO. For the hole-doped materials, a
trivial Berry phase of 0 mod is systematically observed whereas the
electron-doped NdCeCuO exhibits a significant non-zero Berry
phase. These observations set constraints on the nature of the high-field
normal state of the cuprates and points towards contrasting behaviour between
hole-doped and electron-doped materials. We discuss this difference in light of
recent developments related to charge density-wave and broken time-reversal
symmetry states.Comment: new version with added supplementary informatio
Disorder, Metal-Insulator crossover and Phase diagram in high-Tc cuprates
We have studied the influence of disorder induced by electron irradiation on
the normal state resistivities of optimally and underdoped YBa2CuOx
single crystals, using pulsed magnetic fields up to 60T to completely restore
the normal state. We evidence that point defect disorder induces low T upturns
of rho(T) which saturate in some cases at low T in large applied fields as
would be expected for a Kondo-like magnetic response. Moreover the magnitude of
the upturns is related to the residual resistivity, that is to the
concentration of defects and/or their nanoscale morphology. These upturns are
found quantitatively identical to those reported in lower Tc cuprates, which
establishes the importance of disorder in these supposedly pure compounds. We
therefore propose a realistic phase diagram of the cuprates, including
disorder, in which the superconducting state might reach the antiferromagnetic
phase in the clean limit.Comment: version 2 with minor change
Quantum-Classical Crossover and Apparent Metal-Insulator Transition in a Weakly Interacting 2D Fermi Liquid
We report the observation of a parallel magnetic field induced
metal-insulator transition (MIT) in a high-mobility two-dimensional electron
gas (2DEG) for which spin and localization physics most likely play no major
role. The high-mobility metallic phase at low field is consistent with the
established Fermi liquid transport theory including phonon scattering, whereas
the insulating phase at higher field shows a large negative temperature
dependence at resistances much smaller than the quantum of resistance, .
We argue that this observation is a direct manifestation of a quantum-classical
crossover arising predominantly from the magneto-orbital coupling between the
finite width of the 2DEG and the in-plane magnetic field.Comment: 4 pages, 2 figure
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