The anomalous metallic state in the high-temperature superconducting cuprates is masked by superconductivity near a quantum critical point. Applying high magnetic fields to suppress superconductivity has enabled detailed studies of the normal state, yet the direct effect of strong magnetic fields on the metallic state is poorly understood. We report the high-field magnetoresistance of thin-film La Sr CuO cuprate in the vicinity of the critical doping, 0.161 ≤ ≤ 0.190. We find that the metallic state exposed by suppressing superconductivity is characterized by magnetoresistance that is linear in magnetic fields up to 80 tesla. The magnitude of the linear-in-field resistivity mirrors the magnitude and doping evolution of the well-known linear-in-temperature resistivity that has been associated with quantum criticality in high-temperature superconductors.

Magnetic fields change the way that electrons move through solids. The nature of these changes reveals information about the electronic structure of a material and, in auspicious circumstances, can be harnessed for applications. The silver chalcogenides, Ag2Se and Ag2Te, are non-magnetic materials, but their electrical resistance can be made very sensitive to magnetic field by adding small amounts--just 1 part in 10,000--of excess silver. Here we show that the resistance of Ag2Se displays a large, nearly linear increase with applied magnetic field without saturation to the highest fields available, 600,000 gauss, more than a million times the Earth's magnetic field. These characteristics of large (thousands of per cent) and near-linear response over a large field range make the silver chalcogenides attractive as magnetic-field sensors, especially in physically tiny megagauss (10(6) G) pulsed magnets where large fields have been produced but accurate calibration has proved elusive. High-field studies at low temperatures reveal both oscillations in the magnetoresistance and a universal scaling form that point to a quantum origin for this material's unprecedented behaviour.

Specific heat of a material is a measure of heat necessary to raise the temperature of a given amount of material, typically a gram or a mol, by 1 Kelvin. Near absolute zero, this bulk thermodynamic quantity is a sensitive probe of the low energy excitations of a complex quantum

High-temperature superconductivity is achieved by doping copper oxide insulators with charge carriers. The density of carriers in conducting materials can be determined from measurements of the Hall voltage--the voltage transverse to the flow of the electrical current that is proportional to an applied magnetic field. In common metals, this proportionality (the Hall coefficient) is robustly temperature independent. This is in marked contrast to the behaviour seen in high-temperature superconductors when in the 'normal' (resistive) state; the departure from expected behaviour is a key signature of the unconventional nature of the normal state, the origin of which remains a central controversy in condensed matter physics. Here we report the evolution of the low-temperature Hall coefficient in the normal state as the carrier density is increased, from the onset of superconductivity and beyond (where superconductivity has been suppressed by a magnetic field). Surprisingly, the Hall coefficient does not vary monotonically with doping but rather exhibits a sharp change at the optimal doping level for superconductivity. This observation supports the idea that two competing ground states underlie the high-temperature superconducting phase.

Weyl fermions are a recently discovered ingredient for correlated states of electronic matter. A key difficulty has been that real materials also contain non-Weyl quasiparticles, and disentangling the experimental signatures has proven challenging. Here we use magnetic fields up to 95 T to drive the Weyl semimetal TaAs far into its quantum limit, where only the purely chiral 0th Landau levels of the Weyl fermions are occupied. We find the electrical resistivity to be nearly independent of magnetic field up to 50 T: unusual for conventional metals but consistent with the chiral anomaly for Weyl fermions. Above 50 T we observe a two-order-of-magnitude increase in resistivity, indicating that a gap opens in the chiral Landau levels. Above 80 T we observe strong ultrasonic attenuation below 2 K, suggesting a mesoscopically textured state of matter. These results point the way to inducing new correlated states of matter in the quantum limit of Weyl semimetals.

The inhomogeneous distribution of excess or deficient silver atoms lies behind the large and linear transverse magnetoresistance displayed by Ag 2 Se and Ag 2 Te, introducing spatial conductivity fluctuations with length scales independent of the cyclotron radius. We report a negative, nonsaturating longitudinal magnetoresistance up to at least 60 T, which becomes most negative where the bands cross and the effect of conductivity fluctuations is most acute. Thinning samples down to 10 m suppresses the negative response, revealing the essential length scale in the problem and paving the way for designer magnetoresistive devices. DOI: 10.1103/PhysRevLett.95.186603 PACS numbers: 72.20.My, 72.15.Gd, 72.80.Jc The silver chalcogenides provide a striking example of the benefits of imperfection. Perfectly stoichiometric Ag 2 Se and Ag 2 Te are nonmagnetic, narrow-gap semiconductors whose electron and hole bands cross at liquid nitrogen temperatures. They exhibit negligible magnetoresistance [1], as predicted from conventional theories [2]. By contrast, minute amounts of excess Ag or Se=Te-at levels as small as 1 part in 10 000 -lead to a huge and linear magnetoresistance over a broad temperature range [3][4][5][6][7][8]. The unusual linear dependence on magnetic field down to 100 G indicates a particularly long length scale associated with the underlying physics, while, at high field, a nonsaturating response up to at least 0.5 MG exceeds by a factor of 50 to 100 the expected cutoff where the product of the cyclotron frequency and the scattering rate ! 1 [9]. This remarkably robust linear magnetoresistive response makes the silver chalcogenides promising candidates for high field sensors. Missing at present, however, is experimental evidence for the pertinent length scales of the inhomogeneities that determine the unusual physics and that are essential to the materials' usefulness.Abrikosov was the first to stress the importance of the inhomogeneous distribution of the excess or deficient silver ions. In his effective medium theory of quantum linear magnetoresistance [10], disorder and a linear dispersion relation at band crossing [11] combine to produce a linear, rather than a quadratic, magnetic field dependence for the electrical conductivity. As pointed out by Parish and Littlewood [12], fluctuations in the mobility are particularly acute when the gap goes to zero and both positive and negative values can be sampled. Their simulations of large spatial conductivity fluctuations in strongly inhomogeneous semiconductors derive a linear magnetoresistance from the Hall voltage picked up from macroscopically distorted current paths caused by variations in the stoichiometry. The spatial fluctuations in the conductivity are caused by the random distribution of Ag ions, which may take the form of highly conducting nanothreads or lamellae along the grain boundaries of polycrystalline material [13]. The distorted current paths seen in the simulations lead to the emergence of a characteristic length scale that can be associ...

The discovery of superconductivity at 260 K in hydrogen-rich compounds like LaH 10 re-invigorated the quest for room temperature superconductivity. Here, we report the temperature dependence of the upper critical fields μ 0 H c2 ( T ) of superconducting H 3 S under a record-high combination of applied pressures up to 160 GPa and fields up to 65 T. We find that H c2 ( T ) displays a linear dependence on temperature over an extended range as found in multigap or in strongly-coupled superconductors, thus deviating from conventional Werthamer, Helfand, and Hohenberg (WHH) formalism. The best fit of H c2 ( T ) to the WHH formalism yields negligible values for the Maki parameter α and the spin–orbit scattering constant λ SO . However, H c2 ( T ) is well-described by a model based on strong coupling superconductivity with a coupling constant λ ~ 2. We conclude that H 3 S behaves as a strong-coupled orbital-limited superconductor over the entire range of temperatures and fields used for our measurements.

Anelastic loss mechanisms associated with phase transitions in BaCeO 3 have been investigated at relatively high frequency ϳ1 MHz and low stress by resonant ultrasound spectroscopy ͑RUS͒, and at relatively low frequency ϳ1 Hz and high stress by dynamic mechanical analysis ͑DMA͒. Changes in the elastic moduli and dissipation behavior clearly indicate phase transitions due to octahedral tilting: Pnma ↔ Imma ↔ R3c ↔ Pm3m structures at 551 K, 670 K, and 1168 K, and strain analysis shows that they are tricritical, first-order, and second-order phase transitions, respectively. Structures with intermediate tilt states ͑R3c and Imma structures͒ show substantial anelastic softening and dissipation associated with the mobility of twin walls under applied stress. The Pnma structure shows elastic stiffening which may be due to the simultaneous operation of two discrete order parameters with different symmetries. In contrast with studies of other perovskites, BaCeO 3 shows strong dissipation at both DMA and RUS frequencies in the stability field of the Pnma structure. This is evidence that ferroelastic twin walls might become mobile in Pnma perovskites and suggests that shearing of the octahedra may be a significant factor.